RF Projects 3141, 3332
THE OHIO STATE UNIVERSITY
RESEARCH FOUNDATION
1314 KINNEAR ROAD COLUMBUS, OHIO 43212
Final Report
on
AN INVESTIGATION OF THE EFFECTS OF CARBON
MONOXIDE ON HUMANS IN THE DRIVING TASK
by
F. W. Weir and T. H. Rockwell
COORDINATING RESEARCH COUNCIL, INC.
and
ENVIRONMENTAL PROTECTION AGENCY
Contract Nos. 68-02-0329
and
CRC-APRAC Project CAPM-9-69
January 1973
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CRC-APRAC Contract CAPM-9-69
Research Foundation RF 3141, 3332
AN INVESTIGATION OF THE EFFECTS OF CARBON
MONOXIDE ON HUMANS IN THE DRIVING TASK
by the
Preventive Medicine Group and Systems Research Group
F. W. Weir T. H. Rockwell
M. M. Mehta D. A. Attwood
D. F. Johnson G. D. Herrin
D. M. Anglen R. R, Safford
of
The Ohio State University
Columbus, Ohio 43210
January 1973
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PREFACE
This report presents the findings of a two-year investigation of the effects
of carboxyhemoglobin (expressed as percent of hemoglobin combined with carbon
monoxide) on human performance, particularly in regard to the task of driving
an automobile. This study was performed under contract to the Coordinating
Research Council and was financially supported by the U. S. Environmental
Protection Agency, the American Petroleum Industry, and the Motor Vehicle
Manufacturers Association.
The scope of this study includes three major objectives:
1. The development of methods for rapid and accurate laboratory
and field measurement of carboxyhemoglobin (COHb) in man.
2. The determination of the effects of up to 20% COHb concentra-
tions on
a. physiological performance,
b. complex psychophysiological and psychomotor skills,
and
c. driving skills and judgment on the highway.
3. The determination of the predictability of decrement in driving
skills based upon laboratory skills testing.
The opinions, findings, and conclusions in this publication are those of
the authors and not necessarily those of the sponsors.
iii
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ACKNOWLEDGMENTS
Although it is impossible to adequately recognize and credit each indiv-
idual who assisted in this investigation, the authors wish to recognize the following
individuals for their major contributions.
The authors are indebted to Dr. John B. Neuhardt for his technical
counsel on statistical methods and to Charles E. Billings, M. D., for his
medical guidance. For assistance with all phases of the data collection and
analyses we are most grateful to Messrs. Richard Majors, Harold Rude,
David See, Robert Sousek, and Edward Whitehead. Messrs. Larry Tracewell
and Clarence James provided valuable technical assistance with vehicle instru-
mentation.
A special thanks must go to Mrs. Patricia Weir for her assistance in
the planning and analysis of the results of the study, and to Mrs. Lois Graber,
Miss Sandra Gray, Mrs. Sharon Mays, and Mrs. Irene Savage for their labors
and patience in the preparation of this report.
The guidance, encouragement, and helpful suggestions of the Coordinating
Research Council, Inc., were most appreciated.
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SUMMARY
This two-year investigation of the effects of carboxyhemoglobin on human
performance involved the testing of 40 subjects on the highway with a battery of
real driving situations and/or laboratory tasks related to driving skills. In all,
24 tasks were developed and over 130,000 observations taken to study human
performance at carboxyhemoglobin (COHb) levels of nominally 0, 7, 14, and
20%. The first year effort was designed to study the extreme values, 0 and 20%
COHb with 15 subjects while the second year was devoted to examining the lower
levels (0, 7, and 14% COHb) with 25 additional subjects.
Overall the results suggest consistent patterns of performance changes
with increased COHb levels. Differences observed with 20% COHb levels were
directionally preserved with lower (7 and 14% COHb) levels but with smaller
magnitude differences. The results, however, do not suggest a low COHb level
where all performance measures are first affected. Rather, the magnitudes and
directions of performance changes appear to be highly dependent on the particu-
lar task and protocols employed. As expected, laboratory dual tasks (where the
subject is required to perform two tasks simultaneously) exhibited performance
differences at lower COHb levels than more simple tasks. Since accidents are
probably more prevalent when the attention and control demands on the driver
are greatest,\ the dual task results may be more important than results in rou-
tine, over-learned driving situations.
Strong correlations between performance on simple laboratory tasks
and COHb levels were not observed in this research. This was not unexpected
since, again, simple tasks are often over-learned and compensatory subject
reactions may negate possible effects.
Driving performance was categorized into three levels: visual (percep-
tion and information acquisition), control (psychomotor), and dynamic response
(time delayed vehicle response). Of primary importance in this research is the
heirarchy of observed COHb differences. The results of this research suggest
that the largest magnitude effects with increased COHb levels occur at the early
stages of information processing. Visual and psychomotor control measures, in
general, were the first measures to be affected by COHb. These measures, how-
ever, are also the most variable due to large intra- and intersubject variability.
In general, no ostensible performance degradation was observed with
COHb and the normal driving tasks although subtle performance losses were
observed, especially in the information acquisition measures. With heavy in-
formation processing demands and/or other associated debilitating factors in
driving, such as fatigue or alcohol, these subtle effects could be compounded
into gross performance changes.
vii
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TABLE OF CONTENTS
Page
PREFACE iii
ACKNOWLEDGEMENTS v
SUMMARY vii
LIST OF FIGURES xl
LIST OF TABLES xv
CHAPTER
1 RESEARCH OVERVIEW AND BACKGROUND LITERATURE . 1
1.1 Introduction 1
1.2 Research Strategy 1
1.3 Schedule of Tasks 2
1.4 Report Outline 4
1.5 Literature Overview 4
2 CARBON MONOXIDE: ADMINISTRATION, CONTROL,
AND MEASUREMENT 13
2.1 Exposure Facilities 13
2.2 Carboxyhemoglobin "Refreshing Technique" .... 14
2.3 Subjects 14
2.4 Experimental Scheduling 15
2.5 Carboxyhemoglobin Analyses 15
2.6 Atmospheric Carbon Monoxide Analysis 17
2.7 Carboxyhemoglobin Analysis Method Evaluation . . 18
2.8 In Vivo Carboxyhemoglobin Analyses Verification . . 18
2.9 Atmospheric Carbon Monoxide Analysis Method
Evaluations 20
2.10 Results of Subject COHb Analyses 20
3 SIMPLE LABORATORY TESTS 27
3.1 Introduction 27
3.2 Simple Laboratory Tasks Descriptions 27
3.3 Results 31
4 COMPLEX LABORATORY TASKS WITH 20% COHb .... 41
4.1 Description of Tasks 41
4.2 Test Schedules 43
4.3 Phase A Results 45
ix
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4.4 Phase B Results 46
4.5 Summary of Phase B Results 54
5 COMPLEX LABORATORY TASKS WITH 7 and 14% COHb . . 57
5.1 Results 57
5.2 Summary of Phases C and D 65
6 DRIVING TASKS WITH 20% COHb 67
6.1 Independent Variables 67
6.2 Dependent Variables 68
6.3 Equipment 70
6.4 Results 72
6.5 Phase B Analyses 82
6. 6 Summary of Results 84
7 DRIVING TASKS WITH 7 and 14% COHb 85
7.1 Equipment 85
7.2 Independent Variables 85
7.3 Dependent Varibles 88
7.4 Task 24 - Dependent and Independent Variables ... 89
7.5 Models and Notation 90
7.6 Results 93
8 CONCLUSIONS AND RECOMMENDATIONS 115
8.1 Introduction 115
8.2 Interpretation 116
8.3 A Proposed Conceptual Model for the Observed
Experimental Differences 118
8.4 Nonlinear Effects of Elevated COHb Levels .... 123
APPENDIXES
A EQUIPMENT AND SUBJECT INSTRUCTIONS COMPLEX
LABORATORY TASKS 127
B SUBJECT INSTRUCTIONS FOR ROAD TESTS
(TASKS 12 THROUGH 24) 139
C MEASUREMENTS OF CARBOXYHEMOGLOBIN LEVELS
OF FREEWAY DRIVERS 149
D SUBJECT CONSENT FORM, SUBJECT PRESCREENING
DATA FILE, HABIT INVENTORY FORM, & CORNELL
MEDICAL INDEX HEALTH QUESTIONNAIRE 153
BD3LIOGRAPHY 165
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LIST OF FIGURES
Figure Page
2.1 Time sequence of events showing ideal levels
for 20% COHb experiments 16
3.1 Dark adaptation curves 37
3.2 Dark adaptation curves 38
3.3 Dark adaptation curves 40
4.1 Mean choice reaction time (CRT) as a function
of the AIR-CO treatment and the before- versus
after-driving condition 49
4.2 Mean choice reaction time (CRT) as a function
of the size of stimulus set, COHb level, and
. dual-task or CRT-only condition 50
4.3 Average mean absolute tracking error (MAE)
as a function of the AIR-CO treatment and the
before- versus after-driving condition 51
4.4 Average mean absolute tracking error (MAE)
as a function of the level of tracking complexity
AIR-CO exposure 52
4.5 Mean choice reaction time (CRT) versus
average mean absolute tracking error (MAE)
and mean tracking time-lag (LAG) 53
4.6 Mean tracking time-lag (LAG) versus average
mean absolute tracking error (MAE) 55
4.7 Mean tracking time-lag (LAG) as a function of
the level of tracking complexity and the AIR
and CO exposure 56
5.1 Mean CRT latency as a function of COHb
level and tracking complexity 61
xi
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list of Figures (cont'd.)
Figure Page
5.2 Mean CRT latency as a function of COHb
level and stimulus uncertainly 62
5.3 Mean absolute tracking error as a function
of the level of tracking complexity and COHb 63
5.4 Mean absolute tracking error as a function of
COHb level and stimulus uncertainty 66
6.1 Matrix of independent variables for two groups
of six subjects (Phases A and B) 69
7.1 Road Protocol for Phases C and D 86
7.2 Lattice of tasks employed in Phases C and D 87
7.3 Mean velocities for three open road driving tasks 95
7.4 Standard deviation of velocities for three
50 mph driving tasks 97
7.5 Mean headways for car-following tasks 99
7.6 Standard deviation of headways for car-following tasks .... 101
7.7 Relative velocity standard deviations
for car-following tasks 102
7.8 Gas pedal reversals for Tasks 17
through 23 104
7.9 Brake pedal applications while car following 106
7.10 Steering wheel reversals for 50 mph tasks 108
7.11 Perceptual uncertainties for selected subjects 113
8.1 General response to CO 117
8.2 Illustrative results (all tasks) 119
xii
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List of Figures (cont'd.)
Figure Page
8.3 Trends in perceptual measures 120
8.4 Mean straight looks for normal vision
driving tasks 121
8.5 Possible trends in performance
due to COHb levels 124
8.6 Example of quadratic effects 125
A.I Psychomotor task schematic 129
xiii
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LEST OF TABLES
Table Page
1.2 Laboratory and Road Tests Employed 3
2.1 to Vitro Reproducibility Study on % COHb in Blood 19
2.2 In Vivo COHb Analyses Verification 19
2.3 Results of CO Analysis of Samples Containing CO 21
2.4 Carboxyhemoglobin Levels of Phase A Subjects before and
after 120 Minutes of Exposure (490 ppm) and during Driving
Experiment ., , 22
2.5 Carboxyhemoglobin Levels of Phase B Subjects before and
after 120 Minutes Air Exposure and during Driving Experiment. . 23
2.6 Carboxyhemoglobin Levels of Phase B Subjects before and after
120 Minutes CO Exposure (450 ppm) and during Driving
Experiment 23
2.7 Carboxyhemoglobin Levels of Phase C-D Subjects before and
after 90 Minutes Air Exposure and during Driving Experiment . . 24
2.8 Carboxyhemoglobin Levels of Phase C-D Subjects before and
after 90 Minutes CO Exposure (100 ppm) and during Driving
Experiment 25
2.9 Carboxyhemoglobin Levels of Phase C-D Subjects before and
after 90 Minutes CO Exposure (350 ppm) and during Driving
Experiment 26
3.1 Results of Finger-tapping Performance Test 31
3.2 Results of Rail-walking Test 32
3.3 Results of Modified Rail-walking Test 32
3.4 Results of Spatial Relations Test 33
3.5 Results of Brightness Discrimination Test 34
xv
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Table Page
3.6 Analysis of Variance of Brightness Discrimination Data 34
3.7 Analysis of Variance of Brightness Discrimination Data
Disregarding Yellow Light Source 35
3.8 Analysis of Variance of Standard Deviation 35
3.9 Results of Brightness Discrimination Test 36
4.1 Phase B Subject Schedule 44
4.2 Average Time Lag (msec.), Dual Task, Low Complexity 46
4.3 Summary Statistics of Time Estimation Data - Five Subjects ... 47
5.1 Analysis of Variance of Choice Reaction Time, Phases C and
D, 15 Subjects 58
5.2 Analysis of Variance of Mean Absolute Error, Phases C and
D, 15 Subjects 58
5.3 Analysis of Variance of Choice Reaction Time Data Adjusting
for Learning Effects 59
5.4 Analysis of Variance of Mean Absolute Errors Adjusting for
Learning Effects 60
5.5 Subject by COHb Interactions 64
6.1 Spare Capacity as a Function of Percent of Time that Subjects
Kept their Eyes Closed 73
6.2 Spare Capacity as a Function of the Percent of Time that Subject
Drivers were able to Close their Eyes 74
6.3 Mean "Open" Time 75
6.4 Percentage of Time that the Mean Duration Time for "Looks" at
Different Objects or Areas Greater under CO than under Air ... 76
6.5 Numberof Looks at the Lead Car 78
6. 6 Number of Looks at Categories other than Lead Car 79
xvi
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Table
6.7 Blink Rate Analysis 80
6.8 Gas Pedal Reversals Summary for all Subjects Combined .... 81
6.9 Mean Headway Analysis 83
7.1 Models Employed in Data Analysis for Phase C and D Road
Tests 92
7.2 ANOVA for Mean Velocity, Full Data 94
7.3 Average Standard Deviation of Velocities across Tasks T17,
T19, T23 96
7.4 ANOVA for Standard Deviation of Velocities 98
7.5 Gas Pedal Reversal Comparisons 103
7.6 Average Steering Wheel Reversals by Subject 107
7.7 Linear and Quadratic COHb Effects Summary for Visual .
Measures (Phase C) 109
7.8 CO Trends for Normal Vision Tasks Ill
7.9 CO Trends for Occluded Vision Tasks Ill
7.10 COHb Effects for Leapfrog Passing Test 114
C. 1 Summary Data Table for Ancillary Studies 151
xvii
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CHAPTER 1
RESEARCH OVERVIEW AND
BACKGROUND LITERATURE
1.1 Introduction
While a great deal is known about the human physiological response to
acute carbon monoxide poisoning, considerable controversy exists regarding
possible psychophysical and behavioral effects resulting from carbon monoxide
exposures that produce carboxyhemoglobin (COHb) levels less than 20%. Since
a variety of carbon monoxide exposure conditions can produce equivalent resul-
tant COHb levels, the major emphasis of this study was placed on the effects of
specific COHb levels, rather than the effects of certain carbon monoxide ex-
posures.
Since automobile drivers may have a higher risk of carbon monoxide
exposure from automobile exhaust than the general population, this study was
designed to investigate the possible effects of COHb on driving related perfor-
mance. The scope of the investigation included first the development of rapid,
accurate laboratory and field COHb measurements in men. Next, relation of
the various levels of COHb to physiological performance, simple and complex
psychomotor skills, driving performance, and assessment of judgment degrada-
tion were studied. The complex laboratory tasks related to driving included:
pursuit tracking, choice reaction time, and dual tasks (involving both pursuit
tracking and choice reaction time tests performed simultaneously). The driving
performance studies investigated 1) vehicle dynamics such as velocity and spac-
ing while car following, 2) operator control movements, such as steering wheel,
gas, and brake pedal applications, and 3) perceptual measures, such as driver's
visual search and scan patterns measured with The Ohio State University eye-
movement camera technique.
1.2 Research Strategy
Goals were set for each year of the two-year research effort. The first
year effort was designed to screen those factors and tasks which may be suscep-
tible to 20% COHb level effects. Those tests which demonstrated changes at
20% COHb were incorporated into the second year efforts with COHb levels of
nominally 7 and 14%.
An equally important goal of the first year effort was the development of
facilities and protocols to produce desired COHb levels in the subjects. Support
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personnel were trained to monitor carbon monoxide in air and blood in order to
standardize methods. One important goal was maintenance of COHb levels out-
side the laboratory during lengthy test sessions.
Subject safely was of utmost concern, therefore for the first year studies,
single blind techniques were used (only the subjects were unaware of the carbon
monoxide exposure conditions). For the second year, with lower COHb levels,
possible experimenter biases were eliminated with double blind techniques. Only
the medical monitor and the research chemist were aware of CO concentrations
in the testing.
The overall experimental design strategy for the research was to let the
subjects serve as their own controls. This required that there be no transfer
effects across COHb levels and test periods. It further required that there be
small differential subject effects by COHb treatment. Tests were counter-
balanced to guard against biases from learning and/or fatigue.
In retrospect, the use of subjects as their own controls had one signifi-
cant drawback as compared to a completely randomized design. Losses of data
due to weather induced cancellations, equipment failures, failures to meet re-
quired carboxyhemoglobin levels, or subjects' failures to appear for testing,
limit the usual benefits from such designs. Unfortunately, these situations did
occur occasionally throughout the reported testing, necessitating the use of
covariate types of analyses and resulting in less powerful statistical tests. As
such, many of the analyses present more conservative assessments of possible
COHb effects than might be expected with more balanced designs.
1.3 Schedule of Tasks
Table 1.1 presents an overview of the two-year schedule of tasks per-
formed both in laboratory and on the road. These tasks were sequenced in four
phases representing blocks of time for continuous testing. Particular protocols,
orders of administration of tasks, etc., may be found in the methodology sec-
tions for the respective phases. Table 2 presents an abbreviated list of the
24 tests employed in the various research phases.
Complete descriptions of these tasks may be found in the methodology
sections of phases where employed, subject instructions for the tasks are in
Appendixes A and B.
For coherence (since all subjects did not perform all tasks), the forty
subjects in the research will be referred to in the test subscripted SI through
S40. SI through 88 were studied in Phase A, S9 through S15 in Phase B, 816
through 831 in Phase C, and 832 through 840 in Phase D.
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Table 1.1
Schedule of Testing
Lab Tasks
Road Tasks
Nominal COHb Levels
Subjects Tested
Phase A
T1-T11
T15-T20
0, 20%
8
Phase B
T1-T11
T12-T20
0, 20%
7
Phase C
Tl-7, 9-11
T17-T24
0, 7, 14%
16
Phase D
Tl-7, 9-11
T17 - T24
0, 7, 14%
9
Table 1.2
Laboratory and Road Tests Employed
Laboratory Tasks
Tl - Bail Walking
T2 - Mirror Tracing
T3 - Spatial Relations
T4 - Finger Tapping
T5 - Brightness Discrimination
T6 - Dark Adaptation
T7 - flash Blindness
T8 - Time Estimation
T9 - Choice Reaction Time
T10 - Pursuit Tracking
Til - Dual Task (T9 + T10)
Road Tasks
T12 - Headway Estimation & Production
T13 - Velocity Estimation & Production
T14 - Time Estimation
T15 - Constant Speed Car Following
T16 - T15 with Voluntary Occlusion
T17 - Variable Speed Car Following
T18 - T17 with Voluntary Occlusion
T19 - Open Road, 50 mph Driving
T20 - T19 with Voluntary Occlusion
T21 - Open Road, 30 mph Driving
T22 - T21 with Voluntary Occlusion
T23 - Velocity Maintenance
T24 - Leap-Frog Passing
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1.4 Report Outline
The results of the two-year effort are organized into eight chapters in
this report. Chapter 2 describes the administration, control, and measurement
of carbon monoxide and carboxyhemoglobin (COHb) levels. Chapters 3, 4, and
6 describe the results of the first year comparing control COHb levels with 20%
COHb levels. These chapters, together with Chapters 1, 2, and 8 constitute the
final report for the first year.
Chapters 5 and 7 describe the laboratory and road testing results of the
second year. These studies (referred to as Phases C and D) were performed
with COHb levels of nominally 0, 7, and 14%. Chapter 8 presents a summary
of the two year of research with conclusions and recommendations .for the third
year of effort now underway.
Appendix C presents the results of three minor complementary studies
performed in February 1972. One study sampled transient drivers for COHb
levels on the Ohio Turnpike. The second sampled truck drivers on the freeway
and at a local private trucking firm, Suburban Motor Freight Company. The
third study sampled student smokers and nonsmokers on the Ohio State Univer-
sity campus for ambient COHb levels. All three studies used an infrared
measurement (Beckman Analyzer) technique.
1.5 Literature Overview
The remainder of this chapter will be devoted to an overview of the
technical literature related to this research.
1.5.1 Carbon Monoxide; Effects on Man
Several investigations have indicated that the central nervous system
(CNS) is apparently impaired at COHb levels as low as 3-5% (MacFarland, et al.,
1944; Schulte, 1963; Beard and Wertheim, 1967; and Horvath, et al., 1971).
Other investigators have not confirmed these findings (Stewart, et al., 1970; and
O'Donnell, et al., 1971). Readers interested in the toxicological basis of CO
uptake, and the physiological response to CO intoxication, are referred to the
US-HEW 1970 report on air quality criteria for CO, and to Cobura (1970).
It is now widely accepted (Otis, 1970; Brody, 1970) that COHb competes
with oxyhemoglobln (O2Hb) at the cellular level, creating symptoms associated
with anemic hypoxia. Consequently, it is not surprising that some of the behav-
ioral effects that have been observed with CO intoxication are similar to those
manifested by subjects who have been exposed to reduced partial pressures of
atmospheric oxygen sufficient to produce hypoxic hypoxia.
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Research has indicated that human vision is one of the first systems to
be affected in hypoxic conditions, including those resulting from CO intoxication.
Halperin, et al., (1969), while summarizing earlier experiments, reported an
increase in visual threshold at COHb concentrations as low as 4-5%. Lilienthal
and Fugitt (1946) observed that subjects exposed simultaneously to CO and a
reduced oxygen environment exhibited decreased critical flicker fusion (CFF)
frequencies; i. e., the frequency at which a flickering light appeared to be a
steady glow. More recently, Hosko (1970) detected differences in the visual
evoked response (VER) of subjects whose COHb levels were approximately 22%.
At lower COHb levels, no differential VER effects would be detected. The
author suggested that the changes observed in the VER represented the direct
cortical response to activity in the scotopic (rod) visual system. (See below.)
A series of experiments performed by Luria and McKay (1971) indicated
that changes in scotopic sensitivity occurred after a 90 minute exposure to an
atmosphere containing 200 ppm CO. The study also detected changes in the VER
and increases in eye fixations, eye reversals, and in the mean reading time of
a standard passage of text under the influence of CO. Closer inspection of the
data reveals that only two of three subjects showed increased fixations and
reversals.
The exposure conditions of Luria and McKay (90 min. x 200 ppm CO)
should have produced approximately 5% COHb. It is unusual to find such marked
effects at this low level. Stewart, et al., (1970) reported "As COHb saturation
approached 20%, changes were observed in the VER. These changes became
more marked as the COHb saturation neared 30%. The VER was the most sensi-
tive objective indicator of CO effect. " (Emphasis ours.) In another chapter of
the same reference, Hosko states, "The significance of these data are difficult
to project since the functional relationships between VER morphology and vision
remain unknown for the most part." Indeed, he attributes specific VER changes
to shifts in subject attention, a far more exciting finding than a simple visual
phenomenon.
Stewart, et al., (1970) employed a complete battery of psychomotor tests
to study several groups of subjects intoxicated to levels up to 31.8% COHb. At
lower levels of CO intoxication, no significant differences in performance could
be demonstrated between control and CO conditions. At higher levels of intoxi-
cation, two subjects reportedly demonstrated a deterioration in performance on
a Crawford collar and pin test, although performances on a simple reaction time
task, and a time estimation task, were not significantly affected. The authors
note that during this test period, marked fatigue of hands and fingers was observed.
Beard and Wertheim (1967) detected a significant decrement in the ability
of humans to estimate the duration of periods of time after exposure to low
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concentrations of CO. This research began as the result of previous studies
which identified a derangement of the time sense in animals exposed to low con-
centrations of CO.
Central nervous system functions responsible for cognitive behavior have
been thought to be affected by COHb levels as low as 4% (Schulte, 1963). In
motor skill tests, where the contribution of higher mental functions is comparably
reduced, equivocal results on the effects of CO have been obtained.
