Figure 3

Recognition patterns after a stress-based unpaired learning. (A) Participants (n = 12) underwent an unpaired learning (CS+, 370 Hz; CS−, 784 Hz) in which painful stimuli pseudo-randomly occurred during the inter-trial-intervals, and not in association with a specific tone. Twenty-four hours later, subjects performed the 2AFC recognition task (NS+, 466 Hz; NS−, 1046 Hz). (B,C) Explicit detection levels were similarly high for both the CS− and the CS+, thus indicating that painful stimuli during learning trials did not interfere with encoding processes. (D) Subjects were similarly confident for both CSs recognition choices. (E) Participants (n = 12) encoded two tones (CS+, 370 Hz; CS−, 784 Hz) and painful stimuli were delivered 2 s prior to the CS+ onset and never before the CS−. This unpaired learning was aimed at reproducing the temporal proximity between painful stimuli and the CS+ without forming a CS-US predictive association. Twenty-four hours later subjects performed the explicit 2AFC test (NS+, 466 Hz; NS−, 1046 Hz). (F,G) Subjects highly recognized both the CS− and the CS+, thus indicating that the generalization of explicit responses is specifically related to the CS-US predictive association. (H) Confidence ratings did not differ between CS− and NS− or between CS+ and NS+ recognition choices. *P < 0.05, **P < 0.01, ***P < 0.001. All data are mean and SEM. Wilcoxon signed-rank tests [(B,F)]; Mann–Whitney U tests [(D,H)].