Electrophysiological Evidence of Anticipatory Cognitive Control in the Stroop Task

The Stroop task has been largely used to explore the ability to inhibit the automatic process of reading when reporting the ink color of incongruent color-words. Given the extensive literature regarding the processes involved in task performance, here we aimed at exploring the anticipatory brain activities during the Stroop task using the event-related potential (ERP) method. To accomplish this, eighteen participants performed two different blocks where neutral words were intermixed with congruent and incongruent words, respectively. Results revealed consistent pre-stimulus activity over the frontal, premotor and parietal brain areas. The premotor and the parietal activities were also modulated by the Stroop effect, being more enhanced in the incongruent than in the congruent blocks. Present findings add on the current literature pointing at an unexplored locus of anticipatory cognitive control during task preparation, thus offering a new way to investigate top-down preparatory processes of performance control in the Stroop task.

Early, color-specific neural responses to object color knowledge

Some familiar objects are associated with specific colors, e.g., rubber ducks with yellow. Whether and at what stage neural responses occur to these color associations remain open questions. We tested for frequency-tagged electroencephalogram (EEG) responses to periodic presentations of yellow-associated objects, shown among sequences of non-periodic blue-, red-, and green-associated objects. Both color and grayscale versions of the objects elicited yellow-specific responses, indicating an automatic activation of color knowledge from object shape. Follow-up experiments replicated these effects with green-specific responses, and demonstrated modulated responses for incongruent color-object associations. Importantly, the onset of color-specific responses was as early to grayscale as actually colored stimuli (before 100 ms), the latter additionally eliciting a conventional later response (approximately 140-230 ms) to actual stimulus color. This suggests that the neural representation of familiar objects includes both diagnostic shape and color properties, such that shape can elicit associated color-specific responses before actual color-specific responses occur.

Semantic Conflict Processing in the Color-Word Stroop and the Emotional Stroop

With the aim of establishing the temporal locus of the semantic conflict in color-word Stroop and emotional Stroop phenomena, we analyzed the Event-Related Potentials (ERPs) elicited by nonwords, incongruent and congruent color words, colored words with positive and negative emotional valence, and colored words with neutral valence. The incongruent, positive, negative, and neutral stimuli produced interference in the behavioral response to the color of the stimuli. The P150/N170 amplitude was sensitive to the semantic equivalence of both dimensions of the congruent color words. The P3b amplitude was smaller in response to incongruent color words and to positive, negative, and neutral colored words than in response to the congruent color words and colored nonwords. There were no differences in the ERPs induced in response to colored words with positive, negative, and neutral valence. Therefore, the P3b amplitude was sensitive to interference from the semantic content of the incongruent, positive, negative, and neutral words in the color-response task, independently of the emotional content of the colored words. In addition, the P3b amplitude was smaller in response to colored words with positive, negative, and neutral valence than in response to the incongruent color words. Overall, these data indicate that the temporal locus of the semantic conflict generated by the incongruent color words (in the color-word Stroop task) and by colored words with positive, negative, and neutral valence (in the emotional Stroop task) appears to occur in the range 300–450 ms post-stimulus.

Attentional Focus Manipulations Affect Naming Latencies of Neutral But Not of Incongruent Stroop Trials

People are slower and more error-prone when indicating the color of incongruent color words compared to that of neutral stimuli. This Stroop effect results from the concurrent semantic analysis of the word stimulus. It has long been considered a prime example of the automaticity of semantic activation. However, coloring as well as cuing only a single letter both reduce the Stroop effect to the point of being absent. Proposed underlying mechanisms include the blocking of semantic activation, an improved selectivity between the interfering stimulus dimensions, and slowed color processing. In order to test the validity of these differing accounts of the single-letter Stroop effect, we compared vocal responses to standard and single-letter Stroop stimuli in two experiments. Irrespective of whether participants maintained a wide (Experiment 1) or a narrow (Experiment 2) attentional focus, both single-letter coloring and single-letter cuing increased reaction times to neutral Stroop stimuli but left those to incongruent stimuli unaffected. Both curtailed semantic activation and improved selection for action should, however, speed up reactions to incongruent stimuli. Our data thus support an explanation of the single-letter Stroop phenomenon in terms of impeded color processing, possibly as a result of color-color interference.

