Spatiotemporal properties of motion perception for random-check contrast modulations.

To clarify the mechanism of detecting the motion of contrast modulations, the spatiotemporal properties of direction discrimination for contrast motion were examined. The stimulus was a microbalanced random stimulus [Chubb and Sperling (1988) Journal of the Optical Society of America A 5, 1986-2007], termed random-window kinematogram (RWK), a shifting random checkerboard pattern in which each check was either a patch of random dots (uncorrelated between frames) or a patch of uniform gray having the mean luminance of the random dots. The effect of exposure duration (ED) on RWK discrimination could be described as stimulus onset asynchrony (SOA) dependency when EDs of the first and second frames were the same, but the performance was better than predicted from SOA when the first ED was short while the second was long. RWK could be seen at longer inter-stimulus intervals than random-dot kinematogram (RDK) having similar stimulus parameters (e.g. check size, effective contrast). Incoherent motion (e.g. reversed phi) could be seen for RWK. Maximum displacement limit (Dmax) for RWK was comparable to that of RDK, but it increased in proportion to check size, while Dmax for RDK did not. These results suggest that the contrast motion mechanism extracts motion locally, and involves a correlation-type motion extraction stage similar to the luminance motion mechanism. In addition, the spatial ranges of the contrast motion detectors are comparable to those of the luminance motion detectors, but their temporal range is larger. The contrast motion mechanism is more scale-invariant than the luminance motion mechanism.