Conditioned inhibition in flavour aversion learning : odor as a conditioned inhibitor

Two experiments were performed which demonstrated that an olfactory stimulus can become associated with toxicosis over long CS-US delays and, more importantly, that an olfactory stimulus can become a conditioned inhibitor in a feeding situation. In Experiment 1, hooded rats were allowed to drink water while a stream of amyl acetate vapour was directed towards the end of the drinking spout. Toxicosis was then induced via the injection of lithium chloride after delays of 0, 0.5, 1, 4, and 12 hours for different groups. When compared with no-toxicosis controls, it was found that significant aversions were obtained for all groups except the 12 hr delay group. In Experiment 2, hooded rats were given conditioned inhibition training in which the taste of saccharin alone was always followed by induced illness, but the taste of saccharin plus the odor of amyl acetate was not. In a series of three subsequent tests - summation, enhancement of conditioning, and retardation - it was demonstrated that the odor had acquired active inhibitory properties. The results paralleled those obtained with more traditionally studied stimuli and techniques and hence were found to be readily predictable from a recent model of conditioning set forth by Rescorla & Wagner (1972)