Reaction times as an index of visual conspicuity when driving at night.

Conspicuity refers to the visibility of objects that are either close to threshold or viewed in a cluttered environment. Conventional, threshold-based tests of vision are unlikely to be related to target visibility, because visual systems behave differently under supra-threshold and close-to-threshold conditions, or when low luminance levels are used. In these experiments, Reaction Times (RTs) are tested under a wide range of contrasts, luminances and spatial frequencies commonly encountered in the real world. We show that RTs are closely related to sensitivity and can therefore provide a method of measuring supra-threshold visual performance. The data are interpreted in terms of visual performance when driving, where a reduction in target visibility leads to increases in processing time.