Taken together, this experiment and the one discussed just above demonstrate that it is not the nature of information in a given stimulus dimension that drives Stroop interference, but rather the relative automaticity of the two processes.
In the first study discussed, different patterns of activation were observed when color was the task-relevant dimension, depending on the nature of its automaticity vis a vis the task-irrelevant dimension. In the second study, similar patterns of activation were observed even when the task-relevant attribute differed because processing each of those dimensions was less automatic than word reading.
If indeed it is the automaticity of word reading vis a vis another process that engenders Stroop interference, then one should observe similar patterns of brain activation for the color-word and color-emotional word Stroop task. A direct comparison in the same participants showed that that DLPFC activity is observed for the incongruent condition of a color-word task as well as trials in a color-emotion word task containing either a positive and negative emotionally valenced word compared to a neutral non-emotional word e.
These findings are consistent with the idea that the automaticity of word reading or attentional capture by the word so as to engage word reading must be overcome to enable successful color identification. This overlapping pattern of activation in the frontoparietal network DLPFC and parietal regions for the color-emotion word task as compared to the color-word task has been observed in additional non-clinical samples both with positively and negatively valenced words Kaiser et al.
The effects observed in the color-emotional word task suggest that to the degree that a word is salient, it will capture attention so as to enhance word processing. If so, this should be a general mechanism that can help to increase Stroop interference.
This idea is supported by a study Compton et al. More activation was observed in frontoparietal regions for negative words high in arousal as compared to those low in arousal, suggesting that it is the salience of the word that engenders a greater need for control.
Demonstrating that this is a general effect not specific to emotion words per se , in another study, the frequency with which certain items appears was varied, such that a subset of words occurred less frequently i.
DLPFC activation was enhanced for these oddball trials as compared to more frequent trials Milham et al. Thus, any of a number of manipulations that make words more salient so as to increase the engagement of word processing seems to be one locus of the Stroop effect.
While standard computational models of the Stroop task suggest that it can be explained by competition between two distinct processes, neuroimaging data provide a more complicated picture. In particular, if that were simply the only locus of the Stroop effect, then the identity of the task-irrelevant information should not affect brain activation, as for all intents and purposes it is downregulated relative to the task-relevant dimension. However, neuroimaging research provided a contrary result.
Greater activity was observed in brain regions that process the task-irrelevant attribute for incongruent as compared to neutral trials Banich et al. More specifically, different regions of posterior cortex showed greater activity on the contrast of incongruent e. In an attempt to understand the factors that drive this pattern of brain activation, Herd et al.
In the standard computational model, there is an input layer with two subsections — one for the receipt of color information and one for the receipt of word information. These are each linked to an output layer that governs responding. A prefrontal control node modulates processing so as to increase activation of information in the color portion of the input layer in comparison to the word portion of the input layer.
The revised model had three important modifications. First, it included a layer between input and output meant to represent processing of information in posterior cortex in color-specific and word-specific regions, respectively. Part of the goal of including this layer was to see if activation in these portions of the model could mimic the activation observed in posterior brain regions in the empirical neuroimaging studies. Second, it included an additional top-down node to bias toward the abstract concept of color as being critical for the task set.
The rationale was that, outside of the Stroop task, individuals typically do not have an abstract representation of color that excludes color words.
Third, also related to the semantics of color, the model was modified so that there were excitatory linkages between representations of color in the ink processing layer e. This model could replicate both the behavioral results of the Stroop task i. Suggesting that the alterations to the original computational model were critical, neither a model that had the top-down color biasing unit removed nor a model without reciprocal connections between related semantic features could replicate the observed empirical results.
Hence, the outcome of this computational modeling suggests that it is the color-relatedness of a representation that serves as a locus of interference. While the color-relatedness of items is important, studies suggest that the nature of representation to which the semantic category of color is linked can vary and yet still produce interference. Support for this assertion comes from comparison of activation for incongruent vs.
As noted above, in the color-object task, an object with a typical color is displayed in an atypical color e. In the color-object word task, the person simply views the word describing an object that has a typical color e.
Distinct regions of cortex showed activation depending on the nature of the task-irrelevant attribute, suggesting that it was not just an amodal semantic representation of color that is the source of interference.
For example, different regions of the ventral visual processing stream are activated on incongruent trials for the color-word task as compared to the color-object task, suggesting that interference may arise from more orthographically based as compared to visual form-related representations in the former task as compared to the latter. BA 48 became active for the color-object as compared to the color-object word task despite the fact that the interference would arise from the same semantic characteristic e.
This finding also suggests that interference can arise at multiple stimulus-related levels. Another way to examine stimulus-related representations of color is to compare patterns of activation when items have color-related information in both the task-relevant and task-irrelevant dimension as compared to when color-related information is restricted solely to the task-relevant dimension.
