BEHAVIOR AND PHYSIOLOGY OF THE MACAQUE VESTIBULOOCULAR REFLEX RESPONSE TO SUDDEN OFF-AXIS ROTATION - COMPUTING EYE TRANSLATION

The vestibule-ocular reflex (VOR) has historically been considered a c omputationally simple reflex: to stabilize images on the retina agains t imposed head rotation, the eyes must be counterrotated by an equal a mount in the opposite direction. During almost any head rotation, howe ver, the eyes are also translated. We show that the VOR compensates fo r 90% of this translation, and suggest a computational scheme by which this is done, based on a temporal dissection of the VOR response to s udden head rotation. An initial response that corrects only for impose d rotation is refined by a series of three temporally delayed correcti ons of increasing complexity. The first correction takes only head rot ation and viewing distance into account; the second, head rotation, vi ewing distance, and otolith translation; and the third, head rotation, viewing distance, otolith translation, and translation of the eyes re lative to the otoliths. Responses of type I gaze velocity Purkinje (GV P) cells in the cerebellar flocculus and ventral paraflocculus of rhes us monkeys were recorded during sudden head rotation. We show that cel l discharge was modulated both by axis location and by viewing distanc e, suggesting that GVP cells play a role in the VOR response to rotati on-induced eye translation.