O'Donnel, et al., (1971) employed a critical instability tracking task
(CTT) to investigate performance during three -hour exposures to atmospheres
containing 0, 50, and 125 ppm CO. Up to 13% COHb, no effects were found
when compared to control, i. e., approximately 1% COHb levels. Hanks (1970)
found no effect of low CO intoxication on the performance of the CTT.
The above research suggested that performance deterioration at low
levels of COHb increased as the extent of participation of both higher mental
processes and the visual system in the task increases. It is suggested that the
mental processes responsible for psychomotor performance are affected by CO,
but that simple tasks, such as those previously employed, are not sufficiently
sensitive to the subtle effects of low level CO intoxication to show significant
deterioration in task performance.
1.5.2 Carbon Monoxide; Effects on Driving
Ramsey (1970) investigated the effects of inhaled traffic exhaust on the
performance of a simple reaction time task. Subjects drove in rush hour traffic
for 90 minutes, in an atmosphere of an average 38.1 ppm CO. Reaction time of
the exposed group was compared with the performance of a control group which
did not participate in the driving task, and the before-and-after driving perfor-
mance of the exposed group was compared. Results indicated a significant in-
crease in reaction time of drivers and passengers over the reaction times of the
control group. Results were discussed in relation to the percent reduction in
blood O2Hb, rather than the percent increase in COHb. The author admits that
many factors, including CO, could have produced the results.
An investigation by Rockwell and Ray (1967) studied the effects of CO in-
toxication on three subject drivers who drove in normal city traffic. Several
aspects of driving were affected by CO inhalation. The mean driving responses
were not generally affected, but the variance of many of the performance mea-
sures increased significantly, indicating more erratic driving performance.
It is suggested that under loaded conditions, when the operator must
time-share between different independent tasks, CO will reduce the operator's
capability to perform several tasks simultaneously. In effect, CO intoxication
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will reduce the "channel capacity" of the operator's information processing
system. This reduced capacity, not evident in simple tasks, should be mani-
fest in the time-sharing situation by either decreased performance on par-
ticular tasks, or on combinations of the time-shared tasks.
Allen (1970) hypothesized that CO acts in part to destroy visual acuity,
visual motor coordination, and perceptual alertness. He pointed out that any
compeusable visual anomaly becomes progressively less compensable under
the influence of CO. This idea lends itself to the concept of a spare visual
capacity. Allen also suggested that persons with measureable levels of COHb
would have more asthenopia, and more binocular vision and accomodative
problems than persons not exposed to CO. This suggested that fixation times
for persons exposed to carbon monoxide might be increased.
The following section describes a part of driving performance; i.e.,
eye search and scan patterns, which offered potential as indicators of CO
effects.
1.5.3 Eye-Movements and Driving*
Lack of available information concerning normal driver vision is par-
tially due to lack of equipment and techniques to measure the visual behavior
of persons outside fixed laboratory systems. One exception to this is the
"eye-movement camera" equipment developed by the Systems Research Group,
and described by Rockwell, et al., (1972).
The device enables the accurate determination of the eye-movement
behavior of the driver to yield information regarding the driver's visual
sampling behavior. The eye-movement equipment is quite adaptable and can
be used under many driving conditions. Several studies have already, been
conducted using this eye-movement apparatus; some of the studies are described
below.
Whalen (1968) studied the eye movements of drivers operating an instru-
mented vehicle on the open road at two velocity levels, following a car at two
headway levels, passing, and in normal freeway traffic. Significant differences
were found for various driving conditions when spatial temporal analyses of eye
fixations were examined.
Zell (1969) used the same apparatus to study driver eye movements as a
function of driving experience. His results indicated:
A more extensive review of vision and driving may be found in Safford (1971).
7
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1. Drivers' spatial eye-movement patterns changed sub-
stantially as a function of experience. Spatial dif-
ferences between new and experienced drivers could
be detected even after the new drivers had several
months' experience.
2. Differences in temporal aspects of eye movements
between novice and experienced drivers were not
apparent.
3. Experienced drivers tended to adjust their eye-
movement patterns to driving conditions more than
novice drivers; i.e., experienced drivers tended to
seek information at increased distances in front of
their vehicles as speeds increased. Novice drivers
failed to maintain a constant preview and tended to
use a fixed forward reference regardless of speed.
4. Eye-movement patterns of new and experienced
drivers were not noticeably different in car-following
situations, suggesting that the hazard of the lead car forced
the subjects to perform in a similar manner.
In a study to determine the effects of low alcohol concentrations on
driver eye movements, Belt (1969) found a significant increase in the amount
of time drivers spent fixating in a 3° x 3° area of the driving scene (measured
in subtended visual angle). This indicated a "spatial" narrowing which Belt
hypothesized was due to blurring or blunting of the peripheral stimuli forcing
the driver to .use only central vision. Belt also observed that in some
instances, drivers were able to maintain "good lateral control" of their
vehicles while exhibiting the narrowed compensatory eye fixation patterns,
but when subjects reverted to the eye-movement pattern typical of the "normal"
driver, lateral control performance was degraded. Belt found no differences
in "temporal" measures of eye movements that could be related to alcohol
concentrations. Some temporal differences were noticed when eye movements
during "car-following" were compared with movements during "open road"
driving.
Mourant (1971) found that novice drivers of a vehicle at 70 miles per
hour exhibited frequent pursuit "eye movements" similar to the experienced
subjects tested by Kaluger and Smith (1970) after 12 hours of driving and sleep
deprivation the previous night. The experienced drivers tested by Mourant,
however, did not make any pursuit eye movements. Novice drivers also showed
less horizontal and vertical eye movement activity than experienced drivers.
-------
Mourant also found that increased driving task difficulty tended to reduce the
blink rate for novice drivers.
1.5.4 Secondary Task Techniques*
Considerable recent research has been done using secondary task
techniques to evaluate the effects of drugs and alcohol on human performance.
Moskowitz (1970) suggested that deterioration of performance on secondary
(or dual) tasks might be a sensitive method; i.e., when subjects performed
two simultaneous tasks or time-shared between primary and secondary tasks.
Because most driving in traffic involves secondary tasks, this approach to
measuring effects of CO on human performance seemed to offer considerable
potential.
Rolfe (1969) defined methods used in this area of research; secondary
tasks were either subsidiary or loading tasks, depending on their use in the
experiment. If the subject was instructed to aim for error-free performance
on the primary task at the expense of performance on the secondary task, the
second task would be termed a subsidiary task. On the other hand, if the
priorities were reversed, the second task would be termed a loading task. He
noted that non-interference was achieved more often if the workload of the
secondary task could be paced by the operator. Experimenter-paced tasks
might require attention at a time when the operator could least afford it.
Knowles (1963) suggested that the secondary task should require little
learning and should show little inter-subject variability. Learning could be
controlled through (a) initial sessions on the secondary task, and (b) appro-
priate balancing within the experimental schedule. Inter- and intra-subject
variability would be more difficult to control in secondary tasks. A suitable
primary task would be a pursuit tracking task and a representative secondary
task would contain elements of perception, decision making, and reaction time.
Allnutt, et al., (1966) compared the tracking performance of subjects
on each of two displays, while the subjects simultaneously performed visual
reaction time task. Results indicated that both the reaction-time task and the
primary task were sensitive measures of the differences between the two
tracking displays.
One successful application of a secondary task procedure in a simulated
driving condition was reported by Moskowitz (1970). Subjects operating a driving
simulator were required to respond to colored lights presented adjacent to the
drivers central line of sight. The secondary task was sensitive to performance
deterioration at low levels of alcohol intoxication.
*A more extensive review may be found in Attwood (1972).
-------
Stephens and Michaels (1964) simulated two aspects of the driving task
by employing both a compensatory tracking task and a visual search for recog-
nition task. As subjects tracked a one dimensional compensatory display, they
searched for target words on road signs which appeared in a road scene pro-
jected above the tracking display. Results indicated that as the complexity of
either task increased, performance on both tasks deteriorated. A functional
relationship between component tasks relating to consistent whole task per-
formance was suggested.
It was the hypothesis of this research that human information processing
ability would be reduced by inhalation of CO. The reduction was assumed to
be minute to the extent that only when faced with processing demands that tax
the system near its capacity, would the effect of CO be apparent.
1.5.5 Secondary Tasks and Driving
The ability of drivers to perform adequately under "extreme" driving
conditions, or to devote time to additional tasks other than vehicle control,
has been known for some time.
Different types of secondary tasks have been used several times pre-
viously to measure aspects of driving performance. Brown (1961, 1962, 1966,
and 1967) suggested that one can borrow concepts from information theory to
think of the driver as a communications channel with a greater capacity for
dealing with information than is usually required. He also stated that unless
we have some way of measuring the driver's spare capacity, any investigation
is unlikely to differentiate between "concentrated effort and relaxed, over-
learned skill."
Brown, et al.,(1960) measured interference between concurrent tasks of
driving and using a mobile telephone, and found that engaging in the secondary
task increased the "risk taking" of the subjects; i.e., while engaged in tele-
phoning, they attempted maneuvers they had no chance of successfully com-
pleting. They also found a decrease in vehicle speed when telephoning. Subjects
whose vehicle speed decreased most also showed the largest increases in
"errors of judgment." The authors inferred that although the subjects drove
slower to compensate for the stress imposed by driving and telephoning, they
did this only to maintain their accuracy on the secondary task.
In research by Brown and Poulton (1961), "spare mental capacity" was
measured by using a secondary task. The subsidiary tasks were mental arith-
metic and selective attention tasks. Results indicated that the subsidiary tasks
were "sensitive" enough to reveal the greater concentration required to drive in
a shopping area than in a residential area.
10
-------
Brown (1962) also attempted to measure the effects of "fatigue" by a
subsidiary task while studying drivers before and after an eight hour shift of
driving. This experiment indicated that the type of subsidiary task which is
used does not appear to matter very much; however, the relationship between
"cause and effect" can more easily be observed in a subsidiary task which
requires frequent responses.
Brown, et al.,(1967) attempted to evaluate effects of 12 hour automobile
driving by measuring performance of a subsidiary task of time-interval produc-
tion. Performance on the subsidiary task was consistently more variable when
driving was required than on other days, but mean subsidiary task performance
was apparently unrelated to the duration of driving.
11
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CHAPTER 2
CARBON MONOXIDE:
ADMINISTRATION, CONTROL, AND MEASUREMENT
Carbon monoxide (CO) was administered to subjects by two methods.
All subjects were first exposed to air or CO in a dynamic flow chamber for 1.5
to 2.0 hours to produce the desired carboxyhemoglobin (COHb) level. During
specified experiments, subjects remained in the chamber and continued to re-
ceive CO at a concetration sufficient to maintain the desired COHb level. For
experiments involving driving, and for certain laboratory experiments, subjects
were periodically "refreshed" with CO from a pressure cylinder in order to
maintain the desired COHb level.
2.1 Exposure Facilities
A dynamic flow exposure chamber, constructed of vinyl coated masonite
and wood after the design of Hinners (1968), was used for equilibrating subjects
with CO. The cube-shaped chamber measured 2.43 M/side, with a volume of
14,350 liters. The finished chamber was sealed to a tiled floor; the seams
were caulked to eliminate leaks. Two plexiglass windows were fitted on oppo-
site walls. One window was located in the wall opposite the door to facilitate
certain testing; the other was mounted in the aluminum door which afforded the
only access to the chamber. The window in the door allowed the experimenter
to observe the subjects during exposures. Two air-tight portholes were fitted
into the door for transferring materials and taking blood samples from the sub-
jects at various intervals during exposure. An intercom system permitted the
experimenter to maintain continuous voice communication with the subject.
Dynamic flow conditions were maintained by supplying air flow through
the chamber via two vents installed at diametrically opposite corners of the
chamber. A vane-axle fan, installed in the exhaust duct between the chamber
and the exterior of the laboratory, had the capacity to provide one air change
per minute through the chamber. A rectangular mixing duct was attached in
series to the intake vent of the chamber to mix room-air with CO before enter-
ing the exposure chamber. During all experiments, the chamber was operated
at an air flow rate of 0.3 changes per minute. This rate provided a balance be-
tween an acceptable gas equilibration time, chamber noise level, and CO deliv-
ery rate. Pressure in the chamber was maintained at 2 to 4 mm HgO pressure
(negative to ambient) to insure the safety of laboratory personnel. The chamber
was lighfproof when the windows were covered.
13
-------
Several safety devices were incorporated into the exposure facility to
insure subject safety. A high-limit pressure transducer was installed in the
CO delivery system to monitor the absolute flow of CO delivered from the stor-
age cylinder to the chamber intake system. A second pressure transducer was
installed in the chamber influent duct to measure the differential pressure
between the duct and the laboratory. This differential pressure was directly
related to the chamber air flow rate.
Output from the two transducers was connected in series to an electri-
cally operated solenoid valve in the CO delivery system. If the delivery rate
of CO from the cylinder exceeded a predetermined level, the first transducer
interrupted flow by closing the solenoid. If the chamber air flow was decreased
by power failure, significant leakage (e. g., through an open door or porthole,
or a blocked intake or exhaust vent), the chamber transducer output also inter-
rupted CO flow by closing the solenoid.
2.2 Carboxyhemoglobin "Refreshing Technique"
Subjects were administered either air, or a mixture of air and CO
(1000 ppm), by mask through a demand regulator from a pressure cylinder. The
quantity of gas administered was measured by passing all expired air through a
Parkinson Cowan dry gas meter.
Subjects were "refreshed" at intervals of 30-45 minutes to maintain
specified COHb levels. Calculations for quantity of gas to be administered
were based on the interval since last administration using the Colburn (1965)
formula.
Subjects were selected from a group of volunteers who responded to a
series of advertisements in local newspapers soliciting healthy males, over
age 21, who were licensed drivers and were interested in problems of air pol-
lution. Candidates completed the Cornell Medical Health Index Questionnaire
and a habit inventory form (see Appendix D). Prospects that had uneventful
medical histories, and who were professed non-smokers, were selected for
further screening.
Prospects selected from the above group were administered standard
tests for visual acuity and color blindness. If they had adequate uncorrected
vision, they were given a complete physical examination by a physician before
final acceptance. All successful candidates were informed of the experimental
design, advised of health risks, and asked to sign a consent form (see Appendix
D) before the start of the experimental series.
14
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2.4 Experimental Scheduling
Experiments cooperatively conducted by the two research groups required
careful coordination of effort for the most efficient use of 'subjects' and 'investi-
gators' time. The exposure sequence for the experiments conducted in this
study was as follows;
1. Pre-exposure Control Period; Control data were obtained for
psychophysical and psychomotor performance.
2. Exposure Period; Subjects were exposed to controlled concentra-
tions of CO in the test chamber to obtain desired COHb concentrations.
3. Post-exposure Testing Period; Psychophysical and psychomotor
tests conducted during the pre-exposure control period were
repeated.
4. Road Tests; Subjects were tested for driving ability. During this
part of each experiment, it was necessary to "refresh" the subject
periodically at roadside with CO from a storage tank to maintain
the desired COHb levels.
5. Detoxification Period; Subjects were administered oxygen by mask
to reduce blood levels of CO to less than 10%, COHb before release
from the laboratory.
Figure 2.1 is a graphical presentation of the experimental sequence.
2.5 Carboxyhemoglobin Analyses
Blood from all subjects was routinely taken for chemical analyses of COHb.
For most samples, capillary blood from a lanced digit was collected in heparin-
ized microhematocrit tubes. Approximately 0.04 ml blood was adequate for each
analysis. Blood from the cephalic vein was withdrawn from selected subjects for
comparison of venous and capillary samples.
The spectrophotometric method of Commins and Lawther (1965) was evalu-
ated for COHb determination. For this study, the method was modified as follows;
1. Introduction of a self-calibration method, as suggested by
Buchwald (1969).
2. Measure of absorbance at both the bases and the peak in the
Soret band to overcome the error associated with the repro-
ducibility of wavelength in the spectrophotometer.
15
-------
20-
18-
16
14
12-
10-
8-
6-
4-
2-
0
Period 1
Pre-exposure
control
testing
Period 2
Ideal
COHb
levels
o oo
2 hours
Period 3
Post-exposure
laboratory
testing
1 1/2 hours
O O
Period 4
Post-exposure
road testing
O O
2 hours
Period 5
DD
4 hours
1 hour
O Blood COHb determinations
D Oxygen administration
Figure 2.1. —Time sequence of events showing ideal levels for 20% COHb experiments
-------
Radford, et al., (in press) measured the absorbance due to COHb directly
at the isobestic points 413, 431, and the maxima of 421 mu. The modified method
used in this research measured the difference in absorbance between COHb and
an equivalent amount of oxyhemoglobin at 406, 420, and 436 mu, instead of 414,
420, and 426 mu.
The modified method was susceptible to the following sources of errors:
1. Presence of interfering pigments, such as methemoglobin, bile,
salts, etc.;
2. Presence of reduced hemoglobin;
3. Dilution error caused by diluting the blood sample; and
4. Nonconformity with Beer's Law.
These problems were minimized by:
1. All subjects chosen from a select group of healthy males mini-
mizing the possibility of interfering pigments due to illness.
2. Analysis of pre-exposure blood samples for direct comparison
of pre- and post-exposure blood from each subject.
3. Dilution of blood in . 04% ammonia solution. The resulting
solution had a pH of about 10; under this condition, less than
1% reduced hemoglobin is present.
4. Use of gas-free solution and protection of all the solutions
from air. This prevented conversion of COHb to oxyhemoglobin
to minimize dilution error.
5. Determination of difference in absorbance between 100% COHb and
100% oxyhemoglobin for various blood concentrations. The blood
concentration was measured by determining absorbance of 100%
oxyhemoglobin at 370 mu (minima), 414 mu (maxima), and 498 mu
(minima) in the Soret band.
2.6 Atmospheric Carbon Monoxide Analysis
Atmospheric concentrations of CO were measured by one of two methods.
A gas chromatograph (GC) method essentially described by O'Neal, et al., (1968)
was utilized for most experiments.
17
-------
In practice, the gas sample containing CO was passed through a stain-
less steel column packed with 60-80 mesh 5A molecular sieve to separate oxy-
gen, methane, and CO. Prepurified nitrogen was used as the carrier gas.
After separation, the gases were passed through a tubular reactor containing
the reduced nickel catalyst at 320° C. Hydrogen was added to the gases enter-
ing the reactor to convert CO to methane. The effluent from the reactor then
passed to a flame ionization detector.
Sampling of chamber air for CO was conducted by periodic removal of
aliquots in a gas syringe from a port in the effluent duct. The aliquots were
injected immediately into the gas chromatograph.
For later experiments in this series, a Beckman Model 215-B infrared
Analyzer was available to monitor the chamber atmosphere. Air from the
sampling port in the exposure chamber was drawn through an Ascarite "
absorption column to remove carbon dioxide, through a Drierite R absorption
column to remove moisture, and then through the detector of the instrument
using a vacuum pump. Carbon monoxide concentration was displayed on the
analyzer meter in parts per million (ppm) units, and recorded continuously
using a Honeywell strip chart recorder. The analyzer was calibrated before
each exposure using air containing known concentrations of CO from pressure
cylinders.
2.7 Carboxyhemoglobin Analysis Method Evaluation
To determine the reliability of the COHb analysis method, a series of
samples of blood containing various levels of COHb were prepared, coded, and
subsequently analyzed using the technique described. Seven samples of six dif-
ferent concentrations were tested. For this series, a single sample of hepari-
nized human blood was divided into two portions. One portion was equilibrated
with oxygen to convert all hemoglobin to oxyhemoglobin. The second portion
was equilibrated with CO to convert all hemoglobin to COHb. Mixtures of the
two substances were prepared to simulate COHb concentrations from 2% to 40%.
Each mixture was divided into seven containers, coded, and given to a technician
to analyze. Results of these tests appear in Table 2.1.
2.8 In Vivo Carboxyhemoglobin Analyses Verification
Blood samples were withdrawn in triplicate from a subject before expos-
ure to CO, and then two, four, six, and eight hours after the start of an exposure
to 200 ppm CO. The samples were analyzed using the spectrophotometric method
described. Results are presented in Table 2.2.
18
-------
Table 2.1
In Vitro Reproducibility Study on % COHb in Blood
Sample
1
2
3
4
5
6
7
Mean
Standard
Deviation
Concentration
A
1.7
2.1
2.1
2.1
1.8
2.1
2.8
2.1
0.33
B
4.0
4.1
4.0
,4.3
3.9
4.6
4.3
4.2
0.23
C
10.3
9.8
9.6
9.8
10.3
9.6
9.8
9.8
0.27
O
18.0
16.9
17.0
17.5
18.2
18.1
17.8
17.6
0.40
E
29.0
28.8
28.1
28.3
28.7
28.3
28.6
28.5
0.30
F
37.4
40.6
40.0
38.5
39.7
40.4
40.6
39.6
1.13
Table 2.2
In Vivo COHb Analyses Verification
^^^Time
Sample ^^^x.
1
2
3
Mean
Standard
Deviation
Percent (%) Carboxyhemoglobin (COHb) Measured:
Control
1.39
1.99
1.43
1.60
0.11
2 Hours
6.96
7.66
6.86
7.16
0.62
4 Hours
10.6
11.9
10.8
11.1
0.70
6 Hours
13.9
13.3
13.4
13.5
0.32
8 Hours
18.5
18.3
18.6
18.4
0.17
19
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2.9 Atmospheric Carbon Monoxide Analysis Method Evaluations
To determine the reliability of the gas chromatographic method, a series
of air samples containing various concentrations of CO were prepared, coded,
and subsequently tested using the techniques described. Six cylinders containing
CO in concentrations from five to 10,000 ppm were utilized. Results of this
series are presented in Table 2.3.
2.10 Results of Subject COHb Analyses
Results of COHb determination for each subject before exposure to
wither CO or air, at the completion of exposure, and the average levels during
experiments are presented in Tables 2.4 - 2.9 as follows. The levels presented
for the driving experiments were the mean values (2-5 determinations) of blood
samples taken immediately after "refreshment" of the subject.
20
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Table 2.3
Results of CO Analysis of Samples Containing CO
Nominal
Concentration
of Samples
80 ppm
1,000 ppm
10,000 ppm**
80 ppm
10,000 ppm**
5 ppm
Number
of
Tests
12
6
6
3
3
9
Mean
Concentration
Analyzed
69.8
914.8
10,000.0
71.1
10,000.0
5.14
Standard
Deviation
2.35
23.32
91.85
1.20
92.76
0.097
% Coefficient
of
Variation
3.37
2.54
0.92
1.69
0.93
1.89
**
Primary Standard supplied by Matheson Gas Co.
Conditions
Column: 1/2" x 6', packed with 60-80 mesh 5A molecular sieve
Column Temperature: 92° C
Detector Temperature: 132° C
Carrier Gas: Nitrogen
Flow Rate: 38 ml/min.
Hydrogen Flow Rate: 30 ml/min.
Air Flow Rate: 600 ml/min.
Catalyst: Nickel on firebrick at 320° C
Retention Time: 3 minutes
Average Time of Analysis: 5 minutes
21
-------
Table 2.4
Carboxyhemoglobin Levels of Phase A Subjects before and after
120 Minutes of Exposure (490 ppna) and During Driving Experiment
Subject
SI
S2
S3**
S3
S4
S5
S8
S3
S3
S3
S7
S6
Mean
Std. Dev.
%COHb
Pre-exposure
2.0
—
2.0
1.4
2.0
1.3
0.6
1.2
2.4
3.6
2.1
1.9
0.82
End Exposure
_»
18.8
19.5
17.1
19.5
17.3
20.0
19.9
18.4
17.6
18.4
22.9*
19.0
1.63
Road Average
NA
19.0
17.1
NA
NA
20.5
18.8
Two hour exposure
* •"Multiple entries for some subjects denote repeated testing.
22
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Table 2.5
Carboxyhemoglobin Levels of Phase B Subjects before and after
120 Minutes Air Exposure and During Driving Experiment
Subject
89
810
Sll
Sll
S12
S12
S13
S14
S14
Mean
Std. Dev.
%COHb
Pre-exposure
2.2
1.7
2.5
2.0
2.1
2.4
2.3
3.8
1.1
2.2
0.7
End Exposure
2.1
2.2
2.1
1.5
2.0
2.1
1.6
2.4
1.8
2.0
0.3
Road Average
1.8
NA
2.6
2.0
NA
3.2
2.6
2.5
2.2
2.4
0.7
Table 2.6
Carboxyhemoglobin Levels of Phase B Subjects before and after
120 Minutes CO Exposure (450 ppm) and During Driving Experiment
Subject
S9
S10
Sll
S12
S12
S13
S14
S14
Mean
Std. Dev.
