With each movement of the eyes, there are changes in the state of the neural processes that generate eye movements and changes in the perceptual frame of reference. We have electrically stimulated the superior colliculus at various times around visually guided eye movements to understand the collicular contribution to these changes. When the colliculu is stimulated during periods of fixation, the amplitude and direction of th saccadic eye movement is rather constant. When the same stimulation is applied while an eye movement is in progress, there is a systematic shift in the direction of the evoked eye movement. Just as the eye begins to move toward a visual target, the eye movement evoked by stimulation of the colliculus is rotated in a direction opposite to the primary visual saccade by as much as 80 degrees. Electrical stimulation that is applied at progressively later times during the visually guided eye movement will evoke eye movements with progressively less shift. These data suggest that the colliculus participates in the changes in spatial reference during eye movements or that there is a gradual decay in the integration process that the colliculus provides to the oculomotor system.
