Alcohol and visual performance

proS. Neux4’sychophwmamL

& BioL Pq/dtiat. 1999, Vol. 23, pp. 465482 CopyrQht 0 1999 Elsevier Science Inc. Printed in the USA.

AU rights reserved

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ALCOHOL AND VISUAL PERFOFUUANCE ALMUT-J. WEGNER’ and MANFRED FAHLE’*’ ’ Section of Visual Science, University of Tuebingen, Germany; ’ Department of Optometry and Visual Science, City University, London, UK

(Final Form, March 1999)

Abstract Wegner, Almut-J. and Fahle, Manfred: Alcohol and visual performance. Prog. NeuroPsychopharmacol. & Biol. Psychiat. 1999,23, pp. 465482.81999 Elswier sciene Inc. 1. The authors examined the effect of acute alcohol consumption on a set of visual tasks: visual short term memory, depth perception, and attention. 2. In a repeated measurement design, thirteen subjects performed the tasks once sober and once intoxicated with 0.8 g/kg body weight pure ethanol in orange juice (33% alcohol). Subjects underwent a neuropsychological (Benton test) and a psychophysical test (vernier discrimination) both assessing visual short term memory, the test d2 as a measure of attention and concentration, and a psychophysical depth perception task. 3. Subjects demonstrated significant alcohol-related impairments in depth perception and in visual short term memory as assessed by the vernier discrimination task. However, the neuropsychological Benton test and test d2 failed to reveal alcoholrelated changes in performance - probably due to superimposed learning effects. Performance was neither correlated with blood alcohol levels (BAL) nor perceived intoxication. Even though the current BAL was known to the subjects, only half of them demonstrated a close correlation between BAL and perceived intoxication. Keywords: alcohol, attention, depth perception, ethanol, short term memory. Abbreviations:

blood alcohol level (BAL).

Introduction A vast literature exists on alcohol-related impairments of optical and visual performance in humans (Tarter et al., 1971; Franks et al., 1978; Hogan and Linfield, 1983; Baker et al.,

466

A.-J. Wegner and M. Fahle

1985; Hill and Toffolon,

et al., 1992; Watten and Lie,

1990; Wang et al., 1992; Nicholson

1996). However,

data on driving-related

often conflicting

(Wilson

visual abilities like perception

et al., 1981; Hill and Toffolon,

of spatial

1990; Nicholson

depth are

et al.,

1992;

Watten and Lie, 1996). In addition, memory

despite

(Ryback,

of substantial

1971; Jones,

research

in alcohol-related

1973; Miller and Dolan,

and Jones, 1980; Parker et al., 1980; Subhan

loss of verbal

short term

1974; Miller et al., 1978; Jones

and Hindmarch,

1983; Mueller et al., 1983;

Maylor and Rabbitt, 1987; Lamberty et al., 1990; Maylor et al., 1990; Peterson

et al., IQQO),

there exist only few data on the effect of alcohol on visual short term memory

(Subhan

Hindmarch,

1983; Echeverria

The authors therefore term memory

using

attention

aim

measuring

study

thresholds;

discrimination

of these

tasks

we decided

in the

in depth

term

sensitive

results

tests

strongly

in addition depends

visual

tasks

to conventional on a sustained

to control for attentional of the

and visual short

problems

ones. level

accounting

by applying

the

test

of for d2

1994).

of our

impairments

short

in most

decrements

(Brickenkamp, The

tested the effect of alcohol on visual performance

and concentration,

possible

et al., 1991).

newly developed

Since performance

and

memory

was

1) to clarify

perception

by using

2) to investigate by comparing

conflicting

results

a very sensitive

on

alcohol-related

psychophysical

task

the effects of acute alcohol consumption the Benton

task; and 3) to study whether

with the blood alcohol

the

Visual

Retention

the perceived

level (BAL) and/or impairments

Test

for

on visual

and

a vernier

level of intoxication

correlated

in the visual tasks applied

here.

Methods Subiects 13 healthy experiments.

volunteers

- 5 female,

All subjects

8 male,

had normal

aged

or corrected-to-normal

Freiburg visual acuity test (Bach, 1996). Subjects’ testing.

