Multisensory and Unisensory Integration: Distinct Processes with Distinct Products

Terrence R. Stanford, Neurobiology & Anatomy, Wake Forest Univ. Sch. of Medicine

Abstract
The consequences of integrating information originating from different senses (which include neurophysiological enhancements and the behavioral performance benefits they are believed to foster) are well documented. It is widely assumed that this “multisensory synthesis” yields products distinct from those that can be derived from an individual sense. This assumption rings true when a response to a cross-modal (multisensory) stimulus is considered against the usual benchmark of a response to either of the modality-specific (unisensory) consituents, but rarely considers the possible outcomes of integrating multiple stimuli from within the same modality. In the current study, we compared the products of multisensory and unisensory integration directly in the same cat superior colliculus neurons to determine if the underlying computations are truly distinct. While multisensory (visual-auditory) integration was dominated by additivity and superadditivity, unisensory (two excitatory visual stimuli) integration for the same multisensory neurons was commonly subadditive and virtually identical to that observed for unisensory visual neurons. These observations suggest that differences in input pattern and/or local circuits instantiate different rules for the integration of information from within and across sense modalities in the SC. These findings further highlight the unique contribution of multisensory integration to increasing the salience of external events.

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