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CHAPTER 2 36 make a full avoidance response, which was analogous to the safety behavior in the study by Lovibond et al. (2009). However, a second change to the paradigm was that this response was not pressing a button on a response box, but unplugging the headphones from the sound amplifier, which prevented participants from hearing the loud noise. The full avoidance response thus precluded the (potential) occurrence of threat. A third change was that all participants also learned to use subtle safety behavior, which entailed taking off the headphones. This did not prevent participants from hearing the loud noise, but decreased how loud, and thus how unpleasant, it was for participants. Hence, the subtle safety behavior minimized threat severity, but did not preclude the occurrence of threat. In a subsequent Extinction phase, the full avoidance response was available during unreinforced presentations of stimulus C for participants in the Full avoidance condition, but not for participants in the Control condition (analogous to Lovibond et al.’s [2009] experimental condition and control condition, respectively). Note that the effect of subtle safety behavior during unreinforced presentations of stimulus C was investigated in Experiment 2. A fourth and final change was that we did not measure skin conductance responses, because the full avoidance response and subtle safety behavior required participants to move both hands during CS presentations. Movement causes artifacts in skin conductance responses (Society for Psychophysiological Research Ad Hoc Committee on Electrodermal Measures, 2012). Movement also affects another commonly used psychophysiological measure in fear conditioning studies, namely the fear potentiated startle responses (Blumenthal et al., 2005). Additionally, the auditory probes that are used to induce the startle responses may interfere with the acquisition of contingencies (Lonsdorf et al., 2017). An alternative psychophysiological measure of fear learning are pupillary dilation responses (Leuchs, Schneider, Czisch, & Spoormaker, 2017). Pupil dilations in response to conditional stimuli are a measure of autonomic arousal and covary with skin conductance responses (Bradley, Miccoli, Escrig, & Lang, 2008). They can be used as