Abstract
The visual system encodes binocular disparity with either a position or a phase offset between the left and the right eye bandpass filters. However, the local disparity measurement of each subband is ambiguous, particularly when the actual disparity is larger than the half-cycle of the preferred spatial frequency of the filter. We investigated whether the visual system uses a coarse-to-fine interaction to resolve this ambiguity at fine scales in estimating depth from disparity. The stimuli were stereo-grating patches composed of a target and a comparison pattern, which were assigned randomly to the upper and lower halves of the stimuli. The target patterns contained both 1 and 4 cycles per degree (cpd) spatial frequencies, and the comparison patterns were either a compound grating with 1 and 4cpd components or a 1cpd simple grating. The phase disparities of both the low- and high-frequency components were independently changed in the range from -90o (uncrossed) to 90o (crossed). The observers’ task was to indicate whether the target or the comparison pattern appeared closer to them. Regardless of whether the comparison patterns were compound or simple gratings, the perceived depth difference between the target and the comparison increased with the phase disparity of the high-frequency component. This effect occurred not only when the low-frequency component was at the horopter, but also when it contained a -90o or 90o disparity, which corresponded to one cycle of the high-frequency component. Such a result implies a coarse-to-fine interaction in the multi-scale disparity processing, in which the depth interpretation of the high-frequency changes with the disparity of the low-frequency component.