Eye movements evoked by superior colliculus stimulation in the alert cat.

(1) The electrical stimulation of the superior colliculus (SC) in the cat evokes exclusively conjugate and contraversive eye saccades. (2) Their maximum velocity is markedly higher than that of spontaneous saccades. (3) The stimulus parameters (intensity, frequency, pulse width) have but little effect on the characteristics of the saccades. (4) In the anterior half of the SC, corresponding to the projection of the 12-15 central degrees of the retina, amplitude and direction of saccades depend exclusively on the position of the electrode. (5) In the posterior half, corresponding to the projection of the peripheral retina, saccades are 'goal directed' and the position of the goal is determined by the location of the electrode. (6) An increase in stimulus train length produces, in the anterior part, a succession of identical saccades and, in the posterior part, a goal fixation. (7) Taking all these data into consideration, a model of the foveation process in the cat is proposed.