The spatiotemporal frequency property of stereopsis

Purpose: To investigate the spatiotemporal frequency property of stereopsis, we measured disparity and contrast threshold for the depth discrimination of moving gratings with variable spatial and temporal frequencies. Methods: Stimulus display consisted with four squares filled with sinusoidal gratings arranged in a 2×2 array with gaps to separate them. The gratings in the upper right and the lower left squares had the same disparity that was opposite of those in the other two squares and the observers responded which pair appeared to be closer in depth. Disparity threshold was measured by a staircase procedure in each combination of six spatial frequencies (0.23∼7.50c/deg) and six speeds (0.15∼20Hz) at a fixed contrast of 0.1. Contrast threshold was also measured in each condition at a fixed disparity of 10 arc min. Results: The results in both disparity and contrast threshold measurements showed that the spatial frequency property depended on temporal frequency. Disparity threshold was lowest at a spatial frequency of about 2∼3 c/deg (i.e., band pass) when temporal frequency was low (<4Hz) on one hand. When temporal frequency was high (>4Hz), on the other hand, disparity threshold increased with spatial frequency at spatial frequencies higher than about 1 c/deg (i.e., low pass). Similarly, contrast threshold was lowest at a spatial frequency of about 1∼2 c/deg when temporal frequency was low (<4Hz). When temporal frequency was high (>4Hz), contrast threshold increased with spatial frequency at spatial frequencies higher than about 1 c/deg. Conclusions: Our measurements suggest that at least two mechanisms with different spatiotemporal-frequency properties contribute to stereopsis.