Transparent Motion Perception as Detection of Unbalanced Motion
Signals III: Modeling
Ning Qian, Richard A. Andersen and Edward H. Adelson, J. Neurosci.
1994, 14:7381-7392.
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Abstract
In the two companion papers we studied the conditions under which
transparent motion perception occurs through psychophysical
experiments, and investigated the underlining neural mechanisms
through physiological recordings. The main finding of our perceptual
experiments was that whenever a display has finely balanced motion
signals in all local areas, it is perceptually non-transparent, and
that transparent displays always contain motion signals in different
directions that are either spatially unbalanced, or unbalanced in
their disparity or spatial frequency contents. In the physiological
experiments, we found two stages in the processing of transparent
stimuli. The first stage is located primarily in area V1. At this
stage motion measurements are made and V1 cells respond well to both
the balanced, non-transparent stimuli and the unbalanced, perceptually
transparent stimuli. The second stage is located primarily in area
MT. MT cells show strong suppression between opposite directions of
motion. The suppression for the unbalanced, transparent
stimuli is significantly less than that for the balanced, non-transparent
stimuli. Therefore, the activity in the second, MT stage correlates
better with the perception of motion transparency than the first, V1
stage which does not distinguish reliably between transparent and
non-transparent motion.
The above experiments suggest a two stage model of motion perception
with a motion measurement stage in V1 and an opponent-direction
suppression stage in area MT. In this paper we explicitly test
this model through analysis and computer simulations, and compare the
response of the model to the perceptual and physiological results
using the same balanced and unbalanced stimuli we used in the
experiments. In the first stage of the computational model, motion
energies in different spatial frequency and disparity ranges
are extracted from each local region. Similar to V1, this stage does
not distinguish between the balanced and unbalanced stimuli. In the
subsequent stage motion energies of opposite directions but with same
spatial frequency and disparity contents suppress each
other using subtractive or divisive inhibition. This stage responds
significantly better to the transparent stimuli than to the
non-transparent ones, in agreement with MT activity.
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