The emotional Stroop effect in anxiety disorders: General emotionality or disorder specificity?
Introduction
Cognitive models of anxiety have received increasing empirical support over the past decade (e.g., Barlow, 1988, Beck et al., 1985, Eysenck, 1992). These models focus on attentional processes because one function of anxiety is the detection of threat, enabling the individual to react quickly. According to cognitive theories (e.g., Bower, 1981, Bower, 1987, Williams et al., 1988, Williams et al., 1997), anxiety patients' attention should be biased selectively towards threatening stimuli. To understand cognitive biases of attention, psychological theories and clinical research have increasingly turned to information processing paradigms derived from experimental cognitive psychology.
A classical paradigm adapted to this purpose was originally introduced by Stroop (1935). The modified version of the Stroop task is the paradigm most frequently used to show attentional biases in anxiety patients. The general approach of this task is to demonstrate selectively biased attention by showing diminished performance in a task condition where threatening stimuli could cause distraction. Specifically, participants are asked to name the ink color of words, disregarding their content. The basic finding is that, compared to other words and other participants, patients with anxiety disorders take longer to name the color of threatening words.
The modified Stroop task has been used successfully with a variety of anxiety patients, among them patients with panic disorder Ehlers et al., 1988, McNally et al., 1990, McNally et al., 1992, obsessive–compulsive disorder (Ilai, Shoyer, & Foa, 1991), specific phobia (Lavy, van den Hout, & Arntz, 1993), social phobia (SP, Hope, Rapee, Heimberg, & Dombeck, 1990), and posttraumatic stress disorder Foa et al., 1991, Kaspi et al., 1995. Furthermore, there are several studies of patients with generalized anxiety Martin et al., 1991, Mathews & MacLeod, 1985, Mogg et al., 1989. Most of these studies found the expected specific distraction effect, i.e., patients were specifically slowed in naming the print color of threat-related words. This effect occurs both with word-by-word and card-by-card presentation of the words, although it seems to be stronger with the blocked card-by-card format Holle et al., 1997, McNally et al., 1996. The color-naming interference does not seem to be due to inter-item priming, repetition of the items, or even more critically, on conscious attention. Four studies MacLeod & Hagan, 1992, MacLeod & Rutherford, 1992, Mogg et al., 1993, Mogg et al., 1993 could demonstrate distraction by threatening stimuli presented subliminally. Hence, the interference seems to be a genuine bias of anxiety patients.
Mathews and MacLeod (1985) conducted one of the first studies using the modified Stroop task with anxiety patients. They found highly specific effects: patients who worried mostly about physical harm were particularly slow in naming the color of physical threat words, whereas patients worrying about social threat were especially slow in naming social threat words. Similarly, Hope et al. (1990) reported that panic patients were slowed by physical threat cues, but not social threat cues, whereas the opposite held for social phobics. Specific, albeit slightly different, effects were also reported by Mogg et al. (1989). Martin et al. (1991), however, criticized earlier studies for confounding emotionality and threat. They presented evidence that anxiety patients were distracted by emotional words generally, regardless of their specific content.
Thus, there are two competing explanations for the attentional biases observed in the emotional Stroop task: general emotionality (positive or negative) vs. schema congruency or specificity. If emotionality is responsible for the interference, then the schema theories proposing that anxious patients have increased accessibility only to threat information are wrong. However, Mathews and Klug (1993), using threat-related negative and threat-related positive words (antonyms of the threat-related negative ones, e.g., safe), and negative and positive words unrelated to threat, found evidence against the emotionality hypothesis: In their experiment, patients were slowed by all words related to their fears, regardless of the valence of the words. Furthermore, a study by MacLeod and Rutherford (1992) found that specificity of effects depended on the level of processing. In their review, Williams, Mathews, and MacLeod (1996) conclude that the Stroop effect is not due to emotionality per se, but rather to the degree to which words are semantically related to the schema. Furthermore, comparing interference indices over a variety of studies, they find that although “current concern” accounts for much Stroop interference, it does not explain all the interference in patient groups. Besides relatedness, the negativity of the material is important in determining how much color naming will be disrupted.
The present study employed the modified emotional Stroop task to further clarify the role of current concerns, emotionality, and specificity in color-naming interference. In addition to a group of non-anxious control participants, two different groups of anxiety patients participated in the studies, namely patients with generalized anxiety disorder (GAD) and patients with SP, most of whom were afraid of giving speeches. These anxiety disorders were chosen for two reasons: First, they involve anxiety schemata of differing widths, i.e., a rather broad schema (GAD) vs. a very narrow one (SP). GAD patients typically worry about a wide range of topics, while fears of SP patients in this study concentrated on giving speeches. Thus, GAD patients could be expected to have an attentional bias towards a broader range of stimuli (maybe even emotional stimuli in general) than SP patients. The GAD-related words chosen as stimuli were either connected to worry topics or to anxiety symptoms. The SP-related words were connected with giving a speech.
Section snippets
Participants
A total of 32 GAD patients, 29 SP patients, and 31 control participants without a history of any psychiatric disorder participated. GAD patients were invited to participate in a drug-treatment study conducted by the fourth author at a VA Palo Alto Health Care System Hospital, Palo Alto, CA; patients with SP volunteered for a behavior therapy study at the same place. All patients completed the experiments reported here before receiving treatment. Control participants were paid a modest fee for
Participant characteristics
Table 2 shows several demographic data of the three participant groups as well as their mean scores for the SCL-90 (Derogatis et al., 1977), the STAI-Trait questionnaire (Spielberger et al., 1970), and BDI (Beck et al., 1961). As can be seen in Table 2, the three groups were equivalent for age, gender, level of education, first language, and ethnicity. As Table 2 also indicates, the three groups differed on several of the questionnaires (all P<.05, according to the Scheffé test). GAD patients
Discussion
Results of the Stroop task show that patients suffering from GAD displayed an attentional bias. They took longer to name the print color of GAD-related words than SP patients and controls. However, GAD patients also took longer than controls to name the color of positive words and speech-related words. A similar pattern emerged when color-naming times of GAD patients alone were compared. GAD patients took as long to name the color of GAD-related words as speech-related ones, with no difference
Acknowledgements
Preparation of this paper was supported by a fellowship from the German Academic Exchange Service (DAAD) to Eni S. Becker, a fellowship from the German Research Foundation (DFG) to Mike Rinck, and the support of the Veterans Administration and the National Institute of Health to Walton T. Roth. We would like to thank Cassandra Lehmann for recruiting and diagnosing the GAD patients and Cheryl Post for her help in conducting the experiment. Furthermore, we would like to thank Gordon Bower,
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