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CHAPTER 5 138 extinguish when the perceived positive consequences of the safety behavior are removed. For example, in an instrumental extinction phase, participants may learn that safety behavior no longer prevents them from hearing the aversive loud noise, which may reduce their use of safety behavior. Investigating the extinction of instrumentally conditioned safety behavior can provide insights for the improvement of the long-term effects of exposure-based therapy. Furthermore, future studies may include more extinction trials to increase extinction learning and fully diminish threat expectancy. This could also reduce the exclusion rate for insufficient extinction. Note that previous studies used similar exclusion procedures, which resulted in comparable exclusion rates. For instance, Leer et al. (2013) excluded 29 out of 109 participants (i.e., 27%) based on acquisition and extinction, and Dibbets, Poort, and Arntz (2013) excluded 22 out of 70 participants (i.e., 31%). Similarly, we excluded 14 out of 45 participants (i.e., 31%) based on acquisition and extinction criteria, and one additional participant who had misinterpreted the experimental task (i.e., a total of 33%). Finally, we cannot eliminate the possibility that participants were engaged in reasoning that was specific to the laboratory setting. Although the fear conditioning model has proven to be a robust and valid preclinical laboratory model for the return of fear (Milad & Quirk, 2010; Vervliet et al., 2013), research that investigates whether safety behavior is resistant to fear extinction, and whether safety behavior is involved in the return of fear in a clinical setting is needed. In sum, the current findings imply that safety behavior is resistant to extinction of classically conditioned fear, and can trigger a return of fear. This suggests that safety behavior may be involved in relapse. The current data were collected in healthy participants using a fear conditioning paradigm. Future studies should investigate whether safety behavior is resistant to fear extinction during exposure- based therapy in clinical samples, and whether safety behavior after fear extinction causes a return of clinical fear. Investigating how the extinction of safety behavior