Amy
Crowe, Tara Smyser, Mireille Raby, Kirk Bateman and Matthew Rizzo
Department
of Neurology
University
of Iowa
Iowa
City, IA 52242
Purpose
Driving is a complex task that makes
high demands on visual processing capacity. Reduction of visual attention and
processing speed are risk factors for car crash involvement in older drivers
(Owsley et al, 1991; Ball et al, 1993). Impairment of these visual functions
can affect driver safety by impairing the ability to search for information in
a cluttered panorama that includes traffic signals and road signs. The purpose of the
current study was to examine the extent to
which on-road landmark identification during the driving task is predicted by
off-road measures of visual attention.
Method
Subjects were 30 drivers, ages 66-92 (mean
age=74.6; 57% male) enrolled in a larger ongoing study of at-risk older
drivers. All subjects participated in a battery of tests of visual and
cognitive ability. Speed of visual processing, divided attention and selective
attention were measured using the Visual Attention Analyzer, 3000 (Visual
Resources. Inc., Bowling Green, KY). They also took part in a drive that tested
their performance on several attention-related tasks. One of these tasks, a
landmark identification task, was developed to evaluate driver perception and
attention to relevant stimuli along the roadway. This task required drivers to
identify restaurants (N=10) and safety-related signs (N=7-9) while driving an
experimental vehicle along a commercial segment of a four-lane divided state
highway. The specific signs to be identified depended on the direction that the
subjects drove on the highway. Performance on the landmark identification task
was scored in terms of percent correct. Spearman correlation coefficients were
calculated between the attention scores and the percent correct scores on the
Landmark Recognition task.
Results
The 30 drivers generally showed impaired
performances on tasks of visual processing speed (range=16-100, median=16,
mean=24.73, SD=19.80), divided attention speed (range=23-322, median=86.5,
mean=110.67, SD=78.61), and selective attention with identification of a foveal
target (range=356-500, median=500, mean=459.43, SD=57.40), and with
same/different foveal discrimination (range=476-500, median=500, mean=498.87,
SD=4.69). Results showed 76.35 % identification for safety signs and 40.3 %
correct performance for restaurant identification. The same/different foveal discrimination
sub-test showed a significant correlation (p=0.034) with performance on the
restaurant portion of the landmark identification task, yet, surprisingly,
other relationships were not significant. Participants familiarity with the
area did not make a significant difference in their scores (F=0.04, p=0.674).
Traffic circumstances allowed two drivers extra opportunity to identify signs
while stopped at a traffic signal, but this had no significant effect on the
results.
Conclusions
This study shows that scores on a test of
selective visual attention correlated with ability to identify landmarks
(restaurants) on a commercial highway, yet visual processing speed and divided
attention showed no significant correlation. Moreover, ability to identify safety
signs did not correlate with any of the visual measures. Several factors may
have affected the percentage of landmarks (signs and restaurants) identified.
One factor is the variability of ambient traffic, which causes a variation of
driver workload, which in turn affects the ability to search the roadway for
visual targets. Also some drivers tended to call out indiscriminately every
landmark they encountered, which would tend to increase their percent correct
responses. In future analyses we will apply the theory of signal detection to
address this response bias.
Ball,
K., Owsley, C., Sloane, M.E., Roenker, D.L., Bruni, J.R. Visual attention as a
predictor of vehicle crashes in older drivers. Investigative Ophthalmology: Visual Science, 1993; 34:3110-3123.
Owsley,
C., Ball, K., Sloane, M.E., Roenker, D.L., Bruni, J.R. Visual cognitive
correlates of vehicle accidents in older drivers. Psychology and Aging, 1991;6:403-415.