Emotional conflict occurs at an early stage: Evidence from the emotional face–word Stroop task

The perceptual processing of emotional conflict was studied using electrophysiological techniques to measure event-related potentials (ERPs). The emotional face–word Stroop task in which emotion words are written in prominent red color across a face was use to study emotional conflict. In each trial, the emotion word and facial expression were either congruent or incongruent (in conflict). When subjects were asked to identify the expression of the face during a trial, the incongruent condition evoked a more negative N170 ERP component in posterior lateral sites than in the congruent condition. In contrast, when subjects were asked to identify the word during a trial, the incongruent condition evoked a less negative N170 component than the congruent condition. The present findings extend our understanding of the control processes involved in emotional conflict by demonstrating that differentiation of emotional congruency begins at an early perceptual processing stage.     

Nicotine Stroop and addiction memory--an ERP study.

Drug-related cues have been shown to take effects on behavioral performance and physiological parameters such as event-related brain potentials (ERPs). In the present study we obtained EEG data during a modified Stroop task and during a color matching task using smoking related and neutral words (nicotine Stroop) in smokers and non-smoking controls. We assumed that in smokers smoking-related word meanings would interfere with color matching, and that this should be reflected in an ERP activation pattern comparable to that induced by the Stroop task. In smokers and non-smokers the classic Stroop-related interference effect of longer reaction times in the incongruent condition could be observed. This interference effect in both groups was related to a late posterio-central relative negativity and a right frontal relative positivity in the incongruent compared to the congruent condition. The behavioral data in the color matching task (nicotine Stroop) derived from both groups did not show a comparable interference effect related to the use of drug-related words. However, in smokers the smoking-related words elicited ERP activation patterns comparable to those evoked by the Stroop interference task. The ERP results are discussed as possibly reflecting a modulation of color processing of smoking-related words in smokers. The results imply an interference, but also attention enhancing, effect of smoking-related words in smokers, which maybe associated with addiction memory and enhanced sensitivity for drug-cues. Therefore, the addiction memory driven interference effect might be counteracted by performance enhancement induced by the same nicotine cues.     

Interference in the Stroop color-naming task

To clarify the four processing stages in the Stroop task (input, decision, response selection, and output), and to examine on which stage or stages the interference occurs, seven undergraduates were used as subjects in a color-naming task with color names, words strongly associated with color, words weakly associated with color, a neutral word, and "X X X" as control stimulus. Color-patch pieces were also used to measure the operant level of reaction time. Main results were as follows: 1. On the congruent trials, the response time was shorter for color names than for the neutral word, control word, and words with weak association. 2. On the incongruent trials, the response time was longer for color names than for the neutral word, control word, and words with weak and strong association. Moreover, the interaction between pre-exposure duration and word conditions was significant; the difference of response time due to word conditions as significant when the pre-exposure duration was short, while it was not significant when the duration was long. 3. The neutral word and the control word gave similar response time, which was longer than that for color-patch pieces. From these results it is concluded that the interference in the Stroop task is most likely to occur on the decision and the output stages.     

Poor Stroop performances in 15-year-old dyslexic teenagers

The Stroop test enables interference between color naming and reading to be studied. Protopapas et al. (2007) reported more errors in an interference task and longer reaction times in 12.5-year-old dyslexics; also more Stroop interference with lower reading skills. The present study uses a version of the Stroop with four color cards and aims to test interference and flexibility in older dyslexic teenagers. The four cards are: color naming, reading, interference and flexibility. In the latter, subjects have to name the color of the word inhibiting reading except when the word is inside a box. This flexibility task enables the testing of the capacity for cognitive switching between tasks. Ten dyslexics (15.1 ± 0.7 years old) and fourteen controls (14.3 ± 1.6 years old) participated in the study. All performed the color naming, the reading, the interference and the flexibility tasks in the same order. Subsequently, they performed a sequence of 60 saccades left–right followed by the interference task. Generally, dyslexic teenagers behaved similarly to non-dyslexics as they showed fewer errors in reading and color than in the interference and flexibility tasks. However, they made more errors and needed more time to accomplish each task than non-dyslexics. The results suggest that the inhibitory and attention processes required by the Stroop test are dysfunctioning even in older dyslexics. In contrast, the study shows no evidence for particular difficulty in the flexibility task, which would constitute an argument against problems with mental switching. Following the execution of saccades, errors in the interference test were significantly reduced for dyslexics, while the time was reduced for both groups. The effects are attributed to visual attention training via saccades.     