In counterbalanced

another day after alcohol

order, (ethanol)

19 to 54 years

subjects

part in the

acuity as assessed

by the

informed consent was obtained

prior to

performed

consumption.

- took

the tests

once

sober

and

on

Alcohol and vision

467

Ethanol Administration For the alcohol (ethanol

session,

received

0.8 g/kg

were determined

levels

started

performance

varies

tolerance”

(BALs) of 0.8 to 1.3 %a. Every five minutes,

indirectly

were

Benton

in

levels

by means of a breath alcohol analyzer

(Draeger Alcotest

7410).

BALs

since

depending

Visual

Retention

had exceeded on whether

Test: Observers

the maximum

BALs are ascending

Immediately

after removal

it is known

or descending

1 point if correctly

spatial

arrangement.

scored

as errors.

element,

Missing It should

variables

so several

reproductions

of each card, subjects reproduced,

that

(“acute

for 10 set each.

elements

that correct

or those

at a false

reproductions

Delayed

Vernier

Discrimination

visual short term memory

in the correct spatial

and errors contain

position are

more

number

partly

than

one

of correct

displaced

to the right by either

for 100 msec on an analog

one or four set,

a second

(Fahle

and Harris,

but uses very simple visual stimuli,

was

580, 620 or 740 arc sec. The first vernier

was

vernier

buttons (temporal

contained

two alternative

i.e.

segment

monitor

them (Fig 1). The lower

under computer

with either

a smaller

control.

After a delay of

or a larger

for 100 msec at about the same position as the first. The subjects’ time interval

1992):

of two vertical lines, each 50 arc min long and 2 arc

min wide with a 0.5 arc min vertical gap between

which

Each card

and errors was calculated.

The vernier targets consisted

presented

Ten test cards

all correct elements

errors can be made for most cards. The over-all

This test also assesses

presented

Retention

had to copy it from memory.

in this test since eight of the ten items

Short Term Memory:

verniers.

be noted

Visual

forms were presented

i.e. containing

or incorrect

the Benton

visual short term memory.

with up to three geometric

scored

independent

first performed

1996; Forms C and D) assessing complexity

indicate

resulting

blood alcohol

after

of increasing

Visual

alcohol

Instruments

Test (Benton,

either

absolute

or Mellan by effect; Wang et al., 1992).

Assessment

always

body weight

96.9%) in double the dose of orange juice after four hours of fasting,

peak blood alcohol

Tests

subjects

the larger vernier

forced choice task).

offset by pressing

offset was task was to one of two

468

A.-J. Wegner and M. Fahle

100 msec

1 or4 set

100 msec

Fig 1. Schematic of the vernier discrimination task (visual short term memory). The subject had to indicate which of the two verniers presented with a delay of either one or four set had the larger offset (temporal 2 AFC).

I I

111111111

Thresholds for delays of both one and four set were determined in separate blocks by an adaptive staircase procedure (PEST; Taylor and Creelman, 1967). Initial orientation of the stimulus was either horizontal or vertical, counterbalanced between observers. For the second session,

the orientation of the vernier was changed by 90”. Previous studies

(Poggio et al., 1992) have shown that changing the orientation of the vernier by 90” prevents transfer of improvement to the new orientation. Test d2: The test d2 (Brickenkamp,

1994) assesses

the level of attention

and

concentration. Fourteen rows each with 49 “d”s and “p’s are presented. The characters are marked by either one, two, three or four small lines (Fig 2). The subjects’ task is to cross out all “d”s marked by two lines but to ignore all other characters. For each row, there is a time limit of 20 sec. Fig 2. Part of a row of the Test d2. The subjects’ task is to cross out only all the “d’s marked by two small lines.

The percentiles - indicating how many subjects (%) of a control group matched for age and education performed similar or worse - for the total number of characters dealt with, the error rate (%), and the “concentration”, marked characters, were analyzed.

i.e. the number of correctly minus wrongly

469

Alcohol and vision

Stereoscopic Depth Perception: Two verniers reduced to pairs of points were presented dichoptically, such that the left eye saw the mirror image of the right eye’s image. This procedure resulted in a perception of one point lying closer to the subject than the other point (Fig 3). The subjects’ task was to indicate which point appeared nearer by pressing one of two buttons (binary forced choice). Thresholds were determined by means of the adaptive staircase procedure.

