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Abstract
When a swinging pendulum is viewed with a light-attenuating filter before one eye,
the pendulum bob is perceived to move in an elliptical path in depth. It is believed
that the filter causes this illusion, the Pulfrich effect, by delaying processing
of the image in the filtered eye relative to that of the unfiltered eye. We sought
a physiological correlate of this effect by studying binocular integration in cortical
neurons of cats while they viewed moving stimuli. Special attention was focused on
single unit disparity tuning because it is widely believed that depth perception is
related to the responses of disparity selective neurons in visual cortex. We found
that placing a filter before one of the cat's eyes produced a temporal delay in the
cortical response. The temporal delay was always associated with a shift in the neuron's
spatial disparity tuning. The observed temporal delays and disparity shifts are comparable
with the magnitude of the Pulfrich effect in humans.