The ability to inhibit an earlier intended action in a stop-signal task is commonly assessed using the measures of latency and probability. The usual findings from stop-signal trials of lower response probabilities and shorter reaction latencies at reduced stop-signal delays were reported, as described in previous studies in terms of an independent race between stochastic processes (see Logan & Cowan, 1984). In addition, using the less common measure of amplitude, a continuum of reductions in surface EMG onsets was reported. Weakened motor discharges have yet to be explained in terms of a mechanism of inhibitory control. Using computer simulations of neural functioning, the properties of independence and non-independence were examined for their effects on motor pool output in terms of probability, latency, and EMG onsets. The data provided support to question the requirement of independent processes for a theory of inhibitory control.
T. McGarry is with the Faculty of Kinesiology at the University of New Brunswick, Fredericton, New Brunswick, E3B 5A3, Canada. I.M. Franks is with the School of Human Kinetics at the University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.