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Field Dependence and Driver Visual Search Behavior David Shinar, Edward D. McDowell, Nick J. Rackoff and Thomas H. Rockwell Human Factors: The Journal of the Human Factors and Ergonomics Society 1978 20: 553 DOI: 10.1177/001872087802000505 The online version of this article can be found at: http://hfs.sagepub.com/content/20/5/553

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HUMAN

F A C T O R S , 1978,20(5), 553-559

Field Dependence and Driver Visual Search Behavior DAVID SHINAR,' Indiana University, Bloomington, Indiana, EDWARD D. McDOWELL, Oregon State University, CorvaNis, Oregon, NICK J . RACKOFF, GTE Data Services, Inc., Tampa, Florida, and THOMAS H. ROCKWELL, The Ohio State University, Columbus, Ohio

This paper reports on two studies that examined the relationship between field dependence and on-the-road visual search behavior. I n the first study, concerned with eye movements in curve negotiation, it was found that field-dependentsubjects have a less effective visual search pattern. In the second study, young and aged drivers were compared on several information processing tasks and on their ability to maintain their eyes closed part o f the time while driving. O f the various information processing tasks, only field dependence and visual search time correlated significantly with the mean time the drivers needed to maintain their eyes open while driving, Together the two studies indicate that field &pendent subjects require more time to process the available visual information and are less effective in their visual search pattern.

INTRODUCTION

the field-dependent driver behaviors that may cause accidents andlor the field-indeField dependence as a perceptual style pendent behaviors that may avoid accidents refers t o the extent t o which a person is remain to be specified. Several studies have capable of overcoming an embedding context reported relationships between field-depenin order to perceive relevant targets. Initial dence a n d specific driver behaviors, b u t studies conducted by Witkin (Witkin, Lewis, much remains to be done" (p. 55). GoodHertzman, Machover, Meissner, and Wapner, enough then goes on to review research that 1954) demonstrated that people vary widely has correlated field-dependence with recogin that capability and that individual difnition of developing hazards, recognition of ferences in field dependence reflect a relaroad signs in their natural environment, tively stable cognitive style. controlling skidding vehicles, and defensive In a recent review of research on the reladriving in high speed traffic. tionship between field dependence as a cogConspicuously missing in the data critically nitive style and driver behavior, Goodenough reviewed by Goodenough is the relationship (1976) concluded that "while these studies between field-dependence and driver visual suggesi the degree of field dependence is related to accident andlor violation rates, search behavior. Field-dependence is characteristically measured by having a subject scan a complex figure in which a target is Requests for reprints should be sent to Dr. David Shinar, Department of Industrial Engineering, Ben Curion embedded (the Embedded Figure Test). This University. P.O. Box 653, Beer Sheva, Israel. is therefore considered to be a measure of

553 0 1978,The Human Factors Society, Inc. Downloaded from hfs.sagepub.com at HFES-Human Factors and Ergonomics Society on February 8, 2014 All rights reserved.

554- October, 1978

cognitive or perceptual style. Since an extensive amount of research indicates that visual search behavior corresponds closely to information processing strategies (Mackworth and Morandi, 1967; Noton and Stark, 1971; Yarbus, 1967) it is reasonable to assume that some consistent correspondence between visual search behavior and field dependence would be found. With increasing evidence concerning the relationship between various measures of eye movements and driver performance (Kaluger and Smith, 1970;Mourant and Rockwell, 1972: Zell, 1969). one would expect that one of the contributors to the frequently noted large individual differences in eye movement behavior while driving would be the driver’s level of field-dependence/ independence. with this hypothesis in mind, two recent studies on the relationship between eye movement behavior and driving incorporated the Embedded Figure Test as one of the measures of driver characteristics. While various aspects of these studies have been reported elsewhere (Rackoff, 1975; Shinar, 1977;Shinar, McDowell, and Rockwell, 1977), the relationships between field dependence and eye fixation patterns have not been reported. In light of Goodenough’s (1976)excellent review of the state-of-the-art, it was thought that publication of these data would provide one of the links that Goodenough indicated are still missing. EXPERIMENT I: EYE MOVEMENTS IN CURVE NEGOTIATION The purpose of this study was to identify the perceptual search process involved in curve negotiation and attempt to relate it to curves’ accident liability. Partial results of this study have been published elsewhere (Shinar, McDowell, a n d Rockwell, 1977; Shinar, 1977). In brief, the visual search behavior of drivers on straight-road segments

