Suppression of motion-produced smear during smooth pursuit eye movements.

Humans make smooth tracking eye movements to keep the image of a moving target on the foveal region of the retina and, thereby, maintain acute vision. Although the images of physically stationary background stimuli sweep across the retina during smooth pursuit eye movements, non-pursued targets are usually perceived to be neither moving nor smeared. The lack of perceived movement of background stimuli is generally attributed to a 'cancellation' of the retinal image motion by extraretinal information about the eye movement [1,2]; this information comes primarily from a neural facsimile of the efferent command to move the eyes, augmented by afferent signals from receptors in the extraocular muscles [3,4]. Here, we show that a physically stationary target presented during smooth tracking is perceived to have considerably less smear than a target that moves comparably across the retina, but when the eye is stationary. This result implies that extraretinal signals for pursuit eye movements also contribute to the alleviation of perceived smear for non-tracked, background targets.