One can examine this question by determining patterns of brain activation common across both incongruent and congruent trials that are greater than those observed on neutral trials.
Investigations taking such an approach Milham et al. Also suggesting interference at the semantic level, left temporal language areas show activation for the contrast of incongruent and congruent trials, which contain semantically related color information in both the ink color and the word, as compared to neutral trials, which in this case were words unrelated to color e.
In sum, the work reviewed in this section suggests that interference can potentially arise in the Stroop task at a number of stimulus-related dimensions, from visual form to orthography, as they relate to the task-relevant category, and also with regard to semantic representations of task-relevant information. Another series of studies provided evidence that Stroop interference is also engendered at response-related levels.
In the first study of this nature, brain activation was examined for two types of incongruent trials, response-eligible and response-ineligible. In response-eligible trials, the competing word also names a potential response. If a particular brain region is specifically engaged in dealing with response conflict, it should show greater activation to response-eligible than response-ineligible trials. Importantly, in addition, this region should also show no more activation to response-ineligible trials, which have semantic conflict but no response conflict, than to neutral trials, which have neither semantic nor response conflict e.
A region of mid-cingulate cortex showed such a pattern Milham et al. Another way to examine response-related aspects of Stroop interference is to compare processing on different blocks of trials in which the stimulus-response mapping is one-to-one as compared to one-to-many.
More specifically, on some blocks, each incongruent response-ineligible word was mapped to a different color e. Hence, stimulus-response mappings were more overlapping in the former condition than the latter.
Each of these blocks also contained neutral words e. Another way in which response-related interference in the Stroop task has been investigated is via an integrated Simon-Stroop task. In the Simon task, interference arises from stimulus-response interference.
In this task, interference is engendered when a right-sided e. In our integrated Simon-Stroop task, individuals viewed arrows that were located either to the right or left Simon stimuli , or on different trials above or below Stroop stimuli a fixation point. Individuals were trained, for example, to press a right button for an upward arrow and a left button for a downward arrow. Simon interference, which is considered stimulus-response interference, was engendered by placing, for example, an upward arrow to the left of fixation, which then required a right button response to a left-sided stimulus.
Stroop interference, which is considered engendered by conflict between two stimulus dimensions, occurred for example when an upward arrow was positioned below the fixation point. While the contrast of incongruent vs.
In contrast, the stimulus—stimulus interference of the Stroop task engendered activity in inferior parietal and inferior frontal regions that was not observed in the Simon contrast Liu et al. Hence, this body of work suggests that another locus of Stroop interference is at response-related aspects of processing. Consistent with this supposition, certain limitations of the classic computational model of the Stroop task by Cohen et al.
The work described above suggests that Stroop interference can occur at multiple levels. How then can one integrate these findings to shed light on the locus of the Stroop effect? We have argued that, importantly, the degree to which control is exerted at one level of processing can then influence the degree to which interference is engendered or controlled at another.
A pair of early studies helped this idea to come into focus. As reviewed above, our work suggests a broad distinction between control engendered at the level of an abstract task set, mainly implemented by lateral prefrontal cortex, as compared to more response-related aspects of control, mainly implemented by medial prefrontal cortex. In examining differences in brain activation common to incongruent and congruent as compared to neutral trials e.
In particular, younger adults exhibited more activation across frontal and parietal regions. Such findings are consistent with reported compromise with aging of prefrontal regions and processes involving executive function and cognitive control Lockhart and DeCarli, This led us to consider the possibility that due to the lack of top-down control, older individuals were potentially utilizing more response-related mechanisms to deal with the interference.
The converse effect was observed in a study of practice-related effects on the Stroop task. Since the Stroop effect can be maintained over tens of thousands of trials due to the automaticity of word reading, a Stroop task was used in which the interference effect could be reduced with practice.
In this task, individuals were trained to assign a color-word label to a series of nonsense designs e. Then, later, they were shown either incongruent trials, in which a specific nonsense design was displayed in an incongruent color e. To examine learning effects, the experiment was divided into thirds, examining activation for the first third, second third, and last third of trials. While lateral prefrontal activity stayed relatively static across the three portions of the task, that of medial prefrontal activity declined, as did the behavioral Stroop effect, suggesting that individuals were gaining better control over interference.
We interpreted this pattern as suggesting that less late-stage response-related interference was occurring, as reflected in reduced ACC activity, due to better top-down control by lateral prefrontal regions, which stayed engaged across all portions of the task Milham et al.
Participants performed the Stroop task in the magnet and then again while electrophysiological recordings were made. The relationship between ERPs generated by these sources was examined, in addition to how well they could predict, as tested via mediation models, interference on the Stroop task indexed by the difference in performance between incongruent and congruent trials.