HUMAN

FACTORS

prior to curves and within the curved road segments themselves were analyzed a n d related to road design features. The results indicated that the increased perceptual processing demands associated with curve negotiation were reflected in changes in the eye movement patterns (from those observed on straight roads) to a more active one involving more eye movements and more foveal fixations on the road edges rather than on the focus of expansion-that point in the moving visual field straight ahead of the driver where objects appear stationary. On a straight road the focus of expansion coincides with the end of the road, while on a curved road the two a r e located in different parts of t h e visual field. For purpose of the present analyses it was anticipated that the more field-dependent the subject is, the less efficient his visual search pattern would be (manifested by fixations on less informative parts of the visual scene). On a straight road good experienced drivers concentrate most of their fixations at the focus of expansion (Mourant and Rockwell, 1972). This is also considered to be an optimal strategy since it allows the driver to maximize preview time and distance for objects on or immediately off the road. Information on lateral placement is then available from the geometrical perspective of the unchanging pattern formed by the roadway edges (Fry, 1968).On a curved road, however, this strategy would not appear t o be the most efficient one. This is because the changing lateral placement demands require much closer attention to the road edges, and in fact on curved road segments, drivers tend to fixate foveally the lateral placement cues (Shinar, McDowell, and Rockwell, 1977).It was hypothesized that the more field independent the driver is, the more adept he would be a t changing his search pattern when approaching curves.


DAVID SHINAR

October, 1978- 555

Method The subjects were five (three male and two female) undergraduate students with unaided 20120 visual acuity o r better. Each subject drove a n experimental vehicle equipped with eye movement recording apparatus (see Shinar, McDowell, and Rockwell, 1977, for detailed description of apparatus and procedures) over 34 km of rural twolane highways. Eye movement d a t a were analyzed for 22 curved road segments and two straight road segments. To minimize visual fixations that are unrelated to the information acquisition process, the drivers were instructed to maintain an average speed of 96 k d h throughout the route. In a previous study Safford (1971) demonstrated that a driver’s spare visual capacity is reduced as velocity is increased.

Results and Discussion Although the drivers were not originally selected for their level of field dependence/ independence a relatively wide range of scores was obtained from the five subjects. The two females obtained scores of 15 s and 22 s per problem on the average, while the males obtained scores of 27 s, 40 S, and 50 S.

Based on norms published by Witkin, Oltman, Raskin, and Karp (1971) the two females and one male can be considered field independent while the remaining two males are average in their performance. Despite this range of scores on the Embedded Figure Test (EFT), it should be noted that correlations based on data obtained for a sample size of five subjects need to be extremely high in order to be statistically significant. Table 1 summarizes the correlations between the EFT score and the percent times that the subjects spent fixating on the road and on the focus of expansion on curved and straight roads. The results indicate that the more field dependent a subject is, the more likely he is to spend more time on the focus of expansion. While this is generally a good strategy on a straight road, a s has been pointed out above, it is an inefficient strategy while negotiating curves. Furthermore, the high correlation between percent time spent on the focus of expansion in curved a n d straight roads indicates that this tendency is apparently difficult to break. Finally, the correlation between the EFT score and the mean travel distance between successive fixations (r = 0.95, p < 0.05) suggests that the more field dependent a

TABLE 1

Correlations between Embedded Figure Test (EFT)Scores and Percent of Time Drivers Fixate on the Focus of Expansion and on the Road in Curved and Straight Road Segments. Percent Time On Embedded Figure Test

Focus of Expansion In Curves

In Straights

In Curves

In Straights

(1)

(2)

(3)

(4)

(5)

(1) (2)

0.87

0.88

-0.68

-0.40

0.98

-0.83 -0.73

-0.73

(3) Note: n

-

Road

(4) 5, p

6

0.05 when I

0.66


-0.59 0.88

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556-0ctober, 1978

driver is the more concentrated his fixations. These results support the notion that field dependent subjects are less able to adapt themselves to the changing environments encountered when moving from a straight road to a curved road segment. Thus they may be said to be more rigid in their visual search behavior. For more detailed comparisons, a power spectrum analysis was conducted on the horizontal component of the eye movements in three of the curved road segments. The correlation between the EFT scores and the mean to peak power ratio was 0.99, and the correlation between the EFT score and the median frequency was -0.91; both correlations were statistically significant. The peak to mean power ratio can best be described as a measure of concentration, and the positive correlation indicates that the more field dependent the driver is the more he concentrates his fixations within a small region of the total visual field. The median frequency reflects the level of eye movement activity, and the negative correlation indicates that the visual search is a slower process for the field dependent drivers than for the field independent drivers. These results suggest that field dependent drivers tend to concentrate their fixations within a narrow field of view and move their point of regard across shorter distances between successive fixations. It is possible, therefore, t h a t field dependent drivers develop a mild form of tunnel vision o r reduced peripheral vision capabilities. All of the above results are consistent with the hypothesis that the more field dependent a person is the less adaptive and efficient he would be in the curve negotiating environment where the perceptual load is increased a n d the location of the target (i.e., road) within the visual field changes continously.

