Chapter 4 – Experimental learning 137 Manipulation check for the control trials Lastly, as a first manipulation check, it was assessed whether changes in the ratings of the control trials influenced the results of the attenuation phase. A 5x2 mixed model ANOVA revealed no significant differences in the NRS pain ratings for control trials before and after attenuation (F (4,117) = 0.62, P = 0.64, ηp 2 = 0.02). This result indicates that the control trials did not yield significant changes from pre- to post- attenuation and that the reduction in nocebo hyperalgesia was in fact driven by changes in nocebo responses before and after attenuation. To further examine whether control trials could have affected the attenuation results, a 2x2 mixed model ANOVA was conducted with the attenuation group as the between-subjects factor and the magnitude of nocebo hyperalgesia as the within-subjects factor with two levels (nocebo-control difference score pre-attenuation, nocebo-control difference score postattenuation). The analysis revealed a significant interaction between the counterconditioning and extinction groups and the reduction of nocebo responses (F (1,95) = 6.87, P = 0.009, ηp 2 = 0.07), indicating significantly higher efficacy of counterconditioning compared to extinction (Figure 6), also when the control trials where included in the analysis. Figure 6 depicts time-series data for the evocation and attenuation phases and illustrates that control trials did not yield changes from pre- to post- attenuation that would impact nocebo trials. Questionnaires Spearman’s Rank-Order Correlation analyses indicated that there was no significant relationship between the magnitude of nocebo hyperalgesia in the active groups and trait or state anxiety, pain catastrophizing, or optimism scores (STAI trait: r = -0.07, P = 0.49; STAI state pre: r = - 0.06, P = 0.55; STAI state post: r = -0.13, P = 0.19; PCS: r = -0.06, P = 0.54; LOT-R: r = -0.05, P = 0.59).
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