Ratings
The CS+ was rated more unpleasant and more arousing than CS- (see Table 3 for means and standard deviations), F (1,85) = 144.47, p< .001, R 2 = .630 and F (1,85) = 120.40, p < .001, R 2 = .586, respectively. However, no modulation by threat uncertainty was found for the affective ratings as the main effect of Group and Stimulus x Group interaction were not significant (all p values > .219), HU: CS+: M = 7.90, SD = 1.03, CS-: M= 4.37, SD = 2.12, MU: CS+: M = 7.19, SD = 1.51, CS-: M = 4.66, SD = 1.99, LU: CS+: M = 7.15, SD = 1.85, CS-: M = 4.35, SD = 1.62, for valence and HU: CS+: M = 7.80, SD = 1.83, CS-:M = 4.43, SD = 2.13, MU: CS+: M = 6.81, SD = 1.91, CS-: M = 4.22, SD = 2.18, LU: CS+: M = 7.42, SD = 1.60, CS-: M = 3.92, SD = 1.67, for arousal.
The linear mixed models for US-expectancy returned a significant Stimulus x Group x Time interaction, F (2,255) = 4.96, p< .008, R 2 = .037. As shown in Figure 3, when compared to LU, the differential stimulus response in US-expectancy decreased from Acquisition 1 to Acquisition 2 for HU,bTime*Stimulus*Group(LU-HU) = -26.06 , SE = 9.19,t (255.00) = 2.83, p = .005 and for MU,bTime*Stimulus*Group(LU-MU) = -24.39 , SE = 9.06,t (255.00) = 2.69, p = .008. However, this decrease in differential stimulus responding from Acq1 to Acq2 was not significant for the comparison between MU-HU,bTime*Stimulus*Group(HU-MU) = 1.66 , SE = 8.72,t (255.00) = 0.19, p = .849 (Bonferroni correction α < .017).