Contextual control of first- and second-learned excitation and inhibition in equally ambiguous stimuli.

In two three-phase experiments, rats received a final third excitatory (Experiment 1) or inhibitory (Experiment 2) phase of conditioning with a tone. The third phase came immediately prior to a test with the tone, either in the context where the tone was trained or in a different context. Groups differed in each experiment with respect to the first two phases. Rats in Groups EIE (Experiment 1) and EII (Experiment 2) received excitatory conditioning with the tone in Phase 1, followed by inhibitory conditioning with the tone. Rats in Groups IEE (Experiment 1) and IEI (Experiment 2) received inhibitory conditioning in Phase 1, followed by excitatory conditioning in Phase 2. Thus, the association being expressed in Phase 3 was consistent either with what was learned first about the stimuli or with what was learned second. Contrary to expectations, the association being expressed at the end of Phase 3, either excitatory or inhibitory, was affected by a context change, regardless of its consistency with what was learned first about the CS.