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Abstract:
Efficient selection of a particular mode of response when
switching between tasks appears to involve the suppression of
alternative response modes, particularly when those alternatives
are more habitual. Such suppression appears to be highly dependent
upon the integrity of the prefrontal cortex, yet other cortical
areas are probably also necessary to implement the switch. For
example, functional brain imaging studies have shown parietal
cortex activation during repeated response mode switching during
translation. We recorded dense-sensor EEG whilst bilingual subjects
named digits in either their first or second language. The
appropriate task (language) was signalled by the digits' colour. A
single language was used consistently throughout 'pure' blocks;
language switches occurred on every second trial within 'mixed'
blocks. Stimulus duration was 1000msec on 50% of trials and 250msec
on the remaining 50%. Responses were required at stimulus offset;
thus, long stimulus duration trials allowed measurement of ERPs
during stimulus and response processing to be free of movement
artefact. ERP components were found over frontal and parietal areas
consistent with activation of the less habitual task, whether in
pure or mixed blocks. Switch-specific effects were evident over
parietal cortex and right frontal cortex and importantly showed
asymmetry across (first or second) languages. Correspondence with a
frontal component found when suppressing responding in a go/no-go
reaction time task may imply similar inhibitory mechanisms for
task- and response- suppression.
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