Integration of Spoken and Written Words in Beginning Readers: A Topographic ERP Study

Integrating visual and auditory language information is critical for reading. Suppression and congruency effects in audiovisual paradigms with letters and speech sounds have provided information about low-level mechanisms of grapheme-phoneme integration during reading. However, the central question about how such processes relate to reading entire words remains unexplored. Using ERPs, we investigated whether audiovisual integration occurs for words already in beginning readers, and if so, whether this integration is reflected by differences in map strength or topography (aim 1); and moreover, whether such integration is associated with reading fluency (aim 2). A 128-channel EEG was recorded while 69 monolingual (Swiss)-German speaking first-graders performed a detection task with rare targets. Stimuli were presented in blocks either auditorily (A), visually (V) or audiovisually (matching: AVM; nonmatching: AVN). Corresponding ERPs were computed, and unimodal ERPs summated (A + V = sumAV). We applied TANOVAs to identify time windows with significant integration effects: suppression (sumAV–AVM) and congruency (AVN–AVM). They were further characterized using GFP and 3D-centroid analyses, and significant effects were correlated with reading fluency. The results suggest that audiovisual suppression effects occur for familiar German and unfamiliar English words, whereas audiovisual congruency effects can be found only for familiar German words, probably due to lexical-semantic processes involved. Moreover, congruency effects were characterized by topographic differences, indicating that different sources are active during processing of congruent compared to incongruent audiovisual words. Furthermore, no clear associations between audiovisual integration and reading fluency were found. The degree to which such associations develop in beginning readers remains open to further investigation.     

Pure alexia and covert reading: Evidence from Stroop tasks

Abstract

Patients with pure alexia (also referred to as letter-by-letter readers) show a marked word-length effect when naming visually presented words, evidenced by a monotonic increase in response time (or decrease in accuracy) as a function of the number of letters in the string. Interestingly, despite the difficulty in overtly reporting the identity of some words, many patients exhibit fast and above-chance access to lexical and/or semantic information for the same words. To explore the extent of this covert reading, we examined the degree of interference afforded by the inconsistent (word identity and colour label do not match) versus neutral condition in a Stroop task in a pure alexic patient, EL. EL shows evidence of covert reading on a semantic categorisation task and a lexical decision task. She also demonstrates covert reading by exhibiting Stroop interference of the same magnitude as a matched control subject, when naming the colour of the ink in which a word is printed. When the word shares some but not all letters with the colour name (BLOW instead of BLUE), neither subject shows interference. In contrast with the control subject, EL does not show Stroop interference when various orthographic changes (degraded visual input, cursive font) or phonological or semantic changes are made to the word. These findings indicate that although some implicit processing of words may be possible, this processing is rather rudimentary. Not surprising, this implicit activation may be insufficient to support overt word identification. We explain these findings in the context of a single, integrated account of pure alexia.     

Effects of concurrent working memory load on distractor and conflict processing in a name‐face Stroop task

To examine the time course of effects of working memory (WM) load on interference control, ERPs were measured in a combined WM and Stroop task. A WM load of 0, 2, or 4 letters was imposed, and during the maintenance‐interval Stroop trials were presented that required participants to classify names of famous people while ignoring faces that were either congruent or incongruent with the names. Behavioral interference was not modulated by WM load, but WM load led to an overall reduction of Stroop stimulus encoding as reflected by reduced N170 and N250 amplitudes independent of congruency. Incongruent distractor faces induced interference as shown by a delayed and reduced positivity between 480–600 ms (N450) and an enhanced positivity between 760–1000 ms (P600), indicating longer stimulus evaluation, conflict detection, and conflict resolution, respectively. WM load led to an increase of the P600 at frontal and parietal sites, possibly reflecting PFC‐driven top‐down control of posterior sites, necessary for conflict resolution.     

