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

Abstract

It has been proposed that, in a stop-signal task (SST), independent go- and stop-processes "race" to control behavior. If the go-process wins, an overt response is produced, whereas, 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 outcomes) 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 simultaneously 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 that 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.

New & noteworthy: In this study, a startling acoustic stimulus (SAS) was used to determine whether response outcome could be manipulated in a stop-signal task. Results revealed that presenting a SAS during stop-signal trials led to an increase in probability of responding even when presented 200 ms following the stop-signal. The latency of SAS responses indicates that go-activation remains accessible and modifiable well after the response is voluntarily inhibited, providing evidence against an irrevocable commitment to inhibition.

Keywords: inhibition; initiation; response activation; startling acoustic stimulus; stop-signal task.

Fig. 1.

Probability of responding (p-respond) as a function of startling acoustic stimulus (SAS) probe time. The horizontal dashed line indicates the predicted probability of responding of 0.4. The SAS was presented with the go-signal (GO+SAS), concurrent with the stop-signal (SS+SAS), 100 ms following the stop-signal (SS+SAS100), 150 ms following the stop-signal (SS+SAS150), or 200 ms following the stop-signal (SS+SAS200). The black filled portion of the bars represents the proportion of responses initiated after the presentation of the SAS (SAS responses), and the light gray filled portion represents the proportion of responses initiated before the presentation of the SAS (voluntary responses).

Fig. 2.

Premotor reaction time (RT) during the simple reaction time (SRT) and stop-signal tasks (SST) relative to the respective stimulus. Control go-trial RT was calculated relative to go-signal in both the SRT (black square) and SST (gray square). SAS trial RT was calculated relative to SAS onset in both the SRT (black diamond) and SST (gray diamonds) task blocks. Finally, SST voluntary responses (white circles) were calculated relative to go-signal in the SST task (see results). CTL indicates control go-trials (visual go-signal only). The SAS was presented with the go-signal (GO+SAS), concurrent with the stop-signal (SS+SAS), 100 ms following the stop-signal (SS+SAS100), 150 ms following the stop-signal (SS+SAS150), or 200 ms following the stop-signal (SS+SAS200). The black fill represents data from the SRT task, and the light gray fill represents data from the testing SST block. The squares represent control go-responses, diamonds represent responses initiated after the presentation of the SAS (SAS responses), and the circles represent responses initiated before the presentation of the SAS (voluntary responses). Error bars denote within-subject 95% confidence intervals computed between control go-responses and SAS responses and between voluntary responses.

Fig. 3.

Difference in premotor RT relative to the expected speed of the stop-process for both voluntary initiated and SAS initiated responses when the SAS was presented 150 ms (SS+SAS150) and 200 ms (SS+SAS200) following the stop-signal. A positive value represents a response that was initiated after the expected time needed to successfully stop the response, whereas a negative value represents a response that was initiated before the expected time needed to successfully stop the response. Premotor reaction time - [stop-signal delay (SSD)+ stop-signal reaction time (SSRT)]. The light gray bars represent responses initiated before the presentation of the SAS (voluntary responses), and the black filled bars represent responses initiated after the presentation of the SAS (SAS responses). Error bars denote within-subject 95% confidence intervals (Morey 2008).