Exposure Therapy for Acrophobia—Habituation May Not Matter
Exposure therapy is arguably the most effective component of cognitive behavioral treatments for anxiety disorders, and Edna Foa’s emotional processing theory (Foa & Kozak, 1986) has been a major influence for the past 20 years in guiding the application of exposure treatment. One emphasis in the emotional processing theory is the importance of habituation in exposure treatment. Habituation refers to reductions in distress (e.g., fear response) over time when the person encounters a feared stimulus. Treatments based on the emotional processing theory generally keep people in the exposure condition until they report a drop in distress. Emotion processing theory also recommends that the individual experience a relatively high level of fear activation when initially confronted with the exposure for it to be effective.
However, cracks have been showing in the emotional processing theory (see Craske et al., 2008; McNally, 2006 for reviews), and a recent study from Michelle Craske’s lab further undermines its presuppositions. It’s neat study, compact yet elegant. The focus is exposure treatment for acrophobia (i.e., fear of heights).
One thing that immediately struck me about the methodology in this study is that undergraduate students and research coordinators with bachelor’s degrees conducted the exposure. Training consisted of four 2-hour training sessions conducted during a month. This speaks to the ease with which paraprofessionals may be trained in specific exposure techniques.
Forty-nine undergraduate students with a moderate to severe fear of heights participated. Exposure involved participants putting their foot through a 6-inch gap in the concrete wall of a six-story parking garage across 1-2 sessions. Data was collected through a heart rate monitor and subjective ratings of distress during the exposure, and through a self-report measure of acrophobia.
The researchers found no support for the hypotheses that fear activation and within-session habituation (i.e., reduction in fear during exposure) were related to outcomes. Support for between-session habituation—reductions in fear between the first and second exposure sessions—was limited and inconsistent. Additionally, there was no relationship between between-session and within-session habituation, which further suggests that it doesn’t matter whether someone’s distress goes down during exposure.
The authors offer a pretty bluntly worded evaluation of emotional processing theory, stating it is “not a viable explanation of the mechanism of change in exposure therapy” (p. 1141).
What does this mean for the clinician? The most practical implication is that it doesn’t appear to be important that clients’ distress reduces during exposure. This had been one of the guiding principles of emotional processing theory: that the exposure should be conducted until the individual reported reductions in distress. According to Craske’s work, this doesn’t appear to matter. Moreover, it’s not clear whether it’s important to design exposure exercises that will elicit a high fear response. Exposure may be effective regardless of whether there are high levels of arousal.
I think emotional processing theory has been extremely important in guiding anxiety treatment research for the past 25 years. However, it may be time to retire the theory. It’s not clear what will replace it, although Craske and colleagues’ (2008) paper is a great place to start. It’s an exciting time for research on exposure treatment, as researchers continue to refine an approach that’s been around for several decades.
For the full citation:
Baker, A., Mystkowski, J., Culver, N., Mortazavi, A., & Craske, M. (2010). Does Habituation Matter? Emotional Processing Theory and Exposure Therapy for Acrophobia. Behaviour Research and Therapy, 48, 1139-1143.