Factors contributing to the magnitude of conditional fear following a 24-h retention interval: The incubation effect

Two experiments were conducted to examine the effects of the number of conditional stimulus-unconditional stimulus (CS-US) pairings and the intensity of the US on “spontaneous” changes in the magnitude of conditional fear following a 24-h retention interval. The results of the first experiment showed that the magnitude of conditional fear following the interval increased as a function of the number of CS-US pairings. The results of the second experiment showed that, with the number of pairings held constant, increasing the intensity of the US resulted in an increase in the magnitude of conditional fear following the retention interval. These data are consistent with an associatively based account of incubation.