Reduced flexibility of cognitive control: reactive, but not proactive control, underpins the congruency sequence effect.

The congruency sequence effect (CSE) refers to facilitated conflict processing following incongruent than congruent trials, and reflects enhanced cognitive control during conflict processing. Although this effect is mostly conceived as being reactive, proactive control can also unlock it under specific circumstances according to previous studies (e.g., when an informative cue is used). However, whether or not humans can flexibly switch between these two complementing control modes remains unclear. To address this question, 55 participants completed the confound-minimized Stroop task in different blocks where the cue about the upcoming trial's congruency was either informative or not, and orthogonally to it, the cue-stimulus interval (CSI) was either short or long. We tested if the size of the CSE could change depending on the specific combination of these two factors, which would indicate that cognitive control depends on the subtle balance between reactive and proactive control, and is therefore flexible. However, results showed that the CSE was significant and comparable across the four combinations of CSI and Cue type, suggesting that it primarily stemmed from reactive control. We discuss our results against the dual mechanism of control (DMC) framework (Braver in Trends Cogn Sci 16:106-113, 2012).