The specific model examined whether the influence of DLPFC activity in the — ms time range on Stroop performance would be mediated, in part, by later ACC activity in the — ms time range.
This pathway was significant. Moreover, the data showed that for individuals with larger DLPFC amplitude, indicative of higher levels of control, the degree of ACC activity was unrelated to behavioral interference. This finding is consistent with the idea that there is reduced need for late-stage selection when the task set is well specified so as to reduce interference from the task-irrelevant processing stream.
In contrast, individuals with low DLPFC but high ACC amplitude exhibited a greater degree of interference as measured by the reaction time difference between incongruent and congruent trials, but no more errors than individuals with high DLPFC activity. In contrast, those individuals with both low DLPFC amplitude and low ACC amplitude committed more errors, suggesting that the reduced ability of the ACC to engage in late-stage selection led to compromised performance.
An advantage of this approach was that alternative models could be tested. For example, one might argue that this model predicted the data because it posited that the effect of a component occurring earlier in time, that recorded from the DLPFC, was moderated by a component occurring later in time, that recorded from the ACC.
Arguing against such an interpretation, a model positing a pathway from an earlier ACC component in the — ms time range via the DLPFC component at — ms did not predict performance.
Integrating all these findings, we posited a cascade-of-control to control interference in the Stroop task Banich, As discussed earlier and as shown in Figure 1 , this model argues that posterior portions of lateral prefrontal cortex are involved in setting a top-down attentional set i. This idea is consistent with activation of IFG across distinct meta-analyses of Stroop tasks Derrfuss et al.
Such task setting can occur even prior to stimulus presentation in a proactive manner see, for example, Braver, Once a stimulus appears, relevant information is identified and then mid-DLPFC regions are involved in selecting which of the relevant information should be actively maintained in working memory. Regions of mid-DLPFC have been implicated in buffering relevant information in working memory from interference from competing information Burgess and Braver, This information is then sent along to more posterior and dorsal regions of ACC, which are then involved in response-related and late-stage selection, which is required prior to emitting a response.
Research with monkeys implicates the ACC as being particularly important for response selection Isomura et al. Consistent with this notion of a cascade are findings from ERP studies in which the onset of the two stimulus dimensions — task-relevant and task-irrelevant — are varied in time.
These studies reveal that ERP waveforms sensitive to stimulus incongruity vary depending on the stimulus onset asynchrony between these two dimensions, implicating a cascading process of interference effects Appelbaum et al.
Conceptualizing Stroop interference as occurring via a cascade of control provides additional avenues to consider how the locus of Stroop interference might be considered. In this section, we consider some approaches in that regard.
One issue not yet discussed is the mechanism via which top-down biasing by prefrontal regions for a task set influences processing of each of the task-relevant and the task-irrelevant dimension of a Stroop stimulus.
One can ask whether interference occurs because the representation of task-relevant information is not adequately upregulated or because the representation of task-irrelevant information is not adequately downregulated. Because of the specificity of brain regions that process each of the two stimulus dimensions contained in Stroop stimuli, one can leverage brain imaging to examine this question.
A number of studies have examined whether, for example, in the standard color-word Stroop task, activity is increased in color processing regions or downregulated in word processing areas e. This question is generally approached via the utilization of localizer scans where individuals are shown a series of words and then separately colors to identify, on an individual participant basis, those brain regions that are specifically involved in processing words and then those specifically involved in processing color.
One can then examine the degree of activation of each of these regions on average for incongruent trials as compared to congruent trials.
Work using such an approach suggests that both mechanisms upregulation of task-relevant material, downregulation of task-irrelevant material may occur e. Recently, we have expanded on such approaches to specifically examine how processing of task-relevant vs. In our approach, participants performed a localizer task, which in conjunction with multi-voxel pattern analysis Norman et al.
The task employed was an emotional word-emotional face Stroop task in which individuals characterized the valence of a word positive, negative superimposed on a task-irrelevant emotional face sad, happy.
On each trial, we determined how much activity over posterior cortex was similar to that typical for each dimension using a classifier fit , that is, how much the pattern of activity looks like face activity and additionally how much the pattern looked like word activity. The important question for purposes of the present article was the degree to which processing of each of these dimensions could predict RT on a given trial and the degree to which such activity occurs as a result of activity in DLPFC modulating activity of posterior brain regions processing each of the task-relevant and task-irrelevant stimulus dimensions.
The results yielded different patterns for incongruent as compared to congruent trials. On incongruent trials, greater DLPFC activity directly predicted longer RT, suggesting that when individuals were having difficulty on a given trial, they needed to engage more top-down mechanisms. In addition, more DLFPC activity was associated with less of a classifier fit for faces, suggesting that this brain region is downregulating processing of the task-irrelevant face. However, the degree of processing of the task-relevant face did not predict RT.
