Reevaluation of things past. A test of the "retrospection hypothesis" using a CER procedure with rats.

The ability of rats to reevaluate previously presented information in light of subsequently provided information was evaluated using a CER (conditioned emotional response) procedure. In Experiment 1, rats suppressed responding to a compound light + tone stimulus that was repeatedly paired with shock. Groups of rats were then presented with only one element of the compound (the tone), either presented alone or paired with shock, for 15 days. During this 15-day period, two control groups received trials with the shock alone or neither stimulus nor shock. All of the rats were then tested with the other element of the compound (the light). Rats that had received the tone paired with shock during the intervening training continued to suppress to the light, whereas rats that had received the tone alone showed rapid extinction of the CER to light. The control groups showed that this effect was not due to the number of shock presentations received. A subsequent experiment also demonstrated that these results were not due to nonspecific stimulus effects. Apparently, a subsequent change in the associative strength of one element results in a similar change to the other element of a previously established compound stimulus.