Reprinted from

VISION IN VEHICLES - V

Edited by

A.G. GALE University of Derby Derby, U.K.

Co-edited by

1.0. BROWN Cambridge, U.K.

C.M. HASLEGRAVE University of Nottingham Nottingham, U.K.

S.P. TAYLOR Bournemouth, U.K.

1996

ELSEVIER AMSTERDAM • LAUSANNE • NEW YORK• OXFORD • SHANNON • TOKYO

VISION IN VEHICLES - V A.G. Gale et al. (Editors) © 1996 Elsevier Science B.V. Ali rigbts reserved. 389

Performance in Detecting Traffic Signs With and Without Alcohol lngestion (A Laboratory Study)

L. Nunesª, M. Peralbob, A. Rissoº y P. Vieirob

ªArea de Formación y Comportamiento de Conductores, Dirección General de Tráfico, Josefa Valcárcel 28, 28027 Madrid, Spain

bDpto. de Psicología Evolutiva y de la Educación, Universidad de La Coruña, Campus de La Zapateira, 1507 i ·La Coruña, Spain

ºDpto. de Psicología, Universidad de La Coruña, Campus de La Zapateira, 15071 La Coruña, Spain

Abstract The purpose of this work was to examine performance in detecting traffic signs when

subjects had drunk alcohol as compared to when they had not. Five drivers (undergraduate students) performed a detection task with and without ingesting alcohol. The an10unt of alcohol was close to the legal blood alcohol limit in Spain (until 0.8 gr/l for non professional drivers).

Forty-eight computerized stimuli were presented on a colour screen; half of them were pictures of traffic signs and the other half were signs showing irrelevant objects. A point was centred on the screen and preceding each picture, which was displayed peripherally somewhere around the central point. Subjects were instructed to locate the stimulus and to say 'yes' or 'no' depending on whether the given stimulus was a traffic sign or not. A record of eye movements using an NAC-EMR 600 allowed us to obtain measures of the time required to locate the stimulus ( eye movement velocity from the previous fixation point at the centre of the screen), as well as measures of the duration of eye fixation on the target.

Data analysis compared movement velocity and duration offixation separately for traffic and non-traffic signs in each group of subjects. The results showed that performance is slightly deteriorated after consuming alcohol.

Interesting consequences conceming vision during driving were found from these data. If alcohol ingestion affects a very sin1ple task like this, the implications regarding its influence on a highly complex task like driving must obviously be much more important.

l. INTRODUCTION

Many studies have confirmed the influence of alcohol ingestion on driving. However, public service announcements and legal limits do not discourage many people from driving under the influence of alcohol effects. In fact, there is a dangerous perception that driving after drinking is

Alcohol Effects on Detecting Traffic Signs 391

sampling rate of 600 Hz. It uses the CPU board and calibration frame (for calibration chart) for rapid semiautomatic calibration which is required to eliminate the effects of different subjects and the distortion of optics on measurement. It provides an analog OUT terminal so that the coordinate data after eye mark calibration can be outputted as 30 Hz sampling data for realtime processing. Data for both eyes movements (right eye and left pupil) were recorded on video (NTSC system). In addition, special software was used to analyze eye movements and fixations and to project the eye movement trajectory over the video image. A field viewing angle of 30 degrees was best suited for this experimental situation.

In NAC EMR-600, a fixation point is the centre ofthe range in which the eye mark remains for a certain time or more in a particular range. The time and range are specified at fixation point data creation. The minimum time duration was 66.66 milliseconds and the range was 5 degrees. The selected sampling rate was 30 Hz. The distance from the can1era sensor to the viewing plane was 70 cm.

The centroid mode was used to determine the fixation points. This centroid was obtained sequentially and used as the reference to set the fixation point.

2.4. Design The design was intrasubject and multivariate. The levels of the independent variable were:

traffic signs and non-traffic signs. The dependent variables were: a) ocular movement velocity from the last fixation point, in the centre of the screen, to the first point of fixation on the selected stimuli; and b) ocular fixation time on the stimulus target.

2.5. Procedure Firstly, the subject's headmotion was controlled by fixing the head on a specially designed

headrest. Secondly, we fixed the goggle unit with the help of guide LEDs cables. Thirdly, we pointed them towards the cornea and calibrated them using a calibration frame placed 70 cm from the eye. Finally, we fixed the parallax: the subject's sight had to be fixed on the centre of the screen (to correct the initial deviation along X and Y axes and to give an accuracy of ± 1 degree). The subjects were given instructions to begin the task and we began the experimental sess1on.

The stimuli ( each shown for 2000 msec) were presented randomly on a colour screen; but the central point (shown for 2000 msec) appeared befare the display of each stimulus. The subjects had to answer "yes" or "no", according to circumstances ("yes" ifthe stimulus was a traffic sign and "no" if it was a non-traffic sign). Responses were recorded by hand; at the same time we recorded the left eye image and the movements of the right eye.

Each subject had two experimental sessions, the first one without having drunk alcohol, and the second having had a quantity which resulted in a BAC leve! of approximately 0.7 gr/l (calculated from the height, weight and age of the subjects) one hour befare reinitiating the experiment. This second session took place one week after the first one.

The eye marks of the right eye and its calibration data were recorded on video.

