Distinguishing response conflict and task conflict in the Stroop task: Evidence from ex-Gaussian distribution analysis.

It has been suggested that performance in the Stroop task is influenced by response conflict as well as task conflict. The present study investigated the idea that both conflict types can be isolated by applying ex-Gaussian distribution analysis which decomposes response time into a Gaussian and an exponential component. Two experiments were conducted in which manual versions of a standard Stroop task (Experiment 1) and a separated Stroop task (Experiment 2) were performed under task-switching conditions. Effects of response congruency and stimulus bivalency were used to measure response conflict and task conflict, respectively. Ex-Gaussian analysis revealed that response conflict was mainly observed in the Gaussian component, whereas task conflict was stronger in the exponential component. Moreover, task conflict in the exponential component was selectively enhanced under task-switching conditions. The results suggest that ex-Gaussian analysis can be used as a tool to isolate different conflict types in the Stroop task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interpreting Stroop interference: An analysis of differences between task versions.

The present study investigated methodological differences between the clinical version of the Stroop Color and Word Test and the computerized single-trial version. Three experiments show that different presentations of the Stroop task can produce different levels of interference. The 1st experiment examined the effect of blocking; the 2nd experiment examined different control conditions. Greater interference in the blocked clinical version appears to result from lower response times (RTs) in the neutral condition, not from greater RTs in the incongruent condition. Experiment 3 examined the impact of shifting attention across locations while responding to Stroop stimuli. The present set of findings sheds light on the inconsistency in the clinical literature and demonstrates that the method and selection of neutral stimuli (that provide the baseline by which interference is measured) are critical because they clearly can change performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The utility of Stroop task switching as a marker for early-stage Alzheimer's disease.

[Correction Notice: An erratum for this article was reported in Vol 25(4) of Psychology and Aging (see record 2010-22172-001). Author Janet M. Duchek’s name was misspelled as Janet M. Ducheck. The online version has been corrected.] Past studies have suggested attentional control tasks such as the Stroop task and the task-switching paradigm may be sensitive for the early detection of dementia of the Alzheimer's type (DAT). The authors of the current study combined these tasks to create a Stroop switching task. Performance was compared across young adults, older adults, and individuals diagnosed with very mild dementia. Results indicated that this task strongly discriminated individuals with healthy aging from those with early-stage DAT. In a logistic regression analysis, incongruent error rates from the Stroop switching task discriminated healthy aging from DAT better than any of the other 18 cognitive tasks given in a psychometric battery. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Interactions of focal cortical lesions with error processing: Evidence from event-related brain potentials.

Electrophysiological and hemodynamic studies have suggested that structures in the vicinity of the anterior cingulate cortex are involved in performance monitoring, particularly in detection of errors. Bidirectional interactions between the frontomedian system involved in performance monitoring and the lateral prefrontal cortex as well as the orbitofrontal cortex have been proposed, but few studies have directly addressed this issue. The authors used a speeded flankers task to investigate error-related event-related potentials in 3 patient groups with different focal cortical lesions. Whereas bilateral frontopolar lesions involving the orbitofrontal cortex as well as temporal lesions did not alter the error-related negativity (ERN), lesions of the lateral frontal cortex resulted in an abolition of the ERN and in a reduction of the error positivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stroop Dilution Revisited: Evidence for Domain-Specific, Limited-Capacity Processing.

Nine experiments show that in the context of Stroop dilution the extent to which flanking distractors are processed depends on the nature of the material at fixation. A Stroop effect is eliminated if a word or a nonword is colored and appears at fixation and the color word appears as a flanker. A Stroop effect is observed when the color carrier at fixation is from a different domain than the color word distractor (e.g., Arabic digits). It is argued that when the material at fixation is in the same domain as the color word distractor, the distractor is not processed. Taken together, these results implicate a role for material-specific, limited-capacity processing in the context of this variant of the Stroop paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Active inhibition of a distractor word: The distractor precue benefit in the Stroop color-naming task.

