AbstractLogan & Cowen (1984) proposed that in a stop-signal task (SST) independent go- and stop-processes "race" such that if the go-process wins, an overt response is produced, while if the stop-process wins, the response is withheld. Based on this model, one could predict that if a process is provided with additional activation, it would be more likely to win the race. A startling acoustic stimulus (SAS) has been shown to provide added activation, resulting in early release of a response. In the present study a SAS was employed to manipulate response outcome by adding activation to either the go- (prior to the stop-signal) or stop-process (after the stop-signal). Participants produced an isometric wrist extension in response to a visual go-stimulus (green), however, if a subsequent stop-signal appeared (stimulus turned red) they were to inhibit the response. Participants completed 100-trials in a SST, including 25 stop-signal trials presented at a fixed delay corresponding to a probability of responding of 0.4 (determined from a baseline block). On stop-signal trials a SAS was presented either with the go-signal, with the stop-signal, stop-signal+100, stop-signal+150, or stop-signal+200ms. Results showed that presenting a SAS during stop-trials led to an increase in probability of responding regardless of whether the SAS was presented before or after the stop-signal. The increase in probability of responding suggests that activation related to the go-response increases rapidly following the go-signal and remains high after the presentation of the stop-signal (when the stop-process is inhibiting the response). This suggests the two processes interact rather than remain independent.
Acknowledgments: Supported by the Natural Sciences and Engineering Council of Canada & the Ontario Graduate Scholarship Program