%COHb
Pre-exposure
1.0
1.5
1.5
1.2
0.9
1.3
1.0
1.7
1.3
0.4
End Exposure
23.0
24.6
24.4
21.7
20.8
20.8
17.8
15.1
20.7
3.2
Road Average
17.7
20.1
20.1
19.8
18.8
16.0
19.2
16.7
18.0
2.1
23
-------
Table 2.7
Carboxyhemoglobin Levels of Phase C-D Subjects before and after
90 Minutes Air Exposure and During Driving Experiment
O.«1».£,A«*4
Subject
S16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
S33
S34
S35
S36
S37
S38
839
S40
Mean
Std. Dev.
%COHb
Pre-exposure
1.9
0.7
1.4
0.7
0.8
1.4
1.9
0.7
1.3
1.6
0.9
1.1
1.5
1.1
1.2
1.9
_ —
1.2
0.7
1.4
1.4
1.1
1.9
1.5
1.3
0.4
End Exposure
2.0
0.6
2.6
1.3
1.6
0.9
2.9
1.7
1.3
2.2
1.9
— _
1.8
1.6
0.6
1.4
2.9
1.4
2.3
1.2
2.8
2.1
1.7
1.8
0.7
Road Average
3.7
1.1
2.6
1.8
1.7
3.5
8.1
2.7
2.5
1.8
2.5
3.8
2.2
2.7
1.2
2.8
2.4
1.7
2.7*(2.4**)
1.6*(0.8**)
All subjects
**
S26 deleted
24
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Table 2.8
Carboxyhemoglobin Levels of Phases C-D Subjects before and after
90 Minutes CO Exposure (100 ppm) and During Driving Experiment
Subject
816
S17
S18
S19
820
S21
S22
S23
S24
S26
S27
S28
S29
830
831
S32
833
834
835
836
837
838
839
S40
Mean
Std. Dev.
%COHb
Pre-exposure
2.0
2.1
2.1
1.7
1.6
2.1
1.4
3.8
1.1
2.1
2.5
1.3
1.5
2.0
1.3
1.1
1.8
1.1
1.1
1.9
1.9
1.6
1.8
1.2
1.8
0.6
End Exposure
8.9
9.3
10.8
8.9
7.5
—
8.0
8.4
7.3
7.3
5.9
8.6
8.1
6.9
7.9
7.4
6.7
6.8
7.4
8.3
7.1
6.7
9.5
7.3
7.9
1.1
Road Average
7.6
6.9
9.9
8.3
7.3
8.0
8.1
9.2
8.3
7.1
7.5
6.6
6.9
7.6
7.3
8.3
8.4
7.8
0.9
25
-------
Table 2.9
Carboxyhemoglobin Levels of Phase C-D Subjects before and after
90 Minutes CO Exposure (350 ppm) and During Driving Experiment
Subject
816
S17
S18
S19
S20
821
S22
S23
S24
S26
S27
S28
S29
S30
S31
S32
S33
834
S35
S36
S37
S38
S39
840
Mean
Std. Dev.
%COHb
Pre-exposure
1.4
2.1
2.1
1.7
1.0
2.4
2.7
1.7
1.6
1.4
1.4
1.5
1.4
1.7
2.3
0.8
3.6
1.5
1.5
2.1
1.0
2.3
1.9
0.9
1.8
0.6
End Exposure
9.4
9.3
10.8
8.9
9.1
13.0
12.7
17.5
14.4
8.5
12.1
13.2
14.6
9.4
11.6
13.8
10.6
11.9
13.8
11.7
12.2
12.4
11.9
11.1
11.8
2.2
Road Average
8.4
12.6
12.3
14.2
11.7
9.7
11.5
10.1
12.4
12.2
10.8
11.2
9.4
9.9
12.5
10.2
10.7
11.2
1.5
26
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CHAPTER 3
SIMPLE LABORATORY TESTS
3.1 Introduction
Several psychophysical and simple psychomotor tests were evaluated as
part of the comprehensive plan to measure CO effects. Physiological measures
of altered perception were also eliminated because of the poor experience of
others. (See Michon, 1964, for discussion of this problem.)
Tests which measured coordination, concept formation, and various
aspects of visual discrimination were sought. A number of tests not previously
used to demonstrate CO effects were selected. These tests were sufficiently
well-known so that a body of literature and range of normative values existed
for each. Since any psychological test reflects mental process and not discrete
anatomic function, it was reasoned that various measures, as unrelated as
possible to each other, would be more likely to detect pharmacologic effects
which are usually quite broad. Several well known tests including the Porteus
Maze were rejected since large doses of depressants; e.g., alcohol, or stimu-
lants; e.g., amphetamines, were required to obtain exceptional scores, and
the present study was concerned with indications of minimal intoxication.
3.2 Simple Laboratory Tasks Descriptions
The simple psychophysical/psychomotor tasks used were all administered
within 60 minutes, inexpensive, required no apparatus inconvenient to space
considerations, and were scored by technicians with limited experience. Rapid
scoring was required so that extreme scores after administration of CO could
be noted immediately and used as criteria by the medical staff to limit further
exposure and further testing in the driving tasks. The selected tasks were
star-tracing, finger-tapping, rail-walking, Minnesota Spatial Relations Test,
brightness discrimination, and dark adaptation.'
3.2.1 Mirror-Drawing; Star-Tracing
This test demonstrated eye-hand coordination by requiring a subject to
trace .between two eight-point stars, keeping within an 1/8 inch band while
watching the motion of the hand-held stylus in a mirror. Since this activity is
not related to daily experience, all subjects were naive.
27
-------
For this investigation, the Star-Tracing Test was scored by dividing the
total distance correctly drawn; i.e., within the space between the stars, by the
time required to perform the task. This test was administered before and after
air or CO exposure (Nominal 20% COHb) for a total of 12 times to three subjects.
3.2.2 Finger-Tapping
Subjects used a telegraph key to tap as rapidly as possible for one minute
to evaluate fine muscle coordination before and after air or CO exposure.
Impaired performance of this task reflected "traffic control problems in the
central nervous system," Michon (1964). For example, if stimuli were too
complex for immediate transmittal, queuing and timing would be necessary and
frequently led to performance irregularity. For an investigation of tapping as
a measure of CO effects, the gross score (number of taps) over one minute was
accepted without further analysis of tapping pattern (regularity). The test was
administered to six subjects during Phase A.
3.2.3 Rail-Walking
This stationary balancing test with simple instructions, easy scoring,
and modest space requirements seemed ideal for inclusion in the CO study.
The Bail-Walking Test, as originally described (Heath, 1949), consisted
of walking three wooden rails: 9* x 4", 9' x 2", and 6' x 1", of sufficient height
to prevent contact of feet with the floor. Each rail was graded in units of feet,
and was walked barefoot, heel-to-toe, by each subject three times. Because
of the difference in degree of difficulty of each rail, the raw score for the
three rails was weighted 1-2-4. Thus, the total possible score is (1 x 27) +
(2 x 27) + (4 x 18), or 153 points. Heath standardized the test on 1,013 troops
selected from a non-special unit which would be regarded as an average cross
section of the white male population of Army age. The mean rail-walking score
for that group was 130.73 points with a standard deviation of 19.63 points.
The author notes that the poorly coordinated, and some special types of the
retarded, can be identified by this test. A distinct limitation is failure to
differentiate well at the upper levels of locomotor coordination; i.e., above
average and superior.
Subjects participating in the carbon monoxide investigation were able to
complete the Rail-Walking Test as described with little or no error. Therefore,
the test was revised to include an additional rail, 5/8" wide, 10' long, and 4"
high. An arbitrary weighting of score was 6.4 x 30 = 192, for a perfect score
on this rail.
28
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Data were recorded in unassisted distance each subject walked barefoot.
One practice trial was given and the next three trials were recorded. Few
subjects were able to walk the length of the rail without losing balance even
under control conditions. This test was carried out both before and after CO
exposure. Data were collected on 120 trials given to eight different subjects.
3.2.4 Minnesota Spatial Relations Test
The Minnesota Spatial Relations Test was chosen to evaluate the capacity
of CO to alter speed and accuracy in comprehension and manipulation of objects
of different sizes and shapes. This test, first published in 1930, consisted of
four form boards each containing 58 variously shaped cutouts. One set of blocks
was used with Boards A and B, another with Boards C and D. The small forms
were placed into the appropriate holes in the boards as rapidly as possible.
Test score was the time, in seconds, to perform four tasks: (1) move the blocks
from Board A to B, (2) B to A, (3) C to D, and (4) D to C. All the blocks were in
their correct position before the subject could move on to the next board.
The test was administered in the chamber prior to, and again following,
exposure to CO. This test was taken by six different subjects 34 times.
3.2.5 Brightness Discrimination
Recognition of objects is based on perception of brightness difference.
This is important to driving, since an obstacle may appear either as a darker
or a lighter object compared to the horizon or alternate background.
Measurement of the ability to match the intensity of two light sources is
one way to assess this contrast sensitivity.
In this study, measurement of contrast sensitivity (brightness discrimina-
tion) was measured at several wavelengths to maximize the possibility of finding
some degradation in contrast sensitivity under the influence of CO.
In the first series, subjects were required to match brightness of eight
pairs of colored lights while seated in the lightproof exposure chamber. Thirty
minutes dark adaptation preceded each session.
The light box was mounted on the chamber wall 7-1/2" from the seated
subject. Each target was a 1-1/2" diameter circular filter placed 1" from the
edge of the duplicate. The target represented 1° of visual arc. Incandescent
light was passed through Rohm and Haas plexiglas filters to produce the test
colors as follows:
29
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Colors Wavelength (Nanometer)
Red I 700
Red n 680
Orange 640
Yellow 600
Green 540
Violet 450
Blue 420
White
The paired lights were turned on by the experimenter, and the control
target set at control voltage to give 35 millilamberts illumination. The subject
then matched the brightness of the experimental target by turning the potentio-
meter of his hand-held control box. Voltage differences between the two targets
were recorded for each of the colors to the nearest thousandth volt on a digital
recording voltmeter.
Two red filters were used because:
1. the eye does not detect the red light as well as some
of the others (Bernberg, 1960), and
2. the red light is used extensively on the automobile.
Four subjects were tested on all eight colors after CO or air exposures
for the Nominal 20% COHb series.
During later series, tests included only Red I, Green, and White test
lights. Thirteen subjects were tested at each exposure level in the later series.
3.2.6 Dark Adaptation
The Dark Adaptation Tests of Baker (1949), and Wald and Clark (1937),
were modified for this investigation.
Each subject was seated in the lightproof exposure chamber 30 minutes
prior to testing to allow near-maximum rhodopsin regeneration.
At the end of this time, a 90% reflectance screen, placed 7-1/2' from
the subject, was illuminated at 90 millilamberts. After five minutes of bright
light adaptation, the projection screen was darkened and the subject was
requested to identify the dim light target, either a square, circle, triangle, or
diamond. When the subject was able to identify the target, he signaled and the
target light was changed and reduced in intensity. Levels of intensity ranged
from 8 x 10~3 millilamberts to 2 x 10~5 millilamberts. Up to 16 steps could
be tested in the 1000 second test period.
30
-------
Six subjects were tested after exposure to air or CO during the first
series of experiments, (Nominal 20% COHb). Fourteen subjects were tested
during Phase C-D after exposure to air or CO (nominal 7% COHb and 14% COHb).
3.3 Results
3.3.1 Mirror-drawing - Star-tracing
The post-exposure testing of the reversed star-tracing showed no
increased tremulousness after CO exposure (nominal 20% COHb), and most of
the subjects improved at each subsequent trial on this particular task. No
further analyses were conducted on these data.
3.3.2 Finger-tapping
Results of the Finger-tapping test conducted on six subjects are presented
in Table 3.1. Inspection of the data showed that CO has no effect on finger-
tapping performance. This test was not used for the later series of experi-
ments.
Table 3.1
Results of Finger-tapping Performance Test
Experiment
Control
Nominal 20% COHb
Taps/Mn. ^_
Mean
349.3
352.2
Std. Dev.
54.8
52.5
31
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3.3.3 Rail-walking
Results of the Rail-walking Test, performed as originally described on
the first series of five subjects, appear in Table 3.2. The maximum score
for this test was 153. All score means were within 5% of the maximum attain-
able score. This test was not used for subsequent experiments.
Table 3.2
Results of Rail-walking Test
Phase A Subjects
Experiment
Control
Nominal 20% COHb
Mean Rail-walking Performance
Mean
153.0
147.0
Std. Dev.
0
8.6
Results of the Modified Rail-walking Test used in the second series of
subjects appear in Table 3.3. The maximum score for this test was 192.
Although there were differences in the mean scores for this series, none were
significant or related to CO exposure.
Table 3.3
Results of Modified Rail-walking Test
Phase B Subjects
Experiment
Control
Nominal 20% COHb
Mean Rail-walking Performance
(Standard Deviation)
Mean
134.4
152.0
Std. Dev.
48.2
32.4
32
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3.3.4 Spatial Relations Test
Results of the Spatial Relations Test conducted on five subjects in Phase
A are presented in Table 3.4. Inspection of the data suggests the CO may have
had an effect in performance. However, in this series, all control experiments
were conducted before the nominal 20% COHb experiments. Therefore, the
differences observed in Table 3.4 must be attributed to learning.
Table 3.4
Results of Spatial Relations Test
Phase A Subjects
Experiment
Control
Nominal 20% COHb
Board
A
B
C
D
Total
A
B
C
D
Total
Mean Spatial Relations Performance
Time: Seconds
Mean
173.4
161.8
200.0
192.2
727.4
144.5
146.4
167.2
151.6
609.8
Std. Dev.
71.7
42.3
94.1
75.4
227.9
25.9
19.1
45.9
32.5
113.2
3.3.5 Brightness Discrimination
Results of the Brightness Discrimination Test on four subjects in Phase
A using all eight colors appear in Table 3.5. Results are presented as devia-
tion from control voltage, expressed in percent. In all colors except yellow,
there appear to be an increase in difference from the control lamp and an
increased variance.
33
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Table 3.5
Results of Brightness Discrimination Test
Phase A
Light Source
Red I
RedH
Orange
Yellow
Green
Violet
Blue
White
% Difference from Control Lamp
(Standard Deviation)
Control
7.35 (3.19)
3.60 (3.18)
3.98 (1.71)
7.68 (3.95)
2.78 (2.16)
3.98 (2.15)
3.50 (2.64)
3.59 (2.77)
Nominal 20%COHb
7.60 (4.78)
6.72(6.81)
6.66 (6.13)
4.98 (3.03)
6.45 (4.72)
4.66 (3.83)
4.24 (3.59)
3.79 (2.83)
Statistical analyses of the mean percent difference data from Table 3.4
are presented in Table 3.6. For these analyses, the variance was assumed to
be a function of COHb level (C), and the light source (S).
Table 3.6
Analysis of Variance
of Brightness Discrimination Data
Source
Total
C
S
CxS
DF
15
1
7
7
Sum of Squares
43.45
4.47
23.56
15.92
Mean Squares
-
4.47
3.36
2.20
34
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When all light sources were included in the analyses, no statistical
significance (p < .75) could be assigned to the observed effect. However,
if the data for the yellow light source are excluded from consideration, the
observed differences between control and 20% nominal COHb become highly
significant (p > .95). This analyses appears in Table 3.7.
Table 3.7
Analysis of Variance of Brightness Discrimination Data
Disregarding Yellow Light Source
Source
Total
C
S
CxS
DF
13
1
6
6
Sum of Squares
35.38
9.18
19.63
6.56
Mean Squares
-
9.18
3.27
•
1.09
Analysis of variance of the standard deviation calculated from the con-
trol and the 20% COHb data using the eight light sources is presented in Table
3.8. Again, the standard deviation was assumed to be a function of COHb
level and of the different light sources.
Table 3.8
Analysis of Variance of Standard Deviation
Source
Total
CO
LS
COx LS
DF
15
1
7
7
Sum of Squares
30.15
12.20
6.96
10.99
Mean Squares
-
12.20
.99
1.57
35
-------
Analyses of the differences in standard deviation between control and
nominal 20% COHb, including all light sources, indicates that there is a highly
significant (p > .99) increase in variance due to the CO exposure.
It should be noted that increases were observed in both mean difference
from control voltage and in the standard deviation between the control experi-
ment and the 20% COHb experiment except for the yellow light. There is no
obvious explanation for the apparent discrepency in the results from the yellow
light source.
Results of the Brightness Discrimination Test conducted for subsequent
experiments on subjects in Phases C and D at control and nominal 7% and 14%
COHb, appear in Table 3.9. These results are presented as deviation from
control voltage expressed in percent. Inspection of these data indicated that no
differences in contrast sensitivity could be attributed to elevated COHb in this
series. No statistical analysis were conducted on these data.
Table 3.9
Results of Brightness Discrimination Test
Phases C - D
Light
Source
Red I
Green
White
Mean Percent Difference From Control Lamp
(Standard Deviation)
Control COHb
5.37 (4.45)
8.65 (5.82)
4.15 (3.55)
Nominal 7% COHb
4.70 (2.99)
8.24 (4.93)
5.63 (3.82)
Nominal 14% COHb
4.42 (4.16)
9.87 (6.30)
3.57 (3.03)
3.3.6 Dark Adaptation
Results of the dark adaptation test conducted on subjects during this
investigation demonstrated that there is considerable inter- and intra-subject
variability in performance of this test. Figure 3.1 presents an example of the
intra-subject variation observed on S-19 during a series of control trials.
Figure 3.2 presents an example of the inter-subject variation using the most
representative curves from a series of three trials on each of the subjects.
36
-------
-2.00
-4.00 -
Subject 19
Various COHb Levels
100
200
300
400 500 600
TIME (SECS)
Figure 3.1. —Dark Adaptation Curves.
700
800
900
1000
-------
W
H
-2.00-
-2.25-
-2.50-
-2.75-
-3.00-
S H -3.25H
-3.50-
-3.75-
-4.00-
I
0
100
Trial 3
Subject 19
Multiple Trials
200 300
400 500 600
TIME (SECS)
700
800
900 1000
Figure 3.2. —Dark- Adaptation Curves.
-------
The inter- and intra-subject variability in this test exceeded the dif-
ferences observed as a result of CO exposure. An example of the effect that
CO exposure had on subject performance is presented in Figure 3.3. The data
used in Figure 3.3 are the most representative curves selected from three
trials at each exposure level tested. Most subjects tested demonstrated a
pattern similar to the data presented in Figure 3.3. No quantitative analyses
were attempted on these results.
39
-------
en
8
W
s
to
2
H
a
8
-2.00
-2.25-
-2.50-
-2.75-
-3.00-
-3.25-
-3.50-
-3.75-
-4.00-
Subject 19
Subject
—I—
100
200 300
400 500 600
TIME (SECS)
—T~
700
800
900 1000
Figure 3.3.—Dark Adaptation Curves.
-------
CHAPTER 4
COMPLEX LABORATORY TASKS WITH 20% COHb
During the first year of this research (Phases A and B) complex psycho-
motor tests were designed to initially ascertain performance effects due to large
differences in COHb (0 and 20%). These tests and the subsequent results are
reported in this section of the report.
The distinction between Phases A and B is only to designate two different
groups of subjects. The test protocols were for all practical purposes the same.
The initial set of studies (Phase A) should be viewed as preliminary tests to
shakedown the methodology and provide group overall effects prior to Phase B.
4.1 Description of Tasks
4.1.1 Time Estimation Task
During the trials, subjects performed three time estimation tasks. For
the first of these, subjects were presented with an example tone, 4 seconds in
duration, in their earphones. They were instructed to press their pushbutton
each time they felt that four seconds had elapsed. The trial lasted 100 seconds.
At the start of the next trial subjects were presented with a tone two
seconds in duration. They were instructed to press their pushbutton each time
they felt that two seconds had elapsed. This trial lasted 50 seconds. The final
time estimation trial was 200 seconds long. Subjects were first presented with
a tone eight seconds in duration and then instructed to press their pushbuttons
once every eight seconds.
The performance measures for this task included:
1. average time estimates, over 25 estimates, and
2. sample variances of the time estimates.
4.1.2 Choice Reaction Time Tests
Subjects responded selectively to numbers projected on the screen at 1.5
second intervals. The numbers appeared at four different locations on the screen;
right or left of the oscilloscope face and centered at visual angles of three or
nine degrees to the subject's central line of sight. Each stimulus subtended a
41
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visual angle of 50 minutes. Subjects responded to the same set of seven numbers,
arranged in a different random order on each trial. The numbers were divided
into three sets of size one, two, and four stimuli. The members of each set
occurred equally often on each trial.
A target number was first presented. Thereafter, a set of one, two, and
four figures was presented on either side of the scope. If the target number was
presented in either set, the subject was instructed to respond using that button on
the steering wheel corresponding to whether the target was left or right of the
scope.
The performance measure for this task was choice reaction time(CRT)
recorded as a function of stimulus set size and location (angle from line of
sight).
4.1.3 Tracking Task
This was a one dimensional (horizontal) tracking task. The target moved
across the oscilloscope face in a random fashion at various sweep rates. Target
reversal rates were randomly developed in an electronic signal generator. The
subject operated the cursor on the scope by means of the steering wheel and
attempted to superimpose the cursor on the target (see Appendix A). Tracking
complexity was achieved by changing sweep rates.
The measures of performance for this task were:
1. MAE - mean absolute tracking error - the mean of the
absolute deviation of the cursor from the target, and
2. tracking time lag (in seconds) - the cross correlation
function between the input tracking function (target)
and the subjects output function (cursor). This is
merely the average lag between target movement and
cursor movement.
4.1.4 Dual Task; Tracking Plus Choice Reaction Time (CRT)
For 16, 40 second trials subjects simultaneously tracked and responded
to the choice reaction time task. For ease of description these 16 trials will be
termed dual task trials with four trials performed at each of four different levels
of tracking complexity ranging from level zero (CRT only) through the three levels
of tracking complexity (i.e., increasing target speed).
Subjects were presented with fourteen pairs of visual stimuli projected
on the screen surrounding the scope face with one member of the pair located on
either side of the scope face. Eight of the fourteen stimulus pairs contained a
42
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target number and a letter. The number appeared four times on one side of the
scope and four times on the other. The order of presentation of target numbers
was randomly chosen. The subject's task was to press the button on the same
side of the steering wheel as the side of the scope face on which the number
appeared. Stimulus duration was one second and interstimulus intervals were
chosen randomly between 1.0 and 2.5 seconds.
The performance measures for this dual task were:
1. MAE (defined above),
2. CRT (choice reaction time),
3. errors in stimuli detection, and
4. time lag in tracking (defined above).
4.2 Test Schedules
During the Phase A test period, six subjects performed in three separate
experimental sessions, one session on each of three different days. During the
first session, subjects were introduced to the tasks. They practiced the pursuit
tracking portion and were familiarized with the choice reaction time (CRT) and
combined tracking plus choice reaction time tasks. On each of the two remaining
sessions, subjects breathed the experimental atmospheres before participating
in the testing.
The followingorder of tasks was followed throughout the experimentation:
Trials Time Duration Task
1-3 40 seconds Tracking Only
4 100 seconds Time Estimation (4 second intervals)
5 50 seconds Time Estimation (2 second intervals)
6 200 seconds Time Estimation (8 second intervals)
7-14 40 seconds Tracking plus Choice Reaction Time or
Choice Reaction Time Only
15-16 40 seconds Tracking plus Time Estimation
(4 second intervals)
17-24 40 seconds Tracking plus Choice Reaction Time or
Choice Reaction Time Only
25-27 40 seconds Tracking Only
For the second series of tests (Phase B), six additional subjects were
tested with the two treatment conditions (nominally 0 and 20% COHb). Table
4.1 illustrates the subject scheduling over the six calendar days of testing.
Each subject participated in four laboratory test sessions, two before chamber
exposure and two after. In addition, three of the six subjects were tested on
each of two other days after a driving experiment which lasted approximately
two hours.
43
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Table 4.1
Phase B Subject Schedule
Time
6-8 am
8-10 am
10-12 am
1-2 pm
Treatment
Pre- exposure
session
Treatment
Post-exposure
Experimental
session after
driving
Air
Day 1*
S9
S14
S9
Sll
S14
S9
S14
Sll
CO
Day 2
89
S14
89
Sll
S14
S9
S14
Sll
CO
Day 3
Sll
S13
810
Sll
813
Sll
S13
810
Air
Day 4
Sll
813
810
Sll
S13
Sll
813
810
Air
Day 5
810
812
810
812
813
S10
812
813
CO
Day 6
S10
SI 2
810
812
813
810
812
813
*Days denote calendar days of testing.
