How Helpful has the Stroop Method Been in Exploring the Relations Between Emotional and Cognitive Processes?

The Stroop task has been widely employed for almost 70 years to aid the study of human cognitive processes. More specifically it focuses on attentional bias. Attentional bias refers to performance on a dependant variable suffering as a result of allocation of attention to alternative, more salient aspects of the stimulus array (Williams et al, 1997). In the original design of the ‘Stroop Task’ (Stroop, 1935) participants were presented with stimuli printed in coloured ink, and were required to name the colour of the ink while ignoring the stimuli itself. The stimuli would either be meaningless (such as a row of Xs) or be the name of a colour (not that of the ink used to display it). It is a common result that the latter stimuli take longer for ink colour naming by the participant than the meaningless stimuli due to the cognitively antagonistic nature of the colour-name stimuli. Subsequent research found that most words with semantic content produce some interference (Klein, 1964), especially if the word has a generally strong association with a colour (e.g. Sky- blue, grass- green). It was also discovered that more interference was produced if the word had some personal relevance to the participant, or were self-referent and the participant was in a condition of increased self-awareness (such as in front of a mirror). The result of these finding was the adaptation of the original task design to create the ‘Emotional Stroop Test’. This replaced the colour name stimuli with other, ‘emotional’ words in the hope of discovering whether emotion can cause attentional bias. If this was proved to be the case, there would be strong evidence of a relation between the emotional and cognitive processes of humans.

Emotion is a highly contentious issue, and resultantly there is no one definitive description to accurately describe what it entails. What has been broadly recognised, however, is that emotions can be broken down into 5 basic sub-groups: Happiness, Disgust, Sadness, Anger and Fear (Eysenck & Keane, 2000). In exploring the aforementioned emotion-cognition link, many studies have focused on only one or a couple of these sub-groups at a time. The first examples of this are studies into fear, which have broadly focussed on phobias. Watts et al (1986) ran an emotional Stroop test on arachnophobics in which the coloured words presented were meaningless, colour names, general threat words or spider-related words. Arachnophobics were seen to be severely retarded on the colour-naming task when the spider related words were used, but showed only normal levels of conflict with colour names and general threat words. Moreover, desensitisation of the phobics to the spider words significantly reduced interference by them under test conditions. What can be drawn from this is that attention bias is directly affected by fear and anxiety. In this case the phobics had their attention drawn to words that were directly connected to their own psychological fears. Their cognitive process was thus affected by, and is therefore related in some way to, their emotional process. This finding was backed up by Thorpe & Salkovskis (1997). They also used arachnophobics and a spider-word Stroop test. They administered the spider-word Stroop test before and after a session for treatment of arachnophobia, or after a comparable period in the control condition (to ensure any results were not due to test-retest reliability or habituation). It was found that in comparison to participants in the control condition, test condition participants did not suffer a significantly reduced reaction time to spider words. The result of this study is ambiguous. It is still observed that phobics show attention bias to words that are emotionally relevant to their phobias. The fact that this remained unchanged after treatment for the phobia may be a comment that any gains made in this treatment are fairly superficial and do not effect the root of the fear, which is where the relation to the cognitive process of attention lies.

