الگوی هوشیاری بیش از حد - اجتنابی در عنکبوت هراسی

Cognitive-motivational theories of phobias propose that patients’ behavior is characterized by a hypervigilance–avoidance pattern. This implies that phobics initially direct their attention towards fear-relevant stimuli, followed by avoidance that is thought to prevent objective evaluation and habituation. However, previous experiments with highly anxious individuals confirmed initial hypervigilance and yet failed to show subsequent avoidance. In the present study, we administered a visual task in spider phobics and controls, requiring participants to search for spiders. Analyzing eye movements during visual exploration allowed the examination of spatial as well as temporal aspects of phobic behavior. Confirming the hypervigilance–avoidance hypothesis as a whole, our results showed that, relative to controls, phobics detected spiders faster, fixated closer to spiders during the initial search phase and fixated further from spiders subsequently.

Fear is an aversive emotional state that serves a protective purpose. It signals danger and prepares us to deal with it. However, for people with specific phobias, fear is pathological and thus interferes with a person’s ability to cope with everyday situations. In this case, fear is related to the presence or anticipation of a particular object or situation, and patients are usually aware of how unreasonable their fear is (American Psychiatric Association, 2000). Phobic behavior typically includes avoidance, which is supposed to have two main functions. On the one hand, avoidance enables patients to reduce anxious mood states by keeping encounters with fear-relevant stimuli to a minimum (Thorpe & Salkovskis, 1999). On the other hand, the same behavior is regarded as a major factor in maintaining phobia, since avoidance prevents habituation to, or objective evaluation of, fear-related stimuli (Mogg, Bradley, De Bono, & Painter, 1997). Numerous studies have shown that there is an attentional bias in processing fear-related information and that this bias is particularly pronounced in phobics (see Mogg & Bradley, 1998 for a review). For example, Ohman, Flykt, and Lundqvist (2000) provided evidence that healthy subjects detect fear-relevant stimuli such as snakes or spiders faster than fear-irrelevant ones. This ‘snake-in-the-grass effect’ is enhanced in phobics, depending on the nature of their disorder (e.g., spider phobics were faster in detecting spiders as opposed to snakes). The authors attributed their findings to preattentive processes that are triggered by biologically prepared aversive stimuli. Once a threat stimulus is detected, attention automatically shifts to its location. In phobics, the aversive emotion is thought to accelerate detection. A recent study reported that, compared to control subjects, spider phobics more often perceived their responses to spiders as automatic, i.e., not under intentional control (Mayer, Merckelbach, & Muris, 2000). This finding highlights the preattentive and automatic nature of the mechanisms that direct the attention of phobics towards fear-relevant stimuli. Fast detection abilities of phobics have commonly been attributed to the more general concept of hypervigilance, which describes the tendency to constantly scan the environment for any signs of threat (Thorpe & Salkovskis, 1999). The prefix hyper indicates that, although most people are vigilant for potential threat, this vigilance is strongly enhanced in phobics. As fast identification of threat allows early activation of defenses ( Ohman et al., 2000), hypervigilance may serve a protective purpose. However, it is regarded as an important factor in the acquisition of pathological fear as well ( Williams, Watts, MacLeod, & Mathews, 1997). Individuals who are permanently scanning the environment for threat may be more likely to perceive the world as a dangerous place, which in turn enhances their anxious mood and might increase the probability that they develop pathological anxiety ( Mogg & Bradley, 1998). So far, two aspects of phobic behavior with regard to fear-relevant stimuli have been described: avoidance and hypervigilance. It has been assumed that everyday routines of phobics are