SPATIAL DISPARITY AFFECTS VISUAL-AUDITORY INTERACTIONS IN HUMAN SENSORIMOTOR PROCESSING

Information from the auditory and visual systems converges in the nerv ous system with physiological and behavioral consequences. Most of our knowledge about the rules governing such convergence has been obtaine d in experiments where the strength or the timing of the individual au ditory and visual stimuli has been varied. Relatively little attention has been paid to the spatial relationship between different modalitie s of stimuli in multisensory experiments. We studied saccadic reaction times of human subjects to bimodal auditory and visual stimulus prese ntations under two conditions: first, with the targets spatially coinc ident and, second, with various degrees of spatial separation or dispa rity. In the first experiment, we found that the saccadic reaction tim es were consistently shorter than would be predicted by independent pr ocessing of information about the visual and auditory targets. These r esults suggest convergence of multimodal information at one or more lo ci within the nervous system. In the second experiment, we found that saccadic latency gradually increased as spatial distance between the a uditory and visual targets increased. Evidence for neural summation wa s found over a wide range of spatial disparities. These results sugges t that multisensory information can be integrated and have significant influences on behavior over a surprisingly large range of spatial dis parity.