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 oculography. Saccade amplitude, peak velocity, and duration were analyzed trial by trial and compared before, during, and after the right eye was impeded. RESULTS: When the right eye was impeded, the amplitudes of saccades executed by the left eye were reduced. There was no alteration in the main sequence relationships. The amplitude effect had a rapid onset and offset. There was no evidence that the effects built up over a number of trials, nor was there evidence that individual saccades were modified on-line. CONCLUSIONS: These results are consistent with the hypothesis that extraocular muscle afferent signals provide a feedback signal of the movements of the eyes that is used to produce rapid adjustments of oculomotor output when required.