influenced by both tendencies (e.g., Lang, Bradley, & Cuthbert, 1990), although they appear somewhat mutually exclusive at first glance. One might ask how phobics manage to avoid something that permanently attracts their attention. Cognitive-motivational theories (e.g., Mathews, 1990; Mogg, Mathews, & Weinman, 1987) postulate that hypervigilance and avoidance co-occur in phobics’ behavior in a temporally ordered manner. That is, phobics initially direct their attention towards threat, but may then try to avoid detailed processing of such stimuli in an attempt to reduce their anxious mood state (Mogg et al., 1987). This hypervigilance–avoidance hypothesis was investigated in non-clinical anxiety (Mogg et al., 1997) and in subjects with general anxiety disorder (Bradley et al., 1999). Both studies were based on modified versions of the dot probe task. During a typical dot probe task, pairs of stimuli (e.g., a threat word and a neutral word) are presented on a screen, followed by a small dot probe that appears in the location of one of the stimuli. Participants are required to respond manually to the probe as quickly as possible. The idea behind this task is that response latencies will be accelerated when probes occur in an attended, rather than unattended part of the display (Posner, Snyder, & Davidson, 1980). In the two studies mentioned above, the duration of stimulus exposure was manipulated and the focus of analysis was on two predictions. First, due to initial hypervigilance, anxious individuals should respond faster to probes replacing briefly presented threat stimuli than healthy subjects. Second, as a consequence of subsequent avoidance, it was expected that anxious individuals respond more slowly to these probes than controls when longer stimulus durations were applied. Both studies found ample evidence for hypervigilance in anxious individuals. However, the same subjects did not show avoidance after longer stimulus durations. This absence of evidence for avoidance can be interpreted in several ways. Mogg et al. (1997) and Bradley et al. (1999) provided two explanations. First, it was assumed that the hypervigilance–avoidance hypothesis might be incorrect. Results indicated that both initial shifting and subsequent maintenance of attention were consistently biased towards threat information in anxious individuals. Thus, a simple hypervigilance hypothesis would explain the results sufficiently. Second, the stimuli may not have been anxiety-provoking enough to prompt avoidance strategies. In our opinion, there are two further explanations. First, the applied duration of stimulus exposure (i.e., up to 1500 ms) was possibly not long enough to allow for elaborative processing that prompts avoidance behavior. Second, the dot probe task may not be the method of choice to investigate hypervigilance–avoidance patterns. Researchers cannot observe hypervigilance and avoidance behavior per se in this task, since both tendencies have to be inferred from manual reaction times. In order to investigate them in a more direct manner, we used eye movement measurements to analyze phobic behavior. Eye movement tracking allows the registration of temporal as well as spatial aspects of fixations and saccades, which in turn are closely related to attentional mechanisms (e.g., Kowler, Anderson, Dosher, & Blaser, 1995). Thus, eye movement analysis is particularly suitable for investigating attentional biases such as hypervigilance or avoidance. The main objective of the present study was to empirically validate the hypervigilance–avoidance hypothesis (Mogg et al., 1987) in phobics during a visual task that required participants to search for fear-relevant stimuli. Due to a relatively high prevalence rate (Szymanski & O’Donohue, 1995), we decided to concentrate on spider phobia. Data analysis was focussed on variables that represent hypervigilance or avoidance. As a consequence and based on the hypervigilance–avoidance hypothesis, three main predictions were investigated: (a) phobics detect spiders faster than controls; (b) relative to controls, phobics’ fixations are spatially closer to spiders during the initial search phase; and (c) phobics subsequently fixate further from spiders than controls.

