Go-activation endures following the presentation of a stop-signal: Evidence from startle

It has been proposed that in a stop-signal task (SST), independent go- and stop-processes "race" to control behaviour. If the go-process wins, an overt response is produced, while if the stop-process wins, the response is withheld. One prediction that follows from this proposal is that if the activation associated with one process is enhanced, it is more likely to win the race. We looked to determine whether these initiation and inhibition processes (and thus response outcome) could be manipulated by using a startling acoustic stimulus (SAS), which has been shown to provide additional response activation. In the present study participants were to respond to a visual go-stimulus; however, if a subsequent stop-signal appeared they were to inhibit the response. The stop-signal was presented at a delay corresponding to a probability of responding of 0.4 (determined from a baseline block of trials). On stop-trials a SAS was presented either simultaneous with the go-signal or stop-signal, or 100, 150, or 200 ms following the stop-signal. Results showed that presenting a SAS during stop-trials led to an increase in probability of responding when presented with or following the stop-signal. The latency of SAS responses at the stop-signal+150 ms and stop-signal+200 ms probe times suggests they would have been voluntarily inhibited but instead were involuntarily initiated by the SAS. Thus, results demonstrate that go-activation endures even 200 ms following a stop-signal and remains accessible well after the response has been inhibited, providing evidence against a winner take all race between independent go- and stop-processes.

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