Effects of Delay of Intracranial Reinforcement upon Discrimination Learning in the Rat

Abstract

The purpose of the present experiment was to study the effects of delay of intracranial reinforcement upon a simple Y-maze discrimination learning and to consider if secondary reinforcement is so established by central stimulation as food e. g. PERKINS (1947) and WOLFE (1934).
17 rats with a chronically implanted bipolar electrode that had learned enough to press a bar for lateral hypothalamic electrical stimulation in Skinner box were preliminary trained to run a straight alley. On the test trials, individual Ss were randomly assigned to the four different delay groups. Delay of 0, 5, 15, and 45 sec. were employed. All Ss in this period received ten massed runs a day for 8 successive days, respectably with each delay of optimal intracranial reward. After all series had been completed, Ss were sacrificed and electrode loci determined.
Results from four groups were as follows :
1. Three groups with delays of reward 0, 5, and 15 sec. tended to show a correct choice in 60 trials, while the group with 45 sec. delay did not show the satisfactory learning curve. Therefore it was suggested that delay of reinforcement gradient is even in a situation of intracranial reinforcement.
2. The slope of the gradient obtained in the present experiment was not so steep as reported by KEESEY (1964) that set up more less external and internal stimuli during the delay period. This difference of the gradients corresponded with that between GRICE (1948) and PERKINS (1947) or WOLFE (1934).
3. Especially, the fact that learning was established even in delays of 5 and 15 sec. in this experiment suggests that the secondary reinforcing agent acted upon learning for intracranial stimulation. However, the value of the secondary reinforcement was possibly poorer than in peripheral stimulating situation.