AM 69-14 

EFFECTS OF ALCOHOL ON COMPLEX PERFORMANCE 

Approved by 

~~ J. R. DILLE, M.D. 

CHIEF, CIVIL AEROMEDICAL 

INSTITUTE 

W. Dean Chiles, Ph.D. 

Alan E. Jennings, B.S. 

August 1969 

Relegsed by 

P. 

~AM) V. SmoEL, M.D. 

FEDERAL AIR SURGEON 

Department of Transportation 

FEDERAL AVIATION ADMINISTRATION 

Office of Aviation Medicine 
Qualified requesters may obtain Aviation Medical Reports from Defense Documentation 

Center. The general public may purchase from Clearinghouse for Federal Scientific and 

Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151. 
EFFECTS OF ALCOHOL ON COMPLEX PERFORMANCE 

I. Introduction. 

Both field surveys of accidents and laboratory 

studies have been interpreted to show that human 

performance is adversely affected by blood alcohol levels as low as 50 mg.%. In a study of 

fatal, single-vehicle automobile accidents, Haddon and Brodess5 found that half of the drivers 

had blood alcohol levels in excess of 150 mg.% 

at the time of death. Another 20% of the drivers 

showed levels between 50 and 150 mg.%. 

Harper and Albers6 , in a survey of general 

aviation fatal accidents found that in 35.4% of 

the cases the pilot had a blood alcohol level 

greater than 15 mg.%. Dille and Morris4 reported blood alcohol levels greater than 30 mg.% 

in 19.8% of the pilots in another study of fatal 

general aviation accidents: 

Bjerver and Goldberg2 used a special track 

designed to measure ability to operate a car 

within close limits. Such maneuvers as parallel 

parking, driving out of a garage, and turning 

around on ·a narrow roadway were required. The 

time for skilled drivers to perform the tests 

correctly was significantly lengthened when the 

subjects were at blood alcohol levels of about 

40 mg.%. 

Aksnes1 required experienced subjects to fly a 

Link trainer over a U-shaped course involving 

several changes in heading, altitude, and airspeed. A measure of the combined error in these 

three parameters showed that a significant loss 

in overall flying proficiency was produced at a 

blood alcohol level of 50 mg.%. 

Poorer performance under relatively low levels 

of blood alcohol has also been found with single 

tasks. Using·a one dimensional pursuit tracking 

task with a steering wheel control, Loomis and 

West7 reported ·a clear loss in time-on-target at a 

blood alcohol level o:f 68 mg.%. This finding 

was confirmed by Mortimer8 using the same task. 

Carpenter3 found a significant, though small, .increase in response latencies to a visual stimulus 

at 70 to 80 mg.% blood alcohol. Pearson10 re1 

ported decrements in monitoring performance 

and reaction time but not in tracking or arithmetic performance at 85 mg.% blood alcohol. 

The purpose of the present investigation was 

to examine the effects of moderately high levels 

of blood alcohol on complex performance. The 

amount of alcohol ingested by the subjects was 

to be clearly high enough that, on the basis of 

the literature, ·at least some tasks would be expected to reveal decrements. The primary difference between the present study and previous 

investigations is that the time-shared performance 

of several tasks would be required and different 

levels of workload would be used. A second purpose of the study was to examine the tasks and 

task combinations comprising the performance 

battery as regards their sensitivity to a variable 

that would be expected to have an adverse effect 

on performance. 

II. Method. 

Subjects. Nine paid male subjects, all in their 

early twenties, were tested in this experiment. 

Six were Air Force enlisted men and three were 

graduate students from the University of Oklahoma. These subjects served concurrently in another experiment which involved rotational and 

caloric stimulation of vestibular mechanisms. 

Immediately before each baseline session and the 

alcohol session, the subjects experienced a period 

of rotational vestibular stimulation. 