-------
4.3 Phase A Results
The major results of the Phase A psychomotor experiment are sum-
marized as follows:
1. No significant differences (p < .75) were observed in either
CRT or MAE data as a result of 20% COHb intoxication for
individual tasks.
2. A significant (p > .90) increase in tracking time lag was
observed due to 20% COHb for the dual task. This increase
in crosscorrelation in a continuous tracking task has been
compared to an increase in reaction time in discrete tasks.
3. Time estimation performance was slightly affected (p > .75)
by 20% COHb intoxication, however, considerable inter-
ference effects between tasks were observed when tracking
and time estimation were performed simultaneously.
4. Mean absolute errors (MAE) increased significantly (p > .99)
as level of tracking complexity increased. These increases
were even more pronounced in the dual task.
5. Choice reaction times (CRT) did not significantly (p < .75)
increase as tracking complexity increased in the dual task.
4.3.1 Discussion of Results
With two exceptions (points 2 and 3), the above results suggest that the
majority of the performance indices investigated in this preliminary study failed
to deteriorate significantly under the effects of 20% COHb levels. Summary data
for the two performance measures affected by COHb level, pursuit tracking lag
and time estimation, are presented in Tables 4.2 and 4.3, respectively.
The increase in the tracking time lag under the effects of 20% COHb levels
verified the hypothesis that the subjects' response to a change in the direction of
the tracking sensor would be increased with carboxyhemoglobin. The result is
viewed as cautious support for the models proposed by Garvey (1960).
A significant reduction in the mean of the time estimates was demon-
strated over the combined data in the time estimation task. The literature does
not report a precedent for this result, although, close observation of the data
in Stewart, et al. (1970) indicates that in 39 of the 48 categories of time estima-
tion which were tested at elevated CO atmospheres, mean normalized time
estimates were below the mean normalized time estimate for the control condition.
45
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Table 4.2
Average Time Lag (msec.), Dual Task,
Low Complexity
Subject
82
S3
S5
S6
S8
Am
267
200
125
204
77
CO
242
326
143
275
209
A = CO - Am
-25
126
18
71
132
In many instances during the CRT analyses, the trend toward deteriorated
performance under elevated COHb levels did not materialize into a significant
effect because of the 'noise' (variability inherent in the CRT data). While a
large percent of the intra-subject variability indicated in the CRT data is probably
due to the secondary nature of the CRT task, substantial variation must have been
the result of performance on a relatively novel task. In the latter tests, the
detection and control of the learning factors became a necessity.
4.4 Phase B Results
The results of these laboratory studies can be divided into two categories:
1. those which measured effects of experimental control
variables, and
2. those which measured the effects of 20% COHb.
In the former category are such factors as learning (or day) effects, size of the'
stimulus set, tracking complexity, visual angle, and before versus after driving
performance. It will be assumed for purposes of this section of the report that
the effects of these control variables are of interest only as they relate to
possible 20% COHb effects. A more detailed analyses of these variables may
be found in Attwood (1972).
Upon analyzing the results of the Phase B data, it was observed that
subjects S9 and S14 exhibited large "novel learning" effects which were attributed
to experimenter biases in starting the Phase B data collection (subjects S9 and
S14 were the first subjects tested). Rather than inflate the residual error
variances of this factor screening experiment, these two subjects were eliminated
from the analyses which follow.
46
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Table 4.3
Summary Statistics of Time Estimation Data - Five Subjects
TIME ESTIMATION
*
^
Subject g
do
n
S8 x
s
n
S4 x
8
n
S5 x
8
n
S6 x
S
n
S3 x
s
Am
2 sec
16
264
.35
NA
NA
16
3.19
.61
16
2.67
.27
4 sec
16
6.56
.72
NA
NA
16
5.43
.15
16
7.06
1.18
8 sec
16
7.30
.49
NA
NA
15
11.8
1.3
15
11.89
1.69
CO
2 sec
NAW
16
1.83
.26
16
2.34
.188
16
2.62
.5
16
2.28
.28
4 sec
12
4.18
.33
16
4.77
.49
16
4.77
.49
16
5.19
.406
16
3.58
.39
8 sec
NA
16
8.3
.65
16
6.52
.65
16
10.2
1.87
16
7.74
1.37
n = number of samples
x = mean time estimate
s = sample variance of time estimates
WNA = data not available
-------
The data for the remaining four subjects were analyzed with fixed subject
effects models. As a result, all statistical tests for 20% COHb effects on per-
formance showed significant effects for p > .95. The reader should recognize
that these "statistically significant" results cannot necessarily be extrapolated
beyond the four subjects of this particular phase. However, treatment of
subjects as "fixed effects" is not uncommon in exploratory factor screening
research of this kind. The validity and interpretation of the resulting interaction
effects (subjects by COHb level, for example) will be postponed to Phases C
and Dwith a larger sample size (16 subjects).
4.4.1 Choice Reaction Times
The choice reaction times for the three subjects who also participated
in the driving studies, averaged across all data for tasks 9 and 11 (CRT only
and dual task), were compared for 20% COHb differences and before versus after
driving differences. The means for these choice reaction time data are pre-
sented in Figure 4.1.
This figure illustrates a mild degradation in choice reaction times
(increases)with20% COHb exposure. This COHb effect was slightly affected
by the "fatigue" of driving with the COHb effect somewhat smaller after partici-
pation in the driving studies.
The additional effects of loading (task 1 versus task 11) and size of the
stimulus set are illustrated in Figure 4.2. This figure shows (for the "after
driving" data) the additional increases in choice reaction times attributable to
the dual task loading and increased size of the stimulus set. It is interesting
to note that there are no consistent interactions between the COHb level and set
size or task difficulty which would be represented by lack of parallel in the
four lines.
4.4.2 Mean Absolute Error Scores
Similarly, the mean absolute error scores for the three subjects were
analyzed before and after driving as presented in Figure 4.3. This figure also
shows a mild degradation (increases) in scores for the 20% COHb condition.
These increases do not appear to be dependent on the before versus after driving
differences (no lack of parallel). Figure 4.4 shows the dual task mean absolute
errors were highly dependent on level of tracking complexity but there were no
synergistic or interactive COHb by complexity effects.
Figure 4.5 depicts how four subjects (S10 through S13) traded off the
primary and secondary tasks when exposed to CO as compared to air. Subjects
S10 and Sll maintained primary task performance (MAE not affected) but
demonstrated COHb effects in CRT. Subjects S12 and S13 allowed both MAE
48
-------
After driving
Before driving
CRT
(msec)
640-
620 -
600
580
560
540 -
520
4
0
Air
CO
Figure 4.1. —Mean choice reaction time (CRT) as a function of
the AIR-CO treatment and the before- versus after-
driving condition
49
-------
o-
A-
A-
•• Dual Task-CO Exposure
-O Dual Task-AIR Exposure
A CRT Only-CO Exposure
\ CRT Only-Am Exposure
CRT
(msec)
670-
650
630
610
590
570
550
530
510
49
Figure 4.2.—Mean choice reaction time (CRT) as a function
of the size of stimulus set, COHb level, and
dual-task or CRT-only condition
50
-------
• • After driving
A A Before driving
55-
50
MAE
(arbitrary units)
45-
40.
Air
CO
Figure 4.3.—Average mean absolute tracking error (MAE) as a
function of the air-CO treatment and the before-
versus after-driving condition
51
-------
CO-Exposure
AER-Exposure
70
68
66
64
62
60
58
MAE 56
(arbitrary units)
54
52
50
48
46
44
42
40
Lo
Med
Complexity
High
Figure 4.4.—Average mean absolute tracking error (MAE) as a
function of the level of tracking complexity and
air-CO exposure
52
-------
CRT
(msec)
800
750
700
650
600
550
500 .
AIR-Exposure
100
LAG
0
CO-Exposure
MAE
LAG (msec)
150 200
250
S12
S13 .,'
40 45 50 55 60 65 70
MAE (arbitrary units)
Figure 4.5.—Mean choice reaction time (CRT) versus average mean
absolute tracking error (MAE) and mean tracking
time-lag (LAG)
53
-------
and CRT performance to become deteriorated due to CO effects over air. The
results suggest that subjects do not always maintain primary task performance
(MAE) at the expense of secondary task performance (CRT). Dual task research
often indicates that despite instructions, subjects will often choose their own
strategy (rarely a cognitive decision). The important point is that subjects.
although not aware of the air versus CO condition, suffered performance loss
under CO in one or both of the tasks.
4.4.3 Tracking Time Lags
Lag time effects (i.e., the time between target and cursor movement)
were much the same as MAE results. These corresponding trade-offs between
lag times and mean absolute errors for the same four subjects are illustrated
in Figure 4.6. As a single dimensional response, the mean tracking time lags
as functions of tracking complexity and COHb level are presented in Figure 4.7.
Notice in this case, the apparent COHb effect coupled with an interaction effect
of COHb with complexity. The magnitude of the COHb effect was diminished
with increased tracking complexity levels.
4.5 Summary of Phase B Results
The data from the Phase B tests suggest that mild decrements in per-
formance of the time shared psychomotor task (Til) can be expected with 20%
COHb levels. Performance of the choice reaction task (T9) alone was also
observed to deteriorate somewhat with 20% COHb levels. In contrast, per-
formance did not deteriorate with 20% COHb levels in the pursuit tracking task,
T10, when it was performed alone (Figure not presented).
This inconsistency of individual tasks to demonstrate 20% COHb effects
confirmed the necessity for considering dualtask techniques in the future
Phases C and D. The subjects were observed to trade-off performance on the
tracking task for performance on the choice reaction time task as the tracking
task became more complex. This behavior seemed to be an attempt to optimize
total task performance by attending less to the most difficult (tracking) task
and more to the CRT task even though the subjects had been instructed other-
wise.
It is also important to observe the consistent (additive) effect on per-
formance of all the tasks due to driving exposure. There was no evidence of
a synergistic degradation in performance after driving with 20% COHb.
54
-------
Subject
AIR-Exposure 0 »• CO-Exposure
LAG
(msec)
240 .
•
220
200
180 -
•
160 -
140 -
120 ,
100 •
80 .
60.
Sll
40
S13
S10
812
45 50 55
MAE (arbitrary units)
60
65
Figure 4.6.—Mean tracking time-lag (LAG) versus average mean
absolute tracking error (MAE)
55
-------
CO-Exposure
AIR-Exposure
190-
LAG
(msec)
170
150
Lo
Med
Complexity
High
Figure 4.7.—Mean tracking time-lag (LAG) as a function of the
level of tracking complexity and the air and CO
exposure
56
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CHAPTER 5
COMPLEX LABORATORY TASKS
WITH 7 AND 14% COHb
During the second year of this research, the previously discussed
psychomotor tests (developed in year 1) were again employed to ascertain
whether noticed COHb effects with 20% levels would be preserved with lower
levels of nominally 7% and 14% COHb.
Complete descriptions of the tasks employed may be found in Chapter 4
while instrumentation and subject instructions may be found in Appendix A.
Since the majority of the effects of 20% COHb (Phases A and B) were found in
dual task loading (Til), the analyses of the following section are confined to
the dual task data of Phasas C and D.
5.1 Results
Of primary importance in this series of tests was the possible deteriora-
tion of performance in the dual task since this was found at 20% COHb levels.
Data for 15 subjects from two phases (Phases C and D) were combined for
analysis of choice reaction times and mean absolute errors for the dual task.
Table 5.1 presents an analysis of variance for the choice response
times observed as a function of COHb level (M) (treated nominally as 0, 7, and
14%). This analysis shows no significant effect (p < .75) due to COHb level.
This is due to a large differential subject by COHb (S x M) error. As might be
expected with choice reaction times, the CRT complexity (stimulus set size, C)
did significantly affect performance (p > . 99), while MAE complexity (tracking
complexity, T) did not (p < .75). Also, there were no apparent COHb by tracking
complexity (M x T) or COHb by stimulus set size (M x C) effects (p < .75 for
both).
Table 5.2 presents a similar analysis for mean absolute error scores.
Again, subjects are most variable. No significant (p < .75) effects are evidenced
due to COHb level due to a large apparent interactive subject by COHb level
(S x M) effect (p > .99). Also, as expected, there is a highly significant (p > .99)
relation between tracking complexity (T) and mean absolute error scores, with
negligible effect due to stimulus set size (p < .75). Finally, there is no evidence
of differential COHb by tracking complexity (M x T) or stimulus set size (M x C)
effects (p < .75 for both).
57
-------
Table 5.1
Analysis of Variance of Choice Reaction Time,
Phases C and D, 15 Subjects
Source
Subjects (S)
COHb (M)
Sx M
Tracking Complexity (T)
Stimulus Set Size (C)
TxC
MxT
MxC
Residual
df
14
2
28
2
2
4
4
4
344
SS
9.81xl06
36,639
1.4xl06
9,046
664,048
125,998
38,641
15,129
2.937xl06
MS
7.0xl05
18,319
48,169
4,523
332,024
31.499
9,660
3,782
8,537
F
82
<1
5.6
<1
39
3.7
1.1
<1
J?
>.99
<.75
>.99
<.75
>.99
>.99
<.75
<.75
Total
404 1.499xl07
Source
Table 5.2
Analysis of Variance of Mean Absolute Error,
Phases C and D, 15 Subjects
df
SS
MS
Subjects (S)
COHb (M)
Sx M
Tracking Complexity (T)
Stimulus Set Size (C)
TxC
MxT
MxC
Residual
14
2
28
2
2
4
4
4
344
55,498
327
5,194
15,223
32
69
150
133
12,872
3,964
163
186
7,611
16
17
38
33
37,4
106
< 1
4.97
203
< 1
< 1
1.02
< 1
>.99
<.75
>.99
>.99
<.75
<.75
<.75
<.75
58
-------
The existence of a large subject by COHb level interactions suggest
four possible explanations (in both the choice reaction time and mean absolute
error data):
1. there are fixed learning effects (day effects) confounding
this interaction effect,
2. SxM is really random day to day variation by subjects,
3. there are groupings of subjects who predictably exhibit
either better or worse performance, or
4. combinations of the above.
To examine the first possibility, the data were analyzed with the model:
E (performance) = n + Sj + D. + b0COHb + b^COHb)2.
For this model, the expected performance is a function of some mean (n), sub-
ject effect (S ), day or learning effect (D ), and linear and quadratic COHb effects.
For analysis purposes, data for the nine combinations of tracking complexity and
stimulus set size were averaged by subject and day. COHb level was treated
quantitatively by actual level observed. Analyses of variances for this model
for choice reaction times and mean absolute errors are presented in Tables 5.3
and 5.4, respectively. Neither analysis indicates a significant learning (or day)
effect, so suggestion 1 does not explain the large subject by COHb (SxM) inter-
action.
Table 5.3
Analysis of Variance of Choice Reaction Time Data
Adjusting for Learning Effects
Source df_ SS_ MS F p_
Subjects 14 1.4 .100 17.8 >.99
Days 2 10.7X10"4 .54xlO~3 <1 <.75
CO 1 4.9xlO'3 4.9xlO~3 <1 <.75
CO2 1 3.4xlO~3 3.4xlO~3 <1 <.75
Residual 25 .140 5.6xlO~3
Total 43 1.548
59
-------
Table 5.4
Analysis of Variance of Mean Absolute Errors
Adjusting for Learning Effects
Source df SS MS
Subjects
Days
CO
CO2
Residual
14
2
1
1
25
2803
75
137
30
595
200.2
37.5
137
30
23.8
8.4
1.6
5.8
1.26
>.99
<.75
>.95
<.75
Total 43 3641
To examine the data for possible groupings of subjects who predictably
exhibit better or worse performance with COHb, each S x M (subject by COHb)
interaction effect (14 x 2 = 28 effects) were determined with the pooled data.
These effects are presented in Table 5.5. By chance, we would expect
1.4 of the interactions under choice reaction time to be outside + .062 (two
standard deviations) or under mean absolute error outside + 4.1. These critical
values are circled in the table illustrating the lack of assignable groupings to
subject by COHb effects. Thus, it may be concluded that the large subject
by COHb effects found in Tables 5.1 and 5.2 may be more accurately viewed as
random, day to day, variation of subjects (i.e., intra-subject variability).
Figure 5.1 illustrates the inconsistency of the COHb level effects on
choice reaction times in the dual tasks. There is an apparent reduction in
choice reaction times from the 0% to 7% COHb conditions (perhaps a relaxing
effect) followed by an increase in reaction times from the 7% to the 14% COHb
condition. Further, any COHb effects appear to be highly dependent of the level
of tracking complexity with the effects most pronounced in the high complexity
case. Figure 5.2 illustrates similar results for CRT performance related to
stimulus set size and COHb level. In this case, however, there were no
apparent COHb by set size interactions (no lack of parallel).
Mean absolute error scores for the three levels of tracking complexity
in the dual task (Til) are presented in Figure 5.3. In this case, there were
slight linear increases in errors with COHb levels (see Table 5.4).
60
-------
820.00
800.00 -
780.00 -
CRT
(msec)
760.00 .
740.00
A 14%COHb
0%COHb
7%COHb
Lo Med High
Tracking Complexity
Figure 5.1. —Mean CRT latency as a function of COHb level
and tracking complexity
61
-------
CRT
(msec)
835 -
810 -
785 -
760 -
735
/
14% COHb
0% COHb
7% COHb
124
Set Size
Figure 5.2.— Mean CRT latency as a function of COHb level
and stimulus uncertainty
62
-------
55 -
50 -
45
MAE
40 -
35 -
30
Lo
Med
Tracking Complexity
High
Figure 5.3.—Mean absolute tracking error as a function of the
level of tracking complexity and COHb
63
-------
Subject"
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Table 5.5
Subject by COHb Interactions
Choice Reaction Time Mean Absolute Error
COHb COHb
Linear Quadratic Linear Quadratic
+ .0795
- .0550
- .0915
- .0720
+ .0140
- .0300
+ .0140
- .0170
- .0520
+ .0610
- .0270
+ .0415
+ .0330
+ .0570
+ .0405
- .0393
-------
This is an example of "an effect" which is statistically significant for fixed
effects subjects but negligible for random effects subjects (see Table 5.2).
Since the data did not suggest an assignable cause to the subject by COHb
level interactions, we must assume no real COHb effect exists for nominal
7 and 14% COHb levels.
This non-statistically significant COHb effect is again illustrated in
Figure 5.4 in relation to stimulus set size for the dual task data. There was
no significant interaction between COHb level and stimulus set size (see Table
5.2) as might be improperly inferred from the apparent lack of parallel in
the lines of this figure.
5.2 Summary of Phases C and D
The data collected in these phases with lower COHb levels (nominally
7 and 14%) did not show statistically significant (p < .75) effects on reaction
times or tracking error scores due to COHb exposure. The lack of "statistical
significance" may be attributed to the treatment of subjects as random effects.
Analyses treating subjects as fixed effects were performed on the data of Phases
C and D with some resulting "COHb effects" significant for p > .99.
This apparent paradox was resolved by attempting to find assignable
cause for subject by COHb interactions. Since none were formed, it must be
concluded that any minor COHb differences are less than the "noise" of intra-
subject variability and as such require more careful experimental control
for statistical significance. However, since the effects are on the same order
of magnitude as intra-subject variation, they may be of less practical signi-
ficance.
65
-------
48.00
46.00 -
MAE
44.00
42.00 .
40.00
2
Set Size
Figure 5.4.—Mean absolute tracking error as a function of
COHb level and stimulus uncertainty
66
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CHAPTER 6
DRIVING TASKS WITH 20% COHb
This section describes the series of road tests conducted to determine
the effects of nominally 20% COHb on the visual sampling and vehicular control
performance of 12 drivers. Of particular interest was the effect of 20% COHb
on the ability of 6 drivers to engage in a secondary task of voluntary visual
occlusion while driving (Phase A). The additional 6 drivers (Phase B) were
tested for similar purposes, except a cognitive loading task was introduced to
replace the voluntary visual occlusions. These latter drivers were also tested
to determine the effects of 20% COHb on their ability to estimate and produce
prescribed target headways and velocities, and to estimate time while driving.
6.1 Independent Variables
The following independent variables were included in the experimental
design.
I. Task Loading
1. open road driving at fifty miles per hour,
2. car following—with the lead car maintaining
a constant velocity of fifty miles per hour, and
3. car following—with the lead car exhibiting a
variable velocity with an average velocity of
fifty miles per hour.
H-A. Secondary Loading - 6 Phase A Subjects
1. control—full, unhindered vision, and
2. voluntary visual occlusion—subjects
voluntarily closed their eyes whenever
possible.
II-B. Secondary Loading - 6 Phase B Subjects
1. control—no cognitive task, and
2. cognitive load—mental arithmetic.
67
-------
HI. COHb Level
1. control—no carbon monoxide administered, and
2. treatment—carbon monoxide in a quantity sufficient
to produce nominally 20% COHb.
These independent variables are arrayed in a matrix in Figure 6.1. Each subject
utilized in this experimental design participated in six separate tests for each level
of COHb employed. The T15 through T20 notation is used to denote the six com-
binations of task difficulty and secondary loading. Subject instructions for these
six tasks are presented in Appendix B.
6.2 Dependent Variables
During both series of tests the following performance measures were
taken:
1. mean velocity and velocity variance,
2. gas and brake pedal actuations,
3. steering wheel reversals,
4. mean headway and headway variance over
time while car following,
5. relative velocity variance; variability of rate
of closure and separation of two vehicles
while car following, and
6. visual behavior.
The visual behavior data obtained for each task, subject, and COHb level
included:
1. Eye spot fixation location and "look" duration: TV tapes
obtained in the experiment were analyzed for each separate
"look" at an object or area in the scene and its duration.
For purposes of this research the duration of a "look" was
defined as the period of time beginning with the appearance
of the eye spot on an object or area of interest and ending
with the disappearance of the eye spot from that object
or area. A "look", therefore, consisted of one or more
visual fixations.
2. Variance of duration of "looks" in various visual modes
(closed, looking ahead, viewing speedometer, and viewing
mirrors).
3. Percent of time the driver spent in various visual modes.
4. Frequency and duration of blinks.
68
-------
1
GO
«J3 ^ / /
!!
11
£j C
§ 0
0 0
&§•
T20
T19
T16
T15
T18
T17
2 2
5 5 Open Road Car Following Car Following
Constant Variable
Velocity Velocity
Task Difficulty
Figure 6.1. —Matrix of independent variables for two groups of
six subjects (Phases A and B)
69
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6.3 Equipment
6.3.1 Instrumented Vehicle (1970 Chrysler)
The main instrumented vehicle used in this research (i.e., the vehicle
which was driven by the research subjects in all experiments) was a 1970
Chrysler Newport, 4 door sedan.
This vehicle was modified to enable the foflowing parameters to be
recorded and monitored:
1. velocity,
2. gas pedal position,
3. brake pedal actuation,
4. headway (using the "yo-yo", described later)
5. relative velocity (using the "yo-yo"), and
6. driver eye movements (using the Systems
Research Group's eye-movement equipment,
described later).
The above parameters were recorded on a Honeywell model 2206 Visicorder
Oscillograph recorder mounted in the vehicle. An auxiliary power brake which
was capable of being actuated by the right front seat passenger (the "safety
man")was also installed in the vehicle.
6.3.2 Other Instrumented Vehicles
Two other instrumented vehicles were used in this research primarily
as lead vehicles in the car-following tasks. These included a 1965 Plymouth
station wagon and a 1969 Buick Electra sedan. Both of these vehicles, as well
as the 1970 Chrysler described above, were equipped with two-way FM radio
transmitter-receivers to enable intervehicular communication.
6.3.3 Oscillograph Recorder
The recorder used in the instrumented vehicle was a Honeywell Model
2206 Visicorder, a portable direct writing oscillograph recorder, capable of
recording up to 12 channels of information.
6.3.4 Headway and Relative Velocity Measurement Equipment
Headway (the distance between a lead car and the following instrumented
vehicle) and relative velocity were measured in the instrumented vehicle with
a device, often referred to as a "yo-yo" which utilizes a 10-inch diameter
drum mounted on the front of the instrumented vehicle on which is wound up to
70
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1,000 feet of thin stainless steel wire. One end of the wire on the drum is
fastened to the rear of the lead vehicle and the rest is wound on the drum of
the yo-yo. The wire is kept in tension by a clutch faced rotating disc powered
by a McCulloch Model 49C two stroke gasoline engine. Rotary potentiometers
are used to determine how far the drum has turned on its axis and hence, the
headway between the two vehicles while a Weston tachometer generator is used
to determine the rate at which the drum turns and therefore, enables the
realtive velocity between the two vehicles to be determined.
