An Experiment Based on the Stroop Task to See How Mood Disorders Affect Selective Attention


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While significant amounts of research has been performed on people with major depressive disorder to demonstrate its effects on mood, its impact on other areas of cognition have been examined with far less frequency. Some studies have indicated there is a noticeable effect in several areas, such as cognition and selective attention. As things stand, therapeutic treatment of such patients focuses on their mood to the near-exclusion of anything else. In order to examine the possible necessity of expanding the therapeutic arsenal devoted to major depressive disorder, a series of tests could be conducted on an aspect of executive function. This proposed study would determine whether mood enhancement would alter people’s performance on the Stroop task, comparing patients with major depressive disorder with a control group of unaffected people. It is anticipated that the results would show a lack of significant impact on the subjects with the disorder compared both to their own results and those of the control group. The possible indications of these results are discussed. 

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Mood and Executive Function: Relationships and Effects

People often say that how they are feeling affects what they are able to do. When the people in question have mood disorders, it may be more amplified than when the average individual has “spring fever” or is merely bored. It has been noted that people with major depressive disorder (MDD) have issues with performing cognitive tasks (Withal, Harris, & Cumming, 2009). There may even be a physical component to this problem, as suggested by research with teenagers that showed subjects with MDD had a higher concentration of cortisol in their bodies after stressor events compared to a control group (Stewart, Mazurka, Bond, Wynne-Edwards, & Harkness, 2013). And while this course of therapy is not yet accepted by the majority of professionals working with people with MDD, a preliminary study showed that focused therapeutic work to improve cognition and executive function in that population may have a positive effect (Elgamal, McKinnon, Ramakrishnan, Joffe, & MacQueen, 2007). While that specific therapy is not widely available to the general public, access to entertaining and amusing videos is one YouTube visit away for anyone with an Internet connection. Although the effects of viewing material with negative content may exacerbate symptoms of depression (Johnston & Davey, 1997), the question of whether viewing positive content has a measurable effect has not been significantly visited. In fact, there is some indication that in people with MDD, positive material may not stay active in their working memory for as long as neutral or negative information (Levens & Gotlib, 2010). All that being said, the question of whether positive input might have an elevating effect on someone’s ability to perform executive function tasks remains open. This study intends to examine whether or not people with MDD improve their performance on a task after watching upbeat material when compared to not doing so, contrasted against a control group.

Whether there is a relationship between mood disorders and executive function problems in the first place has been examined in different populations. One paper visited this question by studying teenagers diagnosed with pediatric mood disorders for signs of executive function impairment (Holler & Kavanaugh, 2012). Using chart review of assessment test results compiled at a psychiatric care facility over the course of several years, they compared the inpatients’ performance on various metrics relating to executive function against established norms. The patients with mood disorders were found to have impaired executive functioning in several areas, but they differed based on which mood disorder they were diagnosed with. Adolescents with disruptive behavior disorders performed more poorly on standards of response inhibition/interference control while patients with anxiety disorders had lower scores in the area of problem solving and planning (Holler & Kavanaugh, 2012). Some of their results contradicted prior studies, emphasizing a need for more detailed research being done with this age group.

There is other evidence that the type of mood disorder someone has will have a different effect on their executive function capacities. Researchers explored the possible variations between people with depression and anxiety when given a series of tests to explore their abilities in the selection aspect of those functions (Snyder, Kaiser, Whisman, Turner, Guild, & Munakata, 2014). Their results were the opposite of what they predicted. They found that people with anxiety had a harder time with tasks that required them to verbally choose between different options while the depressed group’s scores in that area were considerably higher (Snyder et al, 2014).

Adults with bipolar disorder type I have been the subjects of more than one study in this area. One such contrasted their executive function performance against patients with schizophrenia and people with no diagnosed mental conditions (Khodaee, Nikyar, & Ghorbani, 2015). A descriptive-comparative test was run on 20 members of each group, utilizing computerized tests such as the Tower of London game to evaluate their abilities in areas such as planning and behavioral inhibition. The results which have the most bearing on this study’s hypothesis indicated that adults with bipolar type I disorder demonstrated lower performance scores on the tests compared to the normal participants (Khodaee, Nikyar, & Ghorbani, 2015).