FACTORS

EXPERIMENT 11: AGE RELATED CHANGES IN DRIVERS’ SPARE VISUAL CAPACITY The general objective of this study was to identify aged-related changes in basic information processing capabilities and assess their correlation with driver visual search behavior. Specifically, with respect to field dependence, it was hypothesized that older drivers would require longer times to disembed the simple figure from the complex one and would correspondingly have less spare visual capacity while driving on the road. Spare visual capacity, a concept coined by Safford (1971), can be operationally defined as the inverse of the amount of time a driver must maintain his eyes open in order to perform the driving task successfully. Method

Six young subjects (ages 20 t o 2 5 ) a n d nine aged subjects (ages 63 t o 70) participated in the study. Both groups averaged 20120 corrected vision. Each subject was required to perform six laboratory information processing tests and four driving tasks. The laboratory tests consisted of the Embedded Figure Test, a choice reaction time test from which a measure of information processing rate could be calculated, a visual search test in which a subject scanned a row of 25 circles and had to determine the number of circles without a bisecting line (one, two, three, or four per line), a serial choice reaction test in which each trial is initiated as soon as the subject responds to the stimulus from the previous trial, a memory test in which the same serial choice reaction time test was used but the subject was required to respond to the digit presented two trials earlier, and a movement-time test. The driving tasks consisted of driving under


DAVID SHINAR

October, 1978-557

four different conditions: daytime and night- the present discussion will be limited to the time open road driving at normal speed in results that pertain to these two measures. the absence of traffic within several hundred The mean Embedded Figure Test score was meters, and daytime and nighttime car fol- 0.2 min for the young drivers (i.e. field indelowing behind a car travelling a t approxi- pendent) a n d 1.3 min for the old drivers mately 80 km/h. The same experimental (i.e. field dependent). The mean visual search vehicle and eye movement apparatus was time (in the laboratory test) was 2.3 s for the used a s in Experiment I. A more detailed de- young drivers and 3.2 s for the old drivers. scription of the methodology has been pre- On the road, the mean eyes-open time (for sented elsewhere (Rackoff, 1975). Unlike high open road daytime) was 0.7 s for the young speed curve negotiations, straight road driv- drivers and 1.5 s for the older drivers. All ing has been shown to be a relatively unde- differences were statistically significant a t manding task (Safford, 1971) and a s such p < 0.01. Correlations between these two amenable t o measuring the spare visual laboratory measures and the mean open time capacity that a driver has. All drivers were under the four road driving conditions are therefore required to perform each of the presented in Table 2. These results indicate tasks while maintaining their eyes closed for that the longer the mean time that the driver a s long and as often a s they could, while feels that he has to keep his eyes open on realizing that the safe negotiation of the car the road, the longer the time to locate o r according to the instructions and road de- disembed the simple figure from the complex mands was still their primary responsibility. figure in the Embedded Figure Test. Also significant, though slightly lower, were the Results and Discussion correlations between the visual search time There were significant differences between and the mean time drivers kept their eyes the young and the aged drivers on all the open on all driving conditions. The correlalaboratory tests, but only the performance on tion between the Embedded Figure Test and the Embedded Figure Test a n d the (con- the visual search test was also significant ceptually relevant) visual search test was (r = 0.56). Broadly interpreted, the results consistently and significantly correlated with indicate that the minimum time to acquire driving visual search measures. Therefore minimal information for vehicle control on TABLE 2

The Correlationsbetween the Scores on the Embedded Figure Test and Visual Search Test and the Mean Durations the Eyes were Kept Open in Open Road and Car Following Driving, for Daytime and Nightirne Driving Daytime Driving Open Road

Car Followina

Open Road

Car Following

0.72

0.70

0.73

0.69

0.62

0.54

0.71

0.62

Embedded Figure Test Visual Search Test Note: n

-

15, p c 0.05 when I

Nighttime Driving

0.52


558-0ctober, 1978

the road is associated with the subject’s ability to search and scan for visual information in the laboratory visual search test. No significant correlations were obtained between performance on the Embedded Figure Test and the various central tendency measures of eye movements (mean duration and mean location in the visual field) while driving. Similarly, no significant differences in these eye movement measures were obtained between the two different age group subjects. This result however is not particularly surprising since the eye movement data were collected under normal driving conditions without occlusion, and therefore the drivers’ perceptual capacities were not taxed or overloaded. GENERAL DISCUSSION AND CONCLUSIONS The results of the two studies indicate that under capacity loading conditions such as curve negotiation there is a relationship between field dependence and eye movement behavior. The more field dependent a driver is the longer his eye fixation durations indicating longer time necessary to pick up relevant information, and more importantly the less adaptive the eye fixation pattern with respect to shifting fixations from the focus of expansion to the changing location of the road ahead. The results of the second experiment further indicate that more field dependent drivers require longer time to obtain information from the roadway as manifested by mean open time durations. The fact that this was demonstrated by differences between young and old drivers warrants caution however, since the correlations could be spurious, reflecting interactions with other age-related deteriorations, and not necessarily the effects of field dependence. However, in this context it should be noted that of all the laboratory tests, only the Embedded Figure Test and the visual search test were con-

