Viewing-position effects in the Stroop task: Initial fixation position modulates Stroop effects in fully colored words

In two experiments that we conducted with adult (Experiment 1) and child (Experiment 2) participants, we experimentally controlled the eyes' first fixation in the word using a variable viewing-position technique in a classical all-letter-coloring Stroop procedure. We explored the impact of initial-fixation position (optimal viewing position [OVP] vs. end of the word) on the magnitude of Stroop effects (both interference and facilitation). The results showed that both interference and facilitation effects were reduced when the first fixation was located at the end of the word rather than at the OVP. These data make a new contribution to the study of the role of low-level processes in Stroop effects and add support to the growing body of research indicating that oculomotor processes can act as moderators of cognitive processes in the determination of Stroop effects.     

Single-letter coloring and spatial cuing do not eliminate or reduce a semantic contribution to the Stroop effect

The automaticity of semantic activation in the Stroop task is still the subject of considerable debate (Augustinova & Ferrand, 2007; Manwell, Roberts, & Besner, 2004). The present experiments were designed to assess whether coloring and cuing a single letter (vs. all letters) in the Stroop task reliably eliminates semantically based Stroop interference or whether the elimination observed by Manwell et al. was due to insufficient statistical power. Experiment 1 was an exact replication of the experiment conducted by Manwell and colleagues and involved a large population. Experiment 2 replicated and extended Experiment 1 by controlling for initial fixation. In line with previous findings obtained by Augustinova and Ferrand, both experiments indicated that coloring and cuing a single letter failed to eliminate or even reduce the semantically based Stroop effect. Thus, these results add to the growing body of evidence suggesting that semantic activation in the Stroop task is automatic.     

Stroop interference effects in partially colored Stroop words

In the Stroop task word reading is thought to be automatic since it runs without intentional monitoring and is difficult to avoid. This view has recently been challenged by observations that Stroop interference is reduced when only part of the Stroop word is colored. In this study we asked whether the extent of Stroop interference varies with the position of the colored letter(s). We observed that Stroop interference was smallest when the first letter(s) were colored and largest when either the last letter(s) or whole word were colored. On these findings we suggest that colored and noncolored parts of partially colored words are processed separately and differently, and that selection of the color dimension for explicit report entails inhibition of the to-be-ignored colored letters.     

The eyes fixate the optimal viewing position of task-irrelevant words

We evaluated whether one’s eyes tend to fixate the optimal viewing position (OVP) of words even when the words are task irrelevant and should be ignored. Participants completed the standard Stroop task, in which they named the physical color of congruent and incongruent color words without regard to the meanings of the color words. We monitored the horizontal position of the first eye fixation that occurred after the onset of each color word to evaluate whether these fixations would be at the OVP, which is just to the left of word midline. The results showed that (1) the peak of the distribution of eye fixation positions was to the left of the midline of the color words, (2) the majority of the fixations landed on the left side of the color words, and (3) the average leftward displacement of the first fixation from word midline was greater for longer color words. These results suggest that the eyes tend to fixate the OVP of words even when those words are task irrelevant.     

Coloring single stroop elements: reducing automaticity or slowing color processing?

Automaticity theory and the effect of coloring a single element were tested with all or only 1 element colored in Stroop tasks. The 312 participants in 5 experiments indicated stimulus presentation color by key press. Experiments 1 and 2 replicated those of D. Besner, J. A. Stoltz, and C. Boutilier (1997) with some changes, and revealed similar results: less Stroop interference with only 1 letter colored. Besner et al. (1997) interpreted the results as indicating that coloring a single letter eliminates automatic reading processes. The cause of that reduction in Stroop interference was investigated in Experiments 3, 4, and 5 using color words, bars, and rectangles. The effect of coloring 1 element was to increase color-naming time by the same amount for congruent and neutral, nonverbal stimuli, but not for incongruent stimuli. The results are interpreted in terms of automaticity theory, and a continuous flow approach to the Stroop effect is presented.     

