Fig. 2. Effects of two-trial conditioning. (A) Stimulus schedules (see Fig. 1C for key to shading). Groups 1, 2 and 3 were subjected to two trials of differential conditioning (P+/V-) and elementary aversive (V-) and appetitive (P+) conditioning, respectively. (B) The preferences (PPIs) for peppermint of groups 1 (N=29), 2 (N=15) and 3 (N=18) before training and 2 h after training. Values are means + S.E.M. (C) Performance index (PI) of groups 1, 2 and 3 measured 2 h, 1 day and 4 days after training. Values are means + S.E.M.