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.     

New data analysis of the stroop matching task calls for a reevaluation of theory

In Stroop matching tasks, participants indicate whether the color of an object matches the meaning of a color word printed in color. Previously in this journal, Luo (1999) concluded that interference between two incongruent representations of the same attribute (ink color) occurs prior to the response stage. However, this conclusion was based on questionable data analysis. We suggest analyzing the data by separating "same" and "different" responses and then analyzing three congruency conditions within the "different" responses: (a) congruence between word color and word meaning, (b) congruence between word color and object color, and (c) incongruence between word color, word meaning, and object color. In an experiment similar to Luo's, such an analysis revealed that responding was slowest in the first condition. This pattern of results does not fit with previous conclusions regarding this task, but rather indicates that task conflict and response competition contribute to interference. This analysis has implications for matching tasks other than the Stroop matching task.     

Developmental differences in the impact of contextual factors on susceptibility to retroactive interference

The influence of contextual similarity on children’s recognition memory performance was examined using a retroactive interference paradigm. In the study, 9- and 12-year-olds were randomly assigned to one of two contextual conditions. In both conditions, target and interfering information were presented in distinctive contexts by using different modalities (pictures and words, respectively). However, in one condition the test was presented in the same context as the target information (picture–word–picture [PWP] condition), whereas in the other condition the test was presented in the same context as the interfering information (picture–word–word [PWW] condition). Performance in these conditions was compared with performance in a noninterference control condition (picture–word [P-W]). As predicted, overall recognition performance in the PWP condition was significantly better than in the PWW condition. However, whereas in the PWP condition there was no age difference in performance, in the PWW condition the 12-year-old group produced significantly more hits and fewer false alarms than the 9-year-old group. The theoretical implications of the results are discussed in reference to the effortful engagement of developmentally dependent executive control processes.     

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.     

Case-mixing effects on anagram solution

The effects of mixed-case letters on anagram solution were investigated in 2 studies with college-aged participants. In Experiment 1, the participants attempted to solve anagrams printed in either mixed- or same-case letters. The results showed that mixed-case letters disrupted the solution process. To determine if this effect was a result of the inappropriate grouping of letters of the same case, the authors conducted Experiment 2 as a partial replication of Experiment 1. In Experiment 2, in some cases, uppercase letters in the mixed-case condition formed a word that was of a higher frequency than was the solution word. Once again mixed-case letters disrupted the solution process. However, the authors found no evidence for the hypothesis on the inappropriate grouping of letters as the disruption was independent of having an embedded word in the anagram.     

Large number discrimination in 6-month-old infants

Two experiments with the Stroop paradigm were conducted to investigate the role of phonological codes in access to the meaning of Chinese characters. Subjects named the ink color of viewed characters or color patches. Key items were color characters, their homophones with the same tone, homophones with different tones, and semantic associates. Apart from finding the usual Stroop interference effect, homophones produced significant interference in the incongruent condition, provided that they had the same tone as the color characters. The interference effect from homophones, however, was significantly smaller than that from color characters. Semantic associates generated an interference effect in the incongruent condition, an effect of the same magnitude as the effect from the same-tone homophones. Finally, in the congruent conditions, all the key items yielded facilitations compared to neutral controls, though the facilitation from color characters was larger than the facilitations from other types of characters. These findings suggest that phonological codes in Chinese are activated obligatorily and provide early sources of constraint in access to meaning.     

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.     

Is there a genuine advantage to the upper part of words during lexical access? Evidence from the Stroop task

A number of recent visual-word recognition and reading experiments have concluded that the upper part of words is more important for lexical access than is the lower part, which conforms with Huey’s (1908) observation. Here, we examined whether this phenomenon may simply be due to the fact that words in Indo-European languages tend to have a higher number of confusable letters in the lower than in the upper part. We manipulated the letter ambiguity of the upper and lower parts of words in two experiments in which we asked participants to report the presentation color of the upper and lower parts of color words and noncolor words, and in a baseline condition, of strings of &s (Stroop task). In Experiment 1, the lower part of noncolor words was more ambiguous than the upper part (upward-unbalanced words), whereas in Experiment 2, the ambiguities of the two parts of the noncolor words were similar (balanced words). For the upward-unbalanced noncolor words, the magnitude of lexical interference (relative to the baseline condition) was greater for the upper than for the lower part. Critically, the differences vanished when this factor was controlled (i.e., balanced words; Exp. 2). Thus, the apparent bias in favor of the upper part of words can be parsimoniously described as an idiosyncratic feature of the words’ component letters.     

