Shin'ya Nishida
Spatiotemporal properties
of motion perception for
random-check contrast modulation
Abstract: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 & Sperling, 1988, Journal of the Optical Society of
America, A5, 1986-2007), termed RWK (random window kinematogram), 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 ED
(exposure duration) on RWK discrimination could be described as SOA
(stimulus onset asynchrony) dependency when the 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 RDK (random
dot kinematogram) having similar stimulus parameters (e.g., check size,
effective contrast). Incoherent motion (e.g., reversed phi) could be seen for
RWK. The Dmax (maximum displacement limit) for RWK was comparable
to that of RDK, but it increased in proportion to the check size, while the
Dmax for RDK did not. These results suggest that, like the luminance
motion mechanism, the contrast motion mechanism extracts motion
locally, and its motion extraction stage can be modeled as a correlation-type
detector. Also, the spatial ranges of the contrast motion detectors are
comparable to those of the luminance motion detectors, but their temporal
range is larger. The preprocessing of the contrast motion detector may be
different from that assumed in the model proposed by Chubb & Sperling.