The Effects of Age and Target Location Uncertainty on Decision Making in a Simulated Driving Task

Spatial localization has been identified as an age-sensitive process in selective attention. Because visual search in driving involves uncertainty concerning the location of information necessary for maneuvering decisions, an experiment was conducted to examine the effects of age and target location uncertainty on a simulated driving task. Seventeen younger subjects (aged 30 to 45 years) and 13 older subjects (aged 65 to 75 years) completed three tasks including two reaction-time tasks and a simulated driving task. The reaction-time tasks included three conditions (simple left, simple right, and two-choice) in a laboratory and in a stationary vehicle. The simulated driving task was conducted on a closed driving course while subjects sat in a stationary vehicle. Subjects were required to select one of two lanes using information presented either on a changeable-message sign or on traffic signals. In the high-certainty condition, subjects were told where to look for relevant information; in the low-certainty condition, they were told that information could appear in either place. Response times were measured from sign or traffic signal onset to the subject's activation of the vehicle turn signal. The results indicated small, non-significant differences between age groups for the reaction-time tasks. Significant age-related differences were found in the simulated lane-selection task. Older subjects were 15% slower overall than the younger subjects. Uncertainty concerning the location of relevant information slowed decision-making speed for all subjects, but proportionately more for the older subjects (16% versus 11% for the younger age group). Uncertainty slowed responses to the changeable message sign more than to traffic signals for subjects in both age groups. The results are consistent with the spatial localization hypothesis, and suggest that older drivers may have more difficulty than younger drivers locating targets in visual search while driving. The results also suggest that effective use of changeable-message signs requires placement in locations with high expectancy, and allowing drivers sufficient time to locate the sign before reading the scrolling message.