Experimental tasks. The tasks constituting 

Model 1 of the Tracking and Monitoring Task 

described by Pearson9 were used to provide the 

performance measures. Two active tasks were 

presented-compensatory tracking and mental 

arithmetic. These tasks are generally the primary focus of the subject's attention. The passive tasks required ( 1) monitoring of a pair of 

meters, (2) choice reaction time to a pair of red 

and green lights, and ( 3) reaction time to a 

peripherally-located amber light. 
The tracking task display was a round oscilloscope screen, 12 em. in diameter located in the 

upper center o:f the panel with horizontal and 

vertical lines bisecting the screen to define the 

center. The subject's task was to keep an illuminated dot approximately 1 mm. in diameter centered on the screen at the intersection o:f the two 

lines. He did this by manipulating a small control stick with his right hand. The :forcing :function :for the tracking task was controlled by a 

stepping switch which advanced every 4 seconds. 

Each advance o:f the stepper introduced a new 

random bias into the oscilloscope display. A 

movement o:f the control stick o:f approximately 

25° :from vertical was required to compensate :for 

the maximum deflection caused by the :forcing 

:function. Forward stick movement moved the 

dot down; movement o:f the stick to the right 

moved the dot to the right. Performance on 

tracking was scored by an analog computer with 

individual scores in volts on an arbitrary scale 

:for horizontal and vertical integrated absolute 

error and :for horizontal and vertical integrated 

error squared. The error squared measures were 

converted to RMS (root mean square) error :for 

purposes o:f analysis. 

The mental arithmetic task required the addition o:f two 2-digit numbers and subtraction o:f a 

third. The numbers were presented in succession 

on three, adjacent, rear-projection readouts on the 

performance panel. A buzzer came on with the 

presentation o:f each number and remained on 

until the subject responded to that number. The 

subject responded to the first two numbers by 

pressing a button beneath the appropriate readout. Upon the introduction o:f the third number, 

the subject entered his answer on a keyboard and 

pressed a "solution button" to indicate that he 

had solved the problem. Solution time was measured :from the presentation o:f the third number 

until the subject pressed the solution button. 

Subjects were also scored £or accuracy o£ response, but :feedback as to accuracy was not 

given to the subjects. Problems were presented 

at a maximum average rate o:f three per minute. 

All subjects handled this rate readily during the 

baseline testing session. 

The three passive tasks were choice reaction 

time, meter monitoring, and simple reaction time 

to a peripherally located amber light. During 

the testing session the subject was instructed to 

keep his left hand on a ready key (located at the 

2 

:front o:f the console) except when responding to 

one o:f the tasks. For the choice reaction task, 

the subject was required to respond to a red 

light by pressing a red telegraph key located 

below the light; he responded to a green light 

by pressing a green key. Two measures were 

taken :for this task. Reaction time was measured 

directly :from the time the light came on until 

the subject lifted his hand :from the ready key. 

The total response time was measured :from 

the onset o:f the light until the response key was 

pressed. Movement time was derived by subtracting reaction time :from total time. (No 

analysis was made o:f the total time measure because an earlier study using the same task had 

indicated no new information was contained in 

this measure that was not already available in 

the reaction measures.) Signals were introduced 

on this task at a rate o:f 12 per 5 minutes. The 

sequence o:f intersignal intervals was established 

by random selection :from a distribution o:f intervals ranging :from .3 to .7 minutes. 

The meter monitoring task required the subject 

to monitor the state o:f two meters, one on the 

left side and one on the right side o:f the tracking 

display. The pointers were normally in ·a horizontal position. When a signal was introduced, 

one o:f the meters would drift slowly, either up 

or down, reaching a maximum deflection o:f approximately 20° in 7.5 to 8 seconds. At the end 

o:f this period, the meter ( i:f not responded to) 

would return rapidly to center. The subject 

responded to a meter deflection by pressing the 

appropriate one o:f two buttons located at the 

lower left corner o:f his panel. I:f the subject 

responded correctly before the end o:f the 8-second 

presentation period, the pointer would ":freeze" 

at its current position and a light would come 

on over the affected meter. At the end o:f the 

signal presentation period, the meter returned 

to its normal state and the light went out. The 

meter deflections were programmed so that there 

were either seven or eight meter events per 5 

minutes. 