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Long et al (1994) studied a similar effect produced by food and body-size words on people with eating disorders. They presented a Stroop task with Food and body-size words as the coloured stimuli to three groups, anorexics, obese restrained eaters and a normal control group. There was a similar retardation effect to that seen with the arachnophobics in the anorexics. They were significantly slower than the control group at naming the colour of the food and body-size words. However, the obese restrained eaters produced results that were not significantly above those of the control group. Again, these results do not offer a definitive conclusion what form the sought relation between emotion and cognition takes. It does give some evidence that the relationship exists, but the discrepancy between the results of the two test groups is difficult to explain. It may be that the nature of this relationship is not linear. It could well be that the psychological and emotional problems suffered by anorexics and obese restrained eaters is different. It could also be the case that perhaps these two groups feel emotionally different towards food and body size, or one group is far more sensitive about it than the other. In either of these cases there would be a discrepancy in the results between the two groups. Although the relationship between emotion and cognition is further emphasised, more research is necessary to gain a full understanding of what these results can tell us about it. Another research relating to food was undertaken by Stewart and Samoluk (1997). They took 32 participants and assigned half of them to a food deprivation condition (6 hrs) and the other half were the control condition with no deprivation. All participants were also recorded as High, medium or low restraint eaters depending on their normal lifestyle. All participants then took part in an emotional Stroop test that used food and drink-related words. The results showed no significant differences in response times between the food deprived participants and the control participants. This may have been because in this case there was no emotion-cognition link. It may also have been because 6 hrs of food deprivation is not enough to elicit a strong emotional response. A third option is presented by some other findings in this study. It was shown that highly restrained eaters showed significantly longer latencies in response for the food and drink words than the control words. This may be because whereas the food deprivation was voluntary and temporary it did not deeply emotionally affect the participants. The high restraint in eating was a lifestyle choice of the participants and was much more personally relevant to them. Thus the relationship between emotional and Cognitive Processes may be to do with the depth of the emotion felt as well as the personal relevance of it (perhaps in relation to a concept of selfhood). Again these theories are merely speculatory and would need qualitative research to be validated.

An interesting and slightly divergent finding comes from a study by Bentall and Thompson (1990). Participants were rated as high, medium or low hypnotisability as scored by Chapman’s Hypomanic Personality Scale and then were administered an emotional Stroop test using depressive and euphoria-related words. The results showed a significant association between Hypomanic traits and interference on colour naming of depressive words (but not on the euphoria-related ones). Not only does this identify a relation between attention bias and depressive emotion, but it also shows a relation between level of Hypomanic traits (which are personality traits and so can be considered cognitive in function) and emotional significance of depressive words. Thus it identifies a second possible relationship between emotional and cognitive processes. The disparity of effect between the depressive and euphoric-related words may support the previously mentioned idea regarding the depth and significance of emotional processing. It may be that depression is far more deeply processed and personally significant that euphoria, perhaps especially in hypomanics. Again more research is needed to fully understand the highlighted relationship. In a follow-up study conducted by French et al (1996), the test was repeated but measures of trait anxiety were also taken from all participants. This was to ensure that the effects found by Bentall and Thompson was not mediated by anxiety rather than Hypomania as the study claimed. The results supported the earlier findings, with Hypomania-related interference having the same result as in the previous study, even when anxiety levels were taken into account. French and his colleagues further analyses all their data and concluded that it supported a theory that hypomanic personality might reflect a partially successful means of coping with depressive tendencies. Therefore the Stroop method has been instrumental in uncovering another possible relationship between emotional and cognitive processing.

Another emotion that has been the basis of a modified emotional Stroop task is Anger. In a study by Van Honk et al (2001) selective attention to angry faces was investigated in relation to trait anger. A pictorial version of the emotional Stroop test was created that presented either neutral or angry faces in one of a number of basic colours. As usual the participant had to name the colour of the presented item as quickly as possible. Participants also had their trait anger levels rated using the State Trait Anger Scale. The results showed that individuals who scored higher on trait anger showed a strong attentional bias for angry faces. The results from this Stroop test allowed the researchers to relate their findings to other work they had done and conclude that there is an evolutionary-evolved, content-specific response to the facial expression of anger, and that response is mediated by personal levels of trait anger. Thus the Stroop method was in this case extremely useful in identifying a relationship between Emotional and Cognitive processes.

