The interference of various word parts on color naming in the Stroop test

The loci of Stroop effects: a critical review of methods and evidence for levels of processing contributing to color-word Stroop effects and the implications for the loci of attentional selection

Despite instructions to ignore the irrelevant word in the Stroop task, it robustly influences the time it takes to identify the color, leading to performance decrements (interference) or enhancements (facilitation). The present review addresses two questions: (1) What levels of processing contribute to Stroop effects; and (2) Where does attentional selection occur? The methods that are used in the Stroop literature to measure the candidate varieties of interference and facilitation are critically evaluated and the processing levels that contribute to Stroop effects are discussed. It is concluded that the literature does not provide clear evidence for a distinction between conflicting and facilitating representations at phonological, semantic and response levels (together referred to as informational conflict), because the methods do not currently permit their isolated measurement. In contrast, it is argued that the evidence for task conflict as being distinct from informational conflict is strong and, thus, that there are at least two loci of attentional selection in the Stroop task. Evidence suggests that task conflict occurs earlier, has a different developmental trajectory and is independently controlled which supports the notion of a separate mechanism of attentional selection. The modifying effects of response modes and evidence for Stroop effects at the level of response execution are also discussed. It is argued that multiple studies claiming to have distinguished response and semantic conflict have not done so unambiguously and that models of Stroop task performance need to be modified to more effectively account for the loci of Stroop effects.

A rostro-caudal axis for language in the frontal lobe: the role of executive control in speech production

The present article promotes a formal executive model of frontal functions underlying speech production, bringing together hierarchical theories of adaptive behavior in the (pre-)frontal cortex (pFC) and psycho- and neurolinguistic approaches to spoken language within an information-theoretic framework. Its biological plausibility is revealed through two Activation Likelihood Estimation meta-analyses carried out on a total of 41 hemodynamic studies of overt word and continuous speech production respectively. Their principal findings, considered in light of neuropsychological evidence and earlier models of speech-related frontal functions, support the engagement of a caudal-to-rostral gradient of pFC activity operationalized by the nature and quantity of speech-related information conveyed by task-related external cues (i.e., cue codability) on the one hand, and the total informational content of generated utterances on the other. In particular, overt reading or repetition and picture naming recruit primarily caudal motor-premotor regions involved in the sensorimotor and phonological aspects of speech; word and sentence generation engage mid- ventro- and dorsolateral areas supporting its basic predicative and syntactic functions; finally, rostral- and fronto-polar cortices subsume domain-general strategic processes of discourse generation for creative speech. These different levels interact in a top-down fashion, ranging representationally and temporally from the most general and extended to the most specific and immediate. The end-result is an integrative theory of pFC as the main executive component of the language cortical network, which supports the existence of areas specialized for speech communication and articulation and regions subsuming internal reasoning and planning. Prospective avenues of research pertaining to this model's principal predictions are discussed.

Does response interference contribute to face composite effects?

Holistic processing of faces can be measured as a failure of selective attention to one face-half under instructions to ignore the other face-half in a naming or same/different matching task. But is interference from the irrelevant half due to response interference rather than to holistic processing? Here, participants learned to name two faces "Fred" and two "Bob." At test, composites were created from top and bottom halves of different learned faces or of a novel face, and composites were either aligned or misaligned. Naming was slower when the irrelevant half was from a different face as opposed to the same face, regardless of whether it was associated with the same name, a different name, or no name, suggesting holistic processing. Interference was eliminated when composite halves were misaligned. These results suggest that, unlike Stroop effects, composite effects are not due to response interference.

Orthographic Overlap and Category Size in Unconscious Category Priming

Van den Bussche and Reynvoet (2007, Experiment 1 ) report unconscious priming of comparable magnitude from novel words belonging to small and large categories, evidence that they interpret as demonstrating independence from category size of priming that involves semantic analysis. Three experiments raise the possibility that the findings in Experiment 1c of Van den Bussche and Reynvoet reflect subword processing, not semantic analysis. In Experiments 1 and 2, priming was obtained from primes and targets that shared approximately the same degree of subword features as in Experiment 1c of Van den Bussche and Reynvoet, but no priming occurred when sharing of features was minimized. Experiment 3 demonstrated priming driven by subword features when those features were set in opposition to whole-word meaning. These results indicate that orthographic overlap must be considered a potentially important confound in findings that ostensibly support priming mediated by semantic analysis.

An Optimal Viewing Position Effect in the Stroop Task When Only One Letter Is the Color Carrier

Abstract. Coloring only a single letter in the Stroop task can result in a reduction or elimination of Stroop interference. The present experiments were designed to test whether this modulation of Stroop interference occurs at all letter positions. Specifically, we investigated whether Stroop interference was reduced when the colored letter occupied the optimal viewing position (OVP). The experiments show that Stroop interference is not reduced at the OVP (Experiment 1) and that Stroop interference at the OVP is significantly greater than at other letter positions (Experiments 1 and 2). This finding has important theoretical and methodological consequences for studies of automatic processing in visual word recognition.

