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J Exp Psychol Anim Behav Process. 2008 Jul;34(3):336-51. doi: 10.1037/0097-7403.34.3.336.

Massed extinction trials produce better short-term but worse long-term loss of context conditioned fear responses than spaced trials.

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School of Psychology, The University of New South Wales, Sydney NSW, Australia.


A series of experiments studied the effects of the interval between extinction trials on the loss of context conditioned freezing responses. Rats were shocked in one context (A) but not in another (B) and subjected to extinction trials in context A. In Experiment 1, massed trials produced more rapid loss than spaced trials. A shift from spaced to massed trials maintained this loss, but the shift from massed to spaced trials restored lost responses. Experiments 2-5 examined this effect of massed trials on responding across spaced trials. They provided evidence that (a) a single trial was as effective as multiple daily massed trials, (b) learning occurred on the first of the massed trials but not on later ones, and (c) the first trial reduced the amount learned across subsequent massed trials. Finally, alternating extinction trials in A and B produced more response loss across spaced trials than blocks of trials in A and B. The results were discussed in terms of the role accorded to self-generated priming in the models developed by A. R. Wagner (1978, 1981).

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