6.3.5 Other Sensors
Several other sensors were mounted on the instrumented vehicle to
enable various items of information about vehicle control movements and
vehicle performance to be determined. These included:
1. a potentiometer for measuring gas pedal position,
2. a pressure sensitive switch for determining brake
pedal actuation, and
3. a tachometer generator attached to the vehicle
transmission to enable vehicle velocity to be
determined.
6.3.6 Television Eye-Marker System
A major instrumentation system used in this research was a television
eye-marker system. This system is basically composed of closed circuit
television components connected in such a manner that it is possible to simul-
taneously photograph and record the scene in front of an automobile driver and
a small dot of light indicating the point on that scene on which the driver is
foveally fixating.
The stability of the eye-movement recording device is due primarily to
the helmet worn by each subject participating in the research. This helmet
consists of a light-weight epoxy outer shell and a light-weight polyurethane
inner shell molded to fit the subject's head. This helmet is attached to the
subject's head and is stabilized using a "bite bar" with a custom molded dental
impression connected to the helmet via adjustable side braces. This helmet
enables the weight of the attached "eye marker" equipment to be distributed
uniformly over the driver's skull.
A Shibaden model HV-50S television camera is attached to the left side
of the helmet mounted on the subject's head and is used to photograph the road-
way in front of the driver.
71
-------
A lens system mounted on the right side of the helmet picks up the
reflection of a light, also positioned on the right side of the helmet, off the
cornea of the subject driver's right eye. This corneal reflection is transmitted
by a coherent fiber optic cable to a Shibaden model HV-15 closed circuit TV
camera mounted on the floor of the instrumented vehicle where it is photographed.
A third television camera, a Shibaden model HV-15, photographs a pic-
ture of the driver's eye and the face of an accurate electric clock with a digital
readout in increments of 50 milliseconds. A more complete description of
this television eye-marker system may be found in Rockwell, et al., (1972).
6.4 Results
The results of the various analyses performed on the data collected with
the first group (Phase A) of subjects are presented in this section of the report.
6.4.1 Spare Capacity Analysis
Of primary importance in this series of tests was the determination of
the spare visual capacity of the drivers for the various drivers for various
driving situations considered in the experiments and the effects of 20% carboxy-
hemoglobin on this spare capacity.
Requiring the subject to voluntarily occlude his vision (close his eyes)
was used as a means to determine his spare visual capacity. Voluntary visual
occlusions were recorded for the three tasks: open road driving, constant car
following, and variable car following. Spare capacity will be defined as the
percentage of time that a driver kept his eyes closed for each task.
An analysis of spare visual capacity by subject and trial is presented in
Table 6.1. As can be seen from this table, subjects' abilities differed but
performance was fairly stable for each subject. Task difficulty also had an
effect on spare capacity. As can be seen from the table, only 8 out of 14 pos-
sible 20% COHb versus 0% COHb comparisons indicated a reduction in spare
capacity available to the subject with increased COHb.
An analysis of variance for spare capacity, percent occlusion time,
showed effects due to tasks and decrement associated with the 20% COHb
level were marginally significant (p > .75). Though not statistically significant,
there was an obvious trend (reduction) in average spare visual capacity. Table
6.2 illustrates the changes in spare capacity averaged across subjects.
72
-------
Table 6.1
Spare Capacity as a Function of Percent of Time that Subjects
Kept their Eyes Closed (voluntarily occluded their vision)
Subject
*-*-^ Gas
Task """"* ^^_
T15: Constant
Car Following
T17: Variable
Car Following
T19: Open Road
I
S2
Air
82.0
87.1
75.4
CO
80.9
79.7
83.4
S3
Air
81.1
81.1
86.1
CO
55.2
NA
62.6
S4
Air
26.0
21.6
15.4
CO
NA
NA
NA
S5
Air
35.0
35.1
49.4
CO
44.2
36.3
57.5
S6
Air
60.9
36.1
58.3
CO
46.4
25.5
42.3
S7
Air
54.4
54.5
61.3
CO
56.1
60.1
58.7
co
NA: Not Available
-------
Table 6.2
Spare Capacity as a Function of the Percent
of Time that Subject Drivers Were Able to
Close Their Eyes (Occlude Their Vision)
While Driving
• -_^__ Gas
Test +Mode~~~
T16 Constant Car Following
T18 Variable Car Following
T20 Open Road
Air
62.7
59.0
66.1
CO
56.6
50.4
60.4
% change
^10%
^> 15%
~ 10%
6.4.2 Occlusion Time and Open Time Analyses
For the voluntary occlusion tasks (T16, T18, T20), the mean and
variance of occlusion and open periods was claculated.
Open periods (any time eyes were not closed) may be considered time
required to obtain information while occluded time is the interlock interval in
which no visual information is obtained from the environment in front of the
driver.
Analyses of variance for these measures indicated:
1. differences in the mean occlusion time due to subjects
and tasks (p > .99), but no significant (p < .75) changes
with 20% COHb, and
2. differences in mean "open" periods were significantly
higher for 20% COHb conditions than for air conditions
(p > .75). (See Table 6.3.)
74
-------
Table 6.3
Mean "Open" Time
(seconds)
Subject
^~~^^ G*8
Task "•"»— -^^
T15: Constant
Gar Following
T17: Perturbated
Car Following
T19: Open Road
!
S2
Air
0.68
0.39
1.22
CO
0.73
0.66
0.63
S3
Air
3.69
2.38
2.33
CO
4.40
3.88
2.76
S5
Air
0.54
0.44
0.39
CO
1.76
NA
0.50
S6
Air
1.80
4.05
1.79
CO
3.41
4.48
3.67
S7
Air
3.81
1.69
2.52
CO
3.23
1.61
2.78
en
-------
6.4.3 Means and Variances of "Look" Durations
The average time spent looking at the highway was determined for each
subject, task, and COHb level.
Means and variances of these "looks" were computed for nonocclusion
tasks (T15, T17, T19). The mean duration of looks were compared across CO
levels for each subject and task and the percentage of these comparisons that
were longer with CO than with air was computed. This data is summarized
in the matrix of Table 6.4. As can be seen from the table, 18 out of 29 of these
percentages (p > .95) were greater than 50%. This indicates that under COHb,
the subjects spent more time per look obtaining information from the objects
and areas in their environment.
A similar analysis was performed on the variances of the "look" dura-
tion times. It was found that 48.3% of the values were greater than 50% while
24.5% were less than 50%. This indicated that the variability of "look" times
under 20% COHb levels for all categories (except blinks, out of view, speedometer
and rear mirror) was greater than under air.
Table 6.4
Percentage of Time that the Mean Duration Time for
"Looks" at Different Objects or Areas Greater
Under CO than Under Air
"--^Jubject
Task ^^_
T15
T16
T17
T18
T19
T20
82
100%
100%
0%
67%
80%
0%
S3
—
67%
50%
100%
100%
100%
S5
67%
83%
60%
67%
70%
50%
S6
45%
50%
40%
40%
29%
50%
S7
57%
86%
67%
67%
75%
50%
76
-------
6.4.4 Visual Information Acquisition in Car Following
Table 6.5 presents data for the number of visual fixations made on the
lead car in car-following tests for each subject at both levels of COHb. Table 6.6
presents data for the number of visual fixations made in all other categories
except "lead car".
As can be seen from these tables CO was associated with increased
looks at the lead car to obtain information about position. This is particularly
evident in the data on Task 18 where the subject's spare visual capacity was
eliminated through occlusion. CO also had the effect of reducing the number of
looks that were made on other categories and areas away from the lead car.
Again this was particularly apparent when the excess visual capacity was
eliminated through occlusion.
The data included in Table 6.5 was subjected to a three factor analyses
of variance. Differences due to tasks and subject were both significant (p >. 95)
and differences between levels of carbon monoxide were significant for p> .90.
The data of Table 6.6 was also subjected to a similar analysis which
indicated differences due to the subjects (p > .90) and COHb level (p > .75).
Differences due to the task difficulty were not found to be statistically signi-
ficant (p < .75). Interactions involving the presence or absence of CO (i.e.,
the trial by "environment" and the subject by "environment" interaction) were
marginally significant (p = .75). This analysis indicates a need for increased
foveal concentration on the lead car due to the presence of COHb.
6.4.5 Blink Analysis
Eye blink rates have been found by researchers to be related to the
stress associated with a task. Poulton and Gregory (1952) found that blink
rate varied inversely with the difficulty of a tracking task (i.e., increased
difficulty in the tracking resulted in a decreased blink rate).
Eye blinks were recorded and analyzed in this research study. For
purposes of analysis, the data from Tasks 16, 18, and 20 was deleted since
these tasks required the subjects to engage in voluntary visual occlusions.
The data are displayed in Table 6.7. A three factor analyses of variance was
performed on these blink rate data. Reductions in blink rate associated with
carbon monoxide were found to be significant (p > .99) differences due to subjects
and tasks were also significant (p > .99 and p = .75, respectively). Test by
subject interactions and subject by COHb interactions were also found to be
significant (p > .99).
77
-------
Table 6.5
Number of Looks at the Lead Car
Subject
' -~^_^^ Gas
Task ~— — *^^_
T17: Variable Car
Following
Normal Vision
T18: Perturbated Car
Following
Occlusions
TOTALS
S2
Air
73
30
103
CO
56
68
124
S3
Air
98
67
165
'
CO
124
103
227
S5
Air
66
57
123
CO
68
56
124
S6
Air
83
47
130
CO
103
78
181
S7
Air
47
52 '
99
CO
53
48
»
101
-q
QO
-------
Table 6.6
Number of Looks at Categories Other than Lead Car
Subject
^— ^_Gas
Task """"-— -^^__
T17: Variable Car
Following
Normal Vision
T18: Varible Car
Following
Occlusion
TOTALS
S2
Air
23
38
61
CO
38
1
39
S3
Air
6
2
8
CO
8
2
10
S5
Air
53
70
123
CO
25
3
28
S6
Air
20
13
33
CO
23
13
36
S7
Air
2
2
4
CO
3
12
_,
15
-------
Table 6.7
Blink Rate Analysis
(Rate = Average per 3 minute period)
Subject
~~" -^.^^ Gas
Task ^"">*"-«— ^^^
T15: Constant Car
Following
T17: Variable Car
Following
T19: Open Road
TOTALS
S2
Air
14
20
17*
51
CO
24
40
32*
96
S3
Air
73*
76
71
220
CO
37*
52
23
112
S5
Air
61
36
85
182
CO
52
34
91
177
S6
Air
82
70
88
240
CO
53
47
62
162
S7
Air
88
48
26
152
CO
28
11
22
61
00
o
* Average value computed for analysis purposes.
-------
These blink rates are, as mentioned, primarily indicators of stress and
by themselves do not indicate performance decrement. They are, however,
useful for comparing different conditions which a driver might be subjected to.
6.4.6 Gas and Brake Pedal Movements
Two control related variables which were considered in this series of
experiments were the gas pedal actuation behavior and the brake pedal actua-
tion behavior of the drivers. It was hypothesized that the number of brake
applications and the number of gas pedal releases (periods of time in which
the driver took Ms foot off the gas) as well as the number of gas pedal rever-
sals would be related to task difficulty, secondary task loading, and differences
in the level of the COHb.
The number of gas pedal reversals (i.e., measured by the number of
times that the slope of the gas pedal trace changed sign) exhibited by the subjects
in each of the tasks was obtained. Table 6.8 summarizes this data for combined
subjects. As can be seen from the data, the measure of gas pedal reversals
seems to be a measure that is sensitive to task difficulty, loading, and the
presence of COHb. The results of a three-factor analysis of variance indicated
that gas pedal reversals were significantly different for the two CO levels
(p > .975). Tasks and the presence or absence of spare capacity also showed
significant effects (p > .99). One interaction, the task by "loading" interaction,
was found to be significant (p > .95). The other two interactions, test by CO
and CO by loading were of marginal significance (p = .75).
Table 6.8
Gas Pedal Reversals Summary for all Subjects Combined
(reversals per 3 minute period)
T15: Constant Car
Following
T17: Perturbated Car
Following
T19: Open Road
Column Total
Combined Total
Air
Normal
Vision
65.6
65.7
16.8
148.1
Occluded
Vision
38.2
44.0
12.7
84.9
233.0
20% COHb
Normal
Vision
57.5
64.0
21.5
143.0
Occluded
Vision
26.8
39.2
7.5
73.5
216.5
81
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6.4.7 Headway Analysis
The mean headways exhibited by the subjects while car following were
derived and an analysis of variance performed to test for effects due to dif-
ferences in COHb levels. The analysis failed to indicate any differences due
to CO (p < .75) when all subjects were aggregated. Some interesting trends
were apparent in the data, however, for individual subject's differences between
CO and air.
It was found that under elevated carbon monoxide levels, subjects drove
with shorter mean headways for "variable car following" tests than they did
for "constant car following" tests. (Eight out of ten comparisons of "variable
car following headway means" with "constant car following headway means"
indicated this tendency.) This is the opposite of what was found under the
control condition and could be interpreted as a failure to compensate for
increased task difficulty under CO (see Table 6.9).
6.5 Phase B Analyses
The analyses of Phase B road tests indicated that the secondary
cognitive loading tasks did not produce the sensitivity to performance that
found from the secondary voluntary occlusions in Phase A.
Since no eye-movement data was collected in Phase B, emphasis was
placed on driver input measures. No statistical difference in the speed and
accuracy of the cognitive tasks were noted with respect to CO, although the
trend was that subjects completed fewer cognitive tasks under 20% COHb.
Gas and brake pedal applications did not appear to be sensitive to 20% COHb.
It was surprising to note little change in the psychophysical tests of
time, velocity, and head production (estimation) between the air and CO
conditions. Laboratory tests confirmed the lack of time estimation changes
due to 20% COHb. The same intervals, 2, 4, and 8 seconds were employed
both in the lab and on the road.
82
-------
Table 6.9
Mean Headway Analysis
(Headway in feet separation)
Subject
^"~"~""-— -^^^ Gas
Task ""*~'~1-— »^^
T15: Constant Car
Following
Normal Vision
T16: Constant Car
Following
Voluntary Occlu -
sion
T17: Perturbated Car
Following
Normal Vision
T18: Perturbated Car
Following
Voluntary Occlu-
sion
S2
Air
47.5-
125. 7+
87.8+
180. 8+
CO
66.4
123.5
59.5
79.8
S3
Air
47.5+
55.3+
45.6+
68.5+
CO
33.05
42.38
19.62
56.58
S5
Air
84.1+
137. 6-
115. 7+
147.4-
CO
57.4
249.4
45.0
294.6
S6
Air
132. 3-
246. 6-
130. 2-
198. 6+
CO
166.0
393.1
150.7
152.7
S7
Air
76.3-
114.9+
61.2+
97.8+
CO
163.9
99.1
53.3
87.7
HEADWAY MEANS
oo
w
Note: (+) sign indicates longer headway under air
-------
In general, it may be argued that effects due to 20% COHb are subtle in
driving and show up only when subjects are realistically secondary task loaded.
Perceptual changes, however, are more readily sensitive to CO as might be
expected. These perceptual effects can be compensated for by the driver pro-
vided he has time to adapt. If task loading is applied, apparently his adaptation
is impaired and CO effects become more apparent. This was noted with respect
to gas pedal reversals, for example, in Phase A.
6.6 Summary of Results
The major results of these Phase A and B experiments are presented
below.
1. The measure of visual spare capacity (i.e., the percentage
of time that a driver was able to keep his eyes closed) was
found to be sensitive to 20% carboxyhemoglobin and task
difficulty. Both were associated with decreases in spare
capacity (p > .75 for both).
2. Twenty percent carboxyhemoglobin levels were associated
with increases in the "mean eye open" time in occlusion
tasks (p > .75).
3. Twenty percent carboxyhemoglobin was related to increased
mean "look" durations (i.e., the length of time the driver
looked at an object or area in his field of view) for auto-
mobile drivers (p > .95).
4. Variance of "look" times also increased with 20% CO
(p > .95).
5. Carbon monoxide was also associated with an increase in
the frequency of visual fixations on the lead car in car
following which at the same time caused a decrease in the
frequency of fixations on objects or areas other than the
lead car (p > .90).
6. Blink rates which were measured in the experiments were
found to reflect the stress associated with 20% COHb and
task loading (p > .99 for both).
7. Control actuation was also found to be sensitive to inde-
pendent variables of interest. With respect to gas pedal
reversals, task difficulty increased the number of observed
reversals while 20% COHb levels and the elimination of spare
capacity resulted in a reduction in the number of gas pedal
reversals (p > .99, p > .975, p > .99, respectively).
84
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CHAPTER 7
DRIVING TASKS WITH 7 AND 14% COHb
This chapter describes the series of road tests conducted to determine
the possible effects of COHb at nominally three levels (0%, 7%, and 14%) on the
visual sampling and vehicular control performance of 18 additional drivers.
7.1 Equipment
The equipment used in this testing was identical to that of Phases A and
B. The description of the equipment and their capability will not be reiterated
here but may be found in Chapter 6.
7.2 Independent Variables
In Phases C and D, eighteen drivers were tested on each of three test
days, usually separated by one week. On each test day, each subject performed
eight tests (denoted T17-T24), over a two-hour period of driving. As shown in
Figure 7.1, subjects were paired for CO treatments by day. For example, sub-
jects 29 and 23 were together administered carbon monoxide sufficient to pro-
duce 7% COHb on the second day (D2) they were tested. Subject 29 was tested
in the morning on the road tests so he is further typed AM. Subject 23 per-
formed lab tests in the morning so to examine possible "fatigue" differences
when tested on the road in the afternoon; he is typed PM.
Basically, the tasks employed in both Phases C and D may be summar-
ized as follows:
T17 - variable car following, average speed 50 mph,
test driver with normal vision *
T18 - variable car following, average speed 50 mph,
test driver asked to voluntarily close his eyes whenever possible
T19 - open-road driving, target speed 50 mph,
test driver with normal vision
T20 - open-road driving, target speed 50 mph,
test driver voluntary visual occlusion
*Nonnal vision refers to drivers employing normal search and scan
patterns for the task at hand.
85
-------
Subjects
Phase
D C Type
839
836
838
835
840
837
826
820
827
821
829
823
828
822
831
825
830
824
AM
PM
AM
PM
AM
PM
AM
PM
AM
PM
AM
PM
Nominal CO Level
0%
Dl
D2
D3
D3
D2
Dl
7%
D3
Dl
D2
Dl
D3
D2
14%
D2
D3
Dl
D2
Dl
D3
Figure 7.1. —Road Protocol for Phases C and D
86
-------
T21 - open-road driving, target speed 30 mph,
test driver with normal vision
T22 - open-road driving, target speed 30 mph,
test driver voluntary visual occlusion
T23 - open-road driving, target speed 50 mph,
test driver denied use of speedometer
T24 - leap frog passing
A more complete description of the tasks and subject instructions may be found
in Appendix B.
It may be helpful to the reader to view these tasks in a lattice as
illustrated in Figure 7.2.
VARIABLE
CAR FOLLOWING
AVG. 50 MPH
OPEN ROAD
50 MPH
OPEN ROAD
30 MPH
LEAPFROG
PASSING
NORMAL
VISION
T17
T19
T21
T24
VOLUNTARY
OCCLUSION
T18
T20
T22
NO SPEED-
OMETER
T23
Figure 7. 2. — Lattice of tasks employed in Phases C and D
87
-------
To explain the variability in the dependent variables of interest due to
the tasks, most of the macro analyses employed six comparisons of these task
variables:
OCCL30 = T22 - T21 (occlusion effect @ 30 mph)
OCCL50 = T20 - T19 (occlusion effect @ 50 mph)
OCCLCF = T18 - T17 (occlusion effect in car following)
30VS50 = T19 + T20 - T21 - T22 (effect of target speed 50 - 30)
ORVSCF = T17 + T18 - T19 - T20 (difference between car following
and open-road driving)
SPEEDO = T23 - T20 (difference due to lack of speedometer
information).
The first five comparisons are, of course, orthogonal to one another, and thus
effects are estimated independently.
7.3 Dependent Variables
The primary response or dependent variables of interest apriori for
tasks 17 through 23 included:
1. mean velocity (V BAR),
2. standard deviation of velocity (Sy),
3. mean headway (H BAR),
4. standard deviation of headway (SH),
5. relative velocity standard deviation (Spy),
6. gas pedal deflection rate (G),
7. brake pedal activation rate (B),
8. steering wheel reversal rate (8),
9. mean,
10. standard deviation,
11. percent,
12. mean,
13. standard deviation,
14. percent,
15. mirror usage, and
16. speedometer usage.
"Look" time
"Occluded" time
88
-------
For purposes of analysis, these dependent variables are categorized into three
sets. Measures 1 through 5 represent Vehicle Responses, not under direct,
immediate control of the driver, but rather time delayed measures of vehicle
dynamics. Measures 6 through 8, will be referred to as the Driver Control
responses, measured as frequencies or rates per minute of testing. Finally,
measures 9 through 16 represent the observed visual behavior of the driver in
information acquisition and perceptual demand, and thus, will be called Visual
Information measures.
These latter Visual Information performance measures require ex-
planation. The mean look times and occluded times are measures of the aver-
age duration per occurrence of time spent in either mode. Mean look time is
the average time from first glanding at an object in the visual scene ahead until
leaving the scene to look at, say, the speedometer or rear view mirrors. The
standard deviation is, then, a measure of the variability of these times (con-
sistency), and percent is the fraction of the total time spent in each mode:
Mean x Number of Occurrences „ ., ^^
(i. e., = Percent /100)
Total Time
The speedometer and mirror usages were also documented by mean
duration, standard deviation of looks, percentage of time, and total number of
occurrences. Unfortunately, these responses are highly related to task demand,
other traffic in the vicinity, etc., and were very low frequency events.
7.4 Task 24 - Dependent and Independent Variables
The final task employed in this research will be called Leapfrog passing.
This task was developed to examine the freeway passing behavior of the subject
drivers. The drivers were instructed to drive at about 60 mph while an auxil-
iary research vehicle passed, got about 1,000 feet ahead, and then slowed down.
The subjects were instructed to pass the car and return to the right hand lane
in their normal manner and the procedure was repeated for 20 trials.
This free running task took about 45 minutes to execute 20 trials. The
target speed of the auxiliary research vehicle was either 30 mph and 50 mph
prior to the pass (random presentation), and interferences due to other traffic
was documented and trials deleted.
The dependent, response variables included:
1. mean velocity and standard deviation of velocity,
2. gas pedal and steering wheel reversals,
89
-------
3. lane change rate (LCR) and variation in lane change rate (S_ „„),
4. visual activity (frequency of looks at rearview mirrors prior to
lane change and during pass, and time between last mirror look
and lane change).
These visual measures were acquired without the use of the eye-movement
camera system. The number of looks at the mirrors as well as the time between
last looking at a mirror and changing lanes were viewed as additional measures of
perceived risk or risk acceptance. The independent variables of interest included
possible:
1. subject effects,
2. day (or learning) effects, and
3. COHb effects (linear CO and quadratic CO2).
7.5 Models and Notation
The models of driver behavior and the analytic approaches of the next
section differ from analysis to analysis. This is due in part to the fact that the
results presented are, in themselves, summaries of more comprehensive
analyses too numerous to report here. To avoid the necessity for repeating
the implied model for every response and analysis, this section outlines the
principal analytic models.
The implied model of driver performance in the macro-experimental
design of Phases C and D may be expressed as,
Model I-A (Latin Square)
Yijklm
D x Tj! + €.jklm
where
Y = the observed response
\i = some overall constant mean
Sj = the effect due to subject i = 1, ..., I
90
-------
T. = the effect due to task j = 1, ..., J
CO. = the effect due to COHb at level k, k = 1, 2, 3
Dj = the effect due to day 1 = 1, 2, 3
G = the effect due to group m = 1, AM
2, PM
Three differential (or interaction effects of interest are S x T.. effect of
subject i on task j.
CO x Tjk effect of COHb level k with task k
D x Tji effect of day 1 with task k (differential learning)
Siklm = *°e error Associated with the assumed model including
other interactions which are assumed negligible.
Had the experiment been free of missing observations and COHb levels
sufficiently close to nominal values to be treated qualitatively (low, medium,
and high), the interpretation of results could have been performed with Model
I-A and standard analyses of variance. However, with nonorthogonal (missing)
data secondary analyses were required. In this case with a new Model I-B.
Model I-B
Yijklm = M- + Sj + T. + COjj + Dj + G.
m
+
Some of the performance variables of this research were not affected by
groups (morning versus afternoon implying adequacy of Model I-C.
Model I-C
Yijk= H+VT. + COk + D!* ^jklm
In addition, with some performance measures it was suspected that
CO x T,k may be large (i. e. , the effect of COHb on the performance measure
was different depending on the specific task). To facilitate pictorial presenta-
tion of this factor with nonorthogonal data, a third model was proposed for each
task.
