ONLINE COMPENSATION OF GAZE SHIFTS PERTURBED BY MICRO-STIMULATION OF THE SUPERIOR COLLICULUS IN THE CAT WITH UNRESTRAINED HEAD

Prior studies have led to the gaze feedback hypothesis, which states t hat quick orienting movements of the visual axis (gaze shifts) are con trolled by a feedback system. We have previously provided evidence for this hypothesis by extending the original study of Mays and Sparks (1 980) to the cat with unrestrained head (Pelisson et al. 1989). Vile sh owed that cats compensated for a stimulation-induced perturbation of i nitial gaze position by generating, in the dark, an accurate gaze shif t towards the remembered location of a flashed target. Tn the present study, we investigate goal-directed gaze shifts perturbed ''in flight' ' by a brief stimulation of the superior colliculus. The microstimulat ion parameters were tuned such that significant perturbations were ind uced without halting the movement. The ambient Light was turned off at the onset of the gaze shift, suppressing any visual feedback. We obse rved that, following stimulation offset, the gaze shift showed tempora l and spatial changes in its trajectory to compensate for the transien t perturbation. Such compensations, which occurred ''on-line'' before gaze shift termination, involved both eye and head movements and had d ynamic characteristics resembling those of unperturbed saccadic gaze s hifts. These on-line compensations maintained gaze accuracy when the s timulation was applied during the early phase of large and medium (abo ut 60 and 40 degrees) movements. These results are compatible with the notion of a gaze feedback loop providing a dynamic gaze error signal.