How personal earthquake experience impacts on the Stroop interference effect: An event‐related potential study

Event‐related brain potentials (ERPs) were measured when 24 Chinese subjects performed the classical Stroop task. All of subjects had experienced the great Sichuan earthquake (5/12), with 12 people in each of the Far (Chengdu city) and the Close (Deyang city) earthquake experience groups. The behavioral data showed that the Stroop task yielded a robust Stroop interference effect as indexed by longer RT for incongruent than congruent color words in both the Chengdu and Deyang groups. Scalp ERP data showed that incongruent stimuli elicited a more negative ERP deflection (N400–600; Stroop interference effect) than did congruent stimuli between 400–600 ms in the Chengdu group, while the Stroop interference ERP effect was not found in the Deyang group. Dipole source analysis localized the generator of the N400–600 in the right prefrontal cortex (PFC) and was possibly related to conflict monitoring and cognitive control.     

From orthography to meaning: an electrophysiological investigation of the role of phonology in accessing meaning of Chinese single-character words

Homophone interference effects in Stroop experiments are often taken as evidence for the hypothesis that semantic access in written Chinese language is mediated by activation of phonological processing. We here aim to test this hypothesis with Chinese single-character words by means of event related potential (ERP) recordings. Using color words, homophones of color words and color-word associates as materials in a Stroop task, we found behavioral Stroop interference effects for all stimulus types and an N450 for incongruent color words and color-word associates. Critically, there was no difference in the ERP waveforms elicited by congruent and incongruent homophones in the N450 time window. However, in a later time window (600–800 ms) the incongruent homophones elicited an apparent positivity over left posterior regions. A similar effect was also observed for incongruent color words. These findings thus indicate that phonology does not play an important role in semantic activation of Chinese single-character words, and that the behavioral Stroop effects for homophones possibly arises at later stage of lexical processing.     

Pure alexia and covert reading: Evidence from Stroop tasks

Patients with pure alexia (also referred to as letter-by-letter readers) show a marked word-length effect when naming visually presented words, evidenced by a monotonic increase in response time (or decrease in accuracy) as a function of the number of letters in the string. Interestingly, despite the difficulty in overtly reporting the identity of some words, many patients exhibit fast and above-chance access to lexical and/or semantic information for the same words. To explore the extent of this covert reading, we examined the degree of interference afforded by the inconsistent (word identity and colour label do not match) versus neutral condition in a Stroop task in a pure alexic patient, EL. EL shows evidence of covert reading on a semantic categorisation task and a lexical decision task. She also demonstrates covert reading by exhibiting Stroop interference of the same magnitude as a matched control subject, when naming the colour of the ink in which a word is printed. When the word shares some but not all letters with the colour name (BLOW instead of BLUE), neither subject shows interference. In contrast with the control subject, EL does not show Stroop interference when various orthographic changes (degraded visual input, cursive font) or phonological or semantic changes are made to the word. These findings indicate that although some implicit processing of words may be possible, this processing is rather rudimentary. Not surprising, this implicit activation may be insufficient to support overt word identification. We explain these findings in the context of a single, integrated account of pure alexia.     

The neural oscillations of conflict adaptation in the human frontal region

Incongruency between print color and the semantic meaning of a word in a classical Stroop task activates the human conflict monitoring system and triggers a behavioral conflict. Conflict adaptation has been suggested to mediate the cortical processing of neural oscillations in such a conflict situation. However, the basic mechanisms that underlie the influence of conflict adaptation on the changes of neural oscillations are not clear. In the present study, electroencephalography (EEG) data were recorded from sixteen healthy human participants while they were performing a color-word Stroop task within a novel look-to-do transition design that included two response modalities. In the ‘look’ condition, participants were informed to look at the color of presented words but no responses were required; in the ‘do’ condition, they were informed to make arranged responses to the color of presented words. Behaviorally, a reliable conflict adaptation was observed. Time–frequency analysis revealed that (1) in the ‘look’ condition, theta-band activity in the left- and right-frontal regions reflected a conflict-related process at a response inhibition level; and (2) in the ‘do’ condition, both theta-band activity in the left-frontal region and alpha-band activity in the left-, right-, and centro-frontal regions reflected a process of conflict control, which triggered neural and behavioral adaptation. Taken together, these results suggest that there are frontal mechanisms involving neural oscillations that can mediate response inhibition processes and control behavioral conflict.     