91
-------
Model I-D
Y.k =
+ S. +
e.k (for each task 17-24)
One other model which was employed for clarification of underlying
assumptions of the hypotheses tested assumed again that Days (1) and Groups
(m) did not affect the response variables, but that alternate interactive or dif-
ferential effects may be present as defined in Model IL
Model II
ijk
VT.+
The reader may observe that this model is not directly testable under
the Latin Square design, but was considered for possible elucidation of large
residual error variances in the other models. This model requires fully
balanced, orthogonal data so further subsets of the data base were used.
To summarize these models and the parameters included, the following
table may be helpful.
Table 7. 1
Models Employed in Data Analysis for Phase C and D Road Tests
Testing for
effects due to
I-A
I-B
I-C
I-D
II
V-
si
T.
J
C0k
°1
Gm
SxTij
COxTjk
DxTjl
SxCOik.
X X X X
X X X X
XXX Each
X X X X
XXX
X X
X
X
X
X
X
X
X
X
X
X
92
-------
7.6 Results
This section reports a detailed analysis for each of the dependent vari-
ables of interest in Phases C and D of the road testing in this research. The
order of presentation is the same as listed in the previous methodology section.
The number of subjects examined in the analyses that follow vary pri-
marily due to missing observations. There were a variety of reasons for miss-
ing observations (i. e., equipment failure, subject illness, weather). Data
which was not complete across COHb levels for a particular subject and set of
tasks was eliminated from the statistical analyses.
In addition, due to inaccuracies between the observed and target COHb
levels, all of the analyses for Models I-A, I-B, I-C, and I-D treat COHb as a
continuous, quantitative variable using actual observed values. Model II was
employed only in cases of very large residual errors with Models I-A, I-B,
I-C, and I-D, treating COHb qualitatively [LO(0)f MED (7), HI (14)].
7. 6.1 Mean Velocity (VBAR)
The instantaneous velocity of the research vehicle was recorded continu-
ously throughout all of the testing. The first measure of interest is mean or
average velocity for the various tasks. Sampling velocity at five second inter-
vals produced 36 data points per three minute task trial which were then averaged.
Data for eight subjects, free of missing observations, from Phase C were
used to examine the additive Model I-B:
VBAR = " + V V C V V Gm * W
An analysis of variance (Table 7.2) for this model showed an obvious
effect due to tasks. Tasks 17, 19, 21, and 23 were significantly different
(p >. 999) explaining differences in mean velocity due to target speed, car
following versus open road driving, and with speedometer versus without.
Effects due to occlusion (Task 21 versus 22, for example) were not significant
(p < . 5). There were no apparent effects due to groups (morning versus after-
noon) nor were there any significant differences between day 2 and day 3 speeds.
Day 1, however, showed significantly (p > .99) faster speeds than day 2 or day 3.
(D! = D2 + . 5 mph) suggesting a possible novel learning or familiarization effect
on day 1. The subjects were homogenous in mean velocity and no significant
differences were observed.
There was a significant (p > . 90) effect due to COHb level, composed
primarily of a quadratic component, with a residual error for the full model of
93
-------
.90
p > . 999
p > .99
p > . 999
p > .99
Pl-D2=. 5
p > .90
p > .95
94
-------
50 ..
40 • •
30 ••
(no speedometer)
(target 30 mph)
T21
4
Nominal COHb level (percent)
Figure 7.3.—Mean velocities for three open road driving tasks
95
-------
7. 6.2 Standard Deviation of Velocity (Sy)
The standard deviation of the 36 observations of instantaneous velocity
for each trial was computed as a measure of driving precision. Data for 8 sub-
jects were analyzed with Model I-B.
The results indicated no statistically significant differences between
subjects or days. The tasks, too, were fairly homogeneous with the obvious
exceptions of comparisons for target speed effects and open-road versus car-
following differences. Variations in velocity were significantly higher in car-
following compared to open-road driving at 50 mph. Also, there was a signifi-
cant (p > . 999) effect on standard deviation of velocity due to presence of speed-
ometer information. The drivers were more variable without speedometer than
with speedometer information available.
Although the COHb effect was not statistically significant (p < . 75) in
this analysis, the trends for T17, T19, and T23 which were statistically differ-
ent (above) are shown in Figure 7.4. This figure suggests negative trends which
may not be statistically significant due to CO x Task interactions (or Subjectx CO,
Subject x Task).
Since day effects were negligible, Model II was proposed for T17, T19,
and T23 with 12 subjects. This analysis is supported by Table 7.3 which illus-
trates a mild COHb effect with Subject x CO interactions (subjects react differ-
entially to increasing COHb levels).
Table 7.3
Average Standard Deviation of Velocities across Tasks T17, T19, T23
Nominal COHb Level
Subject 2% 7% 12%
S26 5.02 4.92 4.40
S20 4.71 4.95 5.69
S27 5.13 4.66 5.10
S21 3.73 4.87 4.61
S29 5.26 4.57 4.61
S23 5.42 4.69 5.18
S28 5.31 5.48 5.17
S22 4.74 4.94 4.86
S31 9.00 4.22 4.53
S25 5.40 4.52 4.93
S30 4.31 4.37 4.32
S24 4.14 4.30 3.67
Average 5.18 4.71 4.76
96
-------
7 •
6 •
b"
I
4
§ ~
fi
T17
(constant car following)
T23
T19
(open road, no speedometer)
(open road, speedometer)
t-
2
Nominal COHb level (percent)
Figure 7.4.—Standard deviation of velocities for
three 50 mph driving tasks
97
-------
The analysis of variance for these data with Model II is presented in
Table 4.
Table 7.4
ANOVA for Standard Deviation of Velocities
Source
TOTAL
df
107
MS
Subjects
Task
CO
CO x Subject
CO x Task
Subject x Task
Error
11
2
2
22
4
22
44
2.16
247.0
2.44
2.11
.56
1.09
.79
2.74
312.0
3.09
2.68
<1
1.38
(P> .9)
(p > .9)
7. 6. 3 Mean Headway
The instantaneous headway or separation of lead vehicle and following
vehicle was recorded every five seconds over each task (T17, T18) of three
minute duration. These 36 observations were averaged for seven subjects with
full data for preliminary analysis. The results suggested obvious between-
subject differences and differences between normal vision car following and
occluded vision car following. On the average, the drivers maintained 20 feet
larger headways when asked to voluntarily occlude their vision. Large residual
errors ( o-g/n = . 30) prompted a second analysis for each task. Data for 17
subjects were used with the model I-D:
HBA
CO+C02
for each task.
The results suggested a significant (p = . 85) reduction of 15 feet in head-
way for the nonoccluded (T17) over the range 2% to 12% COHb. The quadratic effect
(Cc£) was not significant (p < . 75). For the occluded task, however, this reduc-
tion in headway was not monotonic as indicated by a significant quadratic CCr
effect (p = . 90), as illustrated in Figure 7. 5.
98
-------
140- '
3? 120
o>
100"
80
T18 (occlusion)
T17 (normal vision)
_H 1 1
2 7 12
Nominal COHb level (percent)
Figure 7.5.—Mean headways for car-following tasks
99
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7. 6.4 Standard Deviation of Headway (SH)
The standard deviation of the 36 observations of instantaneous headway
for each subject on each task were analyzed in identical fashion to headway.
Similar trends were present with COHb as illustrated in Figure 7. 6, however,
the linear (CO) effects were not statistically significant (p < . 75) but quadratic
(CO2) effects were significant (p = . 85).
7. 6. 5 Relative Velocity Standard Deviation (SRV)
In addition to measuring headway continuously throughout the car-
following tasks, the relative velocity or rate of closure and separation of the
vehicles was also recorded continuously. Since this measure will average zero
if the headway at the beginning equals the headway at the end of the run, mean
relative velocity is probably an insensitive measure. The variation or standard
deviation of relative velocity on the other hand is a measure of car-following
stability.
For the two car-following tasks of this research, the measure was
analyzed for seven subjects with the following results.
Source df MS
Subject
Day
Task
CO
Error
6
2
1
2
29
.96
.47
6.84
.77
1.01
<1
<1
6.8
<1
TOTAL 40
The overwhelming task effect (p > . 999) of . 41 ft/sec higher under occluded
car following led to separation of tasks for further analysis. Using 17 subjects
with Model I-D, there was still no significant CO or CCr effects, however, the
trends are presented in Figure 7.7. Notice that with additional subjects, the
average difference between occluded and nonoccluded car following more than
doubled while there was no evidence of a CO x Task interaction (lack of
parallel).
7. 6. 6 Gas Pedal Reversals (G)
Eight subjects for whom all data was available for three days and seven
tasks were employed with the following results using Model I-C.
100
-------
40- •
30"
20-
T18 (occlusion)
-• T17 (normal vision)
2 7 12
Nominal COHb level (percent)
Figure 7.6.—Standard deviation of headways for car-following tasks
101
-------
5.0 - -
o
-------
Source df SS MS
Subjects
Days
Tasks
CO
Error
7
2
6
2
150
1214. 8
166.2
3470. 4
6.3
2203. 3
173.5
83.1
578.4
3.15
14.69
11.8
5.7
39.4
1.0
TOTAL 167 7061.0
There were no obvious effects due to COHb (linear or quadratic) with this
analysis. However, the possibility of COHb x Task interactions suggested that
the analyses be separated by tasks and separate analyses performed. The re-
sultant analysis is presented in graphical form in Figure 7.8.
As can be seen from the figure there is an apparent slight increases in
gas pedal reversals with COHb in tasks 17 through 23 and reductions in tasks
20 and 21. The average performance across tasks increased steadily from
4.92 at 2% to 6.68 at 12% COHb, a relative increase of approximately 36 percent.
These data may be compared with those of the previous year's study as
shown in Table 7.5.
Table 7.5
Gas Pedal Reversal Comparisons
ISC
COHb Level
Task
T19
T20
T17
T18
xear
2%
5.6
4.2
21.9
14.7
20%
7.2
2.5
21.3
13.1
2%
2.8
2.1
14.0
9.8
2nd Ye
7%
2.9
2.8
13.0
9.3
ar
12%
3.7
1.6
14.4
11.9
103
-------
none significant (p < .75)
14 ••
T17
12 - -
310
1
•a
s
!8
6 • -
4 . .
2 - -
T18
6.68
Task
T22
2 7
Nominal COHb level (percent)
Figure 7.8.—Gas pedal reversals for Tasks 17 through 23
104
12
-------
7.6.7 Brake Pedal Applications (B)
The brake pedal was only applied during the car following tasks (T17 and
T18) and analyses were confined to eight subjects with full data for three days
on both tasks with the following result:
Source df SS MS
Subjects
Days
Task
CO
CO
CO2
Error
7
2
1
2
(1)
(2)
34
1.43
.012
.130
.559
.379
.180
5.00
.204
.006
.130
.279
.379
.180
.147
1.39
<1
<1
1.9
2.58
1.22
(p=.75)
TOTAL 46 7.13
Interestingly, this preliminary analysis shows no differences between
subjects, between days, or between occluded versus nonoccluded driving. This
is similar to the mean velocity analysis, and again slight significant differences
(p = . 75) were observed due to COHb. Separating the two tasks (t!7 and T18)
we may diagram this effect as shown in Figure 7.9.
7.6. 8 Steering Wheel Reversals (S)
Assuming no day or group (am/pm) differences, the data for six subjects
under each COHb level (nominally 2, 7, and 12%) for tasks 17, 18, 19, 20 (all
50 mph) were analyzed with Model H. The resulting ANOVA is presented below:
Source df SS MS
Subjects
Tasks
CO
SxT
Sx CO
COx T
Error
5
3
2
15
10
6
30
1079. 8
289.1
269.9
1409. 8
1425. 9
269.2
934.6
216.0
96.4
135.0
94.0
142.6
44.9
31.2
6. 9 p > . 999
3. 1 p > . 95
4. 3 p > . 975
3. 0 p > . 995
4. 5 p > . 999
1.4
TOTAL 71 5678.3
105
-------
'§1-0
° =-• •
0)
T17 (normal vision)
Average
T18 (occlusion)
12
Nominal COHb level (percent)
Figure 7.9.—Brake pedal applications while car following
106
-------
This analysis shows significant effects due to subject and task differences
in addition to a COHb effect and differential subject by COHb and subject by task
effects. The COHb effect is best illustrated by Figure 7.10. The subject x
COHb interactions are shown in Table 7. 6.
Table 7. 6
Average Steering Wheel Reversals by Subject
Nominal COHb Level
Subject 2% 7% 12%
S31
S30
S24
838
S40
S37
47.1
34.8
36.8
37.7
33.7
26.2
31.4
17.6
39.6
34.4
34.4
37.7
35.8
24.6
28.5
33.7
34.5
32.3
Average 36.0 32.5 31.6
7.6.9 Visual Measures
A step-wise regression analysis for all visual data for the 18 Phase C
and D subjects with model I-B was performed for the primary visual measures
of interest. This step-wise entry process was terminated with the first obser-
vation of a "t" value less than 1.0. The resulting regression coefficients for
linear (CO) and quadratic (CO2) effects are presented in Table 7.7 with cor-
responding "t" statistics and significance (p) levels.
Qualitatively, these results suggest that CO intoxication was associated
with higher percentages of "closed"time but less time per closure. The drivers
were apparently unwilling or unable to spend long times away from the road
scene. When they observed the highway, although they spent less total time on
the highway, the average glance was longer suggesting more time may be neces-
sary to retrieve information. The measures of speedometer, rear view mirror,
and side view mirror usage were inconclusive.
Another measure of visual activity termed "out of view" was recorded to
describe the time spent by the driver outside the central 20° x 20° visual angle
scene, looking at such things as road signs, scenery, and other highway traffic.
107
-------
40
• T18
ID
If "
—I (0
0) \
0) 0)
i "3
£ ra
CO
30
25-
—i 1 —i
2 7 12
Nominal COHb level (percent)
Figure 7.10.—Steering wheel reversals for 50 mph tasks
108
-------
Measure
Table 7. 7
Linear and Quadratic COHb Effects Summary
for Visual Measures (Phase C)
CO t p CO2
Mean Straight 0.177 2.08 >.95
Percent Straight -3.85 -2.04 >. 95 .481 2.55 >. 975
Std. Dev. Straight - - - . 107 1.57 >. 80
Mean Closed -0.088 -1.85 >. 90
Percent Closed 2.82 1.39 >. 80 -.327 -1.59 >. 80
Std. Dev. Closed - - - -
Mean Speedometer - - - -
Percent Speedometer 0.169 1.04 >. 70
Mean Side Mirror - - - -
Percent Side Mirror -0.108 -1.55 >. 80
Mean Out of View - - - -
Percent Out of View -0.0048 2.6 >. 975 -
" - " indicates t statistic 1.0.
CO values represent differential due to 1% COHb increase.
A reduction in this measure is sometimes called "tunnel vision" since the driver
makes fewer or shorter excursions to the periphery of the visual scene. This
behavior has been observed in drivers under low blood alcohol concentrations.
Out of view data revealed a mild case of perceptual narrowing with in-
creased COHb levels (p > . 975). However, the average excursion duration to
the periphery did not change significantly with increased COHb levels.
The lack of significant quadratic effects with most visual measures in
this analysis prompted deletion of the nonlinearities with CO in further analysis.
109
-------
Since many of these visual measures are highly task dependent, the analyses
were divided by task and employed model I-D. This allowed removal of any
possible subject by Task or CO by Task interactions from the residual errors.
7. 6.10 Normal Vision Driving
The driving tasks which involved normal vision (with speedometer) were:
open-road driving with target speed of 30 mph (T21), open-road driving with
target speed of 50 mph (T19), and driving while car following with the lead car
varying speed with an overall average of 50 mph (T17). Differential effects due
to CO exposure were computed over the range of actual COHb levels and analy-
ses of variances were performed with model I-D. The results are best illus-
trated in Table 7.8.
Although the large unexplained residual errors (cr£ ) in these analyses
deny statistical significance, there are several interesting trends present.
The mean duration of looks straight ahead increased in all cases with
COHb. Likewise, the average look at the speedometer or rear view mirror
was shorter with increased COHb levels for all three driving tasks.
A similar analysis was performed with visual measures for the occluded
vision tasks; Table 7.9 illustrates magnitudes of these changes expressed as
percentages of residual errors. The two predominant modes for the occluded
tasks were either (a) closed (or occluded) and (b) open, looking straight ahead.
Very few excursions to the periphery were made in these tasks so apparent over-
whelming COHb effects actually represent small magnitude changes appearing
large with respect to very small 2% COHb activity.
From this table it appears that COHb has a different effect on "up" or
straight measures, depending on whether the driver is car following or on the
open road. There were reductions in mean, standard deviation, and percent-
ages "up" for both open-road driving tasks (30 and 50 mph). The (nonstatisti-
cally significant) trends for each of these measures were reversed for the car-
following (loaded) task. The means and standard deviations of "down" or
occluded times were less consistent across tasks. Percentages closed, however,
consistently increased with COHb on all tasks, suggesting more risk acceptance
behavior with COHb.
7.6.11 Perceptual Uncertainty
Examination of the occluded 50 mph task for a sample of six subjects at
both control (1. 5 - 2.0% COHb) and 6-8% COHb introduces an interesting
phenomenon. If the mean look time is divided by the percent closed time and
multiplied by 1000, we get a measure which reflects perceptual confidence or
110
-------
Table 7. 8
CO Trends for Normal Vision Tasks*
Mean Straight
Percent Straight
Mean Speedometer
Percent Speedometer
Mean Mirror
Percent Mirror
Tl
Open Road
30 mph
AGO
-------
the lack thereof. This measure is large when mean look time is long (suggest-
ing visual inefficiency) or when the percent closed time is small (suggesting
uncertainty about car path direction) or a combination of both. The converse
of these factors produces less perceptual uncertainly. Data for six subjects
is shown in Figure 7.11 for both the control and the 6 - 8 % COHb level. Note
that in each case there is greater perceptual uncertainty for elevated COHb
levels. The magnitude of the increase is apparently related to the initial
control level. That individual subjects react differently to this unique task
designed to induce spare visual capacity is not surprising. What is significant
is that all subjects showed greater uncertainly at elevated COHb levels.
7. 6.12 Leapfrog Passing (Task 24)
The results of the leapfrog passing task largely supported the results of
the analyses for other tasks (T17 through T23). Examination of the data for 12
subjects with at least two days (of three) complete data showed that COHb levels
of nominally 14% (actual average near 12%) were associated with
1. slightly lower average speeds and higher variation in speeds
over the 20 trials (p > . 85 and p > . 80, respectively);
2. a mild reduction in the number of gas pedal reversals during
the average pass (p >. 75);
3. reductions in the number of looks at mirrors both prior to and
during the average pass (p > . 95 and p > .85, respectively); and
4. no significant (p < . 75) changes in mean or standard deviation
of lane change rate nor on time between mirror check and lane
change.
Quantitative estimates of these COHb effects are provided in conclusion
in Table 7.10. It is interesting to note the reduction in mirror usage with
elevated COHb levels. This is consistent with the perceptual narrowing phe-
nomenon suggested earlier.
112
-------
Perceptual
Uncertainty
1000
113
82
35
25
13
11
Control COHb « 2%
6% < COHb * 8%
X - mean look time straight
ahead between occlusions
%_T - % time closed or occluded
14
11
10
9.5
X
x"
839 S21 S23 S36 S24 S40
Figure 7.11. —Perceptual uncertainties for selected subjects - Task T20
-------
Table 7.10
COHb Effects for Leapfrog Passing Test
Measure 2% COHb 12% COHb
Mean velocity (p >. 85) 53.7 52.2
Velocity variation (p > . 80) 1.3 2.0
Gas pedal reversals (p > . 75) 3.04 2.01
Number mirror looks prior to pass (p > . 95) 6.16 4.24
Number mirror looks during pass (p > . 85) 4.75 3.43
Lane change rate (p < . 75) (sec.) 2.80 3.20
Std. dev. lane change rate (p < . 75) (sec.) 1.06 0.60
Time between mirror look and lane change 0.47 1.06
(P < . 75)
114
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CHAPTER 8
CONCLUSIONS AND RECOMMENDATIONS
8.1 Introduction
This study provides a challenge to the statistician by virture of the fact
that (1) large inter- and intra-subject variability exist, (2) there are apparently
large subject x carbon monoxide interactions (which illustrate different effects
for different subjects due to carbon monoxide), (3) missing observations often
forced the analysis to less powerful statistical techniques, and (4) lack of pre-
cise control over the prespecified carboxyhemoglobin levels meant that the
COHb level could not be treated nominally, but instead, required covariate
analysis to treat COHb conditions as a variant for each subject treatment.
Because this research is exploratory in nature it is proposed that gener-
ous significance levels be used in granting statistical significance. The authors
within the report often present p values of . 8 as being significant in the spirit of
exploratory research. Since the p values are given for each test, the reader is
free, however, to determine his own criteria for significance. It should also be
noted that statistical significance is not necessarily the best test of experimental
significance. Practical differences associated with mean values of performance
measures at different levels of COHb must also be considered. In fact, through-
out the analysis the authors treat both statistical and practical differences simul-
taneously. For example, a change in a visual performance measure of 100%
may not be statistically significant because of large residual errors in the tests.
On the other hand, an increase of 1.5 miles per hour in speed, for example, is
statistically significant yet hardly of practical significance in terms of its effect
on safe driving performance.
Indeed, one must recognize that with any hypothesis test, failure to
reject the hypothesis of "no COHb effect" is no guarantee that no effect exists.
It simply reports that for this test, significant assignable causes were not
present for the specific experimental conditions employed. The researchers
sought not to find differences but rather to test for both practical and statistical
significant differences which might be present in the data.
115
-------
8.2 Interpretation
Figure 8.1 presents the general characteristics of performance measures
and their response to carbon monoxide. The complex lab tasks, despite the
advantages of laboratory control, showed only moderate changes with respect to
elevated COHb levels. Performance changes were found more in tracking error
than in choice reaction times and more in dual tasks than with individual tasks.
It should be noted that in terms of sensitivity to carbon monoxide, it was
expected that vehicle dynamic measures would be least affected, driver control
next affected, and perceptual measures would be most affected, and this was, in
fact, found in the data. Inherent variability associated with performance also
increased from the vehicle dynamics measures to the perceptual measures. At
the same time safely relevance of performance decrement is probably more
related to perceptual measures than vehicle dynamics because perceptual
failures are usually the initiating factors in the accident chain of events.
Figure 8.2 presents some illustrative results over all tasks in the road
research paradigm which clearly illustrates the dilemma of the analyses. This
plot of the relative change in performance from 2 to 12% COHb in mean values
of performance measures is plotted against the residual error relative to the
base line (2% COHb) mean. These are graduated in broad categories of less
than 10%, 10 to 50%, and greater than 50%. It should be noted that the regions
of both strong statistical and practical significance were actually not found in
the research, \\fere there to be any statistical significance in this figure, one
would have to expect residual error to be less than 50% and typically about 30%
of the mean value of the performance measure. This figure is interesting on
two grounds. First, it should be noted that, as anticipated, vehicle dynamic
measures showed minor changes in mean values and were also those variables
with the smallest residual error. In the middle cells we find the control move-
ments, and in the cells involving more than 50% change in mean value due to
CO levels, we find percpetual measures. These perceptual measures are
associated with large residual error, and hence, the inability to test these
measures for statistical significance. These large residual errors stem from
both the intra-subject variability and subject by CO interaction as well as
perhaps by subtle variation introduced by days and time of day.
The trends and the magnitudes of the performance differences associated
with elevated COHb levels in the perceptual measures suggest that tighter experi-
mental controls, more precise subject instructions, replication of trials, and
prescreening of subjects on tests related to driving might reduce the experi-
mental error such that these large differences might well be explained by non-
chance factors.
116
-------
Type of Measure
Examples
Sensitivity to
CO
Inherent
Variability
Safety
Relevance
Statistical
Significance
Complex
Lab
MAE
CRT
Moderate
Low
-
p< .9
Vehicle
, Dynamics
VlL.o- , H
VEL
Low
Low
Low
P< .9
Driver
Control
SWRR
GPRR
Brake
Moderate
Moderate
Moderate
P< .8
Perceptual
XgT, %ST,
% Down Time
High
High
High
p< .75
Figure1 8.1. —General response to CO
117
-------
8.3 A Proposed Conceptual Model for the Observed Experimental
Differences
The analysis in this report on road performance measures has sug-
gested some trends in driver performance with elevated COHb levels. In
general, largest differences occurred in perceptual measures and the smallest
in the vehicle measures (except for car-following spacing). The literature
supports the findings with the visual measures (e.g., dash-light adaptation and
night vision become deteriorated under elevated COHb levels). Further, the
preliminary Phase A and B laboratory studies demonstrated that central pro-
cessing or information processing might be the bases of any performance
degradation. Current work of Moskowitz (1970) on the effect of marijuana and
the work of Finkleman (1970) on noise suggests that operator capacity to time
share between two tasks is affected by both the external and the internal stress
mechanisms. Often performance degradation which is not found in any single
measure will develop from secondary task loading (as found in driving tasks).