The Influence of Attitude on Learning

Automaticity theory and the effect of coloring a single element were tested with all or only 1 element colored in Stroop tasks. The 312 participants in 5 experiments indicated stimulus presentation color by key press. Experiments 1 and 2 replicated those of D. Besner, J. A. Stoltz, and C. Boutilier (1997) with some changes, and revealed similar results: less Stroop interference with only 1 letter colored. Besner et al. (1997) interpreted the results as indicating that coloring a single letter eliminates automatic reading processes. The cause of that reduction in Stroop interference was investigated in Experiments 3, 4, and 5 using color words, bars, and rectangles. The effect of coloring 1 element was to increase color-naming time by the same amount for congruent and neutral, nonverbal stimuli, but not for incongruent stimuli. The results are interpreted in terms of automaticity theory, and a continuous flow approach to the Stroop effect is presented.     

Presenting two incongruent color words on a single trial does not alter Stroop interference

Two experiments showed that having two incongruent words present on a single Stroop trial (e.g., bothred andgreen in blue, say “blue”) did not alter interference relative to having only one incongruent word. This was true whether the two incongruent words were presented successively at several stimulus onset asynchronies (Experiment 1) or simultaneously in adjacent positions (Experiment 2). We argue that the first word captures attention and “locks out” others, preventing additional interference.     

A slow component of classic Stroop interference

The interference in colour naming may extend beyond critical Stroop trials. This “slow” effect was first discovered in emotional Stroop tasks, but is extended here to classical Stroop. In two experiments, meaningless coloured letter strings followed a colour word or neutral word. Student participants (Experiment 1), and 18 stroke patients and 18 matched controls (Experiment 2) showed substantial interference by incongruent colour words, both in the word trial (fast component) and in the subsequent string trial (slow component). Different patient subgroups emerged from the comparison of Stroop performance with the controls. An association of fast and slow components was only found in one subgroup. Exploratory analyses revealed no clear differences in damage location between subgroups. Fast interference caused by colour-meaning conflict may be specific for classical Stroop, but the broader occurrence of slow effects suggests a more generalised process of disengagement from attention-demanding stimuli.     

Priming and interference effects can be dissociated in the Stroop task: new evidence in favor of the automaticity of word recognition

Recently, Besner, Stolz, and Boutilier (1997) showed that by coloring a single letter instead of the whole word, Stroop interference is reduced or even eliminated, a result that is at odds with the widely accepted assumption that word recognition is automatic. In a replication of the Besner et al. study, we computed priming effects in addition to the standard Stroop interference. Interference results replicated those of Besner et al. Also, negative priming in the all-letter-colored condition and positive priming in the single-letter-colored condition were obtained. Priming findings demonstrate that word processing can take place in the absence of interference effects. These results support the view of automatic processing of words in the Stroop task and call for priming as a more appropriate measure of word processing than interference.     

Stroop interference: An input and an output phenomenon

Three theories of Stroop interference are considered: perceptual conflict theory (Hock and Egeth, 1970), response competition theory (Morton, 1969) and conceptual encoding theory (Seymour, 1977). The first two fail to provide a full explanation of the available data, and Seymour's evidence is incomplete. Two experiments are reported. In the first, typical Stroop interference occurs in naming colour patches. In the second, subjects responded to colour patches with learned letter name responses. Both stimulus-related (incongruent colour names) and response-related (incongruent letters) distractors produced interference. These results indicate that any theory which assumes only a single locus for interference is incomplete. Conceptual encoding conflict and a modified form of response competition are suggested as possible dual mechanisms for Stroop interference effects.     

On the immunity of perceptual implicit memory to manipulations of attention

In four experiments, we examined the effect of manipulating study phase attention in a Stroop task on the extent of repetition priming in the lexical decision task (LDT). Experiment 1 replicated the immunity of the LDT to division of attention reported by Szymanski and MacLeod (1996), using a standard Stroop configuration. Response times to previously encountered words were identical regardless of whether the participants were required to read the words or name the color in which they were presented. Experiment 2 demonstrated that implementing the Stroop manipulation across separate visual objects reduced but did not eliminate priming of unattended words, provided the words remained in the attended region of the stimulus display. When this constraint was removed in Experiment 3, priming of unattended words disappeared. Experiment 4 demonstrated statistically equivalent priming for attended and unattended words when the Stroop manipulation remained in the same visual object but attention was directed to a single letter of the word. In all four experiments, the Stroop manipulation had a clear effect on recognition. These results qualify claims that the LDT might be immune to manipulations of study phase attention and suggest that the LDT has a lower threshold level of attention at encoding than do other standard implicit tests of memory.     

