The functional role of the task-irrelevant stimulus feature in the congruency sequence effect.

Humans have to deal with conflicting information. This is studied in conflict tasks such as the Simon task or the flanker task. For example, participants respond with the left or right hand to the color of a stimulus (task-relevant stimulus feature) which is presented in a left or right position (irrelevant feature) in the Simon task or to a letter (relevant) which is flanked by same or different letters (irrelevant) in the flanker task. In incongruent trials, in which relevant and irrelevant stimulus features require different responses, reaction time is longer and errors are more frequent. This congruency effect is reduced after incongruent trials, dubbed congruency sequence effect (CSE). Here, we show that with temporally separated presentations of relevant and irrelevant stimulus features in the Simon task the CSE is strong with leading irrelevant feature, but declines with leading relevant feature. For the flanker task, this modulation of the CSE was unreliable. By means of an extended leaky, competing accumulator model, we contrasted two mechanisms of the CSE for the Simon task: gating of the irrelevant stimulus information and re-mapping of the stimulus positions to response positions after incongruent trials. The gating model failed to account for some aspects of the observed data which could be simulated by the re-mapping model. For the flanker task, there was not only a CSE, but also overall longer reaction times after incongruent trials. This required an extension of the re-mapping model in terms of higher response thresholds after incongruent than after congruent trials. (PsycInfo Database Record (c) 2025 APA, all rights reserved).