The amber light was located at the lower lefthand corner o:f the subject's panel. It was programmed to produce either one, two, or three 

signals per 5-minute interval. The subject responded to the illumination o:f the amber light 

by depressing a button mounted on the top o:f the 

tracking control. The amber light and tracking 

tasks were the only tasks involving the right hand. 
Procedure. Each subject was tested for one 

session at approximately the same time each day 

for .five successive days. Each testing session 

consisted of three, 15-minute trials with a break 

of approximately 2 minutes between trials. During these trials the three passive tasks operated 

continuously. Three workload conditions were 

presented as follows: The first 5 minutes involved 

tracking (workload A) ; the second 5 minutes 

(workload B) involved arithmetic; and during 

the final 5 minutes (workload C) tracking and 

arithmetic were performed concurrently. During the 5 minutes that the subject was not required to track, the tracking display remained 

on and responsive to the control, but the forcing 

function and scoring were turned off. The first 

three daily sessions were devoted to training and 

practice. Data from the fourth session were 

used as a baseline measure, and the test session 

under the alcohol condition was held the fifth 

day. 

About two hours before the test session, subjects were given 2.5 ml. per kg. of body weight 

of an alcoholic beverage.* The alcoholic beverage was mixed with a quantity of orange juice 

sufficient to bring the total amount of liquid ingested to 700 ml. Subjects one through six had 

alcohol determinations made on samples taken 

30 minutes, 1, 2, and 5 hours after ingestion of 

alcohol. However, because of a slight change in 

scheduling of the vestibular stimulation experiment, the last three subjects had blood alcohol 

tests on samples taken at 30 minutes, 1, and 4 

hours. The estimated blood alcohol level at the 

start of testing for these latter three subjects was 

computed as follows: First, the mean hourly rate 

of decline in blood alcohol was computed for all 

subjects using the 1-hour and 5-hour tests for the 

first six subjects and the 1-hour and 4-hour tests 

for the last three. Using this mean hourly rate, 

of change (11.25 mg.%/hr), separate estimates 

of the 2-hour blood alcohol level for the last 

three subjects were made by working forward 

from the 1-hour test and backward from the 

4-hour test. The mean of the two figures was 

used as the 2-hour blood alcohol level. 

Data analysis. Each measure of performance 

was analyzed separately with three sources o£ 

* The beverage used was Tvarscki, 100 proof vodka. 

Thus, in terms of alcoholic content, the dosage was 

approximately equivalent to 1 g. of ethyl alcohol/kg of 

body weight. 

3 

variance being examined; namely, subjects, workload and alcohol ( vs. baseline). An additional 

source of variance, trials, was included for arithmetic solution time, arithmetic accuracy, and 

meter detection times. Because of lost data on 

one or more trials for the other measures, the 

unit of analysis in those cases was the session 

mean for a given workload condition. The passive tasks were presented under all conditions; 

thus there were three workloads on these tasks. 

The active tasks were presented under two workloads, A and C for tracking and B and C for 

arithmetic. 

III. Results. 

Blood alcohol levels. The mean blood alcohol 

level at the beginning of testing was 102 mg.%. 

The maximum value for any subject was 124 

mg.%; the minimum was 84 mg.% (Table 1). 

TABLE 1. Blood alcohol levels in mg.% 

Subject Minutes after Ingestion 

Number 

30 60 180 240 300 

1 __________ 94 120 103 61 

2 __________ 92 114 110 74 3 __________ 103 125 124 82 

4 __________ 100 122 96 68 5 __________ 99 115 103 60 6 __________ 58 108 98 54 

7 __________ 43 104 *92 68 

g __________ 30 79 *81 71 9 __________ 80 130 *114 86 

Mean ______ 102 

*Values interpolated from 60- and 240-minute 

determinations. 

The alcohol, in conjunction with the vestibular 

stimulation, produced feelings of nausea in three 

subjects prior to the beginning of the alcohol 

test session. One of these subjects vomited and 

the other two indicated a moderate degree of 

discomfort. However, the effect was transitory 

and the subjects reported that they had recovered 

when testing began. Other than this, joint 

alcohol/vestibular effects on the general behavior 

of the subjects were not apparent. 

