Post-stop-signal slowing: strategies dominate reflexes and implicit learning.

Control adjustments are necessary to balance competing cognitive demands. One task that is well-suited to explore control adjustments is the stop-signal paradigm, in which subjects must balance initiation and inhibition. One common adjustment in the stop-signal paradigm is post-stop-signal slowing. Existing models of sequential adjustments in the stop-signal paradigm suggest that post-stop-signal slowing may be based solely on the events of the previous trial, suggesting that post-stop-signal slowing is a reflexive byproduct of a stop signal. Alternatively, post-stop-signal slowing could be the result of implicit learning or strategic adjustment. The authors report three experiments that manipulated the probability of stop trial repetition and found that these contingencies eliminate, reverse, or greatly increase post-stop-signal slowing. When the contingency was not instructed or cued, modest adjustments of post-stop-signal slowing occurred, suggesting implicit learning. When the contingency was cued, performance adjustments occurred on the next trial, suggesting that strategies dominated post-stop-signal slowing. These results show that post-stop-signal slowing is not a reflexive byproduct of the stop signal. The large changes in strategy accompany large changes in task factors, suggesting that the modest post-stop-signal slowing usually observed may be a result of the relatively static task environment that does not encourage large strategic changes.