Color segregation and selective attention in a nonsearch task

Relations between selective attention and perceptual segregation by color were investigated in binary-choice reaction time experiments based on the non search paradigm of Eriksen and Eriksen (1974). In focused attention conditions (Experiment 1), noise letters flanking a central target letter caused less interference when they differed from the target in color, although color carried no information as to whether or not a letter was the target. When blocking of trials favored a strategy of dividing attention between target and noise letters (Experiment 2), no benefit accrued from difference between target color and noise color. The results supported an attentional interpretation of the effect of color demonstrated in Experiment 1, implying that perceptual segregation by color improved the efficiency of focusing attention on the target.     

The development of automatic word recognition and reading skill

The development of automatic word recognition as a function of reading skill was investigated in three experiments using the Stroop task. Reading skill level ranged from nonreaders to readers above the sixth-grade equivalent. Interference with color naming begins to emerge early in the process of learning to read, increases, and then subsequently decreases. Strings of identical letters delayed color naming for children just beginning to learn to read. The interference from words, presumably reflecting semantic processing, began developing early but did not peak until the second- to fourth-grade reading levels. These different sequences of development of interference in the various stimulus conditions suggest that word recognition is the result of a number of component processes that develop as children acquire skill in reading.     

Information influences the pattern of eye fixations during sentence comprehension

How does the pattern of eye fixation vary as an informative part of a word is encountered? If the processing of information lags behind the movement of the eyes, then we should expect no variation in the pattern; but if processing is immediate, then the movements of the reader's eyes should correspond to the distribution of information being inspected. An experiment is reported which examined the ways that the text ahead of the point of current fixation can be used to guide the eyes to future fixations, by monitoring fixations during a sentence comprehension task. The patterns of eye fixations upon words with uneven distributions of information (where, for example, words predictable from the sight of their first few letters but not from their last few letters are defined as containing informative beginnings) were observed, and it was found that more and longer fixations were produced when subjects looked at the informative parts of words, particularly at the informative endings of words. The results support the suggestion that eye movements are under the moment-to-moment control of cognitive mechanisms.     

Division of the articulatory loop according to sensory modality using double dissociation

According to Wilson and Fox (2007), working memory for gestures has the same characteristics as the phonological loop. The purpose of our research was to determine whether there is a common articulatory loop for verbal and gestural learning. We carried out two double dissociation experiments. The first involved 84 participants who had to reproduce a series of three gestures under three conditions: control, gestural interference (repeated gestures) and verbal interference (repeated “blah blah”). A significant difference in performance was observed; gestural interference resulted in the weakest performance, while there was no difference between the verbal interference condition and the control group. The second experiment, with 30 participants, involved the memorisation of letters and digits; performance was significantly affected by verbal interference but there was no difference between the gestural interference condition and the control group. The consequences of the dissociations are discussed in relation to Baddeley's (2000) model.     

Individual differences in Stroop dilution: tests of the attention-capture hypothesis.

Kahneman and Chajczyk (1983) found that naming a colored bar was slowed when a color word was nearby but that this decrement was reduced when a neutral word was also present. This has been referred to as the dilution effect. They accounted for their results with an attention-capture hypothesis. Response time distributions to stimuli that contained a color word and a neutral word within individuals were examined. The dilution effect did not appear within individuals. Some individuals exhibited strong Stroop interference effects, whereas others exhibited no interference. Experiment 2 showed that the interference pattern within individuals was consistent across days. Experiment 3 showed that performance could not be explained by a selection strategy that was based on word length. These experiments showed that performance in a color-plus-neutral word condition reflects a systematic pattern of interference or noninterference that varies across individuals.     

Role of Gestalt grouping in selective attention: evidence from the Stroop task

Selective attention has been intensively studied using the Stroop task. Evidence suggests that Stroop interference in a color-naming task arises partly because of visual attention sharing between color and word: Removing the target color after 150 msec reduces interference (Neumann, 1986). Moreover, removing both the color and the word simultaneously reduces interference less than does removing the color only (La Heij, van der Heijden, & Plooij, 2001). These findings could also be attributed to Gestalt grouping principles, such as common fate. We report three experiments in which the role of Gestalt grouping was further investigated. Experiment I replicated the reduced interference, using words and color patches. In Experiment 2, the color patch was not removed but only repositioned (<2 degrees) after 100 msec, which also reduced interference. In Experiment 3, the distractor was repositioned while the target remained stationary, again reducing interference. These results indicate a role for Gestalt grouping in selective attention.     