Is the optimal viewing position in reading influenced by familiarity of the letter string?

An optimal viewing position (OVP) for word recognition has been proposed by several authors. The location of this position would be located at the center of the word or just left of it. Several hypotheses ranging from perceptual to hemispheric factors have been proposed to explain this phenomenon. In the experiment presented here, the effect of the nature of the stimulus was tested: word, pseudo-word, or nonword on the existence and location of this position. Little research has investigated this issue. Five-letter words, pseudo-words, and non-words were presented, with the subject fixating initially on one of the five possible letter positions. The number of letters correctly identified and reading performance were recorded for each stimulus. Results show that an initial fixation on the third letter entails better letter identification for all kinds of stimuli. However, in terms of reading, only word reading benefit from a fixation on the third letter. These results are discussed in relation to the different hypotheses of OVP in reading. These are (1) hemispheric specialization, (2) reading habits, and (3) lexical constraints.     

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.     

Coloring only a single letter does not eliminate color-word interference in a vocal-response Stroop task: automaticity revealed

The presence of an interference effect in naming the print color of color words (J. R. Stroop, 1935) suggests that responses associated with the irrelevant-word dimension of the display are activated involuntarily. In the present study, the author examined the conditions under which coloring a single letter in a word reduced interference in vocal responding (D. Kahneman & A. Henik, 1981) or eliminated it in manual responding (D. Besner, J. A. Stolz, & C. Boutilier, 1997). In Experiment 1, color-word interference was significant under vocal responding for the Besner et al. displays. In Experiment 2, the author replicated the Kahneman and Henik effect with the Besner et al. stimuli. The results of Experiment 3 showed that semantic effects are not eliminated by coloring only a single letter. Coloring a single letter does not prevent the activation of the irrelevant-word dimension of the colored color word.     

Coloring Only a Single Letter Does Not Eliminate Color-Word Interference in a Vocal-Response Stroop Task: Automaticity Revealed

The presence of an interference effect in naming the print color of color words (J. R. Stroop, 1935) suggests that responses associated with the irrelevant-word dimension of the display are activated involuntarily. In the present study, the author examined the conditions under which coloring a single letter in a word reduced interference in vocal responding (D. Kahneman & A. Henik, 1981) or eliminated it in manual responding (D. Besner, J. A. Stolz, & C. Boutilier, 1997). In Experiment 1, color-word interference was significant under vocal responding for the Besner et al. displays. In Experiment 2, the author replicated the Kahneman and Henik effect with the Besner et al. stimuli. The results of Experiment 3 showed that semantic effects are not eliminated by coloring only a single letter. Coloring a single letter does not prevent the activation of the irrelevant-word dimension of the colored color word.     

Single letter coloring and spatial cuing eliminates a semantic contribution to the Stroop effect

Previous work has shown that the Stroop effect is reduced in size when a single letter is colored and spatially precued. The present experiment addresses a number of criticisms of this work by (1) providing a direct measure of semantic processing, (2) using a vocal response instead of a manual one, and (3) using a more appropriate baseline. A semantically based Stroop effect (slower color naming for color-associated words than for color-neutral words) is observed when all letters in the display are precued and appear in a homogeneous color. This Stroop effect is statistically eliminated when a single letter is precued and is the “odd man out” in terms of its color. Two explanations are considered. In one, single-letter coloring and cuing serve to curtail semantic processing. In the other, single-letter coloring and cuing help to keep the informational sources (i.e, color, word) separate and hence reduce interference, but semantic analysis is not curtailed. The latter account provides a more complete account of existing data.     

