Spatial attention-determined modifications in saccade trajectories.

Normal subjects were required to make horizontal or vertical saccades at the presentation of visual or acoustic imperative stimuli. The locations of visual imperative stimuli were orthogonal to the required saccade. Before stimulus presentation the subjects were cued about its location and instructed to allocate attention to it without moving the eyes. The main aim of the experiment was to establish whether the trajectory of horizontal saccades would be modified by spatial attention. The results showed that, with respect to the condition in which attention was on the horizontal meridian, the allocation of attention to the upper hemifield determined a downward saccade deviation, while the allocation to the lower hemifield determined an opposite deviation. The data strongly support the view that spatial attention and saccade programming share the same neural substrates.