Enhancement of motion perception in the direction opposite to smooth pursuit eye movement

When eyes track a moving target, a stationary background environment moves in the direction opposite to the eye movement on the observer's retina. Here, we report a novel effect in which smooth pursuit can enhance the retinal motion in the direction opposite to eye movement, under certain conditions. While performing smooth pursuit, the observers were presented with a counterphase grating on the retina. The counterphase grating consisted of two drifting component gratings: one drifting in the direction opposite to the eye movement and the other drifting in the same direction as the pursuit. Although the overall perceived motion direction should be ambiguous if only retinal information is considered, our results indicated that the stimulus almost always appeared to be moving in the direction opposite to the pursuit direction. This effect was ascribable to the perceptual dominance of the environmentally stationary component over the other. The effect was robust at suprathreshold contrasts, but it disappeared at lower overall contrasts. The effect was not associated with motion capture by a reference frame served by peripheral moving images. Our findings also indicate that the brain exploits eye-movement information not only for eye-contingent image motion suppression but also to develop an ecologically plausible interpretation of ambiguous retinal motion signals. Based on this biological assumption, we argue that visual processing has the functional consequence of reducing the apparent motion blur of a stationary background pattern during eye movements and that it does so through integration of the trajectories of pattern and color signals.