Modification of visually guided saccades by a nonvisual afferent feedback signal

PURPOSE. To investigate the role of extraocular muscle afferent signals in the control of saccadic eye movements. METHODS. A suction scleral contact lens was used to impede the movements of the right eye while subjects executed visually guided saccades to briefly presented targets. Movements of the left eye were measured using infrared o culography. Saccade amplitude, peak velocity, and duration were analyzed tr ial by trial and compared before, during, and after the right eye was imped ed. RESULTS. When the right eye was impeded, the amplitudes of saccades execute d by the left eye were reduced. There was no alteration in the main sequenc e relationships. Thr amplitude effect had a rapid onset and offset. There w as no evidence that the effects built up over a number of trials, nor was t here evidence that individual saccades were modified on-line. CONCLUSIONS. These results are consistent with the hypothesis that extraocu lar muscle afferent signals provide a feedback signal of the movements of t he eyes that is used to produce rapid adjustments of oculomotor output when required.