The pattern of mood disorders affecting executive function may be established, but the impact of treatment also matters when seeking to demonstrate a link. A study which came up during research discussed the results of a group of patients with treatment-resistant major depressive disorder (MDD) or bipolar disorder in partial remission who received erythropoetin, which improves neuroplasticity (Miskowiak, Vinberg, Glerup, Paulson, Knudsen, et al, 2016). They ran a double-blind test on their subjects and performed working memory tests on them over the course of the four-week study. They found the patients who received the chemical performed significantly better on the tests as well as showing increased brain activity in the appropriate areas when doing them while receiving a fMRI scan (Miskowiak et al, 2016).

Studies of how mood can affect normal people’s performance on tests of executive function have also been performed. A group of researchers examined whether being in a positive mood would improve executive function in people lacking impairments in that area (Phillips, Bull, Adams, & Fraser, 2002). They noted that previous tests had shown that good moods improve creative task performance but degrade ones related to more mundane activities such as deductive reasoning and memorization. Their research results were consistent with the established trend, showing their subjects were stronger on creative tasks while weaker on their responses to a sorting test if they were in a good mood (Phillips, Bull, Adams, & Fraser, 2002).

From this, it appears that investigating whether people who have depressive disorders will perform differently on executive function tests than normal people when both groups receive positive mood stimulation prior to being examined has some merit. Thus, this study has been designed to evaluate the impact of positive emotional stimuli on people with MDD compared to a non-depressed control group. It is intended to provide information on whether the mood uplift effect carries over to a different cohort than normal adults. Based on the available literature on the matter, the expected conclusion is that it will show evidence that people with MDD are less likely to respond to such stimuli. This may in turn enhance the understanding that MDD features differences in processing alongside difficulty in their brains’ regulation of neurotransmitters. The possible effect on therapeutic approaches would also be useful information as investigations into the treatment of MDD move forward. 



Adults (24 women, 16 men, Mage = 39.5, age range: 18-60 years) would be recruited via flyers and social media posts aimed at the student population of National University. They would be drawn from a larger group of respondents who would be evaluated via a demographic survey to rule out people who had been under treatment for any psychiatric disorders within the last five years. Another group of adults (30 women, 10 men, Mage = 32.2, age range: 18-60 years) would be recruited through the outpatient treatment facility at the Gifford Clinic affiliated with the University of California at San Diego. These subjects would be selected due to their being under treatment for major depressive disorder. Each member of both groups would be evaluated against the criteria for major depressive disorder using the Structured Clinical Interview for DSM-5 Disorders. Written and informed consent would be obtained from all participants. Confidentiality agreements would also be signed by all participants to prevent them from discussing the testing with each other or anyone else. All individuals would be compensated with $10 Starbucks gift cards for their participation after they complete both phases of the experiment. Analyses would show the groups do not differ significantly in education or ethnic composition.


A 2 (group: MDD, normal) x 2 (condition: mood elevation, relaxation) design would be used. This method would be utilized because the effect of mood elevation versus a neutral state of being is the target dependent variable. Without checking both the average subjects and the ones with MDD for both pre-test conditions, the data would be incomplete. There would be a potential confounding factor of any participant arriving in a depressed state. It would be addressed by performing a brief evaluation interview of each subject prior to being placed in the appropriate pre-test environment to rule out unusual emotional states. Both sets of participants would be randomly assigned to the two phases of the experiment, giving half of them the mood enhancement treatment before performing the executive function test on their first visit.

Materials and Procedure

Due to their anecdotal value as a mood enhancer, a series of videos featuring juvenile domesticated animals would be assembled. The species balance would be evenly distributed among kittens, puppies, and rabbit kits to reduce the possible confounding factor of people with strong biases against one of the chosen species. The length of the video montage would be approximately 15 minutes. People would be placed in a quiet room containing a monitor attached to a computer in front of a comfortable chair. The computer would run the video when they clicked Play with the attached mouse.