Workload. Means for each workload condition 

for the various measures of performance are 

shown in Tables 2, 3, and 4. Summary tables 

for the analyses of variance are presented m 

Tables 5 through 10 in the Appendix. 
TABLE 2. Monitoring Performance 

(Mean Times in Seconds) 

Workload* 

A B 0 

Reaction Time Baseline __ • 69 . 82 .80 

Total 

. 77 

Test _____ . 76 1.10 1. 04. .97 

TotaL_ .72 .96 . 92 

Movement Time Baseline __ . 54 . 52 . 58 

Test _____ .46 • 65 . 68 

TotaL_ . 50 • 58 . 63 

Simple Reaction Baseline __ 1. 08 1. 55 1. 28 

Time Test _____ 1.14 1.84 1. 28 

TotaL_ 1.11 1. 69 1. 28 

Meter Detection Baseline __ 3.24 3.66 3.49 

Time Test _____ 3.64 4.37 3.98 

TotaL_ 3.44 4.02 3.74 

*A-Monitoring and Tracking 

B-Monitoring and Arithmetic 

0-Monitoring, Tracking and Arithmetic 

TABLE 3. Arithmetic Performance 

Workload* 

B 0 

Solution Time Baseline __ 5.15 4.69 

in Seconds Test _____ 4.96 4.47 

TotaL_ 5.06 4.58 

Percent Correct Baseline __ 90.7 90.3 

Test _____ 88.8 87.5 

TotaL_ 89.7 88.9 

*B-Arithmetic and Monitoring 

0-Arithmetic, Monitoring and Tracking 

. 55 

. 59 

1. 30 

1. 42 

3.47 

4.00 

Total 

4.92 

4.72 

90.5 

88.1 

Movement time on the choice reaction time 

task was significantly affected by workload 

(P<.05; Table 5), but the effect was not large. 

The difference between the tracking and the 

arithmetic plus tracking conditions was only .13 

seconds. Means for this and all of the other 

measures are shown in Table 2. The reaction 

time measure was not significantly affected by 

workload (P<.10; Table 5) even though the 

largest difference (condition A versus condition 

B) was almost twice as great as the largest difference for movement time (.24 seconds as compared to .13 seconds). 

Simple reaction time (the amber light) was 

significantly affected by workload ( P < .01 ; Table 

4 

6). The largest difference, .58 seconds, was between workload conditions A and B, with faster 

responses being associated with condition A, the 

tracking plus monitoring condition. The difference between condition C and condition B was 

.41 seconds; faster response times occurred under 

the heavier workload condition . 

TABLE 4. Tracking Performance 

(Error Measures in Volts [Arbitrary Scales}) 

Workload* 

A c Total 

Horizontal Inte- Baseline __ 48.02 82.67 

grated Absolute Test _____ 62.81 105.70 

Error TotaL_ 55.42 94.19 

Vertical Inte- Baseline __ 42.93 64.79 

grated Absolute Test _____ 48.08 84.50 

Error TotaL_ 45.51 74.64 

Horizontal RMS Baseline __ 3.27 6.12 

Error Test _____ 4.16 6.99 

TotaL_ 3.72 6.55 

Vertical RMS Baseline __ 2.77 4.21 

Error Test _____ 3.24 5.66 

TotaL_ 3.00 4.93 

*A-Tracking and Monitoring 

0-Tracking, Monitoring and Arithmetic 

65.35 

84.25 

53.86 

66.29 

4.70 

5.57 

3.49 

4.45 

Both integrated absolute error and RMS error 

showed workload to have significant effects on 

tracking in the horizontal dimension (P<.01 in 

both cases; Tables 7 and 8). Only RMS error 

showed a significant effect of workload with respect to tracking in the vertical dimension 

(P<.05; Table 8). 

Neither solution time nor percent correct on 

the arithmetic task were affected by workload 

(Table 9), nor was detection time on the meter 

task (Table 10). 

Alcohol. Two of the measures of monitoring 

performance showed an effect of alcohol (Table 

2). Reaction time on the choice reaction time 

task increased by .30 seconds under the alcohol 

condition (P<.05; Table 5), and detection time 

on the meter task increased by .53 seconds 

(P<.01; Table 10). The other two measures of 

monitoring performance, movement time on 

choice reaction and simple reaction time, were 

not affected (Tables 5 and 6). However, the 

alcohol by workload interaction approached significance for movement time (P<.10). 
Neither solution time nor accuracy on the arithmetic task were affected by alcohol (Table 9). 

Tracking in the horizontal dimension showed 

an alcohol effect as measured by integrated absolute error (P<.Ol; Table 7) but not as measured 

by RMS error (.10>P>.05; Table 8). In the 

case o£ absolute error, there ·was a substantial, 

though not significant, interaction bet,veen alcohol and workload ( .10 > P > .05; Table 7). 

