SPATIAL AND TEMPORAL FACTORS DETERMINE AUDITORY-VISUAL INTERACTIONS IN HUMAN SACCADIC EYE-MOVEMENTS

In this paper, we show that human saccadic eye movements toward a visu al target are generated with a reduced latency when this target is spa tially and temporally aligned with an irrelevant auditory nontarget. T his effect gradually disappears if the temporal and/or spatial alignme nt of the visual and auditory stimuli are changed. When subjects are a ble to accurately localize the auditory stimulus in two dimensions, th e spatial dependence of the reduction in latency depends on the actual radial distance between the auditory and the visual stimulus. if howe ver, only the azimuth of the sound source can be determined by the sub jects, the horizontal target separation determines the strength of the interaction. Neither saccade accuracy nor saccade kinematics were aff ected in these paradigms. We propose that, in addition to an aspecific warning signal, the reduction of saccadic latency is due to interacti ons that take place at a multimodal stage of saccade programming, wher e the perceived positions of visual and auditory stimuli are represent ed in a common frame of reference. This hypothesis is in agreement wit h our finding that the saccades often are initially directed to the av erage position of the visual and the auditory target, provided that th eir spatial separation is not too large. Striking similarities with el ectrophysiological findings on multisensory interactions in the deep l ayers of the midbrain superior colliculus are discussed.