تعصبات توجه در اختلالات تغذیه ای: بررسی فراتحلیلی از عملکرد استروپ

The Stroop task has been adapted from cognitive psychology to be able to examine attentional biases in various forms of psychopathology, including the eating disorders. This paper reviews the research on the Stroop task in the eating disorders research area in both descriptive and meta-analytic fashions. Twenty-eight empirical studies are identified, which predominantly examine food and body/weight stimuli in bulimic, anorexic, or dieting/food-restricted samples. It is concluded that there is evidence of an attentional bias in bulimia for a range of stimuli but that the effect seems to be limited to body/weight stimuli in anorexia. The evidence to date is that there is no attentional bias in dieting samples. Limitations of the methodology employed in the extant literature include small sample sizes, unstandardized Stroop methodology, restricted gender, and a general lack of consideration of individual differences variables. Recommendations for future research are provided.

The models that have developed in the area of the eating disorders Fairburn & Brownell, 2002, Garner & Bemis, 1985 and Vitousek & Orimoto, 1993 emphasize multiple possible causal factors in these problems. Among these models, one of the notable developments in psychopathology research has been the growth of investigations and models that emphasize cognitive processes and content (cf. Dobson & Kendall, 1993). In part spurred on by the general “cognitive revolution” in psychology and in part by the success of cognitive-behavioral therapies, this emphasis has yielded several varied and rich technologies to examine psychological processes. Among the range of cognitive factors that have been implicated in the eating disorders are such issues as attitudes and beliefs about ideal body weight, body dissatisfaction, and body image and perception; perfectionism have received considerable attention. For example, in a recent examination of the prediction of binge eating and purging (Byrne & McLean, 2002), it was found that overconcern with body weight and shape, coupled with the adoption of purgative behaviors, was predictive of binge eating and purging. Similarly, a recent review of the issue of body size dissatisfaction in anorexia nervosa (Skrzypek, Weheimer, & Remschmidt, 2001) found that although body size estimation is not impaired in this condition, it is the discrepancy between perceived body size and ideal size that is significantly associated with anorexia nervosa. Findings such as these highlight the role of negative attitudes and beliefs about food and body shape in the eating disorders and suggest the possibility of disordered information processing in these conditions. For example, individuals who have eating disorders have undue concerns about food or body image; it may be that these concerns could be demonstrated through a variety of methods that relate to different cognitive processes. One of the cognitive processes associated with eating disorders that has been the focus of considerable research is that of selective attention. Consistent with the idea that individuals with eating disorders have negative beliefs about food and body shape, it has been suggested that these individuals are also more attentive and responsive to these relevant stimuli than non-eating-disordered individuals. A body of research using a modification of the Stroop task has evolved in which selective attentional processes have been examined. In this paper, we review the use of the Stroop task in examining eating-disordered attentional processes and examine in meta-analytic format the existing data. Conceptual and methodological issues in the extant literature and directions for future investigations are provided. 1.1. The Stroop task The original or Classic Stroop task (Stroop, 1935) was developed as a means to study basic human attentional and informational processes. This task consisted of the presentation of colors printed on either neutral words or incongruent color words. Participants first named the color name of the stimuli and then the color of the stimuli. This method was later revised to include color words (e.g., red and blue) that were printed in either the corresponding color (congruent condition) or other competing colors (incongruent condition). As these tasks are relatively easy, they form a basis for comparing the interference created by naming the color of the stimulus when the actual color is competing (e.g., the word “blue” written in green). Scores derived from the Stroop task consist of either the latency (typically in ms) to name each stimulus or the “interference effect,” which is calculated as the average time taken to name the competing cards divided by the sum of the average time for the two other sets of stimuli. In some studies, the number of correct color names is also recorded. When the Stroop task was first explored (Stroop, 1935), the interference effect was discussed as an example of cognitive competition and how such competition retards the production of correct color names. Replications of the Stroop interference effect have shown that it is reliable Dyer, 1973, Franzen et al., 1987 and MacLeod, 1991. Both Stroop (1935) and MacLeod (1986, as cited in MacLeod, 1991) have reported that in normal controls the latency to name color-only stimuli is about 40% of that for naming incompatible color-word stimuli. MacLeod's (1991) extensive review of the Stroop task identified “more than 700 Stroop-related articles in the literature” (p. 163), many of which focus on the perceptual, cognitive processing, and potential neurological processes underlying the Stroop phenomenon. According to MacLeod, a set of 18 reliable findings emerges in this literature, which relate to the conditions that optimize or suppress interference effects, the effects of cues on Stroop performance, and the effect of different localizations of stimuli, practice effects, and other performance aspects. Notably for the current review, MacLeod's authoritative review does not examine the effect of individual differences on Stroop interference, except to examine gender and age. Despite the much research conducted with the Classic Stroop task on normal participants, it remains unclear whether the Classic Stroop effect is created by difficulties associated with the relative speed of processing color versus language (Klein, 1964), the automaticity of language Logan, 1980 and Posner & Snyder, 1975, the perceptual encoding of the proper stimulus attribute (i.e., is a result of perceptual interference; Dyer, 1973, but see MacLeod, 1991 for evidence refuting this hypothesis), or the interference related to the differential strength of the competing pathways being processed (see Cohen et al., 1990, Cohen et al., 1992, Logan, 1980, Logan, 1985, MacLeod, 1991 and Williams et al., 1996 for discussions of parallel distributed processing). Debate on the issue of which model best explains the Stroop interference effect continues, and “the Stroop effect will continue to be a challenging phenomenon for cognitive psychologists to explain for many years to come” (MacLeod, 1991, p. 193). Notwithstanding the controversy in cognitive psychology about the mechanism that accounts for the Stroop interference effect, the Stroop task has been used in psychopathology research for a considerable period of time. It has been suggested that the Stroop task is a valuable tool for examining cognitive processes in psychopathology Segal, 1988 and Williams et al., 1996 and that it affords an opportunity to compare disordered samples with normal controls in a task with relatively tight experimental control. Stroop research can be in such diverse areas as anxiety disorders, depression, schizophrenia, eating disorders, substance abuse, and studies that relate personality variables to cognitive interference. Recent years have witnessed a dramatic increase in the amount of Stroop research conducted in psychopathology (Williams et al., 1996). In most of the psychopathology Stroop research, the focus is not often on general attentional interference but is rather on the attentional bias that disordered participants exhibit relative to comparable control stimuli. As a result, the Stroop task has often been modified to use both classic and “emotional” or disorder-appropriate stimuli (e.g., anxiety words for studies of anxiety-disordered samples and food words for studies with eating-disordered samples). In effect, the model that has been tested is that appropriate emotional stimuli are more salient to individuals with a particular disorder and that such stimuli will be selectively attended to (i.e., processed more efficiently) than for either individuals without that condition or mismatched stimuli. The large number of studies that has been conducted using this paradigm affords a unique opportunity to make comparisons about the information-processing mechanisms among diverse clinical conditions. For example, Williams et al. (1996) reviewed the Stroop task in depression and anxiety and emphasized the mechanisms (cognitive and artifactual) underlying its interference effect. These authors demonstrated that attentional biases are found in depression and anxiety and argued that the connectionist (parallel distributed processing) model (Cohen et al., 1990) is useful for understanding these biases. The purpose of this study was to review in both descriptive and meta-analytic formats the Stroop task in the eating disorders. There has been a recent “explosion” of research on the Stroop task in eating-disordered samples, as fully 23 of 26 studies discovered in the literature search for this review were published in or since the 1990s. Much of this work has been precipitated by cognitive formulations of eating disorders Fairburn & Garner, 1988 and Polivy & Herman, 1987 particularly the awareness of the sensitivity of patients with eating disorders to food as well as perceptions of body size and weight. The use of the cognitive measures has been increased because of concern that simple questionnaires do not well measure attitudes associated with eating disorders (Vitousek & Hollon, 1990); the use of the Stroop task in particular has been spurred by the development of sets of adjectives specifically designed for this population. Thus, the development of both a “Food Stroop” and a “Body Stroop” (sets of words with food or body shape terms, respectively; Ben-Tovim et al., 1989 and Channon et al., 1988) has enabled researchers in this area to focus on specific matched stimuli rather than the Classic Stroop words. Rather than exploring the mechanisms thought to produce the Stroop interference effect (see Williams et al., 1996), this review assesses the Stroop findings and methodology to further our understanding of psychopathology and to enhance future clinical research. In the literature review that follows, a distinction will be made between “Classic Stroop” and other “Emotional Stroop” methods, where the latter manipulate the content of the stimuli employed. Comparisons will be made between eating-disordered and other groups as well as between eating-related stimuli and other comparison stimuli, where such data exist. The research in eating disorders has focused on three different problem areas: bulimia, anorexia nervosa, and dieting/restrained eaters. There appears to be a uniformity hypothesis in the literature in that the rationale provided in different studies for the use of the Stroop task with different samples is analogous. However, as this distinction is consistently made in the empirical literature, we review the literature on dieting/food-restricted samples separately from those individuals who meet formal diagnostic criteria for an eating disorder and further distinguish eating-disordered samples into those who suffer from either anorexia nervosa or bulimia (American Psychiatric Association, 1994). Explicit tests of the uniformity hypothesis exist and are discussed below.

