The effects of age and task context on Stroop task performance

In this study, we investigated the impact of age and task context on Stroop task performance, using error scores, response latencies, and process dissociation estimates (e.g., Lindsay & Jacoby, 1994). Across three experiments, the findings showed that although older adults were able to evaluate Stroop task demands and modify their representations of task context in response to this knowledge, they were less able to maintain and update these representations on a trial-by-trial basis in tasks with high stimulus uncertainty or ambiguity. Moreover, although there was no age-related decline in the ability to modulate print color information, older adults were consistently less able to control the activation of conflicting word information. Together, these findings suggest that whereas age differences in the Stroop task may be magnified under conditions that promote transient failures to maintain task context, the primary source of these differences seems to be a more enduring decline in the efficiency of processes that are responsible for suppressing the activation of irrelevant lexical information.     

Emotional Stroop task: effect of word arousal and subject anxiety on emotional interference

Inconsistent findings regarding the emotional Stroop effect in healthy subjects may be explained by confounding effects of stimulus valence and arousal, as well as individual differences in anxiety. We examined reaction time data in a healthy sample using the emotional Stroop task while carefully matching arousal level of positive and negative words. Independent of valence, emotional relative to neutral words elicited emotional interference, indicating that arousal determines emotional interference. Independent of valence, emotional words were better re-called and recognized than neutral words. Individual differences in state anxiety were associated with emotional interference, that is, emotional interference was enhanced in subjects with high state anxiety. There was no influence of trait anxiety. These findings indicate that word arousal produces emotional interference independent of valence. State anxiety exacerbates interference of emotional words by further biasing attention towards emotionally salient stimuli. Thomas Dresler and Katja Mériau have contributed equally.     

Adults' versus children's performance on the Stroop task: Interference and facilitation

Stroop tasks (Stroop, 1935) present stimuli having two dimensions, and participants respond to one dimension whilst ignoring the other. The two dimensions are made congruent, incongruent or neutral with respect to one another. Many claim that ‘Stroop interference’ is higher in children than in adults. However, taking interference as the difference between the incongruent condition and the neutral condition, with interference within the congruent condition itself termed the ‘incongruity effect’ then surprisingly few studies directly address this issue. Also, there is recent debate as to whether the ‘facilitation effect’ (the contrast between the congruent and neutral conditions) is just the opposite of interference. The present investigation (N = 31) concerned a direct comparison between children and adults. Although the incongruity effect reduced with age, interference did not. However, facilitation was far higher in children than in adults. The groups' opposite facilitation/interference asymmetry was used to examine the recent claim that these derive from inadvertent word‐reading and suppression of semantic activation, respectively; rather than solely from the latter.     

Effects of Stroop task duration on subsequent cognitive and physical performance

The strength model of self-control purports to explain why brief cognitive response inhibition tasks impair subsequent isometric handgrip endurance. According to the model, ego depleting tasks requiring self-control resources impair performance on subsequent tasks that also require self-control resources. However, several lines of evidence challenge this model, including evidence of improved exercise performance following longer cognitive tasks. Our study investigated the effects of cognitive task duration on (1) subsequent physical endurance performance, (2) concurrent cognitive task performance, and (3) subsequent novel cognitive task performance. Adopting an experimental design, with Stroop task type (incongruent, congruent) and duration (5, 10, 20 min) as between-participant factors, participants (N = 180) completed a color word Stroop task, an isometric handgrip to exhaustion task, and a novel 5-min incongruent number word Stroop task. In the handgrip task, endurance performance was worse following incongruent word Stroop than congruent word Stroop for 10-min tasks but not 5-min and 20-min tasks. In the word Stroop task, accuracy was lower and speed was slower following incongruent word Stroop than congruent word Stroop. Importantly, reaction times improved with longer task durations. In the novel number Stroop task, accuracy was higher following incongruent word Stroop than congruent word Stroop. In conclusion, the finding that the ego depletion effect was moderated by cognitive task duration is better explained by the expected value of control model than the strength model.     

