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Abstract:
he N2pc component (N2 posterior contralateral) of the
event-related potential (ERP) recorded during visual search tasks
has been shown to reflect an attentional process that serves to
filter out competing information from distractor items (Luck et
al., 1997). The N2pc appears about 180-350 ms after stimulus onset
as a negative voltage-deflection over occipital sites contralateral
to the target in a bilateral stimulus array. Apart from the well
defined time course of the N2pc in the EEG, information about its
cortical origin is currently imprecise. The present study was aimed
at providing more detailed information about the topographical
distribution by using combined recordings of MEG (148-channel
magnetometer, BTI) and EEG (32-channel). Magnetic source
localization was computed based on realistic head models
(individual anatomical MRI scans). Subjects were required to
perform a color-orientation discrimination task in a bilateral
stimulus array which elicited a typical N2pc component of the ERP
with a contralateral occipital scalp distribution. MEG source
reconstruction indicated that at least two sources contribute to
the magnetic field in the N2pc time range. In particular, an early
source (around 200 ms) over the parietal cortex is followed by a
source arising from the occipital-temporal cortical region. Hence,
the present data indicate that the N2pc does not reflect a unique
cortical process and the localization and the time course of the
contributing sources is particularly revealing as to the functional
roles of parietal and occipital-temporal cortical regions in
attentional orienting. Luck, S.J., Girelli, M., McDermott, M.T.,
Ford M.A. Bridging the gap between monkey neurophysiology and human
perception: an ambiguity resolution theory of visual selective
attention. Cognit Psychol 1997,33(1):64-87
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