Response interference in compatibility tasks

Affective priming (AP) is a well-established phenomenon in which performance to a valenced target is typically better when it is preceded by an affectively congruent prime than when it is preceded by an incongruent prime. Several studies have emphasized a strong similarity between AP and Stroop suggesting that both are driven by response interference. The present study investigated this hypothesis by testing whether a general prediction of the response interference model was verified in the two tasks. This prediction refers to target strength and states that the size of compatibility effects should increase as the strength of the relevant information decreases. In four experiments, we show that this general prediction of the response interference model was verified in AP and Stroop when the strength of the relevant information was manipulated at the perceptual level (Experiments 1 and 2), while the opposite pattern was observed when this variable was manipulated at the semantic level (Experiments 3 and 4). While the results do not undermine the hypothesis that AP and Stroop effects are governed by response interference, they suggest that the model should be refined in order to account for differential effects of target strength in compatibility tasks.     

Integration versus separation in Stroop‐like counting interference tasks1

Abstract: Two versions of a Stroop‐like counting interference task were compared to examine how irrelevant information is ignored. In the integrated task, participants enumerated digits (inconsistent condition) or letters (neutral condition) while attempting to ignore the identity of the characters. In the newly created separated task, participants enumerated asterisks while attempting to ignore a single digit (inconsistent condition) or letter (neutral condition) at fixation. Interference (longer responses in the inconsistent condition than in the neutral condition) was small but significant in both tasks but was not reduced by separation. Contrasted with the pattern in the color–word Stroop task, these results suggest that dimensional separation has different effects on interference depending on the overall amount of interference.     

Time-course of Spatial-attentional Focusing in the Case of High Processing Demand on the Peripheral Precue

Subjects had to identify pairs of spatially overlapping or neighbouring letters exposed successively at various locations around the central fixation. The first letter (S1) in a pair acted both as a physical precue to indicate the S2 location and as a stimulus letter to be identified. The second letter (S2) in a pair acted only as a letter to be identified. The SOA was varied between 0 and 320 ms in different experiments. Comparison of the time-course functions of S2 identification in the conditions of (1) single pair presentation and (2) presentation of the letter pairs in the context of distractor letters that accompanied S2 in time, but occupied alternative spatial positions, revealed that S2 processing from the covert spatial-attentional focus was open to non-decreasing interference from the distractor letters up to 240 ms SOAs. An unexpected result consisted in equal level of S2 identification regardless of whether S1 had to be identified or not. This shows that if the peripheral precue has to be processed with higher processing demands at the identification level beyond simple location processing (which by itself is sufficient to fulfil the spatial orienting function), then the narrowing down or zooming-in of the attentional area in response to a physical precue can take place as effectively as in the case of a lesser processing demand on that precue. By comparing the relative time-course functions of S1 and S2 identification, it was found that S2 identification gained significant advantage over S1 identification at intermediate SOAs even if the intensity of S1 exceeded that of S2. The results of this investigation refer to the spontaneous, automatic nature of spatial attentional focusing that is evoked by spatially localised transient signals, but also to the possibility of interference between the targets and distractors in the working memory representation.     

The modulation of spatial congruency by object-based attention: analysing the "locus" of the modulation

Earlier studies have demonstrated that spatial cueing differentially reduces stimulus-stimulus congruency (e.g., spatial Stroop) interference but not stimulus-response congruency (e.g., Simon; e.g., Lupiá?ez & Funes, 2005). This spatial cueing modulation over spatial Stroop seems to be entirely attributable to object-based attention (e.g., Luo, Lupiá?ez, Funes, & Fu, 2010). In the present study, two experiments were conducted to further explore whether the cueing modulation of spatial Stroop is object based and/or space based and to analyse the "locus" of this modulation. In Experiment 1, we found that the cueing modulation over spatial Stroop is entirely object based, independent of stimulus-response congruency. In Experiment 2, we observed that the modulation of object-based attention over the spatial Stroop only occurred at a short cue-target interval (i.e., stimulus onset asynchrony; SOA), whereas the stimulus-response congruency effect was not modulated either by object-based or by location-based attentional cueing. The overall pattern of results suggests that the spatial cueing modulation over spatial Stroop arises from object-based attention and occurs at the perceptual stage of processing.