A motion illusion generated by afternystagmus suppression.

After a period of prolonged unidirectional smooth pursuit, the tracking target is seen to drift in the opposite direction when it is stopped, even though its retinal image is stationary. If, however, the tracking target is extinguished during the post-adaptive period, the eyes continue to drift in the tracking direction, a phenomenon known as pursuit afternystagmus. It is proposed that the visual system, in an effort to maintain fixation upon the target, produces a motor signal in the opposite direction in order to offset the residual afternystagmus. The perceptual registration of this efferent signal may then produce the motion illusion.