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Abstract:
Varying the foreperiod (FP) between a warning stimulus and an
imperative stimulus within a block of trials induces a specific
pattern of sequential effects: the response on trial N is slower
when the FP of that trial (i.e., FPn) is shorter than FPn-1 than
when it is as long as or longer than FPn-1. This effect has been
explained by increased motor activation on trial N at the moment
that the imperative stimulus occurred on trial N-1. This hypothesis
was tested by using the contingent negative variation (CNV) and the
lateralized readiness potential (LRP) as psychophysiological
indices of motor activation or preparation. The letter L or R
required a button press with the middle or index finger of one
hand, and the letter was preceded by a tone with an FP of either
500, 1500 or 2500 ms. The required response hand was varied between
blocks. The behavioral results showed the expected pattern. When
FPn was larger than 500 ms, both the CNV and the LRP were more
negative around 500 ms when FPn-1 was 500 ms than when it was 1500
or 2500 ms. These results confirm the proposed hypothesis.
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