Fig 3. Schematic set up of the stereoscopic depth perception task. Two verniers - reduced to points - are dichoptically presented resulting in a depth perception for the two points. The subjects’ task is to indicate which point appears closer. are Thresholds measured by an adaptive staircase procedure.

lefteye

Subjective Judgment of Intoxication: Before each test, subjects were asked to judge their subjective feeling of intoxication on a scale from 1 (no effect) to 20 (totally intoxicated). Subjects were informed about their current BAL immediately after each judgment. The ratings were correlated with the current BAL and the results of the tests described above. Data Analysis: The results of the Benton Visual Retention Test, the vernier discrimination task, the test d2, and the stereoscopic repeated measurements

depth perception task were analyzed using a

ANOVA (soitware: Statview 4.1 on a Power Macintosh) with the

within subject factor “state” (sober, intoxicated) and the between subject factor “group” (first sober, then intoxicated, or vice versa). The subjective judgment and the blood alcohol concentration

(BAL) were correlated with the relative performance in all tasks (% as

compared to performance when sober).

470

A.-J. Wegner and M. Fahle

Results Visual Short Term Memory a) Benton Visual Retention Test: The mean numbers of correct reproductions and errors for sober and intoxicated subjects are shown in Table 1. Neither the number of correct reproductions, nor the error rate was significantly affected by alcohol consumption

(both

p>O.7). The performance difference for sober and intoxicated subjects revealed that half of the subjects performed better when sober, the other half did better when intoxicated, whereas one subject (AC) demonstrated no change in performance (Fig 4). Table 1 Results of the Benton Test. Number of Correct Reproductions and Errors (mean * S.E.) for Sober and Intoxicated Subjects. Benton Test

Sober

Intoxicated

Correct Reproductions

8.23 + 1.42

8.38 f 1.50

Errors

2.23 f 2.16

2.00 f 1.87

I

VM

I

I

I

IW

AF

AH

I

I

hW TV

I

I

I

AC BPF JT

I

MF

II

KR

I

DH ER

I

means

Fig 4. Results of the Benton Visual Retention Test (difference between performance when sober and intoxicated) for all subjects and means. Downward bars indicate more correct reproductions and less errors (i.e. better performance) when intoxicated, upward bars better performance when sober. Six subjects made more correct reproductions and less errors when sober, six demonstrated a better performance when intoxicated and one subject showed no change in performance after alcohol consumption.

471

Alcohol and vision

However, for the error rate, the interaction

“state” x “group” was significant.

This

interaction reveals that intoxicated subjects performing the test for the first time did much worse than intoxicated subjects doing it for the second time (p=O.O232). So, subjects when repeating the test always performed better than the first time, irrespective of their state. The factor “group” was not significant (p>O.7). The number of correct reproductions

did neither show a significant

“state” x “group”

interaction nor a significant “group” effect (both ~‘0.1; Fig 5).

correct reproductions

0

first: sober

q

second: intoxicated

n

first: intoxicated

0

second: sober

errors

10 ,

-1

correct reproductions

errors

Fig 5. Results of the Benton Visual Retention Test: number of correct reproductions and errors for subjects performing the test at first sober, then intoxicated (upper panel), and vice versa (lower panel). Both groups demonstrated training effects the second time, irrespective of state.

b) Vernier Discrimination:

Thresholds

for the vernier discrimination

task significantly

raised when subjects were intoxicated, both for a delay of one set (p=O.O025) and four set (p=O.O154). Individual threshold differences revealed that 22 of 26 thresholds

were

raised after alcohol consumption (Fig 6). A study by Hogan and Gilmartin (1985) and our own observations showed that vernier acuity perse was not affected by alcohol (mean threshold 14.29 arcsec + S.E. 1.9 versus

472

A.-J. Wegner and M. Fahle

14.31 arcsec * SE. 2.3 for intoxicated and sober subjects, respectively). So the threshold elevation in this test reflects visual short term memory loss.

