There is a shift of attention before many eye movements. In recent years, there has been considerable interest in the relationship between attention and eye movements. We have electrically stimulated the superior colliculus to evoke eye movements and evaluated the changes in these evoked eye movements that are induced by attentional and eye movement status of the animal. When monkeys were trained to make eye movements to cued targets, the cueing task caused the electrically evoked eye movement to be shifted toward the cue. This was true whether the cueing was done with a flashed peripheral cue or by a central cue that symbolically indicated the direction of the appropriate target. These data suggest that shifts of attention are intimately linked to the preparation to make eye movements. In other studies, we attempted to determine the organization of the superior colliculus for the generation and coordination of head and eye movements. We have found that the thresholds for evoking eye movements are not the same nor at the same locations as those for evoking head movements. At some sites, stimulation produced very reproducible eye movements, but head movements had considerably more variation. At other sites, the head movements were tightly controlled rather than the eye movement. When we used long-duration trains of stimuli, we were able to evoke multiple head movements, suggesting that these movements are ballistically organized and dissociable from eye movements. We concluded from these data that the colliculus has separate channels for head and eye movements.
