ترس، انزجار و پردازش اطلاعات در هراس خاص :: استفاده از تئوری تشخیص سیگنال

A growing body of research suggests that individuals with small animal and blood-injection-injury (BII) phobias respond to phobia-relevant stimuli with a combination of fear and disgust. Despite the recognition that disgust may serve a functional role in phobic avoidance behavior, little is known about biased information processing for disgust-related material. Two studies examined recognition memory, using signal detection analyses, for phobia-relevant and general disgust pictures. Study 1 failed to find differences between spider phobics, BII phobics, and nonphobics in discrimination ability (d′) and response bias (c) for spider, surgical, and two categories of general disgust pictures. Results indicated that all participants responded in a liberal manner toward surgical and disgust pictures, whereas they responded more conservatively when judging spider pictures. Study 2 also failed to find differences between BII phobics and nonphobics in discrimination ability and response bias for surgical and disgust pictures presented at 500 and 50 ms exposure durations. All participants again adopted a liberal response bias toward surgical and disgust pictures, although only under the 500 ms stimulus presentation condition. These results do not suggest the presence of preferential information processing of phobia-relevant or general disgust elicitors among phobic participants. The functional value of disgust-mediated information processing biases is questioned given the available literature. Implications and suggestions for continued information processing research for fearful and disgusting stimuli in specific phobia are outlined.

Examination of the unique emotional responses of fear and disgust toward threat-relevant stimuli has gained increased empirical attention in recent years (Sawchuk, Lohr, Tolin, Lee, & Kleinknecht, 2000; Woody & Teachman, 2000). Theoretical developments, such as the disease-avoidance model of small animal phobias (Matchett & Davey, 1991), have prompted studies proposing that disgust, either alone or in combination with fear, served a functional role in phobic avoidance behavior (Merckelbach, de Jong, Arntz, & Schouten, 1993). Investigations using self-report questionnaires assessing disgust and disgust sensitivity suggest that small animal and blood-injection-injury (BII) phobics are characterized by elevated disgust reactions toward phobia-relevant stimuli, relative to nonanxious controls (de Jong & Merckelbach, 1998; Mulkens, de Jong, & Merckelbach, 1996; Tolin, Lohr, Sawchuk, & Lee, 1997). Additional research has found that heightened aversion is not only domain-specific, but also generalizes to other domains (e.g., rotting foods, body products, hygiene) seemingly unrelated to phobic concerns (Sawchuk et al., 2000). The findings of questionnaire research have also been largely replicated in experimental studies in which spider phobics and BII phobics were exposed to pictures of phobia-relevant and general disgust pictures (Sawchuk, Lohr, Westendorf, Meunier, & Tolin, in press), and in studies in which phobics engaged in behavioral approach-avoidance tasks (de Jong, Vorage, & van den Hout, 2000; Mulkens et al., 1996; Smits, Telch, & Randall, in press). Fear and disgust are discrete emotional states characterized by differential patterns of physiological reactivity, behavioral tendencies, and facial expressions (Ekman, 1992 and Izard, 1977). However, both emotions tend to present in an interactive, aggregate manner upon exposure to phobic stimuli (Sawchuk et al., in press; Woody & Teachman, 2000). The relationships of fear, disgust, and specific phobia can be further examined through the systematic investigation of cognitive information processing biases of interpretation, attention, and memory. Theories regarding the nature, structure, function, and expression of emotions have been increasingly applied to the experimental psychopathology of anxiety disorders (Foa & Kozak, 1986; Mathews & MacLeod, 1994). Biases in the processing of threat-relevant information (i.e., interpretive, attentional, and memory functions) are presumably related to the maintenance of clinical anxiety (Mathews & Mackintosh, 1998). Various methods for measuring these biases have proliferated in recent years, and a substantial body of empirical research has been generated to explicate these processes (McNally, 1996). The scope of the literature has primarily focused on the emotion of fear mediating the biased processing of threatening information (Sawchuk, Lohr, Lee, & Tolin, 1999). Given that disgust is gaining increased salience in explaining phobic responding to small animal and blood-injury stimuli, applying existing information processing paradigms to disgust stimuli would appear indicated. Despite the argued role of disgust in phobic responding to animal and blood-injury stimuli, the relationship between disgust and biases in information processing has received far less empirical attention (Sawchuk et al., 1999). The limited scope of available studies do not suggest the presence of an attentional bias toward disgust-related words as assessed by the emotional Stroop task in analogue samples of spider phobics (Thorpe & Salkovskis, 1998) and BII phobics (Sawchuk et al., 1999). However, one study has shown Stroop interference for disgust/contamination words in a sample of spider fearful subjects relative to nonanxious controls (Barker & Robertson, 1997). The