-50

’ ,

,

VM

MF

, , KR

AC

, JT

, ,

,

, ,

AF BPF IW TV

AH

,

, ,

HW ER

DH

means

Fig 6. Results of the vernier discrimination task (threshold difference between sober and intoxicated) for all subjects and means. Almost all subjects demonstrated a clear threshold elevation after alcohol consumption. Only four out of 26 thresholds were lower if the subjects were intoxicated. The mean threshold differences (right) are similar for both a delay of one and four seconds and were significantly different from zero, i.e. thresholds were significantly elevated after alcohol consumption.

We did neither observe a “group” effect nor a “group” x “state” interaction in this test (~‘0.1

both for a one set and a four set delay). Subjects yielded about the same

thresholds for both delays when sober and when intoxicated (Wilcoxon signed rank test, both p>O.5; Table 2). Table 2 Vernier Discrimination Task. Thresholds (arcsec) (mean f S.E.) for Comparison of Offset Sizes After Time Delays of One and Four set Between the Presentations of Two Verniers. Vernier Discrimination

Sober

Intoxicated

1 set

43.22 + 6.7

71.41 f 8.12

4 set

47.04 f 6.7

76.54 +10.2

473

Alcohol and vision

Test d2: When intoxicated, subjects worked on significantly less characters than when they were sober (p=O.O257). Individual and mean percentile differences for sober and intoxicated subjects are shown in Fig 7.

70 ,, 60 _/ 0

E

10

0.

0

number of characters

I 1

-10 -20 $

20 i -30 I

AH

MF

KR

TV VM

AF

JT AC

DH BPF ER

means

Fig 7. Results for the variables of the test d2: percentile differences between the performance when sober and intoxicated for the number of characters dealt with, the error rate, and “concentration”. Three subjects performed better when intoxicated, four showed almost no alteration atter alcohol consumption, whereas six subjects performed worse when intoxicated. The mean difference in performance is significant only for the number of characters dealt with.

For both the error rate and the “concentration”, the interaction of “state” x “group” was significant (both p=O.O03), reflecting the fact that subjects performing the test for the first time when intoxicated did much better the second time (sober). However, subjects who performed the test at first sober demonstrated not as drastic changes in performance the second time (i.e. intoxicated). So, the effect of alcohol on error rate and “concentration” was mostly due to the decreased performance of subjects who performed the test for the first time when intoxicated (Fig 8). Stereoscopic Depth Perception: Stereoscopic depth perception in intoxicated subjects deteriorated

(p=O.O653), though there were large interindividual

differences

(Fig 9):

Thresholds ranged from about 2 to 190 arcsec for sober subjects (mean 37 arcsec f SE.

474

A.-J. Wegner and M. Fahle

15) and from 5 to 230 arcsec in intoxicated neither observe

subjects

(mean 97 arcsec + S.E. 35). We did

a “group” effect nor a “state” x “group” interaction

number of characters

in this task (p>O.5).

“concentration”

error rate

200-1 number of characters

I I

1-1 error rate

“concentration”

Fig 8. Results (percentiles) of the test d2 for subjects performing the test at first sober, then intoxicated (upper panel), and vice versa (lower panel). Subjects performing the test at first intoxicated and then sober (lower panel) demonstrated large training effects concerning the error rate and “concentration”. For the opposite order (upper panel), alcohol-related effects are superimposed on learning effects. Note that a higher percentile of error rate indicates a lower number of errors.

Correlation

of Subjective

Judgment

of Intoxication

with Test Performance:

Mean time to

peak BAL was 63.08 min (SE. 8.04 min; range 35 to 125 min). There was no significant correlation

between

the subjective

judgment

of the level of intoxication

alcohol level (BAL) with any results in our visual tests (all ~‘0.1). between

BAL and subjective

judgment

falling parts of the BAL curve. Individual from 0.265 (not significant)

was significant correlations

to 0.918 (p~O.0001).

or the current blood

However,

the correlation

(p
of BAL with subjective

In seven subjects,

scores

ranged

BAL and score were

Alcohol and vision

significantly

correlated,

remaining

i.e. the peaks

six subjects,

subjects,

for BAL and subjective

no significant

peak BAL was reached

475

correlation

could

prior to peak subjective

score

coincided.

be observed. score.

In the

In these

Examples

latter

of individual

BAL and score curves are shown in Fig 10.

better when sober

1

$ f @% aC

08

gg

0,4

[!