Before the adoption of methodologies derived from experimental cognitive psychology, clinical investigators were unable to directly measure the cognitive processes or structures involved in maladaptive functioning. Instead, indirect inferences were often drawn, from self-report data, about the logical underlying cognitive operations associated with psychopathology (Ingram & Kendall, 1986). As Segal (1988) aptly stated, “the strategy of relying on [patient] self-reports to validate a construct whose operation is intended to explain these self-reports becomes increasingly circular unless additional referents can be provided to demonstrate schematic processing” (p. 147). The Stroop methodology has provided one of these additional referents and has permitted researchers to analyze cognitive processing in a way that is less transparent than self-report (Segal, 1988). The current review has demonstrated that performance on the Emotional Stroop task is related to eating disorders. In particular, although selective attention to either Food or Body/Shape stimuli cannot be reliably detected in dieting or eating restrictive samples, sensitivity to Body/Shape stimuli can be seen in anorexic samples, and selective attention to both types of stimuli can be seen in bulimic subjects. These results may indicate stimulus specificity in different disorders or may reflect increasing overall levels of disturbance, and thus broader areas of Stroop task performance, in these various groups. Although the results obtained in the current review help to explicate the relation of the Emotional Stroop task in eating-disordered groups, there are several research directions that have yet to be explored. Principle among these are the longitudinal development of attentional biases in the eating disorders, the covariation of the Emotional Stroop task with other measures of cognitive processing, and the specificity of Emotional Stroop stimuli across various clinical conditions. In summary, the modified Stroop task has demonstrated utility in psychopathology. The areas of theoretical and practical controversy highlighted in this review signify fertile ground for continued investigation and innovation. We anticipate and offer numerous promising areas for the Stroop task in both research and practice and echo MacLeod's (1991) enthusiasm about “the progress that will be examined in the subsequent review of the Stroop literature some time early in the next millennium” (p. 193).