Alcohol Effects on Detecting Traffic Signs

1400 1261

rn 1200 z o 1009

~ 1000 :::> 870 o 813 z~ 800 Ofrl ~~ 600 ¡¡:~

lL o rn 400

~ ::::;: 200

o WITHOUT ALCOHOL WITH ALCOHOL

i?2TRAFFIC SJGNS i!llNON-TRAFFJC SIGNS

Figure 1. Means of fixation durations on traffic and non-traffic signs with and without alcohol ingestion.

350

o 299 w 300 w 35 254 1- 250 z~ W(.) :::<w ~~ 200 Ow :::;:w

~8 150 lL 9. o 100 rn

~ 50 :::;:

o WlTHOUT ALCOHOL WlTH ALCOHOL

~TRAFFIC SIGNS i!llNON-TRAFFlC SIGNS

Figure 2. Means of velocity of eye movements from central point to upper left traffic and non-traffic signs with and without alcohol ingestion.

393

392 L. Nunes et al.

3. RESULTS AND DISCUSSION

The means of the eye fixation times and the velocities of the eye searching movements are shown in Table 1 and Figures 1 and 2. They include the results for the traffic and non traffic signs under the two conditions: with and without alcohol.

Table 1 Results of mean durations of eye fixations and velocities of eye searching movements.

SUBJECTS TRAFFIC SIGNS NON-TRAFFIC SIGNS

MEA NS OF FIXA TION DURA TI O NS (MILLISECONDS)

WITHOUT \.VlTH WITHOUT WITH ALCOHOL ALCOHOL ALCOHOL ALCOHOL

670 1620 400 670

2 660 1080 720 850

3 1020 920 1080 700

4 1440 1430 1170 1150

5 1260 1260 700 980

MEANS OF EYE MOVEMENT SPEED (DEGREES/SECOND)

WITHOUT WITH WITHOUT WITH ALCOHOL ALCOHOL ALCOHOL ALCOHOL

138.33 217.00 242.00 237.50

2 210.00 314.67 282.00 291.00

3 398.00 215.33 453 .00 250.50

4 296.00 236.33 298.00 254.50

5 231 .67 231.00 220.50 234.00

Student's t-test for related samples was used for the statistical analysis. Results showed that under the non-alcohol condition there were no differences between the

traffic and 11011-traffic signs for the fixation point duration (t4=1.67; p>.10), or for the velocity of the searching movements from the centre of the screen to the upper left square t4=-2.05; p>. l O).

Alcohol produced a significant increase in the durations of the fixation points when dealing with traffic signs instead of non-traffic signs (t4=2.78; p<.05). But differences were not found regarding the velocity ofthe eye movements (t4=-1.06; p>.1 O).

The comparison of the fixation times for the traffic signs with and without having ingested alcohol did not revea! significant differences (t4=- l .28; p>.1 O).

The same was found when comparing the velocíty of movement from the centre of the screen (t4=0.23; p>.10). Nevertheless, the fixation durations tended to be higher under the alcohol condition.

394 L. Nunes et al.

Similar results appeared when analyzing eye movements for non-traffic signs under the two conditions (alcohol and non-alcohol). Results were not significant but the fixation times tended to be higher in the alcohol condition (t4=-0.46; p>. l O). Moreover, the velocity of eye movement to the non-traffic signs seemed not to be affected by alcohol (t4=1.12; p>.1 O).

Considering these data, it could be said that the legally permitted dose of alcohol in Spain has some effect on the control of the exploration eye movements and on the discrimination of traffic signs. It shows that alcohol increases the time that is needed for proper stimulus recognition. These findings coincide with other results indicating an increase in eye fixation durations after drugs and alcohol abuse (Stapleton, et al., 1991; Fuster, Wiley & Riley, 1985; Moscowitz, Ziedman & Sharma, 1976).

From our point of view, these results lead to thinking that, even within legal limits of alcohol ingestion, a driver's visual performance is, indeed, affected by alcohol. So, the legal interdiction of alcohol consumption for drivers seems well justified for traffic safety.

REFERENCES

Avant, L.L., Bowes, M., Tepin, M. and Kerwin, K. (1991). Alcohol and visual detection of traffic signs. In A.O. Gale et al. (Eds.): Vision in Vehicles !JI. Amsterdan1, Elsevier Science Publishers B.V., 291-298.

Fuster, J.M., Willey, T.J. and Riley, D.M. (1985) Effects of ethanol on eye movements in the monkey. Alcohol, 2(4), 611-616.

Levett, J. and Hoeft, G. (1977). Voluntary eye movements and alcohol. Aviation, Space and Environmental Medicine, 48, 612-614.

Linfield, P.B. and Dunne, M.C.M. (1988). The effects of alcohol induced binocular instability on a driver's ability to correctly identify road direction signs. In A. G. Gale et al. (Eds.): Vision in vehicles- Il Amsterdam, Elsevier Science Publishers B.V., 75-83.

Moscowitz, H., Ziedman, K, Sharma, S. (1976) Visual search behavior while viewing driving scenes under the influence of alcohol and marihuana. Human Factors, 18(5), 417-431.

Stapleton, J.M., Guthrie, S. and Linnoila, M. (1986). Effects of alcohol and other psychotropic drugs on eye movements: Relevance to traffic safety. Journal aj Studies aj Alcohol, 47(5), 426-432.

Tong, J.E., Knott, V.J., McGraw, D.J. and Gillian, L. (1974). Alcohol, visual discrimination and heart rate: Effects of dose, activation and tobacco. Quarterly Journal olStudies on Alcohol, 35(3-A), 1003-1022.