Age differences in attentional control: an event-related potential approach

We examined age differences in event-related potentials (ERPs) associated with attentional control of task-set selection and response interference by means of a cue-based switching paradigm in which participants performed the color or word Stroop task. The results of ERPs in the cue interval indicated that P3 latencies were slowed for older adults, suggesting age-related slowing in updating currently relevant task sets. Older adults also showed a larger CNV under switching than nonswitching conditions, indicating age differences in maintaining task sets over longer periods of time. The results of target-locked ERPs revealed a negativity to incompatible Stroop trials (Ni) that was prolonged for older adults, suggesting age differences in early conflict processing. Response-locked ERPs showed a negative deflection to incompatible Stroop trials (CRN) only for younger adults, suggesting age differences also in response-related conflict processing.     

Stroop tasks reveal abnormal selective attention among psychopathic offenders

Selective attention among offenders with psychopathy was investigated using 3 Stroop paradigms: a standard color-word (CW) Stroop, a picture-word (PW) Stroop, and a color-word Stroop in which the word and color were spatially separated (separated CW). Consistent with "overselective" attention, offenders with psychopathy displayed reduced Stroop interference on the separated CW and PW tasks relative to offenders who were not psychopathic. However, offenders with psychopathy displayed normal Stroop interference on the standard CW Stroop. Further, the reduced interference of offenders with psychopathy on the separated CW Stroop was accompanied by normal facilitation. These findings suggest a circumscribed attentional deficit in psychopathy that hinders the use of unattended information that is (a) not integrated with deliberately attended information and (b) not compatible with current goal-directed behavior.     

Cognitive control mechanisms resolve conflict through cortical amplification of task-relevant information

A prominent model of how the brain regulates attention proposes that the anterior cingulate cortex monitors the occurrence of conflict between incompatible response tendencies and signals this information to a cognitive control system in dorsolateral prefrontal cortex. Cognitive control is thought to resolve conflict through the attentional biasing of perceptual processing, emphasizing task-relevant stimulus information. It is not known, however, whether conflict resolution is mediated by amplifying neural representations of task-relevant information, inhibiting representations of task-irrelevant information, or both. Here we manipulated trial-by-trial levels of conflict and control during a Stroop task using face stimuli, while recording hemodynamic responses from human visual cortex specialized for face processing. We show that, in response to high conflict, cognitive control mechanisms enhance performance by transiently amplifying cortical responses to task-relevant information rather than by inhibiting responses to task-irrelevant information. These results implicate attentional target-feature amplification as the primary mechanism for conflict resolution through cognitive control.     

An electrophysiological correlate of conflict processing in an auditory spatial Stroop task: The effect of individual differences in navigational style

Recent work has identified an event-related potential (ERP) component, the incongruency negativity (N_inc), which is sensitive to auditory Stroop conflict processing. Here, we investigated how this index of conflict processing is influenced by individual differences in cognitive style. There is evidence that individuals differ in the strategy they use to navigate through the environment; some use a predominantly verbal-egocentric strategy while others rely more heavily on a spatial-allocentric strategy. In addition, navigational strategy, assessed by a way-finding questionnaire, is predictive of performance on an auditory spatial Stroop task, in which either the semantic or spatial dimension of stimuli must be ignored. To explore the influence of individual differences in navigational style on conflict processing, participants took part in an auditory spatial Stroop task while the electroencephalogram (EEG) was recorded. Whereas behavioral performance only showed a main effect of congruency, we observed the predicted three-way interaction between congruency, task type and navigational style with respect to our physiological measure of Stroop conflict. Specifically, congruency-dependent modulation of the N_inc was observed only when participants performed their non-dominant task (e.g., verbal navigators attempting to ignore semantic information). These results confirm that the N_inc reliably indexes auditory Stroop conflict and extend previous results by demonstrating that the N_inc is predictably modulated by individual differences in cognitive style.     

