The influence of natural preference for tactile stimuli on appetitive learning in rat pups

Stimuli of the same modality tend to be organized along a "natural preference scale." This study examined the ability of six- and nine-day-old rat pups to acquire appetitive learning, when the CS was one of two differently "naturally preferred" tactile stimuli (floor textures: rug and plywood). In Experiment 1, all pups showed a relative natural preference for the rug texture over the plywood texture. Pups conditioned on the plywood texture (exposed to a sibling pup as the US) showed a robust increase in preference for the conditioned texture whereas pups conditioned on the rug texture showed a different and more moderate pattern of acquisition. Developmental differences were found only in extinction of the conditioned response: six-day-old (but not nine-day-old) pups displayed extinction of the response over four trials. Experiment 2 indicated that preexposure to the rug CS prior to conditioning (latent inhibition) did not interfere with the learning process on the rug texture. Two major alternative explanations for the differential learning patterns are discussed: motivational and catecholaminergic influences on learning. The results suggest that natural preferences may modulate early learning and memory processes.