Fig. 1.

Schematic representation of the experimental tasks. a Fixation Task. Either an acoustic or visual target was presented anywhere in the frontal hemifield without behavioral requirements. The subject was instructed to respond by looking at the perceived location of the sources. b Memory-saccade task. This task started with a fixation LED presented straight ahead. During fixation, a target was presented elsewhere in the frontal hemifield. The subject’s task was to remember the position of the target while maintaining fixation and to look at it when the fixation LED was turned off. Trials in which the subject oriented to the target before the fixation LED was turned off were immediately terminated. c Dissociated saccade task. A red fixation LED flashing at 5 Hz signaled to the subject the presentation of a trial of this type. The subject was required to fixate the flashing LED at (0°, 0°) or (±16°, 0°) and to align the head with it. Next, a green LED was presented from the same position or either from the left or the right (±16°, 0°) of the subject. The subject was instructed to direct his gaze to the green LED without moving his head; this accomplished the dissociation of eye and head position. Coinciding with the offset of the green LED an acoustic target was presented elsewhere in the frontal hemifield. In some trials the red flashing LED straight ahead turned solid green, effectively aligning the eyes and the head at the starting position. The subject was required to look at the perceived location of the target at the offset of the green LED