Abstract

The visual tasks of recognition and spatial orientation are differentially influenced by reduction of luminance. Spatial orientation is unaffected at luminance levels for which object recognition is systematically degraded. It is suggested that this selective degradation of visual functions plays a role in the high incidence of nighttime traffic accidents. Driving a vehicle involves both orientation, for steering, and recognition, to monitor the road-way for hazards. These functions are selectively impaired after sunset with the result that the vehicle can be adequately steered at luminance levels for which the recognition of hazards is significantly degraded. Because the unaltered orientation-steering function is a continuous task, the driver remains confident about his/her abilities. As a result of this unjustified self-confidence, drivers are neither aware of nor prepared for the consequences of degradation in the ability to recognize and respond to hazards and drive too fast at night. Because alcohol artificially increases self-confidence it can exacerbate the luminance-induced discrepancy between steering and hazard avoidance abilities. Ameliorative measures would include public education to apprise the public of dangers of which they are not normally aware and the establishment of differential day/night speed limits.

© 1985 Optical Society of America