Automaticity in reading and the Stroop task: testing the limits of involuntary word processing

We investigated the parameters of involuntary word reading in the Stroop task in 7 experiments. Experiments 1-4 varied response modality and the presence of congruent word trials in a test of the claim that presenting a Stroop color word with only one letter in the target color eliminates the Stroop effect. Experiments 5 and 6 addressed the roles of spatial attention and orthographic processing as possible mechanisms behind the reduction of Stroop effects with the single-letter format. Experiment 7 investigated the limits of involuntary reading under optimal conditions for selective processing of rectangular color patch targets. We found that the single-letter format reduced but never eliminated Stroop effects, spatial attention but not orthographic processing plays a role in the effect of the single-letter format, and word reading is not completely prevented even with austere presentation conditions. We conclude with a defense of the involuntariness criterion for automaticity in the Stroop task, particularly when word reading is viewed in the context of a skilled performance.     

Suggestion does not de-automatize word reading: Evidence from the semantically based Stroop task

Recent studies have shown that the suggestion for participants to construe words as meaningless symbols reduces, or even eliminates, standard Stroop interference in highly suggestible individuals (Raz, Fan, & Posner, 2005; Raz, Kirsch, Pollard, & Nitkin-Kaner, 2006). In these studies, the researchers consequently concluded that this suggestion de-automatizes word reading. The aim of the present study was to closely examine this claim. To this end, highly suggestible individuals completed both standard and semantically based Stroop tasks, either with or without a suggestion to construe the words as meaningless symbols (manipulated in both a between-participants [Exp. 1] and a within-participants [Exp. 2] design). By showing that suggestion substantially reduced standard Stroop interference, these two experiments replicated Raz et al.'s (2006) results. However, in both experiments we also found significant semantically based Stroop effects of similar magnitudes in all suggestion conditions. Taken together, these results indicate that the suggestion to construe words as meaningless symbols does not eliminate, or even reduce, semantic activation (assessed by the semantically based Stroop effect) in highly suggestible individuals, and that such an intervention most likely reduces nonsemantic task-relevant response competition related to the standard Stroop task. In sum, contrary to Raz et al.'s claim, suggestion does not de-automatize or prevent reading (as shown by a significant amount of semantic processing), but rather seems to influence response competition. These results also add to the growing body of evidence showing that semantic activation in the Stroop task is indeed automatic.     

Hypnotic suggestibility predicts the magnitude of the imaginative word blindness suggestion effect in a non-hypnotic context

The present study investigated how the magnitude the word blindness suggestion effect on Stroop interference depended on hypnotic suggestibility when given as an imaginative suggestion (i.e. not post-hypnotic suggestion) and under conditions in which hypnosis was not mentioned. Hypnotic suggestibility is shown to be a significant predictor of the magnitude of the imaginative word blindness suggestion effect under these conditions. This is therefore the first study to show a linear relationship between the imaginative word blindness suggestion effect and hypnotic suggestibility across the whole hypnotizability spectrum. The results replicate previous findings showing that highs respond to the word blindness suggestion to a greater extent than lows but extend previous work by showing that the advantage for those higher on the hypnotizability spectrum occurs even in a non-hypnotic context. Negative attitudes about hypnosis may not explain the failure to observe similar effects of the word blindness suggestion in less hypnotizable individuals.     

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.     

New insights on eye blindness and hand sight: Temporal constraints of visuo-motor networks

Pioneer experiments on saccadic suppression have shown that this effect is not followed by motor disorientation: Conscious perception of a target displacement can be dissociated from correct manual target reaching. It has subsequently been demonstrated that movement corrections with the same latency and spatial characteristics can be produced in conditions allowing perceptual awareness of perturbation of a target as in condition inducing saccadic suppression. In addition to the qualitative dissociation between motor performance and conscious awareness, quantitative temporal dissociations in action can be observed by manipulating different features of the visual target. When the target of an ongoing simple action is perturbed, a temporal advantage is found for responses to perturbations of location relative to colour and shape. Furthermore, there seems to be a temporal advantage for automatic motor corrections made in response to a target displacement as compared to other responses (other ongoing movement adjustments, movement interruption, conditional motor response such as pressing a key, verbal response, delayed matching-to-sample tasks). Thus, this paper reviews evidence for the fact that the temporal characteristics of any given response to a stimulus are dependent both on the sensory processes and on the type of response generated. Accordingly, identification responses (such as verbal report) to a visual stimulus are much slower than motor corrections of an ongoing movement in response to a target location change because of different processing times of the stimulus features (“What” compared to “Where”) and of the response itself (“What” compared to “How”). The existence of two continua (What/Where and What/How) is proposed between these two extreme stimulus- response combinations. This model may be a useful framework to better understand visuo-motor transformations and the network of connections between visual and motor areas.     