Unconscious semantic priming in the absence of partial awareness

In a recent paper in Psychological Science, Kouider and Dupoux reported obtaining unconscious Stroop priming only when subjects had partial awareness of the masked distractor words (i.e., could consciously perceive subword features that enabled reconstruction of whole words). Kouider and Dupoux conjectured that semantic priming occurs only when such partial awareness is present. The present experiments tested this conjecture in an affective categorization priming task that differed from Kouider and Dupoux's in using masked distractors that subjects had practiced earlier as visible words. Experiment 1 showed priming from practiced words when subjects had no partial awareness of those words. Experiment 2 showed that, in the absence of partial awareness, practiced words yielded priming but not-practiced words did not. Experiment 3 corroborated Experiment 1 and 2s results using a different test of partial awareness. These results suggest that unconscious processing (rather than partial awareness) of subword elements drives masked semantic priming by practiced words.

Stroop-like serial position effects in color naming of words and nonwords

Color-naming latencies to noncolor words and nonwords were faster when the onset or final phoneme of the displays corresponded to the onset or final phoneme of the color response. For example, for displays printed in red, the word rack and nonword rask, which share the initial onset phoneme with the response, led to faster naming than did the control word chap and nonword chup. Conversely, when the onset or final phoneme of the displays matched the onset or final phoneme of a conflicting color response (e.g., rack printed in blue), latencies were longer than to control items. Facilitation effects were stronger than interference effects, and the onset phoneme facilitation effect was augmented by coloring only the initial letter in the display. It is hypothesized that nonlexical processes that govern the translation of print to speech may be a source of facilitation in Stroop-like tasks, whereas lexical processes are more likely to contribute to 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.

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.

Stroop interference and negative priming: problems with inferences from null results

The Stroop color-naming effect has often been taken as evidence for the automaticity of word processing (MacLeod, 1991). Recently, Besner, Stolz, and Boutilier (1997) reported that coloring a single letter instead of the whole word eliminated the Stroop effect. From this finding, they concluded that word processing could not be purely automatic, since it can be prevented. We asked whether the elimination of the Stroop effect is sufficient evidence for concluding that the word is not processed. Combining Besner et al.'s manipulation with a negative-priming procedure, we found intact negative priming from the prime color word in the absence of a Stroop effect. This result clearly indicates that the meaning of the prime word was processed. The findings highlight the importance of using converging methods to evaluate lack of processing.

A position-sensitive Stroop effect: further evidence for a left-to-right component in print-to-speech conversion

In the classical Stroop effect, response times for naming the color in which a word is printed are affected by the presence of semantic, phonological, or orthographic relationships between the stimulus word and the response word. We show that color naming responses are faster when the printed word shares a phoneme with the color name to be produced than when it does not, in conditions where there is no semantic relationship between the printed word and the color name. This result is compatible with a variety of computational models of reading. However, we also found that these effects are much larger when it is the first phoneme that the stimulus and response share than when it is the last. Our data are incompatible with computational models of reading in which the computation of phonology from print is purely parallel. The dual route cascaded model computational model of reading, which has a lexical route that operates in parallel and a nonlexical route that operates serially letter by letter, successfully simulates this position-sensitive Stroop effect. The model also successfully simulates the "onset effect" in masked priming (Forster & Davis, 1991) and the interaction between the regularity effect and the position in a word of a grapheme-phoneme irregularity (Rastle & Coltheart, 1999b)--effects which, we argue, arise for the same reason as the position-sensitive Stroop effect we report.

Nonconscious reading? Evidence from neglect dyslexia

In this study we present evidence which supports the view that reading mechanisms, if implicit assessed, are available also in the presence of a severe deficit of spatial awareness. A Stroop-like task was performed by a right brain-damaged patient affected by severe extrapersonal neglect and neglect dyslexia. In reading words and color words, the patient showed the usual pattern of neglect errors; omission, substitution and addition errors. However, when asked to name the colors in which color words were written, naming time was found to be affected by the meaning of those words he was not able to read correctly. The pattern of results in MD and in a group of normal subjects, who performed a modified version of the Stroop test performed by MD, have been interpreted as evidence of MD's implicit reading of the left-hand letters of color words during the Stroop test. The theoretical implications of this finding are discussed. Moreover, the comparison between the performance of MD and the performance of another group of normal subjects suggested that implicit processing in MD was carried out at a lower level of efficiency than in normals.

The processing of non-target words: semantic or not?

It is known that people reacting to visual words may be affected by the meaning of accompanying non-target words. On the approach to perception developed by Treisman (e.g. 1986), this is surprising, because meaning might be thought to require analysis of conjunctions of physical features and so should remain uncomputed for non-target words. Treisman's approach does, however, assert that analysis of the target may unleash further processes that would prime the system for detection of related words. If this were so, then presentation of the target earlier than the distractors would increase the effect of the latter; whereas if analysis of non-targets were independent of priming, they might be expected to have a smaller effect when delayed. Further, if the sets of words involved are small and familiar, then individual features of primed non-targets, rather than conjunctions of features, might trigger interference. They might especially do so when spatial separation of target and non-target is small. Five experiments using a paradigm developed by Shaffer and LaBerge confirm that the meaning of non-target words affects response to targets; but (1) this is more true for early than for late arrival of the target; (2) it is affected by target/non-target separation in space; (3) it is true for familiar sets of repeated words but not, in these data, for words used once only in the experiment. It is therefore concluded that the results are more consistent with a Treisman type of explanation than with a theory of universal and automatic full analysis.