Chapter 5 – Experimental fear 161 in physiological reactivity. Each 4 consecutive startle probe responses of the same cue (nocebo or control) were averaged for further analyses. Trials during which baseline was higher than startle response peak (due to no eyeblink response, an occasional blink), were reject trials. Hypothesis testing Acquisition of nocebo hyperalgesia First, we examined whether nocebo hyperalgesia was induced and whether it differed between the High-pain and Control groups and the High-threat and Control groups. We expected that the two fear inductions (high pain and threat manipulation) would lead to larger nocebo responses, as compared to the control group. To compare each of the fear groups to the control group, two 2x2 mixed model ANOVAs were performed, with group as the between-subjects factor and trial type as within-subjects factor (first extinction nocebo trial, first extinction control trial). Extinction of nocebo hyperalgesia Next, we examined whether the extinction of nocebo hyperalgesia differed significantly between the High-pain and Control groups and between the High-threat and Control groups. We expected that the two fear inductions would lead to resistance to extinction, as compared to the control group. To compare each of the fear groups to the control group, two 2x2 mixed model ANOVAs were performed with group as the between-subjects factor and time as within-subjects factor for calculated nocebo magnitudes (start of extinction, end of extinction).
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