Academic journal article Psychonomic Bulletin & Review

Stroop Proactive Control and Task Conflict Are Modulated by Concurrent Working Memory Load

Academic journal article Psychonomic Bulletin & Review

Stroop Proactive Control and Task Conflict Are Modulated by Concurrent Working Memory Load

Article excerpt

Published online: 26 September 2014

© Psychonomic Society, Inc. 2014

Abstract Performance on the Stroop task reflects two types of conflict-informational (between the incongruent word and font color) and task (between the contextually relevant color-naming task and the irrelevant, but automatic, word-reading task). According to the dual mechanisms of control theory (DMC; Braver, 2012), variability in Stroop performance can result from variability in the deployment of a proactive task-demand control mechanism. Previous research has shown that when proactive control (PC) is diminished, both increased Stroop interference and a reversed Stroop facilitation (RF) are observed. Although the current DMC model accounts for the former effect, it does not predict the observed RF, which is considered to be behavioral evidence for task conflict in the Stroop task. Here we expanded the DMC model to account for Stroop RF. Assuming that a concurrent working memory (WM) task reduces PC, we predicted both increased interference and an RF. Nineteen participants performed a standard Stroop task combined with a concurrent n-back task, which was aimed at reducing available WM resources, and thus overloading PC. Although the results indicated common Stroop interference and facilitation in the low-load condition (zero-back), in the high-load condition (two-back), both increased Stroop interference and RF were observed, consistent with the model's prediction. These findings indicate that PC is modulated by concurrent WM load and serves as a common control mechanism for both informational and task Stroop conflicts.

Keywords Stroop · Working memory · Executive control · Task conflict · Dual mechanism of control

Cognitive control is a key human capacity that enables us to act in a goal-directed and flexible way, freeing us from the constraints of automaticity or stimulus bounds (Miller & Cohen, 2001;Miyakeetal.,2000). For example, in the Stroop task (Stroop, 1935), participants are required to identify the color in which a color word is presented, while ignoring the word meaning. Since word reading is automatic, participants are faced with a need to inhibit the irrelevant words when they are incongruent with their font color (e.g., to respond red to GREEN written in red color). The Stroop interference-slower reaction times (RTs) for incongruent than for neutral stimuli (e.g., XXXX written in red)-and facilitation-faster RTs for congruent (e.g., RED written in red) than for neutral stimuli-effects are an indication of the fact that this selection is not perfect. Nevertheless, the low error rate in normal participants and the increased error rate in patient populations with executive and frontal deficits (Cohen & Servan-Schreiber, 1992) demonstrate the role of the frontal executive control system in mediating this top-down selection and suppressing automatic responses (Cohen, Dunbar, & McClelland, 1990). The role of the frontal executive system in Stroop top-down control is further supported by individual-differences studies that have demonstrated a correlation between the magnitude of the Stroop effect and working memory (WM) capacity-another important frontal function (e.g., Zhao et al., 2014)-as measured with the operation span task (Turner & Engle, 1989). Low-operation-span participants have longer RTs in incongruent Stroop trials (Kane & Engle, 2003;Meier&Kane,2012), suggesting that the higher the WM capacity, the better one can perform the goal-relevant selection in the Stroop task.

Although these patient and individual-differences studies have provided strong support for the association between the frontal executive system that maintains and updates information in WM and Stroop interference, they do not establish causality. The aim of our study was to do just this, by probing the effect of a task manipulation that would reduce the available resources of the WM system on a concurrent Stroop task (see also de Fockert, Rees, Frith, & Lavie, 2001). …

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