Absence of coactivation in the motor component: evidence from psychophysiological measures of target detection.

Previous research examining response time has supported coactivation under certain conditions. Other research has found more forceful responses to redundant-target than to single-target displays, suggesting coactivation in the motor component. The authors tested for motor coactivation using response time, response force, and other psychophysiological measures. Experiments 1 and 2 showed that response force is determined by the number of stimuli, not the number of targets, when target-distractor discriminations are required. In Experiment 3, 1 stimulus was presented on each trial, and the number of target features was varied. The response time results showed that coactivation occurred somewhere in the information-processing system, but no evidence of motor coactivation was found using any psychophysiological measure. These data disconfirm the motor-coactivation hypothesis for tasks that require visual discriminations.