Tracking in the vertical dimension was significantly affected as measured by both integrated 

absolute error and RMS error (P < .05 in both 

cases; Tables 7 and 8). The interaction between 

alcohol and workload was significant in the case 

o£ RMS error (P<.05; Table 8) but not in the 

case o£ integrated absolute error (.10>P>.05; 

Table 7). 

TABLE 5.-Choice Reaction Time Task 

(Analysis of Variance) 

Subjects (S) _______________ 

Alcohol Condition (C) ______ 

VVorkload (VV) _____________ 

sc _______________________ svv ______________________ cvv ______________________ 

scvv ---------------------

Subjects (S) _______________ 

Alcohol Condition (C)_ _____ VVorkload (VV) _____________ sc _______________________ svv ______________________ cvv ______________________ 

scvv ---------------------

Reaction Time Movement Time 

df MS F p df MS F p 

8 1. 263 8 .215 

1 . 520 6.41 <.05 1 .033 1.01 

2 . 289 2.93 <.10 2 . 081 4.12 <.05 

8 .081 8 .033 

16 .098 16 .020 

2 • 053 2.15 2 .059 2. 77 > .10 

16 .024 16 • 021 

TABLE 6. Simple Reaction Time 

(Analysis of Variance) 

df MS F p 

Subjects (S) ________________ 8 2.22 

Alcohol Condition (C) _______ 1 .18 1.5 

VVorkload (VV) ______________ 2 2.63 7.73 <.01 

sc ________________________ 8 .12 

svv ________________________ 16 . 34 

cvv _______________________ 2 .12 .20 

scvv---------------------- 16 .49 

TABLE 7.-Integrated Absolute Error in Tracking 

(Analysis of Variance) 

Horizontal Dimension 

df MS F p df 

8 4,832 8 

1 3,216 17.19 <.01 1 

1 13,529 13.03 <.01 1 

8 187 8 

8 1,038 8 

1 153 4.65 <.10 1 

8 33 8 

5 

Vertical Dimension 

MS F 

3,923 

1,390 6.49 

7,641 5.03 

214 

1,517 

477 5.18 

91 

p 

<.05 

<.10 

<.10 
Subjects (S) _______________ 

Alcohol Condition (C) ______ VVorkload (VV) _____________ so _______________________ svv ______________________ cvv ______________________ 

scvv ---------------------

Subjects (S) ______________ _ 

Alcohol Condition (C) _____ _ 

VV orkload (VV) ____________ _ 

Testing Interval (T) ______ _ so ______________________ _ svv _____________________ _ ST ______________________ _ 

cvv _____________________ _ CT _____________________ _ 

VVT _____________________ _ 

scvv --------------------- SOT ____________________ _ 

SVVT ____________________ _ 

CVVT ___________________ _ 

SCVVT __________________ _ 

df 

TABLE 8.-Root Mean Square Error in Tracking 

(Analysis of Variance) 

8 

1 

1 

8 

8 

1 

8 

Horizontal Dimension 

MS F p 

14.596 

6.915 4.25 <.10 

72.431 24.86 <.01 

1. 626 

2.914 

.001 .003 

.298 

TABLE 9.-Arithmetic Performance 

(Analysis of Variance) 

Solution Time 

df 

8 

1 

1 

8 

8 

1 

8 

df MS 

71.95 

1. 15 

6.13 

2.06 

F p df 

8 

1 

1 

2 

8 

8 

16 

1 

2 

2 

8 

16 

16 

2 

16 

.71 

2.67 

1. 28 

• 01 

. 54 

.78 

.16 

. 55 

.71 

.49 

.41 

1. 62 

2.30 

1. 61 

.06 

.97 

1.09 

1.21 

8 

1 

1 

2 

8 

8 

16 

1 

2 

2 

8 

16 

16 

2 

16 

Vertical Dimension 

MS F 

13.6989 

8.2560 9.64 

33.4855 8.26 

• 8563 

4.0553 

2.1610 5.78 

. 3735 

Percent Correct 

MS 

808.30 

149.34 

17.76 

104.21 

290.39 

43.54 

83.31 

4.82 

199.76 

179.22 

76.27 

68.17 

67.01 

74.90 

50.91 

F 

• 51 

. 41 

1. 25 

.06 

2.93 

2.67 

1.47 

p 

<.05 

<.05 

<.05 

p 

TABLE 10. Meter Detection Times IV. Discussion. 