Hierarchical structure in printed word recognition

Summary Naming-latency experiments are reported which compare theories of printed word recognition that assume direct vs. indirect mapping of a word's letter pattern onto a lexical representation. Inflected Dutch verbs were presented to subjects with all letters shown at once, and with some letters withheld for 30 or 60 ms. When letters were initially withheld, the part of a wordform first displayed included its stem, its root, its grammatical affix(es), and, if prefixed, its prefix and the part following the prefix. Nonmorphological control conditions were also defined. The priming effects found on naming latencies tend to support some morphologically mediated mapping of letter strings onto lexical items. Most facilitation was found when the stimulus information first presented included a word's root morpheme and was word initial. For lexically prefixed verbs a further division was supported between the morphs composing a word's stem.     

Differences between Chinese morphosyllabic and German alphabetic readers in the Stroop interference effect

The goal of our study was to localize the source of the stronger Stroop interference effect found in morphosyllabic readers as compared with alphabetic readers. Twenty-three Chinese and 24 German undergraduate students were tested in a Stroop paradigm with the following stimuli: color patches, colorneutral words (e.g.,friend printed in yellow), incongruent color-associated words (e.g.,blood printed in blue), and incongruent color words (e.g.,yellow printed in blue). Results revealed no differences in German and Chinese students’ response times to color patches. Chinese participants, however, showed longer color naming latencies for neutral words as well as for color words and color-related words. No differences between German and Chinese participants were found when print color latencies for neutral words were subtracted from print color latencies for color words and color-related words. This result does not support theories which suggest that for morphosyllabic readers there is a direct route from orthography to the semantics of a word. We rather argue, with reference to dual route models of reading, that access from print to phonology is faster for morphosyllabic than for alphabetic readers, and therefore interference caused by conflicting phonologies of color name and written word will be stronger in Chinese readers than in German readers.     

The interfering effect of word perception on letter identification

Subjects identified a single lowercase letter in a visual display by pressing one of two buttons. Two letters were assigned to each response. Groups received one of three context conditions: word, nonword, or single-letter displays. In words and nonwords, the flanking letters adjacent to the target varied as to whether they were response compatible or incompatible with the target. Single letters produced faster response latencies than either multi-letter condition, and words yielded slower latencies than did nonwords. Items Containing an incompatible-response flanking letter produced longer latencies than items containing a compatible flanking letter. Subgroups of subjects with different characteristic processing patterns were identified with a separate test. These subgroups were differentially affected by the context conditions in the letter-identification task. A greater subgroup difference was found in nonwords than in words.     

The availability of useful information to the right of fixation in reading

A series of experiments that examined the characteristics of useful information to the right of fixation during reading is reported. In Experiments 1 and 2, reading performance when the information available to the right of fixation was determined by a fixed number of letters was compared with reading performance when the information to the right of fixation was determined by a fixed number of words. Beyond making more letters visible, both experiments showed that preserving all of the letters of a word was of no special benefit to reading. By explicitly presenting parts of the word to the right of fixation as well as the fixated word, Experiments 3 and 4 followed up on the implication that readers utilize partial letter information from words. Both experiments showed that reading was improved by this partial information and that preserving three letters of the word to the right of fixation improved reading almost as much as presenting the entire word. The implications the results have for models of reading are discussed.     

On access representation in visual word recognition: The temporal separation technique

Summary This paper examines the evidence for an access representation based on the initial part of the word. A temporal separation technique, which presents test words in two parts, was used, and varied as to whether the first part included two, three, or four initial letters of a word. In contrast with previous studies, word-frequency effects were used to assess whether access had occurred from that initial part. Experiment 1 (in English) tested the validity of the temporal separation technique, and showed that it does impose an input segmentation. Experiments 2 (in English) and 3 (in Spanish) examined whether access to a monomorphemic word is achieved, using word frequency as a diagnostic of access. The implications of the findings for the notion of a partial input representation for access are discussed.     

Word-fragment cuing: the lexical search hypothesis

In four experiments we evaluated aspects of the hypothesis that word-fragment completion depends on the results of lexical but not semantic search. Experiment 1 showed that the number of meaningful associates linked to a studied word does not affect its recovery when the test cue consists of letters and spaces for missing letters. Experiments 2 and 3 showed retroactive interference effects in fragment completion when words in a second list were lexically related to words in a first list but not when the words in the second list were meaningfully related. Experiment 4 indicated that for studied words, instructions to search at the word level facilitated completion performance and that instructions to generate letters to fill missing spaces had no effect. Other findings indicated that completion was affected by the number of words lexically related to the fragment and by the number of letters missing from the fragment. In general, experimental manipulations that focused on lexical characteristics were effective, and those that focused on semantic characteristics were ineffective. The findings support the conclusion that word fragments engender a lexical search process that does not depend on retrieving encoded meaning.