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Abstract:
Aim. To investigate the time course of activations in a
mixed-trial version of the Counting Stroop task (Bush et al, 1998)
using high-density ERPs. Methods. Eight healthy volunteers viewed
1-4 identical words, and reported the number of words by pressing
one of four keys. Three trial-types were used: Incongruent number
words (50%), Congruent number words, and Neutral words (25% each).
RT and errors were also recorded. Performance. In the RT analysis,
Incongruent trials were slower than both Neutral (I-N, mean=43
msec, p<.0001) and Congruent trials (I-C, mean=70 msec,
p<.0001). In the error analysis, more errors were found for
Incongruent relative to Congruent and Neutral trials (p<.002 and
p<.003, respectively). ERP effects: Incongruent vs. Congruent.
Four significant effects were found. 300-400 msec. Both Congruent
and Incongruent number words relative to neutral words similarly
engaged left prefrontal cortex. 400-500 msec. Congruent and
Incongruent numbers showed a positive wave over left superior
parietal region. Activation for the Congruent words was greater.
This effect may reflect the successful matching of the meaning of
the word with the outcome of the counting operation. 500-600 msec.
However, incongruence was accompanied by an additional positivity
over anterior medial prefrontal scalp (Anterior Cingulate),
suggesting conflict monitoring. 700-800 msec. Incongruent number
words presented greater positivity over the left temporoparietal
region, indicating the need for additional processing of the word
meaning.
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