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.     

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.     

Anxiety and speaking in people who stutter: An investigation using the emotional Stroop task

People with anxiety disorders show an attentional bias towards threat or negative emotion words. This exploratory study examined whether people who stutter (PWS), who can be anxious when speaking, show similar bias and whether reactions to threat words also influence speech motor planning and execution. Comparisons were made between 31 PWS and 31 fluent controls in a modified emotional Stroop task where, depending on a visual cue, participants named the colour of threat and neutral words at either a normal or fast articulation rate. In a manual version of the same task participants pressed the corresponding colour button with either a long or short duration. PWS but not controls were slower to respond to threat words than neutral words, however, this emotionality effect was only evident for verbal responding. Emotionality did not interact with speech rate, but the size of the emotionality effect among PWS did correlate with frequency of stuttering. Results suggest PWS show an attentional bias to threat words similar to that found in people with anxiety disorder. In addition, this bias appears to be contingent on engaging the speech production system as a response modality. No evidence was found to indicate that emotional reactivity during the Stroop task constrains or destabilises, perhaps via arousal mechanisms, speech motor adjustment or execution for PWS.Educational objectives: The reader will be able to: (1) explain the importance of cognitive aspects of anxiety, such as attentional biases, in the possible cause and/or maintenance of anxiety in people who stutter, (2) explain how the emotional Stroop task can be used as a measure of attentional bias to threat information, and (3) evaluate the findings with respect to the relationship between attentional bias to threat information and speech production in people who stutter.     

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.     

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.     

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.     

A sequential analysis of relevant and irrelevant information in the Stroop task

The effect of repeating relevant (colour) and irrelevant (word) stimulus information is investigated in two Stroop tasks. Thomas (1977) observed that the Stroop effect is reduced when the irrelevant word is repeated from trial n -1 to trial n. A similar effect was observed in the Simon task (Notebaert, Soetens, & Melis, 2001; Notebaert & Soetens, 2003a). MacLeod (1991) interprets this effect as sustained suppression and relates it to negative priming. In this paper we investigate whether the reduced Stroop effect for word repetitions is indeed related to the negative priming effect. In Experiment 1 with a response-stimulus interval (RSI) of 50 ms, the Stroop effect is not influenced by the sequence of the word and there is no negative priming effect. In Experiment 2 with an RSI of 200 ms, the Stroop effect is reduced for word repetitions but there is still no negative priming effect. This does not support the sustained-suppression hypothesis. The reduced Stroop effect for word repetitions is explained in terms of response priming.     

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.     

A reverse Stroop effect without translation or reading difficulty

It is well known that irrelevant color words affect the time needed to identify the color they are displayed in (the Stroop effect). One major view is that a reverse Stroop effect (RSE)—in which the irrelevant color affects the time needed to identify the word—does not occur unless a translation is needed between domain-specific memory codes. In the present article, we report an experiment in which the reverse Stroop effect was investigated by having subjects identify a colored word at fixation by pointing to a location on the screen containing that word. Although the response was untranslated, an RSE was observed. An account is provided in which the strength of association between a stimulus and a specific response plays a central role.     

Generalizability of carry-over effects in the emotional Stroop task

The emotional Stroop task has been the most widely used task to examine attentional bias to emotionally salient stimuli. In one format of this task, words are presented to participants in a mixed randomized or quasi-randomized sequence. Using a mixed smoking Stroop task, we have previously demonstrated that smokers are slower to respond to words which follow smoking-related words than words which follow neutral words. Here we show that this carry-over effect is present in heroin addicts-but not control subjects-in a heroin Stroop task, and in normal subjects in a stress Stroop task. Thus, the effect generalizes to other populations. In addition, an examination of the studies that have collected data from both mixed and blocked formats provides converging evidence for the presence of carry-over effects. We discuss the implications of the carry-over effect for research using the emotional Stroop task.     

Associative facilitation and interference in the Stroop color-word task

It is difficult to name the color of a stimulus when the stimulus is a word naming a different color. When the word is congruent with the color in which it is written, color naming is much quicker. Similar results are also obtained when color-related words are used instead of color names. These results are taken as evidence for the operation of associative factors that could facilitate or impair performance in the color-word task.     

Selective attention and response set in the Stroop task

Response set membership contributes much to the interference in the color-word Stroop task. This may be due to selective allocation of attention to eligible responses or, alternatively, to greater inhibition of distractors that are not responses. In the present article, we report two experiments that were designed to adjudicate between these accounts. In Experiment 1, membership was manipulated on a trial-by-trial basis by cuing the possible responses for each trial. Response time (RT) was longer for distractors that corresponded to a cued, eligible response than to an ineligible one. This cuing effect was independent of the number of different responses. In Experiment 2, the distractor was cued on half the trials. Cuing the distractor decreased RTs on both incongruent and congruent trials. Vincentile analyses in both experiments revealed that the effects were constant throughout the entire RT distributions. These results suggest that response set effects arise because of selective allocation of attention to eligible responses.     

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.     

Sequential modulations of valence processing in the emotional Stroop task

This study investigated trial-to-trial modulations of the processing of irrelevant valence information. Participants (N = 126) responded to the frame color of pictures with positive, neutral, or negative affective content--a procedure known as an emotional Stroop task (EST). As is typically found, positive and negative pictures delayed responses as compared to neutral pictures. However, the type and extent of this valence-based interference depended on the irrelevant picture valence in the preceding trial. Whereas preceding exposure to negative valence prompted interference from positive and negative pictures, such interference was removed after neutral trials. Following positive pictures, interference from negative but not from positive pictures was observed. We suggest that these sequential modulations reflect automatic self-regulatory selection processes that help to keep the balance between attending to task-relevant information and task-irrelevant information that signals important changes in the environment.     

Word reading practice reduces Stroop interference in children

Stroop interference is thought to index reading automaticity and is expected to increase with reading practice and to decrease with improved color naming. We investigated the effects of practice in word reading and color naming on interference in 92 adults and 109 children in Grades 4–5. For children, interference was reduced after reading practice with color words. In neither group was interference affected by practice in color naming of neutral stimuli. These findings are consistent with a direct negative relationship between reading ability and interference and challenge the automaticity account in favor of a blocking mechanism whereby interference is determined by the delay to inhibit the reading response rather than by the efficiency of color naming.     

Exploring the temporal dynamics of social facilitation in the Stroop task

The importance of social context in affecting attention has recently been highlighted by the finding that the presence of a passive, nonevaluative confederate can improve selective attention. The underlying mechanism, however, remains unclear. In this paper, we argue that social facilitation can be caused by distractor inhibition. Two distinct sources of evidence are provided from an experiment employing the Stroop task with and without social presence. First, analysis of the response time (RT) distribution indicates that interference is reduced at relatively long RTs. This is consistent with an inhibitory mechanism, whose effects build up slowly. Further support is provided by showing that social facilitation is prevented by using short response-to-stimulus intervals that are thought to reduce cognitive control processes.