Table 1.

Design of Experiments 1 and 2.

Note: Both Experiments 1 and 2 involved three stages: preexposure, conditioning and test. Rats in groups Sham and HPC received preexposure to two audio-visual compounds (AX and BY) before trace conditioning trials with X and nonreinforced presentations of Y. Rats in Experiment 1 then received tests with the compounds AX and BX (and AY and BY); while those in Experiment 2 received tests with A and B alone.