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Abstract:
This study investigated the executive processes involved in
switching from one task to another through investigating the
electrophysiological (ERP) correlates evoked in a task-switching
paradigm. On every trial, a stimulus comprised of a letter and a
number was presented. For three successive trials, subjects judged
whether the letter was a vowel or a consonant; for the next three
trials, they judged whether the number was even or odd; this
sequence was repeated. Thus, subjects were required to switch
between the two tasks every third trial. Their ERPs and their
behavioral performance (reaction times and error rates), were
recorded, allowing the comparison of three trial-types: 1) the
first trial after a switch of task ('post-switch' trials); 2) the
second trial after a task-switch ('nested' trials); 3) the trial
immediately preceding a task-switch ('pre-switch' trials). The
executive processes required to switch should have been active
before and/or during successful performance of the 'post-switch'
trials. The ERPs associated with these processes were therefore
sought in a) the late stages of the 'pre-switch' trials, and/or b)
the very early stages of the 'post-switch' trials. The 'nested'
trials provided a baseline against which to compare both the
'pre-switch' and the 'post-switch' trials. In the late stages of
'pre-switch' trials we found activity over frontal and parietal
regions that had dissociable time-courses. This suggests a
fronto-parietal system that is involved in switching between
tasks.
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