Temporal integration of vertical-size disparity for slant perception

Spatial property of vertical disparity processing is different from that of horizontal disparity for slant perception. For example, vertical disparities are pooled within a large visual field for slant perception, whereas horizontal disparity is processed at each point for the perceived depth. Regarding the temporal property, although it has been reported that vertical disparity needs longer presentation time for slant perception than horizontal disparity does, the details of the temporal properties of vertical disparity processing is not known yet. In this study, we examined the temporal property of vertical - size disparity processing for slant perception, and discussed the roles of vertical disparity in visual system. We measured the magnitude of perceived slant produced by vertical - or horizontal - size disparity changing in time to investigate the difference in the temporal properties. Two stimuli with different magnitudes of vertical - or horizontal - size disparity were oscillating in one presentation. In experiment 1, the temporally frequency of the oscillation was the variable. In experiment 2, the duration ratio of the two stimuli in one oscillation was the variable. Subjects responded the transition of perceived slant for each presentation. For horizontal - size disparity, they identified two separate surfaces with different slants for all of the tested conditions of frequency (Exp.1). For vertical-size disparity, they perceived only one surface for the conditions with high frequency (Exp.1), and the magnitude of slant correlated to the integrated value of vertical - size disparity during a certain time span (Exp.2). These results indicate that vertical disparities are temporally pooled within a certain time span for slant perception. The difference between the temporal properties of vertical and horizontal disparities is probably due to the difference of the roles of vertical and horizontal disparities in visual system.