[Effect of light intensity on binocular distance perception].

Empirical investigations of perceived binocular distance often use an experimental setting in which real point-like light sources are presented in a completely dark surround. The results obtained, however, may be a consequence of the joint influence of binocular and monocular depth cues. Here, for the first time, the effect of (monocular) illumination cues on the locus of perceived equidistance is experimentally investigated by manipulating the luminous intensity of the stimuli. In a computer-controlled setup, small light-emitting diodes were presented in complete darkness. Five subjects judged the perceived distance of stimuli, which appeared in four directions and at five levels of luminous intensity, with respect to a fixed standard. Adaptive methods were used to determine perceived equidistance. Although the results show a significant effect of illumination cues, their influence on the locus of perceived equidistance turned out to be far less than previously supposed. For three subjects it was practically negligible.