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Abstract:
In humans, there is little evidence of a delayed response
deficit after a frontal lesion. Two aspects underlie delayed
responses: working memory and response preparation. Working memory
capacity is not strongly affected after a frontal excision (Richer
et al., 1996). However, response preparation processes may be
affected. We tested this question by looking at reaction time (RT)
in a delayed choice response task, in nine frontal patients, nine
temporal patients and nine control subjects. We manipulated the
temporal predictability of the response in four conditions in which
subject responded either: 1) as soon as the choice stimulus
appeared, 2) after a short unpredictable delay (1.00-1.50 s), 3)
after a long unpredictable delay (4.75-5.25 s), or 4) after a long
delay filled with a visual countdown cueing the arrival of the
response signal. Frontal patients showed normal RT and error rates.
However, their inter-trial RT variance was increased when the
response signal was unpredictable, but not when the response signal
was cued. These results suggest that the temporal programming of
response preparation is affected after a frontal lesion.
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