(Analysis of Variance) 

df MS F 

Subjects (S) _______________ _ 8 34.27 

Alcohol Condition (C) ______ _ 1 11.45 32.71 

VVorkload (VV) _____________ _ 2 4.41 2.61 

Testing Interval (T) ________ _ 2 • 66 1. 50 

so------------------------ 8 .35 svv _______________________ _ 16 1. 69 

ST _______________________ _ 16 .44 cvv ______________________ _ 2 .32 . 83 

CT _ -------------------- __ _ 2 .18 .50 

VVT ______________________ _ 4 .21 . 32 

scvv---------------------- 16 . 39 

SCT ______________________ _ 16 .31' 

SVVT _____________________ _ 32 . 65 

CVVT _____________________ _ 4 .18 . 77 

SCVVT ____________ -- _-- ---- 32 . 24 

p 

<.01 

6 

Workload effects. The effects of the different 

workload conditions on movement time in responding to the choice reaction time task were 

probably a result of some sort of perceptualmotor conflict. First, when problems were being 

presented on the arithmetic task, at least occasionally, a red or green light would be illuminated at the same time. This might very well 

have generated a momentary conflict situation 

sufficient to account for at least part of the increased movement time associated with the two 

task combinations involving arithmetic. A second factor was introduced by the nature of the 

programming of the choice reaction time task. 

As noted in the procedure section, the subject 

was required to keep his left hand on a ready 

switch when not responding to one of the tasks 

with that hand. If the programming equipment 
attempted to illuminate a red or green light at a 

time when the ready switch was not depressed, 

that signal would be "stored" until such time as 

the subject returned his hand to the ready switch. 

At that point, depression of the switch in effect 

turned on the light selected by the programming 

mechanism to be illuminated. Since the subject's 

hand was off the switch a substantial portion of 

time when he was solving arithmetic problems, 

a number of signals were introduced in this 

manner. Thus, a very plausible second explanation of the increases in movement time would be 

that movements immediately following the return of the subject's hand to the switch would 

be slower than those when the hand was initially 

in a resting position on the switch. The increase 

in reaction time under the two arithmetic workload conditions, though not significant, is compatible with this interpretation. 

The increase in the response times to the amber 

light during arithmetic performance is probably 

directly a function of where the subject was 

focusing his attention. Since the arithmetic 

problems are presented by means of displays on 

the right side of the panel and the response buttons are also located there, that is where the 

subject tends to look when arithmetic performance is required. Under condition B, arithmetic 

plus monitoring, the only reason for the subject 

to look away from the arithmetic task mechanisms is to scan the remainder of the panel. 

Thus, during this workload condition, he generally does not see the amber light as it comes 

on except between problems on the arithmetic 

task. The light is in the periphery when he is 

looking at the arithmetic mechanisms and it does 

not have sufficient attention value for him to see 

it. When both tracking and arithmetic are being 

performed, the subject is required to divide his 

attention between the two. The location of the 

amber light in relation to the focus of the subject's attention when he is tracking is such that 

the subject can readily see the light. This would 

seem to account for the intermediate position of 

the heavier workload condition with respect to 

the simple reaction time measure; the tracking 

task forces him to look a greater proportion of 

the time at a section of the panel where he can 

see the amber light. 

The effects of workload on the tracking task 

can be explained in a straightforward manner. 

When the subject is working arithmetic problems, 

7 

it takes him an average of about 4.5 seconds to 

compute and enter his answer after being given 

the third number. Much of this time the subject 

does not look at the tracking display. During 

the presentation of each of the first two numbers 

of the problem, the subject also looks away from 

the tracking display to determine what the 

number is and to acknowledge that he has seen 

it. Thus, of the approximately 20 seconds per 

arithmetic problem, the subject looks away from 

the tracking display for perhaps as much as a 

third of the time. In contrast, when the subject 

is concerned with tracking and only the monitoring tasks, only brief glances at the monitoring 

displays are required to keep up with those tasks. 

