Separate signals for target selection and movement specification in the superior colliculus.

At any given instant, multiple potential targets for saccades are present in the visual world, implying that a "selection process" within the brain determines the target of the next eye movement. Some superior colliculus (SC) neurons begin discharging seconds before saccade initiation, suggesting involvement in target selection or, alternatively, in postselectional saccade preparation. SC neurons were recorded in monkeys who selected saccade targets on the basis of motion direction in a visual display. Some neurons carried a direction-selective visual signal, consistent with a role in target selection in this task, whereas other SC neurons appeared to be more involved in postselection specification of saccade parameters.