Journal of Neuroscience, Vol 14, 7357-7366, Copyright © 1994 by Society for Neuroscience
Transparent motion perception as detection of unbalanced motion signals. I. Psychophysics
N Qian, RA Andersen and EH Adelson
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02139.
Our visual system can solve the difficult problem of representing multiple
motions in the same part of the visual space, the motion transparency
problem. We investigated the conditions under which transparent motion
perception occurs through psychophysical observations, using a series of
visual displays composed of two simple patterns moving in opposite
directions. We found that whenever a display has finely balanced opposing
motion signals in all local regions, it is perceptually nontransparent. The
displays that appeared transparent always contain locally unbalanced motion
signals, with some local regions having net motion signals in one direction
and some other regions in the opposite direction. These interdigitating net
motion signals in both directions appear to be integrated separately to
form two overlapping transparent surfaces. Displays that were spatially
balanced could be made perceptually transparent if the two components
moving in opposite directions were at different stereo depth planes or had
different spatial frequency contents. Our results can be explained by
proposing a disparity- and spatial frequency-specific suppression stage in
the motion pathway, at which motion signals of different directions, but of
the same disparity and spatial frequency contents, locally inhibit each
other. Such a mechanism would suppress noise input to the motion system,
which generally activates several direction channels simultaneously, and
would still not eliminate activity evoked by transparent surfaces that are
at different depths or have different textures.
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