Spatio-temporal dynamics of depth propagation on uniform region

The depth of each point on a binocularly presented untextured horizontal bar is physically ambiguous except for the two vertical edges at both ends, since the correspondence between left and right images is not unique on such a uniform region. These depths, however, are unambiguously perceived, and this suggests the existence of some mechanism that interpolates the depth information from the two ends toward the center. Temporal properties of this integration process were examined by a phase-matching task, which allowed us to measure the phase of the perceived depth at the center of a horizontal bar when disparities at the ends were sinusoidally oscillated. We found that the perceived depth at the center of the bar was slightly temporally delayed for 7-60 ms relative to the physical depth at the ends. The difference increased with the length of the bar, decreased as the vertical position of the bar became farther from the fixation point, and increased in the presence of occluders. This finding indicates that depth information is propagated over an object to solve this ambiguity by using a time-consuming process. Accordingly, we suggest that depth propagation is accomplished by spatially local diffusion-like interactions of locally represented depth information.