P1-3: Individual Differences in Chromostereopsis under Natural Viewing Conditions

Chromostereopsis is a type of visual perception where a specific color is perceived closer to or farther from the observer than other colors in the plane pattern. The mechanism is considered to be binocular stereopsis by the chromatic aberration of the eyeball optical subsystem, but there are large individual differences in natural viewing conditions. For example, in the case of a red-blue pattern with black background, about 70% of observers perceive the red pattern to be closer while 20% perceive the blue pattern to be closer. In the present research, the binocular disparity of the chromostereopsis was estimated both experimentally and numerically and the reason for the individual differences studied. First, the disparity was measured using a constant method, in which a stereo pair of red-blue stimulus patterns (random dots) was presented on a black background. The distance between the red and blue patterns for the right eye image was varied to generate a binocular disparity. It was found that the range of the equivalent disparity was between −1.3 and 2.1 arcmin among 24 subjects. Numerical simulation based on ray-tracing using LeGrand's model eye showed good agreement with the experimental results. The simulation results indicate that when the outer or inner edge of the pupil is shielded, the binocular disparity of the chromostereopsis was drastically changed. We conclude that this situation might occur due to the eccentricity of the center of the pupil and be the main factor of the individual differences in the chromostereopsis in natural viewing conditions