Surround Motion Silences Signals From Same-Direction Motion

The response of motion-sensitive neurons to stimuli presented within their receptive field is often affected by stimulation in the surrounding region. These effects have perceptually relevant consequences that can be measured using behavioral techniques. We used psychophysical reverse correlation to characterize directional selectivity in human observers while they processed a local motion stimulus and studied the effect of adding an additional motion signal in the surrounding region. The surround had no effect on response gain for signals of opposite direction but selectively reduced gain for those of same direction. Surprisingly this reduction was close to 100%, effectively amounting to a gating process whereby signals of same direction were completely silenced. Our data indicate that by far the most prominent perceptual manifestation of center-surround antagonism is gain suppression by motion in the same direction without any appreciable change in directional tuning.