Why do we slow down after an error? Mechanisms underlying the effects of posterror slowing.

People often become slower in their performance after committing an error, which is usually explained by strategic control adjustments towards a more conservative response threshold. The present study tested an alternative hypothesis for explaining posterror slowing in terms of behavioural interferences resulting from error monitoring by manipulating stimulus contrast and categorization difficulty in a choice reaction time task. The response-stimulus interval (RSI) was either short or long, using a between-subject (Experiment 1) and a within-subject design (Experiment 2). Posterror slowing was larger and posterror accuracy lower in short than in long RSI situations. Effects of stimulus contrast disappeared in posterror trials when RSI was short. At long RSIs, stimulus contrast was additive with posterror slowing. The results support the idea that at least two mechanisms contribute to posterror slowing: a capacity-limited error-monitoring process with the strongest influence at short RSIs and a criterion adjustment mechanism at longer RSIs.