Thus far only negative emotions have been discussed, but there has been evidence using the Stroop method that positive emotions also have a relationship with cognitive processing. Segerstrom (2001) employed the emotional Stroop test to assess the relationship between optimism and unconscious attentional bias for ‘positively valenced, negatively valenced and neutral stimuli’. Participants completed personality measures to test level of optimism and then an emotional Stroop task with positive, negative and neutral words. Optimism was associated with a much higher attentional bias for positive stimuli than negative stimuli. Segerstrom also concluded that unconscious attentional biases may contribute to the better adjustment associated with optimism. So far we have not only seen a relationship between emotional and cognitive process in relation to both positive and negative emotions, but also that they seem connected by type. This has been shown by angry people giving attentional biases to angry faces and optimistic people focussing on positive stimuli. Thus it would seem that emotional state might directly correlate to cognitive processes, it is seen to do so at least with attentional bias.

The Stroop method has also been employed in the research of malfunctioning cognitive and emotional processes, such as incidences of delusional thinking, Obsessive-Compulsive Disorder (OCD) and Post Traumatic Stress Disorder (PTSD). The work on delusional thinking was performed by Bentall and Kaney (1989). Patents suffering from persecutory delusions were given an emotional Stroop test using Meaningless strings of O’s, neutral words, words indicating negative affect, and words judged to be of paranoid content. Their results were then compared to those of a control group. Repeated analysis showed a very strong increase in response time (and therefore attentional bias) towards the paranoid words by the delusional patients. This may well help in understanding the causes and possible treatments for delusional individuals. It shows that an active component in the aetiology of their condition is emotionally based. Unoki et al (1999) ran the study into OCD. They presented anxiety-relevant, compulsion-relevant, positive and neutral words using the Stroop method to a group of OCD sufferers and a control group. The words were presented subliminally and supraliminally in separate conditions. In the supraliminal condition no significant difference in reaction times was seen between the two groups. In the subliminal condition, however, OCD patients showed a much greater delay for anxiety and compulsion relevant words than the control group. In a subdivision of results between checking OCD and cleaning OCD, it was shown that the checking OCD patients responded much more slowly to these words than the cleaning OCD patients. It was concluded that OCD sufferers (especially those with checking OCD) might have a deficit in automatic processing of threat information. Thus the subliminal and automatic cognitive processing of OCD sufferers has a direct relation to their emotional processing, a finding demonstrated by the Stroop method. Moradi et al (1999) investigated the effect of PTSD (an emotional processing disorder) in relation to attentional bias. Children and adolescents with PTSD were presented neutral and trauma-related words in an emotional Stroop test and their results were compared to a control group of 9 –17 year olds. The results indicated a strong attentional bias in the PTSD group to trauma-related words relative to the neutral words and to the performance of the control group. This was said to indicate that attentional bias to trauma-congruent information is a function of PTSD in young age groups. Therefore it can be seen that the Stroop method has also been useful in exploring the emotion-cognition relationship in cases of impaired processing.

One of the ways in which the Stroop method has perhaps been most directly useful in exploring this link is presented by Osimani et al (1997). They employed the emotional Stroop method to test whether it could be used to detect faked cognitive processing problems. 20 participants suffered genuine cognitive deficits due to brain damage and other miscellaneous problems. 10 participants were healthy individuals, unfamiliar with the Stroop test and its derivates, who were asked to simulate cognitive impairment. 10 participants were healthy psychology students, trained in the use of the test, who were asked to simulate cognitive impairment. 20 healthy participants were used as a control group. Results were analysed for reaction time, error percentage and the Stroop effect. There was a significant difference in reaction time among the groups. Controls and patients with genuine problems showed a clear Stroop effect. Simulators had a significantly prolonged reaction time, increased error percentage and inverted or absent Stroop effect. This presentation of the Stroop effect is never present in any real cognitive deficits and so was said to be characteristic of feigning, regardless of familiarity with the test and underlying theory. Thus Osimani and colleagues concluded that the emotional Stroop test could be effectively employed as a valuable tool to detect feigned cognitive impairment.

