Evidence for interactions between target selection and visual fixation for saccade generation in humans.

We examined the processes controlling selective orientation, specifically the processes required for generating saccadic eye movements in humans. Before a saccadic eye movement can be initiated, active visual fixation must be disengaged from the current point of fixation and a new target selected. We investigated whether these neural processes occur independently or interactively by devising a simple, multimodal choice reaction task in which subjects were asked to direct their gaze away from a central visual fixation target to an eccentric visual target while ignoring a simultaneous auditory distractor. Subjects had more difficulty suppressing incorrect movements toward the distractor when the fixation target was extinguished prior to onset of the eccentric target than when the fixation target remained illuminated during eccentric target presentation. Subjects with the shortest saccadic reaction times produced the most incorrect movements. These results support a recent hypothesis suggesting that the processes of disengaging active visual fixation and selecting a new saccade target are interrelated and arise, at least in part, from a change of activity within the superior colliculus.