Saccadic countermanding: a comparison of central and peripheral stop signals.

We compared the effectiveness of central and peripheral targets in a saccadic countermanding task. Stop-signal reaction times (SSRTs) do not differ significantly for central and peripheral stop signals. Further, when central and peripheral stop signals are presented together, SSRTs behave as expected of independent processes in parallel. A linear rise-to-threshold race model (LATER) with independent go and stop processes describes the behavioural data successfully, predicting not only the latency distribution of saccades that escaped inhibition, but also the probability of successful countermanding. Central and peripheral stop signals appear to act independently and with equal effectiveness.