Visual Cortical Activation During Auditory Word Categorization: Evidence for Multiple Sensory Interaction From Normal Sighted Participants

Sensory substitution has been reported in recent brain imaging studies with blind people and others with sensory deficits so that sensory cortical regions traditionally considered unimodal respond to stimulation from other sensory modalities. Similar effects are also found for normal sighted people with sensory deprivation (blindfolded), indicative of pre-existing neuronal pathways for multiple sensory interactions. Such pathways are considered latent in that they only become unmasked or potentiated in the event of sensory deafferentation, although whether sensory deprivation is necessary to expose these pathways is unclear due to inconclusive evidence. With a relatively strong power in experimental design, visual cortical activation was observed when normal sighted participants (not blindfolded) judged whether auditorily-presented nouns referred to artificial or natural objects. The results suggest the above mentioned pathways can be exposed without sensory deafferentation and therefore are not totally latent. This establishes a boundary condition constraining theoretical models for the neural basis of multiple sensory interactions.