Figure 8.3 depicts the trends in perceptual measures with elevated
COHb levels. Occluded studies permit us to study perceptual uncertainty,
spare visual capacity, visual efficiency, and risk (or the time the subject
would operate without information). Normal vision research tests permit us to
find the average amount of time spent in looks directly ahead and the percent
of time the subject concentrates on the immediate roadway environment ahead
of the car. In addition, inter-signal sampling intervals in car following can
also be extracted from normal vision studies. As a result of elevated COHb
levels, we find an increase in perceptual uncertainty, a decrease in the spare
visual capacity of the subjects (as measured by percent closed) and reduced
visual efficiency in the occlusion car-following tasks. (This is only at moderate
levels of COHb. See Figure 8.6.) In the normal vision tests, we find increased
levels of COHb result in increases in both open-road and car following mean
time straight ahead, again suggesting reduced visual efficiency and increases
in percent of time spent on the road directly ahead. Figure 8.4 demonstrates
the secondary task loading effect found in the lab studies and the need to
separate analysis by driving task. For example, COHb apparently affects
mean straight time more in car-following tasks than in open-road driving.
Taken together these combined effects suggest a form of perceptual narrowing
on the part of the subject, a reduced perceptual certainty, and a reduced visual
efficiency. It might be noted that in each of these instances, the data of Phases
A and B by and large, support the work of Phases C and D. For example, in
Phase A, larger values in the percent straight visual measure were found at
20% COHb than those found at the lower COHb levels studied in Phases C and D.
Reduced visual efficiency as reflected in increased open times during occluded
tasks were found in the Phase A study above the levels of Phases C and D
118
-------
X value
10-50%
= region of statistical and practical significance
o- (-63, 125)
STR
XSTR <40' 69>
SWRR(-11, 15)X
H(-15, 30)
'///// //
Measure Mean
(X, Y)
50%
12% COHb mean - 2% COHb mean
2% COHb mean
2% COHb mean
x 100
crnn
olxv
STR
= mean look time straight ahead
= % of look time straight ahead
SWRR = steering wheel reversal rate
%__ = % time eyes closed
CL
o- = STD deviation looks
straight ahead
or = Relative Velocity
STD deviation
H = mean headway
VEL = mean velocity
Figure 8.2. —Illustrative results (all tasks)
119
-------
OCCLUDED STUDIES
Perceptual Uncertainty!
Spare Visual Capacity
Visual Efficiency
ELEVATED
COHb LEVELS
INCREASED Perceptual Uncertainty
DECREASED Spare Visual Capacity
REDUCED Visual Efficiency
(car following)
NORMAL VISION
\
'STR* STR
STR
= % time eyes closed
= % of look time straight
ahead
= mean look time straight
ahead
OR = open road
= car following
fxSTR(OR&CF)
f %ST
I
PERCEPTUAL NARROWING - REDUCED PERCEPTUAL CERTAINTY
REDUCED VISUAL EFFICIENCY
Figure 8.3.—Trends in perceptual measures
120
-------
5.0
4.0--
03
O
V
•2.
g
1H
m
I
3.0--
2.0-•
1.0--
Car Following
12
Nominal COHb level (percent)
Figure 8.4. —Mean straight looks for normal vision
driving tasks
121
-------
(where effects were shown only in occluded car following). The percent
straight measure in both open road and car following appears to make its
effect known in lower levels of COHb and there appears to be little increase
in moving from the 7 to 12% region to the 20% region used in Phases A and B.
In examining the vehicle dynamics and driver control measures as a
function of elevated COHb levels, it was found that steering wheel reversal
rates decreased with elevated COHb levels. If carbon monoxide acts in the
same way as driving fatigue, this result would be consistent with the work of
Platt (1964) and others who have examined operator control movements as a
function of driving time. Since brake pedal and gas pedal applications were
only relevant in the car-following case, their interpretations must be tempered.
It was found that in the car-following tests, elevated COHb levels led to increased
gas pedal reversal rates and increased brake applications, perhaps reflecting
some of the perceptual uncertainly indicated above.
In terms of car-following performance (as measured by headway and
relative velocity), it is noted that there was an increase in the relative velocity
variation associated with elevated COHb levels and a corresponding decrease in
headway maintained at elevated COHb levels. In one sense, this is an apparent
contradiction since research in the psychophysics of car following would suggest
that as the driver gets closer to the car ahead, his ability to sense changes in
spacing should improve simply on the basis of his Weber function. The decrease
in mean headway is supported in the work of Phase A where 14 out of 20 cases
showed a reduced headway. This fairly consistent reduction of headway under
elevated COHb levels appears to be an anomaly not easily explainable in terms
of perceptual measures described earlier. The driver's perceptual narrowing
mentioned earlier may suggest that over-concentration of visual activity on the
lead car would lead to lack of other cues to provide spacing information. This
would explain changes in headway but not necessarily the fact that the changes
were negative.
Since headway refers to elected spacing in car following, the observed
reduced headways may have their locus not in perception but in risk acceptance
whereby elevated COHb levels serve to relax driving inhibitions. In any event,
reduced headways, lack of mirror sampling, increased perceptual uncertainty,
and reduced visual efficiency, taken together, are required for decreased safety
in car following (visually loaded tasks). It might be of interest in future research
to examine the pattern of accidents of older cars with exhaust system failures
against newer models and patterns of heavy smokers versus non-smokers.
122
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8.4 Nonlinear Effects of Elevated COHb Levels
One of the reasons for testing subjects at three levels of COHb (controls,
7 and 14% target values) was to ascertain if ovserved effects would be linear with
COHb levels. Beard (1967) and others have shown peculiar nonlinear effects of
COHb levels for certain performance measures. Other investigators have found
small amounts of alcohol in the blood stream can actually lead to smoother per-
formance. This research has also demonstrated in several cases the existence
of quadratic terms in the analysis. In many cases these quadratic terms are
highly significant. This frequent reappearance of significant nonlinear terms
presents a difficult interpretation problem. For monotonically increasing or
decreasing effects, one could argue that threshold conditions are different from
magnitude effects (see Figure 8.5, curve 3). Curve 1 suggests little effect until
COHb levels reach a threshold level and the effects accelerate beyond that point.
Curve 2 suggests early effects which taper off as COHb levels increase. Mean
open time for the occluded tasks apparently follow curve 1 showing much more
effect at the very high levels of COHb tested. On the other hand, percent
straight measures appear to follow curve 2 since most of the changes take place
at low levels of COHb and little change in performance is observed beyond the
lower levels.
Figure 8.6, however, depicts pure quadratic effects found for percent
closed for occluded sample driving. This curve supports the data on the six
subjects presented earlier which clearly showed a reduction in percent closed
in moving from the 2% to the 6 to 8% COHb level. However, when the data is
examined beyond the 6 to 8% level up to the 12 to 14% level we find a reverse
effect where very little difference in percent closed between 2 and 12% is
observed. The covariate analyses demonstrated this clearly by suggesting no
linear effect but a strong quadratic effect. It is doubtful that this effect is
purely random. No physiological evidence, however, exists which could account
for such relationships. Two general explanations might be possible. One, a
change might occur in driver compensatory processes due to elevated COHb
levels wherein the driver subjectively alters his adaptive process once he
becomes subconsciously aware of decrement at the middle COHb level. The
second explanation comes from an arousal theory which proposed that small
stressor effects may alter the driver's arousal level differently from large
effects. In any event, more research is needed to ascertain if these nonlinear
effects are real or chance effects, and whether a causal mechanism can be
found.
123
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8
§
*
Low
Medium
COHb Levels
High
Figure 8. 5. —Possible trends in performance due to COHb levels
124
-------
SO-
o
0
50-
40-
% COHb level
12
Occluded - OR - 50 mph
Figure 8. 6. —Example of quadratic effects
125
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APPENDIX A
EQUIPMENT AND SUBJECT INSTRUCTIONS
COMPLEX LABORATORY TASKS
127
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The complex task for the series of experiments resulted from the simul-
taneous employment of two basic psychomotor tasks; one visual choice reaction
time task, and the other a pursuit tracking task. This section describes the
task hardware employed during the series of studies. Figure A. 1 is a general
schematic illustrating the equipment and its interface with the computer.
A.I Choice Reaction Time Apparatus
The visual stimuli for the two-choice reaction time task were projected
on to a screen surrounding the face of an oscilloscope from a 16 mm Data
Analyst movie projector. The projector was located behind and above the sub-
ject at a distance of approximately eight feet from the screen. The screen was
located approximately five feet in front of the subject.
The stimuli were white one inch letters and numbers photographed on a
black matte background and projected through a 1-5/8 inch lens. At a five foot
viewing distance, the stimuli subtended approximately 50 minutes of arc hori-
zontally. The stimuli were centered approximately three degrees horizontally
on either side of the subject's central line of sight.
The onset of each stimulus was detected and recorded electronically.
Each frame of 16 n\m film which contained an active stimulus was coded by
means of white squares which were photographed in the upper corners.
Light shining through the corners was intercepted by one of three cad-
mium sulfide cells, implanted in a metal housing which was located several
inches in front of the lens of the projector. The onset of the light triggered a
low voltage pulse through the cell which activated a galvanometer on a Consoli-
dated Electrodynamics Corporation, 50 channel oscillograph recorder. The
subject viewed only the lower half of the frame of film, containing the stimulus
and, consequently, was unaware of the coded light pulses.
Timing of the stimulus sequences was dictated by the frame speed of the
movie film. The experimenter was alerted to the beginning and end of each
trial through the onset of a light on the experimenter's console. The lamp was
triggered from a third cadmium sulfide cell located between the stimulus cells.
Subjects responded to selected stimuli by pressing either of two momen-
tary contact pushbuttons mounted on the spokes of a steering wheel. The func-
tion of the wheel will be explained in a later section.
The response voltages were recorded by a CEC oscillograph recorder.
128
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-------
A. 2 Data Collection Apparatus
The onset of each stimulus was detected and recorded electronically in
the same manner as described above. However, the pulses produced by the
stimuli were routed both to the CEC recorder and a Digital Equipment Corpora-
tion, PDP-8, digital computer. The use of the computer will be detailed in a
later section.
A.3 Tracking Apparatus
The subject's tracking display consisted of two vertical bars of light,
3/4 inch in height, which traversed horizontally across the face of a Dummont
dual-beam oscilloscope.
A 1000 Hz sinusoid was applied to the vertical axes of each beam to
create the light bars. The upper bar was driven in the horizontal plane by the
tracking system forcing function. The lower bar was driven in the horizontal
plane by voltage resulting from the rotation of the subject's steering wheel.
A weight attached to the shaft of the steering wheel returned the wheel to center
when pressure was released.
A.4 Digital Computer System
Data collection and reduction for a large portion of the tests was per-
formed by an on-line digital computer system which consisted of:
1. Digital Equipment Corporation PDP-8L digital computer
equipped with a high speed paper tape reader and punch,
2. a Teletype printer and keyboard which were operated by
the computer,
3. seven (7) analog-to-digital channels which transformed
the analog voltages received from the tracking and choice
reaction time equipment to digital data for analysis,
4. two (2) interrupt channels which triggered the internal
digital logic on the occurrence of either a stimulus or
response, and
5. assorted peripheral solid state logic and conditioning
circuitry necessary to interface the computer with the
task.
130
-------
The digital computer was programmed to output the following informa-
tion at the end of each 40 second trial and at the option of the experimenter:
1. mean absolute tracking error (MAE),
2. mean tracking error,
3. choice reaction time data including the time
of stimulus or response onset,
4. cross correlation between the forcing function
voltage (i(t) and the tracking voltage function
y(t)) in the same form as each appeared on the
oscilloscope,
5. autocorrelation of the error voltage,
e(t) = i(t)-y(t),
6. complete data dump of e(t) onto punch paper
tape, and
7. subject eye-movement data.
A.5 Eye-Movement System
A commercially available Biometrics SGHV/2 eye-movement system
was employed to measure the horizontal deflection of the subject's right eye
during certain CRT tests. A detailed description of this system is available
from the manufacturer.
During each experimental session, the subject grasped a bite bar
between his teeth in order to keep his head stationary and produce accurate
eye-movement measurements. The bite var was rigidly attached to a bracket
which protruded from a sturdy partition.
The subject's eye movements were calibrated every three minutes by
having the subject fixate on known targets spaced across the subject's field of
view.
The output voltage from the Biometrics system was attached both to the
CEC oscillograph recorder and an A/D channel of the digital computer.
Maximum output voltages varied both from subject to subject and within
subjects on during separate experimental sessions. Voltages rarely exceeded
+ 1.0 volts DC.
131
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A.6 Subject Instructions
A.6.1 Tracking Only
The purpose of this first portion of the experiment is to test your ability
to follow the movements of a visual target.
In front of you, you will notice an oscilloscope tube with two vertical
lighted bars on its face. The upper vertical bar moves randomly back and
forth across the face of the tube. The lower vertical bar moves only when
the steering wheel in front of you is rotated.
Your task is to keep the lower bar lined up as closely as possible with
the upper bar during each trial of this session.
There will be a number of short trials. Between each trial you will be
given a brief rest. The end of each will be signalled by a brief tone in your
earphones. The upper bar will continue to move but you will not follow it.
At the end of each rest period another tone will sound in your earphones.
Begin to line up the bars immediately after hearing this tone.
Questions ?
Please keep both hands on the wheel at all times even during the rest
period. It is important that you grasp the wheel so that your thumbs rest
lightly on the red buttons. The experimenter will inform you when this portion
of the experiment is over.
The earphones are to be worn at all times during the session. They will
normally play static to eliminate outside noise.
Please put on your earphones now and be prepared to begin the experi-
ment at the sound of the tone.
A.6.2 Choice Reaction Time
This portion of the experiment will test your ability to respond to visual
stimuli as rapidly as possible. The experiment is divided into a number of
short trials. At the beginning of each trial, a number or a group of numbers
will be projected on the screen above the oscilloscope. This number or group
of numbers are the target stimuli for that trial.
132
-------
Similarly, this stimulus is a 5 and, you would respond with your right
(left) hand pushbutton.
Advance
This next stimulus is not a 5, so you would respond by pushing your left
(right) hand pushbutton as rapidly as possible as soon as it appeared.
Advance
Similarly, you would respond with your left (right) hand pushbutton as
soon as this stimulus appeared.
Advance
Similarly, this stimulus
Advance
and this stimulus would require a response with your left (right) hand pushbutton.
Advance 2 frames
At the beginning of some trials, a 4-9 combination will appear above the
scope.
Advance
4-9 target
For the remainder of that trial, you will respond by pushing your right (left)
hand pushbutton as rapidly as possible whenever a 4 or a 9 appear in any loca-
tion on the screen. You will respond with your left (right) hand whenever any
other number appears.
Advance
133
-------
Your task is to respond by pushing your right (left) hand pushbutton as
rapidly as possible if the number that appears is the same as any of the target
numbers. Whenever any other number appears, you are to push your left
(right) hand pushbutton as rapidly as possible. As soon as you respond to one
number another will appear.
For the remainder of the trial different numbers will be projected on
either side of the oscilloscope, one after another. The numbers may appear
either near the oscilloscope or farther away from the scope.
Advance 1 frame
5 target
For example, in this slide a 5 is shown as the target number. You
would push your right (left) hand pushbutton as rapidly as possible each time it
appeared during the trial. If any other number appeared, you would push your
left (right) hand pushbutton as rapidly as possible.
Advance 1 frame
For example, you would push your right (left) hand pushbutton as rapidly
as possible when this stimulus appeared.
Advance
For this stimulus you would again respond with your right (left) hand
pushbutton.
Advance
This stimulus is a 5 also, so again you would respond with your right
(left) hand pushbutton.
Advance
134
-------
For example, in this slide a 4 appears. You would respond with your
right (left) .'hand=as rapidly as possible.
Advance
rSimilarly, when .a '9 appears you would also .push your right (left) hand
pushbutton as .rapidly as possible.
To be certain .that you understand the instructions, I'll advance through the
'the next few slides .and you tell me which pushbutton, the right or the left you
would-push each time :a'Stimulus appears.
Advance
Advance
Advance
Advance
Advance
Advance
Advance
3 right (left)
9 right (left)
4 right (left)
5 left (right)
3 left (right)
0 left (right)
1 left (right)
Advance 2 frames
At the ^beginning of'some trials, a group of numbers consisting of a 0, 1,
3, and 7 will .-appear above the :scope face.
Advance
01 target
37
135
-------
For the remainder of that trial you will respond with your right (left)
hand whenever a 0, 1, 3, or 7 appears on the screen on either side of the scope.
You will respond with your left (right) hand when any other number appears.
Afain, to be certain that you understand the instructions, I'll advance
through the next few slides and you tell me which pushbutton, the right or the
left you would push when each stimulus appears.
Advance
Advance
Advance
Advance
Advance
Advance
Advance
0 right (left)
1 right (left)
3 right (left)
7 right (left)
5 right (left)
4 right (left)
9 right (left)
Are there any questions so far?
There will be a number of trials. At the start of each trial, you will
hear a tone in your earphones and the target number or numbers will appear
above the scope face.
At the end of each trial, another tone will sound. You may then take a
short rest. After the rest period, another tone will sound. At that tone be
prepared to begin the next trial.
When the experiment is over, you will hear a number of beeps in your
earphone. At that time, remove your earphones for further instructions.
136
-------
Please try to respond as fast as possible to each number, without
making mistakes.
Questions ?
Please keep your hands on the wheel and your thumbs resting lightly over
the pushbuttons at all times during the experiment.
Put on your earphones now and be prepared to begin the trial at the
sound of the tone.
A.6.3 Dual-Task
This portion of the experiment will test your ability to respond to visual
signals while at the same time following the movements of a visual target.
One of your tasks will be to keep the upper and lower bars on the oscil-
loscope lined up as closely as possible, as you have previously done.
Your second task will be to respond to numbers projected on the screen
on either side of the oscilloscope as you have also previously done.
As before, a tone will sound to alert you to the start of each trial. When
the tone sounds begin to line up the bars. Do not begin to respond to stimuli
until a new stimulus appears at the side of the scope face.
At the end of each trial another tone will sound in your earphones.
You may take a short rest at this time. As previously, near the end of
the rest period the target stimuli for the next trial will be projected briefly
over the face of the scope. When you hear the alerting tone begin to line up the
bars and when a new stimulus appears at the side of the scope, begin to respond.
The experimenter will inform you when this portion of the experiment is
over.
Again, please wear your earphones at all times during the experiment
and keep your hands on the wheel and thumbs resting lightly over the push-
buttons at all times.
A.7 Feedback of Results
It is important during this experiment, that you perform the bar following
task as well as possible. Respond as quickly as you can to the numbers when
they appear, but try not to let your responses affect your performance on the
bar following task. Is this clear ?
137
-------
During this experiment, the meter located on the console in front of you
will keep you informed of your performance on the bar following or tracking
task. At the end of each tracking trial, the meter will briefly present you with
a score of your performance. This score will be based on a comparison of your
performance on that trial and previous performance on the same task. For
example, if your tracking performance is average for a trial you will receive
a score of 50 on the meter. If you perform below average you will receive a
score of 25. If you perform above average you will receive a score of 75. The
meter will return to zero before the next trial begins. Do you understand this
scoring method ?
A. 8 Eye-Movement Recording
The glasses you are wearing will permit us to record where you are
looking at any instant. It is important, once we have calibrated the glasses,
that you do not move your head. The bite-bar will ensure that your head
remains stationary as long as you maintain a firm pressure on the bar with
your teeth.
You will be asked to assist in calibrating the equipment several times
throughout the session. For this procedure, a numbered piece of cardboard will
be raised in front of you. You are asked to look directly at each of the black
spots beneath the numbers as the numbers are called out.
Please do not attempt voice communication once you have the bar in your
mouth, unless it is absolutely necessary.
As previously, before each trial begins, you will be presented with the
master stimuli for that trial. When the alerting tone sounds begin to line up
the bars. Do not begin to respond to stimuli until a new stimulus appears at the
side of the scope face.
Please keep your hands on the wheel and your thumbs resting lightly over
the pushbuttons at all times. You will be informed each time we wish to cali-
brate or when the experiment is over. Are there any questions ?
Please put on your earphones now and be prepared to begin the experi-
ment at the sound of the tone.
138
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APPENDIX B
SUBJECT INSTRUCTIONS FOR ROAD TESTS
(TASKS 12 THROUGH 24)
139
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Task 12
Description: Headway Production Task
Subject Instructions:
During this part of the experiment, we would like to test your ability
to estimate different headways or distances between cars.
Your task will be to accelerate or decelerate the vehicle and then
hold it at a distance from the lead car which I will read to you.
After you have produced the desired distance, please say the words
"at distance. " I will then immediately read off another distance which
you should try also to produce. Are there any questions ?
Target Headways:
Headway Trial Headway Trial Headway Trial Headway
1
2
3
4
5
6
7
8
9
10
90
172
186
268
262
352
370
100
178
368
11
12
13
14
15
16
17
18
19
20
358
86
182
362
82
264
366
88
174
354
21
22
23
24
25
26
27
28
29
84
280
272
24
176
94
274
360
96
31
32
33
34
35
36
37
38
39
356
98
369
260
184
270
188
276
190
30
180
40
278
140
-------
Task 13
Description: Velocity production task
Subject Instructions:
During this part of the experiment, you will be driving the vehicle
without the use of the speedometer. We would also like to test your
ability to estimate different velocities during this part of the experiment.
Your task will be to accelerate or decelerate the vehicle and then
hold it at a speed which I will read to you. After you have produced
the required speed, please say the words "at speed. " I will then
immediately read off another speed which you should try to also
produce. Are there any questions ?
Target Speeds:
Trial Velocity Trial Velocity Trial Velocity Trial Velocity
1 62 11 26 21 48 31 67
2 57 12 66 22 54 32 35
3 49 13 50 23 27 33 41
4 38 14 67 24 64 34 56
5 51 15 33 25 47 35 36
6 37 16 40 26 39 36 53
7 31 17 63 27 30 37 70
8 44 18 69 28 60 38 52
9 58 19 61 29 34 39 42
10 32 20 43 30 29 40 55
141
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Task 14
Description: Time Estimation Task
Subject Instructions:
1. During this portion of the experiment, we would like you to
drive the car in your normal manner. We also would like to test
your ability to estimate time intervals while you are driving.
Your first task will be to estimate two second time intervals. When
I say start, begin to estimate a two second interval. When you feel
that two seconds have elapsed, press the button in your right hand and
begin to estimate the next two second interval. Continue this task
until we tell you to stop.
ft is important that you attempt to judge the two second interval without
counting. If you are wearing a watch, please do not use it. Are there
any questions ?
2. Your second task is to estimate eight second time intervals.
When I say start, begin to estimate an eight second time interval.
When you feel that eight seconds have elapsed, press the button in
your right hand and begin to estimate the next eight second interval.
Continue this task until we tell you to stop.
Again it is important that you attempt to judge the eight second interval
without counting. If you are wearing a watch, please do not use it.
Are there any questions ?
3. Your third task is to estimate four second time intervals. When
I say start, begin to estimate a four second interval. When you feel
that four seconds have elapsed, press the button in your right hand
and begin to estimate the next four second interval. Continue this
task until we tell you to stop.
As before, it is important that you attempt to judge the four second
interval without counting. If you are wearing a watch, please do not
use it. Are there any questions ?
142
-------
Task 15
Description: Constant speed, (50 mph) car following, normal vision
Subject Instructions:
Please drive this car behind the lead car as if you were on
a two-lane highway attempting to pass the lead car but were unable
to because of oncoming traffic in the left lane. Are there any questions?
Task Duration: 3 minutes
Task 16
Description: Constant speed (50 mph) car following, voluntary occlusion
Subject Instructions:
Please drive this car behind the lead car as if you were on
a two-lane highway attempting to pass the lead car, but were unable
to do so because of oncoming traffic in the left lane.
During this part of the experiment we would like you, in addition
to driving as we just described, to close your eyes whenever possible.
That is, we would like you to keep your eyes shut as much as possible
and when you open your eyes to keep them open for as short a time as
possible. The "safety man" seated next to you will be observing your
behavior and that of the other traffic near this vehicle. He will alert
you by stating the word "open" if he feels that you should open your
eyes. If at any time, during this run you feel that you should open your
eyes and keep them open, do not hesitate to do so.
