Preparation and inhibition of interceptive actions.

Two experiments aimed to provide an estimate of the last moment at which visual information needs to be obtained in order for it to be used to initiate execution of an interceptive movement or to withhold execution of such a movement. In experiment 1, we sought to estimate the minimum time required to suppress the movement when the participants were first asked to intercept a moving target. In experiment 2, we sought to determine the minimum time required to initiate an interceptive movement when the participants were initially asked to keep stationary. Participants were trained to hit moving targets using movements of a pre-specified duration. This permitted an estimate of movement onset (MO) time. In both experiments the requirement to switch from one prepared course of action to the other was indicated by changing the colour of the moving target at times prior to the estimated MO. The results of the experiments showed that the decision to execute or suppress the interception must be made no less than about 200 ms before MO.