The only aspect of this finding that was at all 

surprising is the fact that the workload effect 

was not significant in the case of integrated absolute error in the vertical dimension. This 

presumably was a result of the substantial 

variability in the specific strategies adopted by 

different subjects in time-sharing the tracking 

and arithmetic tasks. 

Another factor that probably contributed to 

the magnitude of the workload effect with respect 

to the horizontal dimension was that a certain 

amount of cross-coupling between the two arms 

occurred when arithmetic and tracking were 

performed concurrently. When the subject responded to the arithmetic task, he was required 

to reach across the panel with his left hand to a 

position approximately in front of the tracking 

control. In making this movement, there is a 

marked tendency for the subject's body to move 

laterally, and, in so doing, he inadvertently introduces inputs to the tracking task. These inputs 

are much more likely to be in a plane that affects 

the horizontal dimension rather than the vertical. 

The subject can anchor his wrist on the table so 

that fore/aft movements of his arm are virtually 

eliminated. Slight rotational movements of the 

wrist (which would affect the horizontal but not 

the vertical dimension) are much more difficult 

to eliminate. 

'Vorkload did not affect the performance of the 

arithmetic task. The only suggestive effect was 

that the mean response time was shorter (though 

not significantly-Table 3) for the tracking plus 

arithmetic condition. The most likely explanation for this lack of effect is that subjects placed 

a relatively high subjective priority on the arith-
metic task and tended to "protect" their performance of this task. 

Alcohol effects. The increase in choice reaction 

time under the alcohol condition is consistent 

with previous research findings. In fact, a lack 

of an effect would have been quite surprising 

since Carpenter3 found significant increases in 

reaction time at a somewhat lower blood alcohol 

level (70 to 80 mg.% as compared to 102 mg.%). 

The fact that movement time was not affected 

suggests that the alcohol caused a deterioration 

in some sort of central attentional or decision 

process rather than a direct alteration of the subject's neuromuscular system. However, if this 

is in fact the case, the inference applies only to 

tasks in which the motor response, once initiated, 

does not involve any particular degree of precision in its execution. 

The increase in detection times for the meter 

signals is in line with the results reported by 

Pearson10 with the same task. The response required to indicate detection of a meter did not 

require precisiOn. Thus, if the movement time 

data on the choice reaction time task are extrapolated to the meter task (an admittedly tenuous 

procedure) then it could be inferred that these 

decrements are reflective of a change in an attentional process. The inference is supported 

by the fact that the magnitude of the increase, 

.53 seconds, is more than twice as great as the 

combined increases in reaction time and movement time for the choice reaction time task. 

The absence of an effect on the amber light 

task was also a finding of Pearson. 10 As shown 

by the means for this task in Table 2, the variability across the three task combinations was 

rather large, and, hence, the error variance associated with the statistical test for the alcohol 

effect was also rather large. This variability 

was undoubtedly also· a product of the fact that 

signals occurred only infrequently on this task 

(approximately two signals per 5-minute period) 

and there was no alerting signal as' is the case 

with the typical laboratory study of displays 

reaction time. 

Perhaps the most interesting outcome of this 

study was the fact that mental arithmetic performance was not impaired by alcohol. \V e offer 

two possible explanations. First, the arithmetic 

task was basically not very difficult and the 

subjects had been given substantial practice. 

8 

Second, there is good reason to believe that the 

subjects placed a relatively higher priority on 

doing the arithmetic because this was a task that 

they clearly understood and it involves an intellectual skill that most people consider to be 

rather important. Thus, the subjects presumably 

diverted a sufficient proportion of their mental 

capacities to the performance of this task to 

assure that their performance would not suffer. 

The fact .that the different workloads affected 

tracking but did not affect arithmetic under both 

the baseline and the alcohol conditions tends to 

support the "priorities hypothesis." Thus, the 

demands of this particular arithmetic task are 

apparently not great enough, even at rather high 

blood alcohol levels, to preclude the subject's 

maintaining his performance by increased concentration. Of course, it is also possible, though 

we consider it unlikely, that alcohol has no effect 

on processes such as simple mental arithmetic. 

