Order effects after blocked preexposure to two compound flavors.

In the first three experiments two groups of rats received prolonged blocked preexposure to AX-BX or to BX-AX. Experiment 1 showed that conditioning of AX after preexposure resulted in less generalization to BX in the AX-BX group than in the BX-AX group. Experiments 2 and 3 constituted, respectively, retardation and summation tests of the inhibitory properties acquired by B after preexposure and conditioning of A. Excitatory conditioning of B was retarded in the AX-BX group (Experiment 2) and only in this group B was able to alleviate the aversion conditioned to a new stimulus (Experiment 3). These results are explained as a consequence of the formation, in the AX-BX group, of inhibitory associations directed from B to A. A fourth experiment provided evidence that the A↔X association was preserved until the end of the preexposure phase in this group, which is a requisite for the formation of these inhibitory associations.