spider fearful group, however, exhibited slowed information processing across all word categories (spider, contamination, and neutral words), suggesting that interference effects were not specific to threat-relevant material. Only one published study thus far has examined selective memory for disgust information among phobic populations (Sawchuk et al., 1999). Using a word-stem completion task, analogue BII phobics demonstrated a significant implicit memory bias for previously seen medical and disgust words, relative to nonanxious controls and other matched negative and neutral word categories. These results are consistent with the broader literature suggesting that memory biases noted across various anxiety disorders tend to be observed using implicit, as opposed to explicit, memory paradigms (Becker, Roth, Andrich, & Margraf, 1999; MacLeod, 1990). Signal detection theory (SDT) offers a novel avenue by which to examine memory processing and performance in anxiety disorders. Statistical analyses within the signal detection paradigm allow researchers to distinguish between discrimination ability and the use of particular response styles (McNicol, 1972). Discrimination ability or sensitivity (d′) refers to the individual’s ability to correctly distinguish target stimuli that appeared during the initial encoding phase from distractors presented at the time of recall. The d′ statistic, therefore, is calculated as a ratio of “hits” (correct identification of targets) to “false alarms” (incorrect identification of distractors as targets). The decision-making criteria adopted by the individual during the memory task may range between a liberal to conservative response style, as indexed by the β or c statistic. Liberal response styles are adopted when individuals are attempting to maximize the likelihood of correctly identifying targets at the expense of increasing the number of false positive responses. Conservative response styles, on the other hand, are adopted when individuals are motivated to reduce the number of false positives recorded at the expense of reducing the likelihood of correctly identifying targets. Cognitive theories of anxiety postulate that biased information processing occurs in the detection, discrimination, and response to stimuli that signal threat and safety (Gray, 1982; Mathews & Mackintosh, 1998). Traditional information processing theories would predict that anxious individuals should demonstrate differential patterns of sensitivity and response bias toward meaningful threat stimuli (Foa & Kozak, 1986; Mathews & MacLeod, 1994). Specifically, these models would suggest that phobic responding is characterized by both the rapid detection of threat and an over-response to threat upon exposure (e.g., exaggerated startle response, escape, avoidance). Based on these assumptions, SDT would predict the following performance of anxious individuals when processing threat-relevant information: (a) the rapid detection and subsequent avoidance of threat results in poor discrimination between threat-relevant targets and distractors; and (b) the over-response to threat results in the adoption of a liberal response criterion. Few published studies have applied signal detection analyses to the information processing performance of anxious individuals. Mixed results have been reported, as significant differences in study design, subject samples, mode of stimulus presentation, type of memory task, and statistical analyses employed, render comparisons between studies problematic. Comparisons between spider phobic and nonphobic participants discriminating between previously seen and new spiders revealed that the phobic group tended to be less sensitive in discriminating among the large, as opposed, to small spiders, while no between-group differences emerged on the response bias analyses (Watts, Trezise, & Sharrock, 1986). Litz et al. (1986) found that PTSD subjects, relative to a mixed group of anxious participants and nonanxious controls, were characterized by a liberal response bias toward recognizing combat-related words that appeared on a Stroop task as well as a list of matched threat distractors. In another study examining recognition performance for lists of threat, neutral, and positive words, panic subjects and nonanxious controls both responded with a higher degree of sensitivity and adopted a liberal response bias toward threat words relative to the other word categories, although no between-group differences emerged (Ehlers, Margraf, Davies, & Roth, 1988). In a more recent study examining recognition memory for threatening and reassuring facial expression pictures, social phobics were less sensitive than nonanxious controls in discriminating among previously seen facial expressions, although the groups did not differ on the response bias analyses (Pérez-López & Woody, 2001). The current paper describes two programmatic studies examining memory biases for fearful and disgusting stimuli in analogue spider and BII phobias. Previous research has mainly used words to manipulate threat content (Bradley, Mogg, Falia, & Hamilton, 1998). The current investigations utilized pictures of phobic and disgusting material that more closely approximate actual phobic stimuli (Bradley et al., 1998; Wenzel & Holt, 1999) in order to examine differential memory performance within a signal detection paradigm. A further attempt was made to explore the manipulation of stimulus exposure time on sensitivity and response bias analyses.