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B. E. Stein, B. A. Rowland, T. J. Perrault, Jr., S. Pluta; The Influence of Competing Stimuli on Visual-Nonvisual Integration. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6455.
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Physiological and behavioral responses to visual stimuli can be significantly influenced by the presence of inputs from other sensory modalities, a phenomenon known as "multisensory integration." This process is particularly evident in the superior colliculus (SC), a midbrain structure involved in gaze shifts. Spatiotemporally concordant visual and non-visual stimuli significantly enhance the responsiveness of individual multisensory SC neurons and the probability of detecting and localizing the initiating event; whereas simultaneous but spatially disparate visual-nonvisual stimuli do the opposite (the "spatial principle of multisensory integration").
Most single neuron electrophysiological studies of this phenomenon have been limited to circumstances in which stimuli are presented against blank backgrounds - circumstances very unlike those commonly encountered in non-laboratory environments, and circumstances that eliminate the influences of stimuli outside a neuron’s multisensory receptive fields (i.e., stimuli that are "eccentric" instead of "centric"). Here we demonstrated the potent influence of these "eccentric" stimuli, results that were striking and not predictable from what is presently known about visual-nonvisual interactions or the structure of SC receptive fields.
As predicted, single eccentric modality-specific stimuli (either visual or auditory) moderately suppress the effectiveness of a within-field visual stimulus. However, an eccentric cross-modal (visual-auditory) stimulus had a far stronger effect, generally eliminating even robust responses to a within-field visual stimulus, and did so even when suppressive surrounds could not be demonstrated for both stimulus modalities. In contrast, when the same cross-modal stimulus was eccentric it barely exerted a suppressive effect on the within-field cross-modal response, resulting in a large increase in multisensory enhancement.
These data suggest that, contrary to current thinking, "multisensory integration" is most potent when there are competing environmental events, especially when those events contain cross-modal stimuli.
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