The current study investigated attentional control through active inhibition of the identity of the distractor. Adapting a Stroop paradigm, the distractor word was presented in advance and made to disappear, followed by the presentation of a Stroop stimulus. Participants were instructed to inhibit the distractor in order to reduce its interference. Experiments 1 and 2 demonstrated that the distractor precue facilitated Stroop color naming by reducing Stroop interference. Experiment 3 demonstrated beneficial effects of the distractor precue when congruent trials were introduced. Experiment 4 showed that the distractor precue benefit was observed when the cue and target were in different forms. Experiment 5 indicated that if the item used as the cue became the target, naming it took longer in order to overcome the inhibitory effect. Experiment 6 demonstrated that the benefit of the distractor precue was not observed when the cue was uninformative. Finally, Experiment 7 demonstrated that active inhibition required working-memory resources to operate. This study suggests that the best explanation for the distractor precue benefit is the active inhibition account. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Automatic processing of psychological distance: Evidence from a Stroop task.

A picture-word version of the Stroop task was used to test the automatic activation of psychological distance by words carrying various senses of psychological distance: temporal (tomorrow, in a year), social (friend, enemy), and hypotheticality (sure, maybe). The pictures implied depth, with the words appearing relatively close to or distant from the observer. The participants classified the spatial distance of words faster when the word's implicit psychological distance matched its spatial distance (e.g., a geographically close word was classified faster when it was "friend" than when it was "enemy"). The findings are consistent with the idea that psychological distance is accessed automatically, even when it is not directly related to people's current goals, and suggest that psychological distance is an important dimension of meaning, common to spatial distance, temporal distance, social distance, and hypotheticality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Skeletal Structure of Printed Words: Evidence From the Stroop Task.

Do readers encode the sequencing of consonant (C) and vowel (V) phonemes (skeletal structure) in printed words? The authors used the Stroop task to examine readers' sensitivity to skeletal structure. In Experiment 1, CVC nonwords (e.g., pof) facilitated the naming of colors with congruent frames (e.g., red, a CVC word) but not with incongruent ones (e.g., green). In Experiment 2, the color black (a CCVC frame) was named faster with a congruent CCVC frame (e.g., grof) compared to either CCVCC (e.g., groft) or CVC (e.g., gof) incongruent controls. Finally, in Experiment 3, the color pink (a CVCC frame) was named faster with a CVCC frame (e.g., goft) compared to either CCVCC or CVC incongruent controls. In most cases, congruent frames shared no segments with the color name. These findings demonstrate that readers automatically assemble the skeletal structure of printed words. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analyzing the generality of conflict adaptation effects.

Conflict adaptation effects refer to the reduction of interference when the incongruent stimulus occurs immediately after an incongruent trial, compared with when it occurs after a congruent trial. The present study analyzes the key conditions that lead to adaptation effects that are specific to the type of conflict involved versus those that are conflict general. In the first 2 experiments, we combined 2 types of conflict for which compatibility arises from clearly different sources in terms of dimensional overlap while keeping the task context constant across conflict types. We found a clear pattern of specificity on conflict adaptation across conflict types. In subsequent experiments, we tested whether this pattern could be accounted in terms of feature integration processes contributing differently to repetition versus alternation of conflict types. The results clearly indicated that feature integration was not key to generating conflict type specificity on conflict adaptation. The data are consistent with there being separate modes of control for different types of cognitive conflict. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Goal-referenced selection of verbal action: Modeling attentional control in the Stroop task.

This article presents a new account of the color-word Stroop phenomenon (J. R. Stroop, 1935) based on an implemented model of word production, WEAVER++ (W. J. M. Levelt, A. Roelofs, & A. S. Meyer, 1999b; A. Roelofs, 1992, 1997c). Stroop effects are claimed to arise from processing interactions within the language-production architecture and explicit goal-referenced control. WEAVER++ successfully simulates 16 classic data sets, mostly taken from the review by C. M. MacLeod (1991), including incongruency, congruency, reverse-Stroop, response-set, semantic-gradient, time-course, stimulus, spatial, multiple-task, manual, bilingual, training, age, and pathological effects. Three new experiments tested the account against alternative explanations. It is shown that WEAVER++ offers a more satisfactory account of the data than other models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional dilution of the Stroop effect: A new tool for assessing attention under emotion.

