Effect of the irrelevant location of the response signal on choice reaction time: An electromyographic study in humans

Choice reaction time (RT) is shorter when the stimulus corresponds spatiall y to the response than when the stimulus does not, even when the stimulus l ocation is irrelevant to the task. We used electromyographic measures to do cument that this effect is the result of a response conflict. The activity of the prime movers of two alternative responses was recorded during the pe rformance of a visual RT task in which the irrelevant spatial correspondenc e between the stimuli and the responses was varied. Only the premotor compo nent of RT was affected by the stimulus-response correspondence. Correct tr ials were distinguished according to whether or not the activation of the p rime mover involved in the required response was preceded by an activation of the prime mover involved in the alternative response. Double muscular ac tivation trials were more numerous for noncorresponding than for correspond ing stimulus-response associations. Furthermore, these trials yielded longe r RTs than the single muscular activation trials.