(a) Experimental design and timeline. (b) Mean SCRs (CSa+, CSb+, CS−) during acquisition (late phase), extinction (last trial) and re-extinction (first trial). Subjects had equivalent levels of acquisition and extinction of conditioned fear to the two conditioned stimuli. The index of fear recovery was the first trial of re-extinction (following reinstatement) minus the last trial of extinction (before reinstatement). Fear reinstatement was found only to CSb+, (not reminded before extinction training) but not CSa+ (reminded 10 min before extinction training). *Significant difference between acquisition and extinction, or extinction and re-extinction for each stimulus at p < 0.05; Error bars represent standard errors