It has been suggested that voluntary daytime headlight use by motorcyclists might increase their conspicuity at the expense of reducing the conspicuity of non-users. Due to repeated encounters with headlight users, other motorists might develop a perceptual "set" for detecting point sources of illumination (headlights) rather than moving objects (motorcycles). This experiment investigated this issue experimentally, by encouraging subjects to use either shape or illumination as a cue to the presence of a motorcyclist. The principal findings of this study are: a) that headlight use improved motorcyclist conspicuity, and that this enhancement was greatest for motorcycles that were furthest from the viewer; and b) that repeated exposure to motorcyclists with their headlights on resulted in delayed detection of a motorcyclist with his headlight off, despite the latter being readily detectable in other circumstances.
Abstract