V1 Responses to Transparent and Non-transparent Motions
Ning Qian and Richard A. Andersen, Exp. Brain Res., 1995, 103:41-50.
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It is well known that a stimulus composed of two independent sets of
random dots moving in opposite directions produces a percept of two
overlapping transparent surfaces moving across each other while a
counterphase grating consisted of two identical sine wave gratings
drifting in opposite directions does not. We recorded from the
directionally selective V1 cells of behaving macaque monkeys using
these two types of stimuli in order to investigate the physiological
basis of transparent motion perception. Previous single unit
recording experiments from our laboratory indicated that many V1 cells
respond well to transparent random dot patterns while MT cells'
responses to the same patterns are strongly suppressed in comparison
with their preferred direction responses. This observation alone
would seem to suggest that V1 activity could better explain
transparent motion perception than MT activity. However, one could
argue to the contrary based on the psychophysical observation that
there is a motion threshold elevation under the transparency
condition. We decided to determine the correlation between V1
activity and the transparent motion perception directly by recording
from V1 cells using both transparent random dot patterns and
non-transparent counterphase gratings. It is found that V1 cells on
the average could not reliably tell the two types of patterns apart.
Our results lend further notion to the idea that additional processing
beyond V1 is involved in transparent motion analysis.
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