Discrimination training in infant,preweanling, and weanling rats: Effects of prior learning experiences with the discriminanda

Rats were given continuous reinforcement (CRF), partial reinforcement (PRF), or successive discrimination (D) training in an alley from 11–14 (Age 1) or 15–18 (Age 2) days of age. Reinforcement was the opportunity to suckle the dry nipples of an anesthetized dam. Following a 10-day interval, all animals were given 4 successive days of discrimination training with food pellets as reinforcement. Control groups were given only the second phase of training. In the first phase, D subjects of both ages responded appropriately to the discriminative stimuli, and the PRF subjects of both ages ran significantly slower than CRF subjects. In the second phase, only the CRF subjects of Age 1 showed behavioral discrimination. All three Age 2 groups discriminated, but the discrimination developed earliest after Phase I CRF and latest after Phase I PRF. Both Age 1 control groups showed a late-developing discrimination, but neither Age 2 control group discriminated. The results suggest that infant and preweanling rats can learn both positive and negative expectancies of appetitive events, respond appropriately, and retain and transfer these expectancies to new learning. The reinforcement value of dry suckling and the effects of stimulus preexposure in infant rats are also discussed.