Age-related differences in sensory conditioning in rats.

Four experiments tested rats 8, 12, or 21 days postnatal for sensory conditioning in terms of the association acquired between two odors presented simultaneously or sequentially. The sensory conditioning of 8- and 12-day-old rats exceeded that of rats 21 days of age when the odors were presented simultaneously. When one odor was presented immediately followed by another, however, 21-day-old rats conditioned as effectively as the younger animals, and with a sufficiently long interval between odors (20 min), the sensory conditioning of the 21-day-old rats surpassed that of the rats 12 days of age. Although consistent across a variety of procedures, in previous experiments and within the present study, the age-related differences in sensory conditioning after simultaneous presentation of two odors are difficult to understand. Increasing knowledge of the ontogeny of orienting may lead to an explanation in terms of Thompson's (1972) theory linking sensory conditioning with orienting and sensitization.