Our data do not permit any clear-cut description of the manner i~ which alcohol affected 

tracking performance. An immediate question 

arises from the fact that we found an effect of 

alcohol on tracking whereas Pearson10, using the 

same basic tasks at only a slightly lower blood 

alcohol level, found none. The first and probably most important difference between the two 

studies is' that we included a condition involving 

a much heavier workload than that used by 

Pearson. His subjects were concerned only with 

the two meters and the amber light while tracking. For our tracking-only condition, we added 

the choice reaction time to the tasks he used and 

the arithmetic task was added for our heavy 

workload condition. Second, although we do not 

have details on Pearson's tracking task, there is 

<rood reason to believe that it was substantially b 

more difficult than ours. Thus, with the amounts 

of training given our subjects, their levels of 

skill probably resulted in somewhat lower variability than was the case for Pearson's subjects. 

In an attempt to further examine the workload 

hypothesis as an explanation of the discrepancy 

bebveen Pearson's10 results and ours, we analyzed 

the simple effects of alcohol for each of the two 

levels of \<:orkload under which the tracking task 

was performed. The results of these tests showed 

that for no measure was tracking significantly 

affected by the alcohol when tracking was performed by itself. (Actually, the t-test for the 

horizontal absolute error fell just short of sig-
nificance; t.05=2.306, and the obtained t was 

2.293.) In all three cases in which an over-all 

effect of alcohol was found, a significant t was 

found for tracking when performed concurrently 

with arithmetic. (As noted under Results and 

as shown in' Tables 7 · and 8, alcohol workload 

interaction was significant (P < .05) for vertical 

RMS error and borderline (P<.lO) for horizontal and vertical absolute error.) 

Thus, a decrease in the ability of the subject 

to time-share the performance of tasks requiring 

the exercise of different psychological functions 

may be the most important detrimental effect of 

alcohol on trained subjects. Motor effects may 

be somewhat less important. 

Finally, it is necessary to comment briefly on 

the possible implications of the fact that our 

subjects were also serving in a study on the 

effects of alcohol on vestibular functions. Although all subjects reported that they had recovered from any discomfort produced by riding 

the rotating chair before our testing began, one 

should perhaps exercise caution in accepting the. 

statements of subjects whose mean blood alcohol 

levels are 102 mg.% at the time those statements 

are made. Thus, it is not possible, on the basis 

of our data, to completely rule out the possibility that after-effects of vestibular disturbances 

at least contributed to the production of decrements in performance under the alcohol condition. 

V. Summary and Conclusions. 

The performance of nine subjects was measured beginning approximately two hours after 

they had ingested 2.5 ml. of an alcoholic beverage 

per kilogram of body weight. Before being 

tested the subjects underwent several sessions on 

a rotating chair, but aU reported that they had 

recovered from any effects of that experience 

prior to the beginning of testing. T.he performance tasks used involved monitoring (simple 

9 

reaction time, choice reaction time, and meter 

monitoring), two-dimensional compensatory 

tracking and mental arithmetic. Three workloads were presented by varying the combinations 

of tasks the subject had to perform concurrently. 

These were: (A) monitoring plus tracking, (B) 

monitoring plus arithmetic, and (C) monitoring 

plus tracking plus arithmetic. 

Significant workload effects were found for 

three of the four measures of tracking performance, for simple reaction time, and for movement 

time in the choice reaction time task. 

Significant alcohol effects were found for reaction time in choice reactions, detection time for 

meter signals, and for three of the four measures 

of tracking. Mental arithmetic scores were not 

affected. There was a significant interaction between workload and alcohol with one tracking 

measure-RMS error in the vertical dimension. 

Nonsignificant interactions (P<.lO) were found 

. between alcohol and workload for absolute error 

in both dimensions for tracking performance and 

for reaction time and movement time in the 

choice reaction time task. 

The conclusions to be drawn from this study 

support the previously reported findings with 

respect to the effects of alcohol on performance, 

a possible exception being the absence of a significant effect on mental arithmetic. 

An important methodological conclusion to be 

drawn is that the time-shared performance of 

tasks involving the exercise of different psychological functions is a highly desirable condition 

to be used in conducting research on the effects 

of adverse factors on human performance. We 

also conclude that the sensitivity of these tasks 

to the effects of variables such as high blood 

alcohol levels is at least tentatively established. 

Modifications to decrease the variability of the 

simple reaction time measure and to increase the 

difficulty of the arithmetic task would seem to 

be in order. 
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