Although we are asking you to keep your eyes closed as much as
possible, we still expect you to maintain normal control of the vehicle
and to keep the car in the right hand lane. The safety man's role will
be that of alerting you to unusual occurrences that might develop.
During this run, the lead car will maintian approximately the
same speed at all times. Are there any questions ?
Task Duration: 3 minutes
143
-------
Task 17
Description: Variable speed car following (mean speed 50 mph)
normal vision
Subject Instructions: Same as T15
Task Duration: 3 minutes
Task 18
Description: Variable speed car following (mean speed 50 mph)
voluntary occlusion
Subject Instructions: Same as T16 with the exception of the
following at the end of the instructions
During this run, the lead vehicle will upon occasion
change speeds in a gradual manner. That is, it will slow
down or speed up, but it will not do so suddenly. Are there
any questions ?
Task 19
Description: Open road driving, target speed 50 mph, normal
vision
Subject Instructions:
Please drive this car in your normal manner at about 50
mph. Please keep to the right hand side of the road whenever
possible. If you desire to pass anyone, please let us know and
we will tell you when it is safe to do so. Are there any questions ?
Task Duration: 3 minutes
Task 20
Description: Open road driving, target speed 50 mph, voluntary
visual occlusion
Subject Instructions:
Please drive this car in your normal manner at about 50 mph,
and keep to the right hand side of the road whenever possible.
144
-------
During this part of the experiment we would like you, in
addition .to driving as we just described, to close your eyes when-
ever possible. That is, we would like you to keep your eyes shut
as much as possible and when you open your eyes to keep them
open for as short a time as possible. The "safety man" seated
next to you will be observing your behavior and that of the other
traffic near this vehicle. He will alert you by stating the word
"open" if he feels that you should open your eyes. If at any time
during this run you feel that you should open your eyes and keep
them open, do not hesitate to do so.
Although we are asking you to keep your eyes closed as
much as possible, we still expect you to maintain normal control
of the vehicle and to keep the car in the right hand lane. The
safety man's role will be that of alerting you to unusual occurrences
that might develop. Are there any questions?
Task Duration 3 minutes
Phase B; For the cognitive loading task of Phase B, the following
instructions were substituted:
Please, drive this car in your normal manner at about 50
mph. Please keep to the right hand side of the road whenever
possible. During this part of the experiment, we would like
you in addition to driving as we have just described, to perform
the following task as much as possible.
The subject was then told to perform one of the following secondary tasks:
Task 1
Using the mirror mounted on the front roof pillar of the car,
please read the first three numbers on the digital clock into the
microphone. Then read the speed to the nearest mile; e.g., 53,
68, 64, etc., from the speedometer into the microphone. Then
mentally add the two numbers together and read the sum into the
microphone. After doing this, please start the task again as
quickly as possible. Are there any questions?
Task 2
Using the mirror mounted on the front roof pillar of the car,
please read the first three numbers on the digital clock into the
microphone. Then mentally divide that number by two and read the
answer into the microphone. After doing this, please start the task
again as quickly as possible. Are there any questions?
145
-------
Task 1 was used as a secondary task during the first replication of the
series of tests. It was observed; however, that the subject kept the vehicle
speed as close as he could to fifty miles per hour in order to simplify the
secondary task. Task 2 was adopted for the second replication of the series
of tests in order to avoid this problem.
Task Duration: 6 minutes
Task 21
Description: Open road driving, target speed 30 mph, normal vision
Subject Instructions: Same as Task 19 with "30 mph" substituted for
"50 mph"
Task Duration: 3 minutes
Task 22
Description: Open road driving, target speed 30 mph, voluntary visual
occlusion
Subject Instructions: Same as Task 20 with "30 mph" substituted for
"50 mph"
Task Duration: 3 minutes
Task 23
Description: Velocity maintenance, target speed 50 mph, no
speedometer variable
Subject Instructions:
For the next few minutes we would like for you to try to
hold your speed as close to 50 mph as possible. You may use the
speedometer to find 50 mph before we begin, after which we will
cover up the speedometer. Are there any questions ?
Task 24
Description: Leap frog passing test
146
-------
Subject Instructions:
During this part of the experiment we would like for you
to drive about 60 mph. The other vehicle will pass you, get some
distance ahead, and then slow down. When you close in on the
other vehicle we would like to pass it in your normal manner.
After passing, please return to the right hand lane in your normal
manner and we will repeat the test 20 times. Are there any
questions ?
Task Duration: approximately 45 minutes
147
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APPENDIX C
MEASUREMENTS OF CARBOXYHEMOGLOBIN LEVEIfi
OF FREEWAY DRIVERS
149
-------
Three ancillary studies performed in conjunction with the main studies
of this report are provided in this appendix. The data was collected during the
winter months (January through March, 1972).
Study 1
Almost five hundred (498) drivers on the Ohio Turnpile were tested for
COHb. Fifty-two (52) of these drivers were truck drivers and are reported
under Study 2. A test station was established at the Portage Plaza rest area
through the gracious cooperation of Messers. Allen Johnson and J. Budd
Morrison of the Ohio Turnpike Commission. The test station was operated
around the clock from Friday afternoon through Sunday evening on two weekends
in February, 1972.
Study 2
Seventy-seven (77) truck drivers were tested for COHb levels. Twenty-
five (25) of the truck drivers were employed by Suburban Motor Freight Com-
pany of Columbus, Ohio. We are grateful to the drivers and Mr. Larry
Legrange for their cooperation in this study. The remaining fifty-two (52)
drivers were tested at the turnpike test station of Study 1.
Study 3
One hundred and thirty (130) students and staff who had occasion to
enter the Baker Industrial and Systems Engineering Building on The Ohio State
University campus were tested for COHb levels.
This site was chosen for this third study to screen for effects due to
smoking by screening for subjects who had not driven for over one hour prior
to being tested.
Results
All COHb levels were determined using a Beckman infra-red breath-
analyzer. Summary statistics for these three studies are presented in Table
C.I.
150
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Table C.I
Summary Data Table for Ancillary Studies
Study 1
Total Ohio Turnpike Study
Study 2
Truck Study
Study 3
^University Study
Number of
persons
tested
Mean COHb
level in %
Std. Dev. of
COHb level
Range of
COHb level
Maximum
COHb level
Minimum
COHb level
cigarette
smokers
212
4.64%
1.77%
9.0%
11.0%
2.0%
pipe and
cigar
smokers
22
3.05%
1.86%
8.0%
10.0%
2.0%
non-
smoker
male
132
2.11%
.38%
3.0%
4.0%
2.0%
non-
smoker
female
80
2.02%
.35%
2.0%
3.0%
1.0%
non-
smoker
28
2.61%
.99%
4.0%
5.0%
1.0%
smoker
49
4.33%
1.48%
7.0%
9.0%
2.0%
non-
smoker
85
2.05%
.26%
2.0%
4.0%
2.0%
smoker
45
3.64%
1.52%
6.0%
8.0%
2.0%
-------
APPENDIX D
SUBJECT CONSENT FORM
SUBJECT PRESCREENING DATA FILE
HABIT INVENTORY FORM
CORNELL MEDICAL INDEX HEALTH QUESTIONNAIRE
153
-------
DESCRIPTION OF KNOWN RISKS ASSOCIATED WITH THE INVESTIGATION
OF THE EFFECTS OF CARBON MONOXIDE ON DRIVING
I, have been informed of the
(name)
dangers associated with carbon monoxide (headache, nausea, possible phlebitis
from blood sampling), and automobile driving by the staff and associated of
Dr. C. E. Billings. I understand that the purpose of this research is to
determine the effects of carbon-monoxide exposure on driving performance.
I also understand that drivers on the streets and highways have been found to
have COHb levels greater than 30% and that smokers can readily obtain a COHb
level of 16% or greater. I have also been informed that there are no detectable
physiological effects of carbon monoxide below the level of 20% COHb, and that
there are no damaging effects below a 30% COHb level.
I therefore consent to allow Dr. Billings and his associates to administer carbon
monoxide to me in amounts that will result in COHb levels up to 20% on the con-
dition that there will be a licensed medical doctor available at all times during
the experiments, and that my COHb level will not exceed 20% at any time.
Signed
Witnessed by:
Investigator
154
-------
Subjects RF Project 3332
Date:
1. Name:
2. Address:
3. Telephone:
4. Age: 5. Date of birth:
7. Next of kin:
Address:
6. SS#
Phone:
8. Married:
10. Military Service:
12. Number of years:
14. Present status: _
15. Do you smoke? _
9. No. children:
11. Branch:
13. Rank:
16. Have you smoked in last 6 months ?
17. Have you ever been employed by The Ohio State University in any position
prior to this interview?
18. If the answer to the above question is yes, what department did you work in?
19. Why do you want to be a part of this study?
20. Have you ever spent any length of time away from your home?
155
-------
21. Have you ever been confined to a hospital or had a serious health problem?
If yes, give explanation:
22. Major and minor academic interests:
156
-------
HABIT INVENTORY
Do you smoke?
Cigarettes
Pipe
Cigars
Age you started to smoke.
Age you last quit smoking.
Was it difficult to stop?
Number of smokes per day?
What is your maximum weight?
Your present weight?
How many meals eaten daily?
Time of day meals eaten (a.m., p.m.)
Breakfast
Lunch
Supper
Quantity of food taken at each mean (small, medium, large)
Breakfast
Lunch
Supper
Do you snack during daytime or night?
How much?
Do any foods make you sick?
List
157
-------
Number of glasses of water daily
Does chlorinated, fluoridated, or chlorinated and fluoridated drinking water
make you sick?
Number of glasses of milk daily
Number of cups of coffee daily
Number of cups (glasses) of tea daily
Alcohol usage
Kind
Amount
Frequency
Other beverages
Kind
Amount
Frequency
Sleep
Number of hours per night
Time of retiring
Time of arising
Difficulty with sleeping?
Do you take naps ?
When?
Bowel and Bladder
Number of bowel movements a day(s)
Number of urinations during day
Number of urinations during night
Exercise
Frequency of exercise
Kind of exercise (mild, moderate, strenuous, exhausting)
Describe
What length of time do you exercise ?
What time of day do you exercise ?
158
-------
Drugs
Drugs currently being used (list - e.g., aspirin)
Frequency of use.
Is drug controlled by a physician or yourself?
List physician's name and address:
Hobbies
List hobbies
How much time are you involved with hobbies ?
Reading
Books (list type)
Newspapers (names)
Magazines (names)
Time spent reading daily
Television and Radio
Time viewing TV daily
Time listening to radio daily
Describe what type TV and radio programs you enjoy (e.g., music,
sports, comedy, etc.)
159
-------
THIS FORM IS STKICILY CCirjITZI.Ti
DULY FOR PURPOSES OF THIS STUDY.
KEREIH WILL BE USED
Dau
HEALTH QUESTIONNAIRE
Print
Your
Mime.
How Old Are You?.
Your
Home
Address.
. Circle II You Are . . Single, Married, Widowed, Separated, Divorced.
Circle the Highest
Year You Reached
In School |12345678| | 1 234 |
Elementary School High
|1234|
College
What Is Your
Occupation7—
Directions: This questionnaire is for MEN ONLY.
If you can answer YES to the question asked, put a circle around the C Yes
If you have to answer NO to the question asked, put a circle arou
Answer all questions. If you are not sure, guess.
A
1.
2.
3.
Do you need glasses to read?
Yes No
Do you need classes to see things at a dis-
tance? ________________ . . Yes No
Has your eyesight often blacked out com-
pletely? ____________________ Yes No
4. Do your eyes continually blink or water? . . Yes No
5. Do yon often have bad pains in your eyes? . Yes No
& Are your eyes often red or inflamed? . .. Yes No
7. Are you hard of hearing? ... --- Yea No
8. Have you ever had a bad running ear? -- Yes No
9. Do >ou have constant noises in your ears? Yes No
B
10. Do )ou have to clear your throat frequently? Yes No
11. Do you often feel a choking lump in your
throat? ---- . .... Yes No
12. Are you often troubled with bad spells of
sneezing? . . _ ....... Yes No
13. Is your nose continually stuffed up? . . Yes No
14. Do you suffer from a constantly running
nose? ... . Yes No
IS. Ilaie >ou at timrs had bad nose bleeds7 Yes No
16 Do >ou often catch severe colds? . Yes No
17. Do >ou frequently suffer from heavy chest
colds7 Yes No
18. When jou c.itrh a cnld, do )ou alwa)s have
In co to !--H' Yes No
19. Ihi Ircqucnl culds keep you miserable all
»mter? --- ----- . .. Yes No
20. Do you get hay fever? _ . ... .. Yes
21. Do >ou suffer from asthma? . . Yes
22. Are you troubled by constant coughing? Yes
23. Hate >ou e\er coughed up blood? Yes
24. Do you sometimes have severe soaking sweats
at night? .__._. Yes
25. Have >ou eier had a chronic chest condition? Yes
26. Have you eter had T.D. (Tuberculosis) ? Yes
27. Did you ever live «ith anyone who had T.&? Yes
No
No
No
No
No
No
No
28. Has a doctor ever said your blood pressure
was loo high? Yes
29. Has a doctor ever said your blood pressure
uas too low? . . . Yes
30. Do >ou have pains in the heart or chest? Yea
No
No
No
31. Are >ou often bothered by thumping of the
heart? ..... . Ye«* No
No
No
32. Docs jour heart often race like mad? Yes
33 Do )ou often have difficulty in breathing? Yes
34. Do >ou get out of breath long before anyone
Yes No
35. Do >ou sometimes get out of breath just sil-
ling still? Yes
36 Are your ankles often badly swollen7
Yes
37. Do cold hands or feet trouble )ou even in hot
Heather? Yes
38. Do you suffer from ficquenl rramin in your
legs? . Yes
V) Has a durlor ciur s.iid >ou haJ lirarl Irnulili:' Yes
40. Does heart trouble run in )our family? Yes
No
No
No
No
No
No
OPEN TO NEXT PACE
160
-------
41. Have you lost more than half jour teeth? _ Yes No
42. Are jou troubled.by bleeding gums7 Yes No
43. 'Have jou'often had severe toothaches7 . Yes No
44. Is jour tongue usually badly coated? _ Yes No
45. 'Is jour appetite al»ajs,poor? Yes No
46. Do jou usually oat sweets .or other Hood be-
tween meals? . _ Yes No
47. Do jou alwaj-s gulp jour food in a hurry? Yes No
48. Do-jou often suffer from an upset stomach7 Yes No
49. 'Do you usual!) "feel .bloated after eating? . Yes No
SO. Do jou usually belch a lot after eating? Yes No
51. Are you often sick to'tour stomach? Yes No
52. 'Do tou suffer from indigestion? _ _ Yes No
S3. .'Do severe pains in the'Stomach often double
you up7 . — _ . _ Yes No
54. Doiyou suffer from constant stomach trouble? Yes No
55. Does stomach trouble Tun in your family? Yes No
56. Has a doctor ever said you had stomach
ulcers? Yes No
57. Do yoa suffer from .frequent loose bowel
movements'' ._
Yes No
58. Hate jou ever had setere'bloody diarrhea? _ Yes No
59. Were you 'ever troubled •with intestinal
worms7 _ _ _ . __ _ -
60. .Do tou constantly suffer from bad con-
stipation? .
61. Hate 'you e\er had piles (rectal hemor-
rhoids)? ._
62. Have \o\i eter had jaundice (yellow eyes
andslm)7 . . ._
63. Have >ou ncr had serious liver or gall blad-
der our joints often painfullt swollen' Yes No
65. Do your muscles and joints constantly feel
stiff? - . 'Yes No
66. Do jou.usuallt have severe pains in the arms
or legs7
Yes No
67. Are tou cnu,ilcd with «»v*r rh«im,iti«ni
(arthritis) ' Yes No
! D"*-* rli>
family '
farthnl O run in jour
'
Yes No
69. Do tvcaL or painful .(cct make jour life
miserable7 ....... _ . _ Yes No
70. Do pains in the back make it hard for jou to
.keep up uilh jour work? ... _ . Yes No
71. Are \ou troubled 'With a serious bodily dis-
ability or deformity' . .... Yes No
72. Is your skin very sensitive or tender? . Yes No
73. Do cuts in jour skin usually stay open a long
time? . _ _ . Yes
74. Does jour face often get badly flushed? . Yes
75. Do jou sweat a great deal even in cold
weather? . . .Yes
76. Are you often bothered by severe itching? Yes
77. Does your skin often break out in a rash? . Yes
78. Are you often troubled .with boils7 Yes
No
No
No
No
No
No
79. Do you suffer badly from frequent severe
headaches? . Yes No
80. iDoes pressure or pain in the head often make
life miserable? .. Yes No
81. Are headaches common in your family? _ Yes No
82. Do you have hot or cold spells? Yes No
83. Do you often have spells of severe dizziness? Yes No
84. Do you frequently feel faint? .Yes No
85. -Have you fainted 'more than twice in your
We? - - .Yes No
86. Do you 'hate constant numbness or tingling
in any part of your body? Yes No
87. Was any part of your body ever paralyzed? Ycs(M No
88. Were jou ever knocked unconscious?. . Yes No
89. Have jou at limes had a twitching of the face,
'head or shoulders7 _ Yes No
90. Did you ever hate a fit or convulsion (epi-
lepsy)7 . . Yes No
91. Has ant one in your family etcr had fits or
convulsions (epilepsy)? . Yes No
92. Do jou bite jour nails badly7 . . Yes No
93. Are you troubled bj stuttering or stammer-
ing7 Yes No
94 Are jou a sleep walker? . Yes No
'Jo Are jou j Led welter7' Yes No
96. Were jou a bed wetter between the ages o!
8 and U? Yes No
CO TO NEXT PACE
161
-------
H
97. Have you eier had anything seriously wrong
with jour genitals (pritales)7 _ . Yes No
98. Are >our genitals often painful or sore? . Yes No
99. Have you ever had treatment for jour geni-
tals? . Yes No
100. Has a doctor ever said >ou had a hernia
(rupture)? ._ Yes No
ID1. Hate >ou ever passed blood while urinating
(passing Hater)7 . _ . . Yes No
102. Do you hate trouble starling your stream
when uriiwlmg? . . . Yea No
103. Do you hate to get up etery night and
urinate? .... Yes No
104. During Ihr day, do >ou usually have to urinate
frequently7 . . _ ._ Yes No
103. Do you ofli-n hate severe burning pain when
you urinate? . . ._ _ . Yea No
106. Do vou sometimes lose control of your blao?
der? ._ Yes No
107. Has a doctor ever maid tou had kidney or
bladacr disease? Yea No
108. Do you often get spells of complete exhaustion
or fatigue? ... Yea No
109. Does Korkmg lire you out completely? _. _ Yes No
110. Do )ou usually get up tired and exhausted in
the morning' . .
111. Doesctcry lillle effort wear you out7 _ .
112. Are >ou constantly too tired and exhausted
even to eat7 —
113 Do you suffer from set ere nervous exhaus-
tion7
Yes No
Yea No
No
Yea No
111 Does ncnous exhaustion run in )our family7 Yes No
115 Are you frequently ill7 . .... Yea No
116. Are tuu frequently confined to bed by ill-
ness' _ _
117 Arc )ou aluats in poor health7
118. Are you considered a sickly person7
119. Do you come from a sickly family7
Yea No
Yes No
Yes No
Yea No
120. Da setcre pains and aches make it impossible
for )ou to do tour uurk9 Yes
121. Do tou near toursclf out worrying about
your health7 ... Yes
122. Are )ou always ill and unhappy?
Yea
123. Are you constant!) made miserable by poor
health? . . Ye
124. Did you eter have scarlet fever?
123. As a child, did you have rheumatic {eter,
growing pains or twitching of the limbs?
126. Did you eter have malaria?
127. Were you eter treated for severe anemia (thin
blood)'
128. Were you ever treated (or "bad blood"
(venereal disease) ? ...
129. Do you have diabetes (sugar disease)?
130. Did a doctor ever aay you had a goiter (in
your neck)' _ .
131. Did a doctor ever treat you for tumor or
132. Do you suffer from any chronic disease?
133. Are you definitely under weight?
134. Are you definitely over Height7
135. Did a doctor eter say you had varicose veins
(swollen veins) in your legs? . .
136. Did you ever have a serious operation7 ..
137. Did you ever have a serious injury? , . _
138. Do you often have small accidents or in-
No
No
No
No
Yea No
Yea No
Yes No
Yes No
Yes No
Yes No
Yea No
Yes No
Yes No
Yes No
Yes No
Yes No
Yea No
Yes No
•*<
Yes No
139. Do you usually hate great difficulty in falling
asleep or slaying asleep' • Yes No
140 Do you find it impossible to lake a regular
rest period each day7 Yes No
141 Do you find it impassible to take regular daily
exercise? Yes No
142. Do tou smoke more than 20 cigarriics a
day? Yes No
143. Do you drink more than sit cups of cufTi t. or
tea a day' • Yes No
144. Do you usually take tt>o or more alcoholic
drinks a day7 Yes No
TURN TO NEXT PACE
162
-------
M
145. Do )ou suc.il or Irrmble a lot during exam-
inations or questioning' Yes
140. Do >ou pel ncr\ous and shaky xthen ap-
proached b) a supenor7 _. Yes
147 Docs >our xtork fall to pieces vthen the boss
or • superior is watching )ou? _ .. Yes
148. Does >our thinking got complctclx mixed up
u hen you haxe to do things quickly? Yes
149. Must xou do ihmps xery slowh in order to
do them xiilhoul mistakes' Yes
150. Do tou aluats pel directions and orders
..... Yes
151. Do strange people or places make you
afraid? . . ___ . . Yes
152 Arc \ou scared to be alone when there are no
friends near >ou7 .. ..... Yes
153. Is it always hard for you to make up your
mind' ______ ._ . ___ Yes
154. Do )ou »ish you aUa'ys had someone at your
side to advise >ou? ___________ Yes
155. Are )ou considered a clumsy person? __ Yes
156. Don it bother you to eat an) » here except in
yo]a own home? -- ------- Yes
N
157. Do you fed alone and sad at a party? ... Yes
158. Do you usuall) ferl unhappy and depressed? Yes
159. Do you often cr>? . __ Yes
160. Arc >ou alua>s miserable and blue' . _ Yes
161. Docs life look rntird) hopeless' .... Yes
162. Do }ou often wish jou were dead and away
from it all' ..... _ _ Yes
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
163 Docs worry mg continual!) get you down' Yes
16V Docs nom ing run in your family' Yes
165 Docs cxcry lillli- Ilim: gel on >our nerxes and
near >ou out' Yes
166 Arc )ou con«nlrro>l a ncrxuus person' Yes
167 !<»•. nrvi • ••, i m xour fa-iilv' Vrs \o
168 Did >ou excr hate a ncrxous breakdown' Yes NO
169. Did an>one in )our family ever hate a ner-
TOUS breakdoun' _ Yes No
No
No
No
\o
170. Were you e\er a patient in a menial hospital
(for >our nencs)' Yes No
171. Was an)one in \our family cxer a patient in
a menu/ hospital (for their nerves)? Yes No
172. Are you extremely shy or sensitive? . Yea No
173. Do >ou come from a shy or sensitue famil)' Yes No
174. Are your feelings easily hurt? ... Yes No
175. Does criticism always upset >ou? _ Yes No
176 Are >ou considered a touchy person? Yes No
177. Do people usually misunderstand you? . Yes No
17a Do you have to be on your guard even with
179. Do >ou alv>a)s do things on sudden impulse?
180. Are you easily upset or irritated' .
181. Do you go to pieces if you don't constantly
control yourself? . .
182. Do little annoyances get on your nerves and
make you angry? .
183. Does it make you angry to have anyone tell
you xx hat to do? .
184. Do people often annoy and irritate you?
185. Do you flare up in anger if you can't have
what you want right ana)-'
186. Do you often get into a violent rage? .
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No
Yes No
R
187. Do you often shake or tremble' Yes No
188. Are you constantly keyed up and jilli-y ' Yes No
189. Do sudden noises make you jump or shake
b«%' Ya No
190. Do you tremble or feel weak whenever some-
one shouts at you' Yes pjo
191. Do you become scared at sudden movements
or noisrs at night' Yes No
192 Arc loil often auakrnerl out of xour slcrp liy
frighlcninz dreams' Yes No
1!U Do friL-hlcnm: thoughts keep ci.ming b.uk in
^ur n.ind' y^ -^
101 Do xou often become sutldenl) seared for no
Eood reason' Yes No
195 Do >ou often break out in a cold sweat' Yes No
163
-------
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