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CHAPTER 2 40 chin- and forehead rest to restrict head movements. A nine-point calibration procedure was performed for the eye tracker. Participants practiced rating threat expectancy twice, making the full avoidance response twice, and using subtle safety behavior twice. The experimental task then started. Each trial consisted of the presentation of a CS for 5 s in the middle of the screen, followed by a 5-s waiting period during which participants rated threat expectancy, followed by the US or nothing. The inter-trial interval was 3 s. During each CS presentation, a dark grey picture of a plug was visible in the upper right corner of the screen, and a dark grey picture of headphones was visible in the upper left corner of the screen. These pictures indicated availability and unavailability of the full avoidance response and subtle safety behavior. If the picture of the plug turned green, participants could unplug the headphones from the sound amplifier (full avoidance), and if the headphones turned green, participants could take off the headphones (subtle safety behavior). If the full avoidance response or subtle safety behavior had been available, an instruction screen would appear at the end of the trial to inform participants to plug the headphones back into the sound amplifier, or to put the headphones back on. The design of the study is shown in Table 1. A, B, and C were randomly allocated to the three different shapes for each participant. In the Pavlovian acquisition phase, A and C were followed by the loud noise, and B was not. In the Safety behavior acquisition phase, full avoidance and subtle safety behavior were available during presentation of A. A was also presented without full avoidance or subtle safety behavior availability to remind participants that A was still followed by the loud noise if the full avoidance response was not available (cf. Engelhard, van Uijen, van Seters, & Velu, 2015; Lovibond et al., 2009).