Extinction of the A↔X association after blocked preexposure to AX-BX was studied in two experiments. In Experiment 1, two groups of rats received long (14 trials) or short (4 trials) blocked preexposure to AX-BX and subsequent conditioning of X. The results showed that the AX association was equally preserved after long and short preexposure. Experiment 2 studied the effect of blocked preexposure to 0, 1 or 2 ruptures of the AX association on extinction. In this experiment a “rupture” is produced when, in subsequent blocks, one element of the original compound is presented in compound with a different element. A significant extinction was observed only when the AX association was broken twice

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