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FACTORS

sistently correlated with the visual occlusion measures under all conditions of driving. No consistent and significant correlations were obtained between the mean open times on the road a n d the measures of short term memory, movement capacity, and information processing rate. Hence the longer EFT times obtained for the older drivers cannot be explained by slowed reaction time alone. Furthermore, detailed analysis of individual differences showed that of the aged drivers, the two who were subjectively labeled “better drivers” also had the best scores on the Embedded Figure Test within their age group (which were substantially longer times than those obtained from the young drivers) a n d had the shortest mean open times for their age group. The results of these two studies fit nicely with Goodenough’s (1976) theoretical formulation that field dependent subjects would be likely to exhibit more difficulty in obtaining critical cues from the road environment, and with Mihal and Barrett’s (1976) finding that field dependent subjects require more time to identify roadway signs embedded in their natural environment, and have a higher accident frequency. than field independent subjects. Given the current philosophy of licensing drivers on the basis of performance an tasks that are directly driving-related (e.g. knowledge, vision, driving), it is unlikely that any test of cognitive style could be used for screening purposes. On the other hand, since performance on the Embedded Figure Test has been shown to be highly related to a consistent cognitive style, and eye movement patterns have been shown to be consistent within subject and different between subjects (Rockwell, 1972), it is likely that training programs may be differentially effective for field dependent subjects, though it remains an open question as to whether these people can in fact modify their visual


DAVID SHINAR

search behavior accordingly. The fact that a systematic change in the visual behavior of novice drivers has been observed at different periods of training (Mourant and Rockwell, 1972) suggests t h a t this aspect of driver behavior may be amenable to training and may be highly cost-effective. ACKNOWLEDGMENTS This work was supported in part by funds from the Federal Highway Administration, U.S. Department of Transportation, and the Ohio Department of Transportation to Project EES 428. and in part by the National Highway Traffic Safety Administration, U.S. Department of Transportation, Contract No. DOT-HS-I 15-3-772. both to the Ohio State University.

REFERENCES Fry. G. A. The use of the eyes in steering a car on straight and curved roads. American Journal o f Optometry, 1968.45.374-391. Goodenough. D. R. A review of individual differences in field dependence as a factor in auto safety. Human Factors, 1976.18, 53-62. Kaluger, N. A. and Smith, G . L..Jr. Driver eye-movement patterns under conditions of prolonged driving and sleep deprivation. Highway Research Record, No. 336, 1970. Mackworth, N. H. and Morandi, A. J. The gaze selects informative details within pictures. Perception and Pscyhophysics, 1967,2, 547-551. Mihal. W. L. and Barrett. G. V. Individual differences in perceptual informational processing and their relation

October, 1978-559

to automobile accident involvement. Journal ofApplied Psychology, 1976,61, 229-233. Mourant, R. R. and Rockwell, T. H. Strategies of visual search by novice and experienced drivers. Human Factors, 1972,14, 325-335. Noton, D. and Stark, L. Scanpaths in saccadic eyemovements while viewing and recognizing patterns. Vision Research, 1971, If. 929-942. Rackoff, N. J. An investigation of age-related changes in drivers visual search patterns in driving performance and the relation to tasks of basic functional capacities. Proceedings of the 19th annual meeting ofthe Human Factors Society, Dallas, Texas, 1975. Rockwell, T. H. Eye movement analysis of visual information acquisition in driving: An overview. Proceedings of the 6th conference of the Australian Road Research Board, 1972.6,316-331. Safford, R. R. Visual spare capacity in automobile driving and its sensitivity to carboxyhemoglobin. Unpublished doctoral dissertation, The Ohio State University, 1971, Shinar. D. Curve perception and accidents on curves: An illusive curve phenomenon? Zeitschrifr f i r Verkhrssicherheit Uournal of Traffic Safety), 1977.23, 16-21. Shinar, D., McDowell, E. D.. and Rockwell. T. H. Eye movements in curve negotiations. Human Factors, 1977.19. 63-11. Witkin. H. A., Lewis, H. B., Hertzman, M.,Machover. K., Meissner, P. B., and Wapner, S . Personality through perception. New York: Harper, 1954. Witkin, H. A., Oltman. P. K. Raskin, E.,and Karp, S . A. Manual of the Embedakd Figures Test, Palo Alto, California: Consulting Psychologists Press. 1971. Yarbus, A. L. Eye movements and vision. New York: Plenum, 1967. Zell, J. K. Driver eye movement as a function of driving experience. Columbus, Ohio: The Ohio State University, Engineering Experiment Station, Technical Report, IE-16, 1969.