Elsevier

Neuropsychologia

Volume 47, Issue 3, February 2009, Pages 663-670
Neuropsychologia

Neural time course of conflict adaptation effects on the Stroop task

https://doi.org/10.1016/j.neuropsychologia.2008.11.013Get rights and content

Abstract

Cognitive control theory suggests conflict effects are reduced following high- relative to low-conflict trials. Such reactive adjustments in control, frequently termed “conflict adaptation effects,” indicate a dynamic interplay between regulative and evaluative components of cognitive control necessary for adaptable goal-directed behavior. The current study examined conflict adaptation effects while 36 neurologically-normal participants performed a single-trial color-naming Stroop task. Trials preceded by incongruent (high conflict) and congruent (low conflict) trials were compared for behavioral (response time [RT] and error rate) and electrophysiological (N450 and conflict SP components of the event-related potential [ERP]) concomitants of cognitive control. A conflict adaptation effect was present for RTs that could not be accounted for by associative or negative priming. ERPs revealed a parietal conflict slow potential (conflict SP) that differentiated incongruent from congruent trials and monotonically differentiated current trial congruency on the basis of previous-trial context (i.e., showed conflict adaptation); the fronto-medial N450 was sensitive to current trial congruency but not to previous-trial context. Direct comparison of normalized conflict SP and N450 amplitudes showed the conflict SP was sensitive to the effects of previous-trial context, while the N450 was so to a lesser extent and in a different pattern. Findings provide clarification on the neural time course of conflict adaptation and raise further questions regarding the relative roles of the parietal conflict SP and fronto-medial N450 in conflict detection and processing.

Section snippets

Alternatives to conflict adaptation

Several alternatives to the conflict adaptation explanation of repetition effects should also be considered and addressed. Mayr, Awh, and Laurey (2003) suggest that the repetition of the exact stimulus or stimulus attributes (e.g., the color of the word in the Stroop color-naming condition) accounts for the conflict adaptation effect following iI trials relative to cI trials. That is, the conflict adaptation effect may be accounted for by bottom-up associative priming (i.e., feature repetition)

Current study

Given the paucity of information on the neural time course of behavioral adjustments in cognitive control and the relative ambiguity of the role of the conflict SP in conflict processing/response selection, the current study was designed to: (1) replicate previous findings of conflict adaptation effects on RTs (i.e., an interaction between previous and current trial congruency) and determine the role of associative priming in these effects; (2) examine the role of previous-trial context in

Participants

Participants were recruited from undergraduate psychology courses as well as via flyer and advertisement from the local community. Study enrollment included 36 right-handed individuals (20 female) with a mean age of 24.3 years (S.D. = 7.9, range 18–49 years). All participants were screened for potential psychiatric disorders using the Mental Health Screening Form-III (Carroll and McGinley, 2000, Carroll and McGinley, 2001). Pre-screening also excluded participants if they endorsed a history of

Behavioral performance

Data for RTs and error rates as a function of previous-trial congruency and current-trial congruency are presented in Table 1. Analyses of correct-trial RTs, excluding post-error trials, revealed the expected main effect of current-trial congruency reflecting Stroop RT interference (i.e., longer RTs to incongruent than congruent current trials), F(1,35) = 132.22, p < .001, η2 = .79. The main effect of previous-trial congruency was not significant, F(1,35) = .52, p > .47, η2 = .02. Most importantly, a

Discussion

In this study we examined the behavioral and electrophysiological correlates of conflict processing and conflict adaptation effects. Behavioral data revealed the anticipated increases in RTs and error rates on incongruent relative to congruent trials (i.e., Stroop interference). Replicating several previous studies using the Stroop task (Egner & Hirsch, 2005; Kerns et al., 2004, Notebaert et al., 2006), a conflict adaptation effect was observed for RT data that remained when color and negative

Summary and conclusions

Present findings are consistent with previous studies indicating robust behavioral conflict adaptation effects that cannot be accounted for solely by associative or negative priming. The neural time course of conflict adaptation effects, as measured by ERPs, revealed a parietal conflict SP that monotonically differentiated Stroop stimuli on the basis of previous-trial context and a fronto-medial N450 that was sensitive to current-trial congruency but was not differentiated by previous-trial

Acknowledgements

This original research has not been published elsewhere and was supported by a pre-doctoral National Institute of Health (NIH) Fellowship to MJL (F31 NS053335) and grants K01 MH01857 and R21 MH073076 from the NIH to WMP. We extend our appreciation to Cortney Mauer, Megan McIntyre, Drew Nagle, Allen Sirizi, and Raechel Steckley for their assistance in data collection.

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