The hypervigilance–avoidance hypothesis (Mogg et al., 1987) states that, when confronted with threat stimuli, phobics initially direct their attention towards, and subsequently away from threat. Previous empirical validation attempts (Bradley et al., 1999 and Mogg et al., 1997) confirmed initial hypervigilance and yet failed to show subsequent avoidance. The results of the present visual search task contribute to this line of research in two important respects. On the one hand and in contrast to previous findings, avoidance occurred in phobic behavior and it followed hypervigilance as proposed by the hypervigilance–avoidance hypothesis. On the other hand, our results can be used to explain why previous studies did not reveal avoidance. The main focus of analysis was on three predictions inferred from the hypervigilance–avoidance hypothesis. First, due to initial hypervigilance, phobics were expected to fixate fear-relevant stimuli earlier than controls. This is in line with previous findings about fast detection abilities in phobics (Ohman et al., 2000). Our results verified the prediction and thereby constitute further evidence that these abilities indeed exist. The second prediction was that phobics fixated closer to fear-relevant stimuli than controls during the initial phase of search behavior, again due to hypervigilance. Confirming findings from studies that applied dot probe tasks (Bradley et al., 1999 and Mogg et al., 1997), the present results verified this second prediction as well. Third and due to avoidance, it was assumed that phobics fixate further from spiders than controls during subsequent stages of information processing. Contrasting with previous findings, our results confirmed such avoidance in phobic behavior. To the best of our knowledge, the present study is therefore the first empirical validation of the vigilance–avoidance hypothesis as a whole. Given the absence of evidence for avoidance in previous studies (Bradley et al., 1999 and Mogg et al., 1997), one is tempted to ask why such behavior was shown by phobics in our study. First, eye movement analysis may be a more direct method for investigating avoidance than dot probe tasks. Eye movement tracking allows the assessment of both hypervigilance and avoidance by analyzing the temporal and spatial distribution of fixations, whereas dot probe tasks require inferences from manual reaction times. A second explanation is related to the time frame that was under investigation. While previous studies applied time frames of up to 1500 ms, our results showed that avoidance became evident after 1700 ms of stimulus exposure at the earliest. Controlled avoidance strategies might thus need that much time to fully develop and replace initial hypervigilance. Beside the three predictions that directly refer to the hypervigilance–avoidance hypothesis, a further focus of analysis was on search performance. In this regard, the two groups did not differ significantly from each other, as indicated by the number of omissions in the forced-choice task. Hence, the hypervigilance–avoidance pattern observed in phobics’ fixation behavior had no effect on search performance. This may, however, depend on the time frame of 5 s in our experiment. Given the findings that, relative to controls, phobics fixated earlier on a spider and closer to spiders up to the fifth fixation, it seems plausible that a time frame of 2 s could have allowed phobics to surpass controls with regard to search performance. Since the main focus of the present study was on the hypervigilance–avoidance hypothesis rather than on search performance, we decided to apply a relatively long time frame in order to include fast detection as well as subsequent avoidance. A third focus of analysis was on fixation duration and saccade amplitude. These two basic oculomotor parameters were used to evaluate general group differences in visual search behavior. Results showed that phobics made slightly shorter fixations and significantly longer saccades than controls during the search task. This can be interpreted in terms of an accelerated and more far-ranging search behavior in phobics, possibly due to the arousing nature of the stimuli and/or the task per se. Although search performance was not group-specific, these results nevertheless indicate that the stimuli of our experiment were not excessively frightening for phobics. Otherwise we might probably have observed a near-to-refusal avoidance with enhanced fixation durations, smaller saccadic amplitudes, and a poorer search performance in phobics. In sum, the main objective of the present study was to empirically validate the hypervigilance–avoidance hypothesis (Mogg et al., 1987) in spider phobics during a visual task that required participants to search for spiders. Our results clearly confirmed this hypothesis. In contrast to previous findings that exclusively demonstrated initial hypervigilance (Bradley et al., 1999 and Mogg et al., 1997), the present study revealed evidence for subsequent avoidance as well, possibly due to a more appropriate methodology (i.e., eye movement analysis instead of dot probe tasks, extended time frame). We thus consider our findings as the first empirical validation of the hypervigilance–avoidance hypothesis as a whole. According to Mogg et al. (1997), this behavioral pattern may be a key factor in maintaining phobia. As a consequence of initial hypervigilance, phobics are more likely to detect potentially threatening events and thus perceive the world as a dangerous place, while subsequent cognitive avoidance prevents objective evaluation and habituation to such events. In this respect, the present study contributed to the empirical validation of a clinically relevant concept in phobia research.