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Abstract:
Integration of information from multiple senses is
fundamental to perception and cognition, but how and where this is
accomplished in the brain is not well understood. We examined the
timing and topography of cortical auditory-visual neural
interactions using high-density ERPs during a simple reaction time
(RT) task. Visual and auditory stimuli were presented alone and
simultaneously. ERPs to unisensory presentations were summed
('sum') and compared to the responses to bimodal stimulation
('pair'). Divergence between 'pair' and 'sum' ERPs indicated neural
response interactions. Such interactions were found over visual
areas from 46-66ms and 160-190 ms. Over auditory areas, significant
interactions were found from 50-64 and 110-130 ms. The topography
and timing of the earliest interactions are consistent with a
system of areas in both visual and auditory association cortices
that subserve multisensory auditory-visual interactions,
surprisingly early in the cortical processing hierarchy and in
brain regions traditionally held to be unisensory. Behaviorally,
RTs were faster to bimodal than unimodal presentations, indicative
of a redundant target effect. However, probability summation could
fully account for this RT facilitation, providing no indication
that neural interactions facilitated RT performance. Further
analyses were conducted to assess the relationship of magnitude of
early response interactions to speed of RT.
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