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Behac. Res. Ther. Vol. 33, No. 6, pp. 699-700, 1995 Copyright ~t~ 1995 Elsevier Science Ltd

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Stimulus estimation and the overprediction of fear: a comment on two studies

STEVEN T A Y L O R

Department o f Psychiatry, University o f British Columbia, Vancouver, BC, Canada V6T 2A 1

(Received 4 October 1994)

Summary--The overprediction of fear is the tendency to overestimate the amount of fear one will experience in a subjectively threatening situation. This bias is thought to promote excessive avoidance and limit the opportunity for corrective learning. The stimulus estimation model states that the overprediction of fear arises from the overprediction of the danger features of the stimulus and the underprediction of available safety resources. Two recent studies reportedly failed to support the model (Arntz, Hildebrande & van den Hout, Behaviour Research and Therapy, 32, 709-722, 1994; Telch, Valentiner & BoRe, Behaviour Research and Therapy, 32, 747-751, 1994). The present commentary shows that both studies suffered significant methodological problems and neither can be said to have tested the model. Criteria for evaluating the model are briefly discussed.

Fearful people, including those with anxiety disorders, tend to overpredict the probability of aversive events (Beck, Laude & Bohnert, 1974; Butler & Mathews, 1983; Lucock & Salkovskis, 1988) and underpredict the probability of pleasant events (Lucock & Salkovskis, 1988). Although accurate predictions help people avoid unexpected aversive events, such events are better avoided by erring on the side of caution. That is, by overpredicting their likelihood of occurrence. This commentary is concerned with one such bias known as the overprediction of fear.

The overprediction of fear is the tendency to overestimate the probability or intensity of fear that will be experienced in a given situation (Rachman, 1994). Examples include the agoraphobic who overestimates the amount of fear that will be evoked by entering a department store, and the snake-phobic who anticipates more fear than is actually experienced when encountering a snake. The overprediction of fear is thought to promote excessive avoidance behaviour, which limits the opportunity for reducing unrealistic fears (Rachman, 1994),

In an effort to account for this bias, Taylor and Rachman (1994) developed the stimulus estimation model, which states that the overprediction of fear arises from the overprediction of danger elements of the stimulus and underprediction of available safety resources (e.g. availability of escape routes). Taylor and Rachman (1994) tested the model by exposing snake-fearful Ss (N = 224) to a live, harmless snake. Using 0-I00 scales, Ss made predictions and reports of their peak fear levels, along with predictions and reports of danger-relevant features (snake length, activity level, and a global rating of dangerousness), and predictions and reports of safety-relevant features (control over whether the snake touched the subject, and a global rating of safety). It was found that Ss overpredicted their fears. They also overpredicted danger and underpredicted safety. Structural equation modelling supported the stimulus estimation model.

Telch, Valentiner and Bolte (1994) sought to further test the model by having claustrophobic students (N = 138) complete a fear-evoking task, which required them to enter a long, dark narrow chamber. The S looked into the chamber for 5 sec and the task was explained to him/her. Subjects were allocated to one of two safety conditions, with safety defined as proximity to the exit. Subjects in the low safety condition were asked to walk to the end of the chamber and remain there for several min. Subjects in the high safety condition were asked to enter the chamber and simply stand by the door for several min. After the task requirements were explained, the S predicted his or her peak fear on a 0-100 scale, entered the chamber, and then reported the peak level of fear that was experienced.

Subjects in the low safety condition tended to underpredict their fears, which Telch et al. regarded as a failure to support the stimulus estimation model. This conclusion is based on a misunderstanding of the model. Telch et al. believed the model predicts that Ss in the low safety condition should overpredict their fears. However, the model does not state that Ss invariably overpredict their fears; it predicts that the low safety condition will produce an overprediction of fear onl3" if it induces the underprediction of safety or overprediction of danger. If, on the other hand, the low safety condition causes Ss to overpredict safety (and underpredict danger), then the model predicts that Ss will underpredict their fears. Oddly enough, Telch et al. sought to test the model without obtaining predictions or reports of safety (or danger), and so we don't know whether safety was overpredicted, underpredicted, or correctly predicted. Thus, Telch et al?s study is methodologically inappropriate for testing the model.

Although the study cannot test the model, it is interesting to speculate on how the model would account for the fact that Ss tended to underpredict their fears in the low safety condition. Telch et al. informally collected comments from claustrophobic Ss when they returned from the back of the chamber. Subjects made comments such as "1 did not realize how far away I was from the door until I went into the chamber" (Telch et al., 1994, p. 747), which suggests that they tended to overpredict safety. This is not surprising, since the experimental chamber was dark and unusually long (11.4 m) which may have caused Ss to overestimate the ease of escape from the end of the chamber. Of course if Ss tended to overpredict safety, then the model predicts that they should underpredict their fears. The latter is precisely what was found.

