Figure 1. A schematic overview of the experimental phases.

The upper panel represents the trials used in the matching-to-sample training, symmetry test and equivalence test, in order to create two novel stimulus categories (A1-B1-C1-D1 and A2-B2-C2-D2). The first stimulus always represents the sample stimulus, the other three stimuli are the comparison stimuli. The correct comparison stimulus is indicated in bold. The lower panel represents the fear conditioning phase (acquisition, generalization of acquisition test, extinction, generalization of extinction test). The “+”sign indicates that this stimulus is followed by an electric shock in 8 out of 10 trials. The “−”sign indicates that this stimulus is never followed by a shock during those trials.