Sentence interference in the Stroop task

In two experiments on Stroop interference, we examined whether sentences can be processed without the intention of the reader. Participants named the ink colors in which words in sentences were printed, and the ink colors in which the same words, randomly arranged, were printed. In Experiment 1, sentences yielded longer response times (RTs) and more errors than did nonsentences, but only when they included words that were highly relevant to the color-naming task (i.e., color and color-related words). In Experiment 2, sentences yielded more errors than did nonsentences, and sentences in which the color words matched the set of ink colors yielded longer RTs than did nonsentences. The results indicate that sentence processing can be obligatory when the component words are highly relevant to the task.     

Influence of color word availability on the Stroop color-naming effect

Three experiments tested whether the Stroop color-naming effect is a consequence of word recognition's being automatic or of the color word's capturing visual attention. In Experiment 1, a color bar was presented at fixation as the color carrier, with color and neutral words presented in locations above or below the color bar; Experiment 2 was similar, except that the color carrier could occur in one of the peripheral locations and the color word at fixation. The Stroop effect increased as display duration increased, and the Stroop dilution effect (a reduced Stroop effect when a neutral word is also present) was an approximately constant proportion of the Stroop effect at all display durations, regardless of whether the color bar or color word was at fixation. In Experiment 3, the interval between the onsets of the to-be-named color and the color word was manipulated. The Stroop effect decreased with increasing delay of the color word onset, but the absolute amount of Stroop dilution produced by the neutral word increased. This study's results imply that an attention shift from the color carrier to the color word is an important factor modulating the size of the Stroop effect.     

Posthypnotic suggestion and the modulation of Stroop interference under cycloplegia

Recent data indicate that under a specific posthypnotic suggestion to circumvent reading, highly suggestible subjects successfully eliminated the Stroop interference effect. The present study examined whether an optical explanation (e.g., visual blurring or looking away) could account for this finding. Using cyclopentolate hydrochloride eye drops to pharmacologically prevent visual accommodation in all subjects, behavioral Stroop data were collected from six highly hypnotizables and six less suggestibles using an optical setup that guaranteed either sharply focused or blurred vision. The highly suggestibles performed the Stroop task when naturally vigilant, under posthypnotic suggestion not to read, and while visually blurred; the less suggestibles ran naturally vigilant, while looking away, and while visually blurred. Although visual accommodation was precluded for all subjects, posthypnotic suggestion effectively eliminated Stroop interference and was comparable to looking away in controls. These data strengthen the view that Stroop interference is neither robust nor inevitable and support the hypothesis that posthypnotic suggestion may exert a top-down influence on neural processing.     

Multiple levels of control in the Stroop task

Multiple levels of control may be used in service of reducing Stroop interference. One is list-wide, whereby interference is reduced strategically in lists that include disproportionately more incongruent trials. A second, item-specific control is observed when proportion congruence is manipulated at the level of items. Item-specific control reduces interference for mostly incongruent relative to mostly congruent items. First, we show that item-specific control may drive both list-wide and item-specific proportion congruence effects (Experiment 1). We then show that item-specific control affects Stroop interference similarly when a single feature (a word) as opposed to a feature combination (a word 1 font type) signals proportion congruence (Experiment 2). Although this suggests that font type offers little advantage for controlling Stroop interference beyond the word, a novel, font-specific proportion congruence effect is observed in Experiment 3, indicating that font type can be used to control interference. These findings support the idea that multiple levels of control are used in reducing Stroop interference.     

Adjustment of control in the numerical Stroop task

In the numerical Stroop task, participants are asked to compare the physical sizes (physical task) or numerical values (numerical task) of two digits and ignore the irrelevant dimension. Participants are unable to ignore the irrelevant dimension as indicated by facilitation and interference effects. The literature suggests that there is asymmetry in the ability to adjust control in the physical and numerical tasks. The present study examined this suggestion in two experiments in which we manipulated the proportion of neutral/congruent trials in an experimental block. In addition, we examined the effects of control adjustment on the resolution of the task and informational conflicts. Our results suggest that adjustment of control can be bidirectional and is dependent on task requirements. Moreover, it might be easier to inhibit irrelevant information than to inhibit irrelevant task activation.     