Relationship of regular physical activity with neuroelectric indices of interference processing in young adults

The relationship of physical activity with interference processing was examined using behavioral and neuroelectrical measures in young adults divided into more active and less active groups. The participants completed Stroop (i.e., color-naming) and reverse Stroop (i.e., word-meaning) tasks that differed in the level of difficulty while event-related potentials were assessed. In the low interference Stroop task, participants were asked to respond to the ink color of the word, while the meaning was either congruent or incongruent with the color. In the high interference reverse Stroop task, participants had to indicate the meaning of colored words while ignoring the color of the font. The results indicated that young adults in the more active group exhibited a shorter response time (RT) and a lower intra-individual variability of RT than did those in the less active group. These behavioral differences were associated with larger P2 and P3 and smaller N450 amplitudes in the Stroop task and with larger P2 and N2 and smaller N450 amplitudes in the reverse Stroop task. No differences were observed in the contingent negative variation (CNV) between the groups. These findings suggest that, for young adults, regular physical activity is positively associated with a better neural efficiency in resource allocation for tasks that require the ability to inhibit cognitive interference and provide evidence for the potential neural mechanisms underlying the improved Stroop performance.     

Experimental evidence for interpretive but not attention biases towards somatic information in patients with chronic fatigue syndrome

Objective: This study tested whether CFS patients have an attentional information processing bias for illness‐related information and a tendency to interpret ambiguous information in a somatic fashion. Design:25 patients meeting research criteria for a diagnosis of CFS were compared to 24 healthy matched controls on a modified Stroop task and an ambiguous cues task. Method: In the modified Stroop task, participants colour named a series of somatic, depressed and neutral words in order to ascertain whether the somatic words were more distracting to the CFS patients than the depressed and neutral words when compared to controls. In the ambiguous cues task, participants were presented with a tape‐recorded list of 30 words including 15 ambiguous illness words (e.g., vein/vain) and 15 unambiguous words. For each word, they were asked to write down the first word that came into their head. A somatic bias score was obtained for each subject by summing the number of somatic responses to the ambiguous word cues. Results: Although CFS patients were significantly slower in colour naming all of the Stroop word categories than controls, there was no evidence for illness or depressed words creating greater interference than neutral words. However, on the ambiguous cues task, CFS patients made significantly more somatic interpretations than controls and this bias was significantly associated with the extent to which they currently reported symptoms. Conclusion: CFS patients have an interpretive bias for somatic information which may play a part in the maintenance of the disorder by heightening patients' experience of physical symptoms and helping to maintain their negative illness schemas. Although patients did not show an attentional bias in this study, this may be related to the methodology employed.     

Pleasant mood intensifies brain processing of cognitive control: ERP correlates

The present study investigated the impact of auditory-induced mood on brain processing of cognitive control using a Stroop color-word interference task. A total of 135 positive, negative, and neutral sounds (45 of each) were presented in separate blocks for a mood induction procedure, which was then followed by a Stroop color-word task in each trial. Event-related potentials (ERPs) were recorded for color-word congruent, incongruent and neutral (color-word irrelevant) words and subjects named the printed colors of the words by pressing the appropriate key (irrespective of word meaning). Response latency was delayed during incongruent vs. neutral trials, and this cost did not interact significantly with mood states. ERP data showed prolonged peak latencies in the P200 component and more negative deflections in the Late Positive Component (LPC, 450-550 ms) during incongruent vs. neutral conditions, regardless of mood states. Moreover, the negative deflections (N450) in the 450-550 ms interval of the incongruent- neutral difference waves, which index cognitive control effect in brain potentials, was more pronounced in the pleasant, but not in the unpleasant, mood state when compared with the neutral mood state. These data suggest that, pleasant mood intensifies brain processing of cognitive control, in a situation requiring effective inhibition of task-irrelevant distracting information. In addition, N450 component serves as an affective marker, embodying not only cognitive control effect in the brain but also its interaction with mood states.     

Children With ADHD Show Impairments in Multiple Stages of Information Processing in a Stroop Task: An ERP Study

This study investigated the role of impaired inhibitory control as a factor underlying attention deficit hyperactivity disorder (ADHD). Children with ADHD and typically developing children completed an animal Stroop task while electroencephalogram (EEG) was recorded. The lateralized readiness potential and event-related brain potentials associated with perceptual and conflict processing were analyzed. Children with ADHD were slower to give correct responses irrespective of congruency, and slower to prepare correct responses in the incongruent condition. This delay could result from enhanced effort allocation at earlier processing stages, indicated by differences in P1, N1, and conflict sustained potential. Results suggest multiple deficits in information processing rather than a specific response inhibition impairment.