For the people who were assigned to the set of subjects that were given time to relax after the intake interview, a room furnished with comfortable chairs and a couch would be set up. Participants could choose to sit or recline, and relaxing music was played over a sound system they could choose to listen to or turn off as they needed. The room would be decorated in neutral shades so as not to affect their mood in any significant fashion. They would be provided 15 minutes inside that room before being asked to perform the test.

In order to evaluate the subjects’ executive functions, a computerized version of the Stroop task (Stroop, 1935) would be utilized. It is a well-known and deeply studied test for evaluating selective attention skills (as reviewed in MacLeod, 1992). Participants are asked to sort target words by their font color, with the words for the various colors both matching and differing from their display font as an active test against a neutral one which uses words without a color association as the sorting base. This is meant to evaluate someone’s ability to manipulate conflicting mental processes (MacLeod, 1992).

This would be a two-part test conducted over a period of two weeks. On their first visit, half of the participants would watch the baby animal video prior to being given the computerized version of the Stroop task (Stroop, 1935) while the others would be given the test after sitting in the relaxation room. In the second week, the groups switched their pre-testing assigned task. Participants would be brought in two at a time over the course of a three-day period for each phase to reduce the chance of cross-contamination by way of idle conversation. Each half of the test (color words and non-color words) would be administered three times per session. Time of day would not be accounted for as a factor.


Analyses would focus on the reaction times of all participants in the two trials conducted. Due to the existence of two dependent variables, a MANOVA test would need to be performed on the data. Outlier scores caused by unusually depressed emotional states would be discarded. In the course of the hypothetical study, it may be anticipated that one participant from the control group would need to have their results rejected due to suffering a death in the family between the two trial periods, thus negatively affecting their results. A MANOVA would also be performed to investigate whether gender had any effect on the test results. It is expected that there would not be a statistically significant effect found between them when compared across which pre-test room they were assigned to (λ = 0.2, F = (3, 14), p = 0.14). The control group would be found to be significantly less depressed than the group with MDD in the intake interview (λ = 1.7, F = (7, 21), p = <0.05) As for the results comparing the normal subjects to the people with MDD, a more significant set of results across group vs. condition would be anticipated (λ = 2.3, F = (5, 34), p = <0.05).

Post-test analyses of the data would entail a t-test for dependent groups, since participants would be exposed to both pre-test conditions as part of the procedure. Also, evaluating the control group’s performance independently of the other group would be necessary to demonstrate the degree of the effect. The control group’s performance on the Stroop task when given time to relax (M = 49.3, SD = 5.92) versus their scores after watching the video montage (M = 67.2, SD = 6.1) would stand in contrast to the group with major depressive disorder in both instances [(M = 33.4, SD = 4.87) for relaxation, (M = 59.4, SD = 5.21) for the video].


While an uptick was seen in both groups’ performance on the Stroop task, the fact the people with MDD did not do as well in either condition as the control group would suggest that their executive functions are impaired regardless of whether they receive palliative treatment prior to any sorting tests they may perform. This is consistent to results on similar tasks performed by patients with depressive disorders compared to standard results seen in other research (Holler & Kavanaugh, 2012). This data suggests research for mood disorders must continue to focus on finding deeper causes and effects, since simple improvements to general demeanor have no significant impact on certain symptoms of these conditions.

There is a possibility of the relaxation room enhancing the depressed subjects’ negative mood due to their having no distractions from any thought processes which might affect their performance (Watkins & Brown, 2007). While the construction of this test did not account for that possibility, future researchers attempting to replicate its results may wish to adjust the materials for that room to include mood-neutral thought distraction tools, such as fidget spinners.

The tests performed focused on only one aspect of executive function, that being sorting tasks which require higher levels of attention. Whether a better mood would improve the results for people with MDD on other aspects was not examined. The fact other research has found an improved mood can worsen a normal person’s performance in some areas of executive function further emphasizes this need (Phillips, Bull, Adams, & Fraser, 2002).

Regardless of any previously stated conditionals, these results would still indicate that the effect of MDD is pervasive across several areas of mental function. This stands in contrast to current therapies, which focus more on mood. Further exploration of these would seem valuable in order to truly improve states of mind and being in patients being treated for this and related conditions. 

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