Skin conductance responses (SCR) across all experimental phases. A. Responses to CS + and CS- (single trials shown). On day 2, the order of recall and renewal was counterbalanced between subjects to correct for order effects. B. Differential SCR (CS + minus CS-). Differential learning in all phases was compared to last habituation trial. Habit. = Habituation, Cond. = Conditioning, Ext. = Extinction, μS = microsiemens, *p < 0.05; **p < 0.01.