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Abstract:
Event related potentials (ERPs) were used to examine
mechanisms of selective processing of stimuli across sense
modalities and spatial locations. Lateralized stimuli were
asynchronously presented in the auditory, visual, and tactile
sensory modalities. Thus, there were always stimuli presented on
six stimulus channels (left and right: auditory, visual, and
tactile). Subjects were asked to selectively attend to one of these
six channels while ignoring stimuli presented on the other five
concurrently presented channels. Attentional focus was assessed by
requiring subjects to respond to occasional deviant stimuli
(intensity increments) in the attended channel. Statistical
analysis confirmed that ERPs elicited by focally attended stimuli
in a specific sense modality and hemispace were enhanced (starting
as early as 80 ms) relative to ERPs elicited by these same stimuli
when they were nonattended and in the hemispace opposite to the
focus of attention. This difference diminished when comparing ERPs
elicited by these same nonattended stimuli when the focus of
attention was on a different modality but the same hemispace. This
smaller difference was due to an apparent enhancement between
250-600 ms of the ERPs elicited by nonattended stimuli,
particularly at electrodes over parietal areas. These results
confirm earlier findings in our lab which suggest that hemispace
represents a fundamental feature along which stimulus
representations are encoded as the basis for selective attention
across sensory modalities.
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