In order to gauge in a precise fashion the capture of attention by emotional stimuli, we developed a new tool that imports the classic Stroop effect into the realm of emotion. Strooping the typical emotion tasks enabled the derivation of a pure intraitem measure of attention under emotion. The results of two experiments showed that the classic Stroop effects were smaller with emotion than with neutral words, demonstrating the power of emotion to bias attention. This emotional dilution of the Stroop effect can serve as a general-purpose tool for assessing attention under emotion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential analysis of the numerical Stroop effect reveals response suppression.

Automatic processing of irrelevant stimulus dimensions has been demonstrated in a variety of tasks. Previous studies have shown that conflict between relevant and irrelevant dimensions can be reduced when a feature of the irrelevant dimension is repeated. The specific level at which the automatic process is suppressed (e.g., perceptual repetition, response repetition), however, is less understood. In the current experiment we used the numerical Stroop paradigm, in which the processing of irrelevant numerical values of 2 digits interferes with the processing of their physical size, to pinpoint the precise level of the suppression. Using a sequential analysis, we dissociated perceptual repetition from response repetition of the relevant and irrelevant dimension. Our analyses of reaction times, error rates, and diffusion modeling revealed that the congruity effect is significantly reduced or even absent when the response sequence of the irrelevant dimension, rather than the numerical value or the physical size, is repeated. These results suggest that automatic activation of the irrelevant dimension is suppressed at the response level. The current results shed light on the level of interaction between numerical magnitude and physical size as well as the effect of variability of responses and stimuli on automatic processing. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Conflict adaptation depends on task structure.

The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adjustments of conflict monitoring in Parkinson's disease.

Objective: In Stroop-like tasks, the detection of conflict triggers adjustments of cognitive control to reduce conflict in subsequent trials. The present study tested the hypothesis of an impaired modulation of conflict monitoring in Parkinson's disease (PD). Method: 18 PD patients and 18 healthy control (HC) participants performed a Stroop-like task in 2 conditions differing in terms of incongruent/congruent stimuli ratio. Results: HC participants demonstrated a sustained modulation of interference effect, the interference effect being decreased when the proportion of incongruent stimuli was high. A trial-by-trial analysis also showed that in the HC group, processing an incongruent stimulus reduced interference in the subsequent trial. Unlike controls, PD patients did not demonstrate any transient or sustained reduction of the interference effect. Conclusion: Within the framework of recent models, these results can be interpreted as an impairment of a proactive mode of cognitive control in patients with PD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lexical characteristics of words used in emotional Stroop experiments.

Validity of the emotional Stroop task hinges on equivalence between the emotion and the control words in terms of lexical features related to word recognition. The authors evaluated the lexical features of 1,033 words used in 32 published emotional Stroop studies. Emotion words were significantly lower in frequency of use, longer in length, and had smaller orthographic neighborhoods than words used as controls. These lexical features contribute to slower word recognition and hence are likely to contribute to delayed latencies in color naming. The often-replicated slowdown in color naming of emotion words may be due, in part, to lexical differences between the emotion and control words used in the majority of such studies to date. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anterior cingulate activity and level of cognitive conflict: Explicit comparisons.

The role of anterior cingulate cortex (ACC) in attention is a matter of debate. One hypothesis suggests that its role is to monitor response-level conflict, but explicit evidence is somewhat lacking. In this study, the activation of ACC was compared in (a) color and number standard Stroop tasks in which response preparation and interference shared modality (response-level conflict) and (b) color and number matching Stroop tasks in which response preparation and interference did not share modality (non-response-level conflict). In the congruent conditions, there was no effect of task type. In the interference conditions, anterior cingulate activity in the matching tasks was less than that in the standard tasks. These results support the hypothesis that ACC specifically mediates generalized modality-independent selection processes invoked by response competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A paradoxical exposure-duration effect in the Stroop task: Temporal segregation between stimulus attributes facilitates selection.

