Two experiments were conducted to study the effect of US experience upon CR in the taste-aversion learning situation. In Experiment I, like many other learning situations (e.g., CER situation), it was tested whether the US experience had any effect on CR in the taste-aversion learning. After conditioning (CS1: saccharin solution (0.1%), US: LiCl solution (0.15 mol)), rats received US alone six times. At this time, the effects of contextual cues were also tested. Then, the extinction procedure was administered to test the retroactive effect of US experience and the aversion to the CS1 was tested. Further, rats were conditioned to the CS2 (NaCl solution (9 g/1)) to study the proactive effect of the US experience. In Experiment II, the strength of US presented alone after conditioning was systematically varied across groups (0. 05, 0. 075, 0.15, 0. 3, and 0. 45 mol). The rest of the procedures were the same as in Experiment I. From Experiments I and II, it was found that the stronger the US strength was, the more reduced was the CR to the CS1, and the more retarded was the formation of CR to the CS2. The results suggest that the CS-US association exists in the taste-aversion learning, and the appearance of the CR was dependent on the state of the US memory.
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