02

0,8

‘t 8

0 -0,2 -0,4 BPFMF

IW DH AF AC ER JT AH VM TV HW KR

means

Fig 9. Results of the depth perception task. Due to a large inter-individual variance, differences were plotted in log thresholds. Ten out of 13 subjects demonstrated a clear threshold elevation after alcohol consumption. The mean difference is significant.

Discussion Visual Short Term Memory The authors compared the Benton

Visual

discrimination.

two different kinds of tasks to assess

Retention

Test and a psychophysical

While the widely

visual short term memory:

task using

used neuropsychological

Benton

failed to show any alcohol effects on visual short term memory, related memory

impairment

was similar for memory

The difference Benton

in performance

Test uses

semantically. the

using the vernier

significant

discrimination

geometric

The unchanged impairment

discrimination

a delayed

Visual

vernier

Retention

Test

we found a clear alcohol-

task. The loss in visual

short term

spans of one and four seconds. in these forms

which

performance in visual

two tests is probably

of intoxicated

short

task implies that intoxicated

can be coded

term

due to the fact that the

not only visually,

but also

subjects in this test together

memory

assessed

by the

with

vernier

subjects were able to use coping strategies

to

476

A.-J. Wegner and M. Fahle

compensate for low-level visual memory loss. One might speculate that these coping strategies are based predominantly arrangement of the configuration. subjects had to discriminate

on semantic

codings

of the shape and spatial

In the vernier discrimination

task, on the other hand,

a feature of a low-level stimulus - in this case, the exact

spatial arrangement of two lines - which could be stored only visually.

-3. _

_

;

W1,2-

,- ,- l.

b

o-44 0 30

d

l

,--, .,-

l

-3

!?!

-15

8

l--._ .

3 60

90

120 150 0

30

60

90

120 150 180

time (min)

Fig 10. Individual examples of blood alcohol level (BAL) curves and subjective scores. Some subjects showed good correlations between blood alcohol level and score (a and b) whereas other demonstrated almost no correlation (c and d).

Echeverria et al. (1991) using the Benton Test also failed to show a loss of visual short term memory after alcohol investigating

consumption.

However, Subhan

and Hindmarch

(1983)

iconic memory for letters presented for 50 msec found a clear alcohol-

related impairment. Hence, it seems that the presentation time of visual material might also be a critical factor for the detection of alcohol-induced visual short term memory loss.

477

Alcohol and vision

In addition, the authors observed a significant subjects

performed

better the second

learning effect in the Benton test, i.e.

time irrespective

of their “state”

(sober

or

intoxicated). These results are in line with observations of Tarter et al. (1971) who pointed out that alcohol does not prevent practice over repeated testings

and that training

mitigates the effects of alcohol. However, such a training effect was not found for the vernier discrimination

task. Here, transfer of learning

(“practice”) was prevented by

changing the orientation of the vernier by 90”. Therefore, the vernier discrimination seems more suitable for the assessment

task

of visual short term memory, especially in a

repeated measurements design. Regarding the time of fading from visual short term memory, the authors observed no significant differences in thresholds for the one set and the four set delay both in sober and intoxicated subjects. After alcohol consumption, fading from visual short term memory is more pronounced during the first second after presentation,

but does not progress

faster than in sober subjects thereafter. Test d2 In this study, the test d2 revealed an impairment of attention after alcohol consumption manifesting

itself only in the total number of characters dealt with. This result is in

accordance with the findings of Ruedell et al. (1981) who also reported an impairment in performance of the test d2 during acute intoxication with alcohol. However, both for error rate and “concentration” we found a significant learning effect, i.e. an improvement in performance the second time subjects completed the test, especially if they were sober during the second time. The observed interaction reveals that not only the subjects’ state (sober or intoxicated) accounted for the present results but that the order in which subjects performed the test has to be considered too. These results demonstrate the limitations

of the test d2 in assessing

attention and concentration

in a repeated

measurement design. Stereoscopic Depth Perception The perception of stereoscopic depth shows large inter-individual

variations, even in

sober subjects (Fig 9). Nevertheless, we found a significant and ofien quite large increase

A.-J. Wegner and M. Fahle

478

in thresholds

after alcohol consumption.

