A horse race between independent processes: evidence for a phantom point of no return in preparation of a speeded motor response.

Electromyographic (EMG) data show that a speeded elbow extension response can be interrupted at any time after its execution. Submaximal, or partial, EMG data are also observed in some cases, from which 2 alternatives were considered. The partial response might in fact be interrupted early in response production or, alternately, it might arise from stopping processes that incompletely suppress the response production processes prior to their execution. An interrupted response is easily accounted for by a horse race between independent response production and stopping processes, whereas a partial response can only be reconciled if leakage between the two processes is allowed for. If the distinction between an interrupted and a partial response is correct, then the data yielded evidence for a phantom point of no return that locates late in the premotor component of the response and, thus, prior to the onset of EMG activity.