Age-Related Trends of Interference Control in School-Age Children and Young Adults in the Stroop Color–Word Test

In this cross-sectional study, differences in interference control, one component of executive function, were investigated among three age groups, 15 early childhood (7- to 8-yr.-olds), 25 middle childhood (9- to 12-yr.-olds), and 20 young adults (21- to 30-yr.-olds). Participants were administered a computer version of the Stroop color–word test with an oral response; correct responses, response time (RT), and the interference ratio were examined. The data indicated that (1) most of the participants showed no errors in word reading, color-naming, and incongruent color-naming tasks; (2) in word-reading and color-naming tasks, RT for 7- to 8-yr.-olds was longer than that for 9- to 12-yr.-olds, while RT of 9- to 12-yr.-olds and young adults were comparable; (3) in an incongruent color-naming task, RT for 7- to 8-yr.-olds was longer than RT for 9- to 12-yr.-olds, which was longer than RT for young adults; and (4) the interference ratio was higher in 7- to 8-yr.-olds than in 9- to 12-yr.-olds, which was higher than in young adults. These results suggested the difference in interference control between early and middle childhood reported on the go/no-go task and the stop-signal procedure would be observed in the Stroop color–word paradigm as well. The utility of this modified Stroop color–word test for those with intellectual and developmental disabilities was discussed.

The autonomous computation of morpho-phonological structure in reading

Is morphological decomposition automatic? To address this question, we examine whether Hebrew readers decompose morphologically complex words when reading is not required, in the Stroop task. Morphological decomposition is assessed using two markers. One marker examines whether color-naming is modulated by morphologically complex words generated from color roots. For example, we compare words generated from the Hebrew root of “blue” displayed in either blue or an incongruent color. The second marker examines whether color-naming is sensitive to root phonotactics. Here we compare color-naming with words whose (color-unrelated) roots are either phonologically illicit (e.g., ssm) or well-formed (e.g., smm). Results suggest that morphological decomposition proceeds even when reading is discouraged, but unlike previous research with intentional reading tasks, Stroop-like conditions do not allow for a detailed representation of the root’s internal structure.

Stroop Interference and Color-Word Similarity

Stroop interference refers to the finding that it takes longer to name the color of an incongruent color word (e g, the word blue shown in green) than it does to name the color of a neutral stimulus (e g, a series of number signs shown in green) Incongruent color-word stimuli can differ in the similarity between the color in which the word is printed and the color denoted by the word (e g, the word blue shown in green vs yellow) This research shows that the amount of interference obtained is related to color-word similarity, suggesting that word-reading and color-naming processes interact at a conceptual level prior to response emission

The Stroop Congruency Effect is More Observable under a Speed Strategy Than an Accuracy Strategy

Naming the ink color of an incongruent color word (e.g., RED printed in green) usually takes longer than naming the ink color of a color bar. However, when the ink matches the word (e.g., red printed in red), naming tends to be faster. These phenomena are known as the Stroop interference effect and the Stroop congruency effect, respectively. Although the interference effect has been robust and reliable across studies, the congruency effect tends to be elusive. It was hypothesized that this variation in outcomes might be related to subjects' response strategy. The experiment conducted to test this hypothesis induced either a speed or an accuracy strategy in two separate groups of subjects. Significant interference effects were found for both groups and the magnitudes did not differ. At the same time, the congruency effect was observed in the speed group but not in the accuracy group. These results suggest that researchers who wish to observe and study the Stroop congruency and interference effects should place special emphasis on speed. Implications of the study for a model of the Stroop effect are also discussed.