Subjects in the high safety condition (i.e. those required simply to stand inside the door) had plenty of information about the task and probably made accurate ratings of safety. If safety was accurately predicted, then the model states that fear predictions also would be accurate. In fact, Telch et al. found fear predictions in this condition tended to be accurate.

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Arntz, Hildebrand and van den Hout (1994) also set out to test the stimulus estimation model. They asked I I anxiety disordered patients to complete a series of fear-evoking trials. For example, a panic disordered patient troubled by tension-induced chest pain was asked to run up a flight of stairs. For each trial, predictions and reports of fear were obtained on 0-100 scales, along with 0-100 ratings of the strength of a dysfunctional belief (e.g. "my chest pain will increase because physical exercise causes an increase in chest pain if I suffer from angina pectoris") and strength of a functional belief ("my chest pain will not increase during the exercise, which indicates that I am not suffering from angina pectoris"). (Both quotes are from Arntz et al., 1994, p. 715.) One functional and one dysfunctional belief was assessed on each trial. The overprediction of danger was measured by the difference between pre- and post-trial ratings of strength of the dysfunctional belief, and underprediction of safety was measured by pre-post differences or ratings of strength of the functional belief. These pre-post scores did not significantly predict the overprediction of fear, which was taken as a failure to support the model. Some support was provided when the trials were repeated with other samples.

This study is not a test of the stimulus estimation model because Arntz et al. did not measure the overprediction of danger or underprediction of safety; they simply obtained pre-post changes in belief strength. Clearly, to measure the overprediction of danger and underprediction of safety it is necessary to obtain predictions and reports of danger and safety. The post-trial ratings of belief strength are not measures of reported danger or reported safety. The post-trial ratings are more like predictions since they entail expectations about future events (e.g. "if I exert myself I will experience chest pain").* In summary, the study by Arntz et al., like the one by Telch et al., is methodologically inappropriate for testing the stimulus estimation model. Neither provide evidence for or against the model. This is not to say the studies were entirely without merit; both examined several other interesting issues apart from the stimulus estimation model. However, these are beyond the scope of the present commentary.

To test the stimulus estimation model it is necessary to obtain predictions and reports of (a) fear, (b) danger elements of the stimulus (e.g. sources of harm) and (c) available safety resources (e.g. availability to escape routes or access to protective others). The model states that the overprediction of danger and underprediction of safety are determinants of the overprediction of fear. This could be tested in a correlational design or, better still, in an experimental design that directly manipulates the overprediction of danger and underprediction of safety. If one manipulates safety resources (e.g. by varying the proximity of escape exits) then it is essential to determine what effect this manipulation has on the underprediction of danger and overprediction of safety. It is not sufficient to deem one condition as 'high safety' and another as 'low safety,' since this tells us nothing about whether these conditions cause the overprediction, underprediction, or correct prediction of safety.

The overprediction of fear and overprediction of panic can persist even after numerous exposure trials (Schmidt, Jacquin & Telch, 1994; van Hout & Emmelkamp, 1994). It follows from the stimulus estimation model that fear and panic will be overpredicted as long as the S continues to overestimate danger and/or underestimate safety. Treatments that correct the biases in predicting danger and safety should reduce the overprediction of fear. These deductions can be readily tested and may shed light on why the overprediction of fear often persists over trials.

REFERENCES

Arntz, A., Hildebrand, M. & van den Hout, M. (1994). Overprediction of anxiety, and disconfirmatory processes, in anxiety disorders. Behaviour Research and Therapy, 32, 709-722.

Beck, A. T., Laude, R. & Bohnert, M. (1974). Ideational components of anxiety neurosis. Archives o f General Psychiatry, 31, 319-325.

Butler, G. & Mathews, A. (1983). Cognitive processes in anxiety. Advances in Behaviour Research and Therapy, 5, 51-62. Lucock, M. P. & Salkovskis, P. M. (1988). Cognitive factors in social anxiety and its treatment. Behaviour Research and

Therapy, 26, 297-302. Rachman, S. (1994). The overprediction of fear: a review. Behaviour Research and Therapy, 32, 683-690. Schmidt, N. B., Jacquin, K. & Telch, M. J. (1994). The overprediction of fear and panic in panic disorder. Behaviour

Research and Therapy, 32, 701-707. Taylor, S. & Rachman, S. (1994). Stimulus estimation and the overprediction of fear. British Journal of Clinical Psychology,

33, 173-181. Telch, M. J., Valentiner, D. & Bolte, M. (1994). Proximity to safety and its effects on fear prediction bias. Behaviour Research

and Therapy, 32, 747-751. van Hout, W. J. P. J. & Emmelkamp, P. M. G. (1994). Overprediction of fear in panic disorder patients with agoraphobia:

does the (mis)match model generalize to exposure in vivo therapy? Behaviour Research and Therapy, 32, 723-734.

*The error of this approach can be seen by applying the same logic to the measurement of the overprediction of fear. If one obtained pre- and post-trial predictions of fear, it would be fallacious to claim that the pre-post difference score is a measure of the overpredietion of fear.