Abstract
Vertical size disparity of a vertical line varies as a function of eccentricity and distance, but it has not been reported that the vertical size disparity of such the small stimulus contributes to the perceived eccentricity and distance. For large stimulus, some studies have shown that vertical disparity affects the perception of straight-ahead (Berends et al. 2002) and distance (Rogers Bradshaw 1995). In this study, we investigated the perceived eccentricity and distance for the small stimulus with manipulated vertical size disparity using perceptual and action tasks. The stimulus was a vertical single-line composed of dots. The head-centric eccentricity and the magnitude of vertical size disparity of the stimulus were manipulated. Subjects responded the two-dimensional position of the line on a horizontal plane by perceptual and action tasks. The perceptual task was a relative judgment of the positions for successively presented two stimuli. The action task was pointing the perceived position by unseen finger. The results were the same for both of the tasks. Perceived distance to the stimulus at large eccentricity depended on the magnitude of vertical size disparity, but that near the median plane did not affected by vertical size disparity. These results for perceived distance are consistent quantitatively with the predicted distance from vertical size disparity along the presented eccentricity. Perceived eccentricity to the stimulus was kept stable in all of the eccentricity condition tested. This result for perceived eccentricity is consistent with the result of perceived eccentricity to large size stimulus (Banks et al. 2002). These results indicates that the perceived eccentricity of an object is determined by the position of the eyes and the image position on the retina, and that the perceived distance of the object is affected by the vertical size disparity along the given eccentricity.