Hence, interference, at least in the population of individuals in this study, late adolescents, seems to be predicted on incongruent trials by the degree to which DLPFC mechanisms must be engaged. On congruent trials, as on incongruent trials, more DLPFC activity was associated with a poor classifier fit i. It may seem as though the Stroop effect is just a fascinating experiment with no real effect on human psychology.
In truth, it illustrates a lot about the way we process information and helps us assess our ability to override our instinctual fast thinking. While the Stroop test is interesting, it also has incredible uses in the world of psychology and the study of the brain. According to a study published on the National Center for Biotechnology Information, the Stroop test is valuable when assessing interference control and task-set coordinating in adults with ADHD.
Also, a study published in found that it was Later studies confirmed these findings, and the Stroop test is often used to assess selective attention in traumatic brain injury patients. Multiple studies, including the original experiments by Stroop, suggest that practice can decrease Stroop inference. This has implications for our learning skills, ability to multitask, and how we form habits. Kahneman believes by understanding how our brains make connections, we can overcome them to reach more logical conclusions by calling on System 2, our controlled thinking, quicker.
Exploring the Stroop effect continues to play a role in studies and experiments involving automatic and controlled thinking, selective attention, our cognitive processing, and more.
Even though the Stroop effect has never been definitively explained, it provides a tried and true benchmark for psychologists and scientists that has been referred to for many years. Does the study of cognitive processes interest you? Consider an online psychology degree from Lesley University. Our program explores the complexities of the human brain and how it affects behavior. Plus, our online format allows you the convenience needed to fit your studies into your life.
More at lesley. Fall Reopening Plans. We will reopen our campuses for classes, activities, and residential living in Fall Find the latest information on our Fall Plan page. Home Menu. His research method is now one of the most famous and well-known examples of a psychological test, and is elegant in its simplicity. First, the participant reads a list of words for colors, but the words are printed in a color different to the word itself. Next, the participant has to repeat the test with a new list of words, but should name the colors that the words are printed in.
First, time yourself while you read the following text, ignoring the colors the words are printed in. Now time yourself while you state the colors of the following words, ignoring the actual text as best as you can! In most cases, it takes longer to state the colors of the words, rather than to read the text they are printed in, despite the incongruence being essentially the same across both lists i.
It appears we are more influenced by the physical text than than the text color. As habitual readers, we encounter and comprehend words on such a persistent basis that the reading occurs almost effortlessly, whereas declaration of a color requires more cognitive effort. When there is a conflict between these two sources of information, our cognitive load is increased, and our brains have to work harder to resolve the required difference.
Performing these tasks preventing reading, processing word color, and resolving information conflict ultimately slows down our responses, and makes the task take longer. There are a few theories that slightly differ in their definitions of the Stroop Effect, yet their differences mostly lie in which part that they emphasize.
For example, one theory emphasizes that the automaticity of reading as the principal cause of Stroop interference, while another emphasizes the mental prioritizing which we perform when reading, as compared to defining colors. While differences in theories may therefore exist, all essentially converge on the central premise that reading is a simpler and more automatic task than stating colors, and that a conflict between the two will increase the time needed for processing.
These skills and facets are implicit in so many ways in which we interact with the world, suggesting that this test reveals a brief — yet incisive — view into human thought and behavior. The test is also used in a variety of different ways to the original, in an effort to exploit the experimental setup to reveal more about a clinical population, for example. Even neurodevelopmental disorders such as schizophrenia and autism have been examined with the Stroop test.
Furthermore, there are several variations and differing implementations of the test available, allowing different aspects of cognition to be honed in on. Research has shown that anxious people were likely to experience more interference i. Experimental designs like this allow researchers to target and observe cognitive processes that underlie explicit thought. The test reveals the working of non-conscious brain function and reduces some of the biases that can otherwise emerge in testing.
Other experimental setups utilize the lessons of the Stroop Effect — that incongruent information will require more mental resources to resolve correctly — with numbers, rather than words. For an example, see the image below:. This experiment shows that, with all else being controlled for, incongruence in numerical size will cause the greatest interference, increasing the delay in comprehension. An interesting feature with the Numerical Stroop is that the interference is found for both types of incongruence — when the numbers are incongruent with size, then a delay is shown for reporting the size, as well as for reporting the numbers.
The Stroop test can be simply administered with a basic experimental setup. At its most fundamental, all you need is an image of the Stroop test words, a stopwatch, and someone to record the time and answers and a willing participant!
However, if you want to gain more insights from the data, there are plenty of ways to take the test further. With iMotions you can simply set up and present the Stroop test, while also expanding the data collection possibilities.
Using the survey function, the test can be quickly and simply added.
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