The present research measured participants’ event-related brain activity while they performed a Stroop-priming task that induced the implementation of expectancy-based strategic processes. Participants identified a colored (red vs. green) target patch preceded by a prime word (GREEN or RED), with incongruent prime-target pairings being more frequent (75 %) than congruent pairs (25 %). The prime-target stimulus onset asynchrony (SOA) was manipulated at two levels: 300 vs. 700 ms. Participants also performed a change localization task to assess their working memory capacity (WMC). At the 300 ms SOA, all participants presented a Stroop-priming congruency effect (slower responses on incongruent than on congruent trials) and an increased N2 amplitude in incongruent trials, irrespective of their WMC. At the 700-ms SOA, the lower-WMC group showed again a larger negative-going waveform to incongruent targets, whereas the higher-WMC group exhibited a reversed Stroop-priming congruency effect (faster responses to incongruent targets) and the N2 component was absent.
Working memory (WM) is the cognitive system that allows us to actively retain and manipulate a limited amount of internal information (e.g., Baddeley, 1986). WM function is not only important for storage and manipulation of information but also supports attentional selection: WM maintains the goal-directed focus on the relevant aspects of the environment, while actively blocking the processing of irrelevant or distracting information (e.g., Gazzaley & Nobre, 2012; Kane, Bleckley, Conway, & Engle, 2001; Lavie, Hirst, de Fockert, & Viding, 2004).
A line of investigation that provides direct evidence for a close association between WM and selective attention uses a methodological strategy based on "extreme-groups", in which WM capacities of a large sample of participants are first assessed by means of several WM tasks. Participants showing higher and lower scores on those tasks (e.g., first vs. fourth quartiles) are then required to perform selective attention tasks. For instance, when participants have to name the ink color of a color word in a conventional Stroop task, individuals with a high WM capacity (WMC) are usually more effective at selectively attending to the relevant ink color and at suppressing the influence of the irrelevant name of the color word, compared to low-WMC participants. Similar differences between high-WMC and low-WMC individuals have been reported in other selective attention tasks (e.g., Ahmed & De Fockert, 2012; Conway, Tuholski, Shisler, & Engle, 1999; Kane & Engle, 2003; Kiefer, Ahlegian, & Spitzer, 2005; Megías, Ortells, Noguera, Carmona, & Marí-Beffa, 2020; Ortells, Noguera, Alvarez, ´ Carmona, & Houghton, 2016; see also Wiemers & Redick, 2018).