Temporal pooling of vertical size disparity for slant perception

Spatial property of vertical disparity processing is different from that of horizontal disparity processing for slant perception. Vertical disparities are spatially pooled within a large visual field for slant perception, whereas horizontal disparity is processed at each point for depth perception. It has been reported that it takes longer duration to perceive slant for vertical disparity than for horizontal disparity, suggesting that the temporal property of vertical disparity is also different from that of horizontal disparity. Here, the question arises whether vertical disparities are temporally pooled within a longer span for slant perception or the processing of vertical disparity itself takes longer time. To answer this question, we investigated the temporal property of vertical-size disparity processing for slant perception. In the first experiment, two sets of random dot stimuli with vertical- or horizontal-size disparities producing two different slants were presented alternatively in one presentation. The results showed that, for the presentation having vertical size disparity, the subjects perceived the averaged slants of the two sets if the temporal frequency of alternation was high, whereas they perceived two slants if the temporal frequency was low. For the presentation having horizontal size disparity, two slants were always seen. In the second experiment, the stimuli with uniform vertical size disparity were divided into many pieces, and these pieces were presented sequentially. The results showed that the perceived slant increased as the area presented within a certain duration increased. These results indicated that vertical disparities are temporally and spatio-temporally pooled for slant perception. The similarity between the duration of temporal pooling found in this study and the duration of fixation in normal viewing is consistent with the notion that vertical disparity is used the retinal information of eye positions.