A reason for this impairment

after alcohol

consumption may be a disturbance of oculomotor coordination. The present findings confirm the majority of studies on the deleterious effects of alcohol on depth perception (Nicholson et al., 1992; Wang et al., 1992; Watten and Lie, 1996). But they seem to contradict a study by Hill and Toffolon (1990) who reported that depth perception was not altered after alcohol consumption. probably due to the difference in assessing

However, this discrepancy

is

depth perception in the two studies. Hill and

Toffolon (1990) used Titmus stereo charts with a maximal disparity of 40 arcsec. Eight of their ten subjects demonstrated maximal performance (40 arcsec) both when sober and intoxicated. Similarly, seven of our 13 subjects showed a performance better than 40 arcsec even when intoxicated, and two subjects had a threshold intoxicated. Only four intoxicated subjects yielded thresholds

of 50 arcsec when

higher than 40 arcsec

(between 140 and 340 arcsec). Hence, it seems that Titmus charts are not sensitive enough to detect the sometimes

quite large changes in depth perception in the range

below 40 arcsec. Subjective Judgment of Intoxication Neither the subjective judgment of intoxication, nor the BAL were significantly correlated with the performance in the visual tasks applied here. This finding confirms a study by Hrouda et al. (1980) who failed to find a correlation between blood alcohol level and behavioral modifications

concerning attention, learning, short term memory, and motor

reflexes. Andre et al. (1994) also observed no correlation between BAL or subjective score of intoxication with contrast sensitivity for stationary gratings (but a correlation of BAL with contrast sensitivity for moving targets). Furthermore, in a study by Nicholson et al. (1992) alcohol-related

impairments

in a reaction and an anticipation

time task were not

predictable by BAL. On the other hand, these authors reported a significant

correlation

between perceived intoxication (subjective score) and performance in these tasks. Mills and Bisgrove (1983) found a linear relationship between both BAL and subjective score with alcohol-related impairments in a divided attention task. However, correlations in both studies were based on several testings of the same tasks in each intoxicated subject whereas intoxicated

in the present

study,

interindividual

correlations

were

subjects were tested only once thus limiting comparisons.

calculated

since

Alcohol and vision

4.79

Half of our subjects demonstrated a significant correlation between BAL and subjective score whereas the other half showed a clear discrepancy between perceived intoxication and BAL, even though subjects were informed

about their current BAL after each

subjective estimation. These findings contradict studies by Lukas et al. (1986) and Andre et al. (1994) both testing subjects on the ascending limb of the blood alcohol curve who failed to find a correlation of BAL and subjective estimate of intoxication but reported an earlier decrease in perceived intoxication than in BALs. Nicholson et al. (1995) studying contrast sensitivity on the descending

limb of the blood alcohol curve even reported a

negative correlation

between BAL and perceived intoxication

or self estimated

Positive correlations

were reported by Moss et al. (1989), Nicholson et al. (1992)

BAL. and

Wilson and Plomin (1985). In all these studies, subjects were not notified of their current BAL. However, as demonstrated in the present study, even information about the present BAL is not always a guarantee for a close correlation

of objective and subjective

estimations of BAL.

Conclusions The present study investigated the effects of acute alcohol consumption term memory, stereoscopic

on visual short

depth perception, as well as attention and concentration.

Performing all tests on the descending limb of the blood alcohol curve, subjects showed clear impairments in visual short term memory as assessed with a vernier discrimination task but not when applying the Benton Test. Attention and concentration (test d2) were only slightly affected by alcohol. However, the test d2 and the Benton Test showed clear limitations individual

when applied in a repeated measurement variations,

the majority of subjects

perception after alcohol consumption.

design. Despite of large inter-

were impaired

in stereoscopic

Hence, the vernier discrimination

depth

task assessing

visual short term memory and the depth perception task were the most sensitive of the tests applied here to reveal impairments

of visual perception related to acute alcohol

consumption.

Acknowledgments This research was supported by the state of Baden-Wuerttemberg, Schwerpunkt Suchtforschung”, University Tuebingen, Germany.

“Forschungs-

480

A.-J. Wegner and M. Fahle

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WILSON

Inquiries and reprint requests should be addressed to: Manfred Fahle Humanbiologie Universitat Bremen Argonnenstr. 3 28211 Bremen Germany

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