Effects of interrun interval shift and pattern length on serial pattern learning in rats

Abstract

The present experiment examined effects of interrun interval (IRI) shift and pattern length on serial pattern learning in rats. Rats in a runway received varying number of 45mg food pellets as items of a series. In Phase 1, two groups were given long series (18-10-6-3-1-0 pellets), and the other two groups were given short series (18-1-0 pellets), under short (15-20s) or long (5-7min) IRI. All of the groups were presented their series at one time per day. All the groups developed reliable anticipation of 0 pellet. In Phase 2, each IRI was shifted from short to long or vice versa. The shift in IRI deteriorated the 0 pellet anticipation only in the group which was given 6 item series under short IRI-in Phase 1 and long IRI in Phase 2. No reliable deterioration of 0 pellet anticipation was observed in any other three groups. The interactive effect between direction of shift in IRI and pattern length on pattern tracking performance is explained most appropriately by Hulse's dual theoretical approach which suggests that either associative learning or rule learning mediate serial pattern learning depending on IRI and pattern length.