A choice-reaction time task utilizing congruent and incongruent colour/word stimuli: another reaction to Stroop

A choice reaction time task was devised, using incongruent colour/word (Stroop-type) and congruent colour/word stimuli. A significant difference was found between reaction times to the two stimulus types with the Stroop-type stimuli eliciting longer reaction times. It is argued that traditional hypotheses about channel limitation can not explain this finding; the suggestion that the delay may lie in the decision-making process is put forward.     

Evidence for task conflict in the Stroop effect

C. M. MacLeod and P. A. MacDonald (2000) suggested that congruent and incongruent Stroop stimuli cause more task conflict than neutral stimuli because the anterior cingulate cortex is more activated with these stimuli. This study investigated behavioral expression for this pattern. Experiment 1 reduced task conflict control by increasing the proportion of nonword neutrals. Additionally, half the trials had conflict or neutral cues. The control reduction revealed the task conflict. For noncued trials, response time was longer for congruent stimuli than for neutral stimuli (reverse facilitation effect). In addition, response time for congruent stimuli was longer when stimuli were uncued vs. cued. Experiment 2 increased task conflict control by changing the neutral stimuli to noncolor words. Consequently, the task conflict expression disappeared.     

The influence of mere social presence on Stroop interference: New evidence from the semantically-based Stroop task

Several studies have shown that mere social presence reduces Stroop interference but processes underlying such effect are still poorly understood. Given that the standard Stroop task used in those studies confounds semantic and response competition, it remains unclear whether Stroop words are processed normally (Sharma, Booth, Brown, & Huguet, 2010) or whether the processing of their semantic representations is altered (Huguet, Galvaing, Monteil, & Dumas, 1999, Exp. 1). The direct evidence from the semantically-based Stroop task (i.e., a task that is free of response competition and thus isolates the semantic component of the Stroop interference, Neely & Kahan, 2001) provided in this paper attests normal semantic processing. Such result refutes the idea that semantic activation can be prevented or controlled by social presence and thus adds to the growing body of evidence showing that semantic activation is indeed automatic. Also importantly, this paper offers an alternative explanation of past findings, which holds that social presence simply reduces the response competition that occurs in the standard Stroop task and sheds some light on the processes that underlie social-facilitating effects of mere presence in the Stroop task.     

Exploring relations between task conflict and informational conflict in the Stroop task

In this study, we tested the proposal that the Stroop task involves two conflicts—task conflict and informational conflict. Task conflict was defined as the latency difference between color words and non-letter neutrals, and manipulated by varying the proportion of color words versus non-letter neutrals. Informational conflict was defined as the latency difference between incongruent and congruent trials and manipulated by varying the congruent-to-incongruent trial ratio. We replicated previous findings showing that increasing the ratio of incongruent-to-congruent trials reduces the latency difference between the incongruent and congruent condition (i.e., informational conflict), as does increasing the proportion of color words (i.e., task conflict). A significant under-additive interaction between the two proportion manipulations (congruent vs. incongruent and color words vs. neutrals) indicated that the effects of task conflict and informational conflict were not additive. By assessing task conflict as the contrast between color words and neutrals, we found that task conflict existed in all of our experimental conditions. Under specific conditions, when task conflict dominated behavior by explaining most of the variability between congruency conditions, we also found negative facilitation, thus demonstrating that this effect is a special case of task conflict.     

Attention, spatial integration, and the tail of response time distributions in Stroop task performance

A few studies have examined selective attention in Stroop task performance through ex-Gaussian analyses of response time (RT) distributions. It has remained unclear whether the tail of the RT distribution in vocal responding reflects spatial integration of relevant and irrelevant attributes, as suggested by Spieler, Balota, and Faust (2000). Here, two colour-word Stroop experiments with vocal responding are reported in which the spatial relation between colour and word was manipulated. Participants named colours (e.g., green; say "green") while trying to ignore distractors that were incongruent or congruent words (e.g., red or green), or neutral series of Xs. The vocal RT was measured. Colour words in colour, white words superimposed onto colour rectangles (Experiment 1), and colour rectangles combined with auditory words (Experiment 2) yielded Stroop effects in both the leading edge and the tail of the RT distributions. These results indicate that spatial integration is not necessary for effects in the tail to occur in vocal responding. It is argued that the findings are compatible with an association of the tail effects with task conflict.