Directionalization of visual targets during involuntary eye movement.

Perceived visual direction with respect to one's self (egocentric direction) depends upon the retinal location of a target's image (its oculocentric direction) and concurrent information about the position of the eyes in the head. Information about eye position is presumably obtained from efference copy signals. However, in order to explain illusory target motion that can occur during reflexive eye movements (e.g., post-rotary nystagmus), these signals have been suggested to accompany only voluntary oculomotor responses. In the experiment reported here, manual pointing was used to assess the perceived direction of targets flashed during optokinetic afternystagmus, an involuntary movement of the eyes that occurs in darkness following optokinetic stimulation. Egocentric directionalization was essentially veridical, indicating that accurate eye position information is available during optokinetic afternystagmus. A model is proposed that accounts for illusory target motion during involuntary oculomotor responses by the cancellation of efference copy information about these eye movements with signals of oppositely directed head motion.