| |
Abstract:
We examined the timecourse and scalp-topography of
auditory-somatosensory (A-S) neural response interactions in
humans, using high-density (128-channel) electrical mapping.
Stimuli were vibrotactile stimulation of the thumb and index finger
of either hand and noise bursts at speakers placed next to each
hand. Stimuli appeared either unimodally or bimodally in either
conjunctive (same side) or disjunctive (different sides)
combinations. Subjects performed a simple RT task via foot-pedal
responses while centrally fixating. ERPs to bimodal stimuli were
compared to summed ERPs from the corresponding unimodal conditions.
These would be equivalent if neural responses to the unimodal
stimuli were independent, whereas divergence indicates neural
response interactions. We previously demonstrated A-S neural
response interactions at ~50ms during passive conditions (Foxe et
al., Cog. Brain Res., 2000). In this study, both conjunctive and
disjunctive bimodal stimulus combinations yielded similar
interaction effects. The topography and timing of these interaction
effects suggests multisensory integration early in the cortical
processing hierarchy, in brain areas traditionally thought to be
unisensory. RTs were faster to bimodal than to unimodal stimuli,
demonstrating a redundant target effect (RTE). However, probability
summation could fully account for this RTE. Although multisensory
A-S neural response interactions occur early in cortical
processing, they need not be invoked mechanistically to describe
the RT facilitation of the RTE.
|