In comparison with the situation in which target and distractor are presented until response, Stroop interference substantially decreases when the target color is removed from the display 150–160 ms after stimulus onset (W. La Heij, N. A. Kaptein, A. C. Kalff, & L. de Lange, 1995; 0. Neumann, 1986). Six experiments showed that this paradoxical exposure-duration effect is robust, that it is not due to the target's exposure duration per se, and that it is not due to an increased spatial selectivity of input selection. The present findings support and extend earlier observations that changes in the display during stimulus exposure affect attentional selection. The findings are tentatively interpreted in terms of (a) reduced duration of input selection or (b) facilitation of attribute selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning-induced attentional bias for face stimuli measured with the emotional Stroop task.

People with anxiety disorder display attentional bias toward threat-related objects. Using classical fear conditioning, the authors investigated the possible source of such bias in normal participants. Following differential fear conditioning in which an angry face of either male or female (conditioned stimulus: CS+) was paired with mild electric fingershock (unconditioned stimulus: US) but the angry face of the other gender and all other facial expressions unpaired (CS-), an emotional Stroop task was administered. In the Stroop task, participants were required to identify the color of the facial stimuli (red, green, blue, or yellow). Response latency was significantly longer for the CS+ angry face than the other unpaired facial stimuli (CS-). Furthermore, this acquired attentional bias was positively correlated with the level of trait-anxiety measured before the conditioning and the degree of self-reported aversiveness of the US. Our results demonstrated that attentional bias could be induced in normal individuals through a simple associative learning procedure, and the acquisition is modulated by the level of trait anxiety and the level of perceived fear of the aversive US. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple systems for cognitive control: Evidence from a hybrid prime-Simon task.

Cognitive control resolves conflicts between appropriate and inappropriate response tendencies. Is this achieved by a unitary all-purpose conflict control system, or do independent subsystems deal with different aspects of conflicting information? In a fully factorial hybrid prime-Simon task, participants responded to the identity of targets displayed at different nominally irrelevant screen locations, preceded by nominally irrelevant, consciously or nonconsciously perceived primes. The response required by the target's identity could match or mismatch (a) the target's location, and (b) the prime's identity, resulting in potential conflict (a) across and (b) within stimulus domains. Conflict effects were investigated within and across trials. Results suggest that (i) nonconsciously perceived information elicits within-trial control, but—unlike consciously perceived information—no across-trial behavioral modulation; (ii) separate subsystems deal with conflicts arising from different stimulus domains; and (iii) occasional apparent interactions between domains reflect a particular difficulty in reactivating a just-discarded response (reactivation aversion effect, RAE). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Stroop interference and attention-deficit/hyperactivity disorder: A review and meta-analysis.

Previous reviews and meta-analyses that addressed abnormal Stroop interference in attention-deficit/hyperactivity disorder (ADHD) yielded mixed results. The authors of the present study argue that the inconsistencies may reflect the problematic nature of 2 frequently used methods to quantify Stroop interference-the difference score and Golden's method (C. J. Golden, 1978). Golden's method correction for base-word reading is inadequate, and the difference score is sensitive to the nature of the outcome variable. The latter can be remedied with a ratio score. Contrasting previous meta-analyses, this meta-analysis covers all age groups and all Stroop test variants, and it excludes studies using the Golden quantification method. Mean effect sizes for interference in ADHD as quantified by difference scores relative to control scores were 0.24 across all studies but 1.11 for time-per-item studies; outcome variable was a significant moderator variable, reflecting the sensitivity of the difference score to this variable. Consistency analysis of ratio scores across 19 studies reveals more interference for the ADHD groups relative to the control groups. It is concluded that interference control is consistently compromised in individuals with ADHD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)