In conclusion there is a large body of evidence that the Stroop method has provided some help in exploring many of the aspects of the emotional and cognitive processing relationship. The first important thing to note, however is that the help it has provided has been variable. In some cases it has been seen to provide enough information to help formulate conclusive theories about certain aspects of this relationship. In other areas it has merely identified that this relationship exists and provided an area for future research to explore. Also, without valid empirical evidence to back them up, many of the theories that can be offered about the emotion-cognition relationship remain unsubstantiated speculation. The creation and success of the emotional Stroop test does still give clear evidence that there is a strong relationship between human emotional and cognitive processes. It is also important to note that, with a few exceptions, the Stroop method has not generally explored cognitive processes beyond that of attention. Therefore the contribution it can make to such an exploration is fairly limited. This being said, the findings of the Stroop method so far in the field of emotional and cognitive processes will almost certainly influence the shape of future research in this area.

References:

-Bentall, R.P. & Kaney, S. Content Specific Information Processing and Persecutory Delusions: An Investigation Using the Emotional Stroop Test in The British Journal of Medical Psychology, Vol. 62, 355-364.

-Bentall, R.P. & Thompson, M. (1990) Emotional Stroop Performance and the Manic Defence in The British Journal of Clinical Psychology, Vol. 29, 235-237.

-Eysenck, M.W. & Keane, M.T. (2000) Cognitive Psychology: A Student’s Handbook –East Sussex: Psychology Press.

-French, C.C., Richards, A & Scholfield, E.J. (1996) Hypomania, Anxiety and the Emotional Stroop in The British Journal of Clinical Psychology, Vol. 35, 617-626.

-Klein, G.S. (1964) Semantic Power Measured Through the interference of Words With Colour Naming in American Journal of Psychology, Vol. 115, 26-38.

-Long, C.G., Hinton, C & Gillespie, N.K. (1994) Selective Processing of Food and Body Size Words: Application of the Stroop Test with Obese Restrained Eaters, Anorexics and Normals in The International journal of Eating Disorders. Vol. 15, 279-283.

-Moradi, A.R., Taghavi, M.R., Neshat Doost, H.T., Yule, W. & Dalgleish, T. (1999) Performance of Children and Adolescents with PTSD on the Stroop Colour-Naming Task in Psychological Medicine #29, 415-419.

-Osimani, A., Alon, A., Berger, A. & Abarbanel, J.M. (1997) Use of the Stroop Phenomenon as a Diagnostic Tool for Malingering in Journal of Neurology, Neurosurgery, and Psychiatry, Vol. 62, 617-621.

-Segerstrom, S.C. (2001) Optimism and Attentional Bias for Negative and Positive Stimuli in Personality and Social Psychology, Vol. 27, 1334-1343.

-Stewart, S.H. & Samoluk, S.B. (1997) Effects of Short Term Food Deprivation and Chronic Dietary Restraint on the Selective Processing of Appetite-Related Cues in The International Journal of Eating Disorders, vol. 21, 129-135.

-Stroop, J.R. (1935) Studies of Interference in Serial Verbal Reactions in The Journal of Experimental Psychology, Vol. 18, 643-662.

-Thorpe, S.J. & Salkovskis, P.M. (1997) The Effect of One-Session Treatment For Spider Phobia on Attentional Bias and Beliefs in The British Journal of Clinical Psychology, Vol. 36, 225-241.

-Unoki, K., Kasuga, T., Matsushima, E. & Ohta, K. (1999) Attentional Processing of Emotional Information in Obsessive-Compulsive Disorder in Psychiatry and Clinical Neurosciences #53, 635-642.

-Van Honk, J., Tuiten, A, De Haan, E., Den Hout, M.V. & Stam, H. (2001) Attentional Bias for Angry Faces: Relationships to Trait Anger and Anxiety in Cognition and Emotion, #15, 279-297.

-Watts, F.N., McKenna, F.P., Sharrock, R. & Trezise, L. (1986) Colour Naming of Phobia –Related Words in The British Journal of Psychology, Vol. 77, 97-108.

-Williams, J.M.G., Watts, F.N., MacLeod, C. & Mathews, T. (1997) Cognitive Psychology and Emotional Disorders (2nd Ed) –Chichester: Wiley.