Irrelevant Relations in Rat Serial Pattern Learning

Abstract

Researchers have long questioned whether animals learn patterned sequences based on pairwise associations between consecutive items, as in Skinner's (1934) chaining theory, or if their sequence learning is more flexible and like that of humans. Recently, evidence has emerged indicating animals flexibly represent sequential events by coding hierarchical representations characterized by relations between nonadjacent events. However, the processes through which they accomplish this are unclear. Here, I performed three experiments to elucidate these mechanisms. In Experiment 1, I explored the ability of rats to abstract a serial pattern when the pattern contained misleading, ambiguous information in the form of irrelevant relations between pattern elements. Rats learned to press levers for brain stimulation reward in a circular array according to the same structured subpattern interleaved with repeating responses on lever 2, 6, or 8: 122232-223242-324252-425262-526272 (Beginning), 162636-263646-364656-465666-566676 (End), or 182838-283848-384858-485868-586878 (No Irrelevant Relations), where digits indicate the clockwise position of the correct lever in the array for each trial. Results indicated irrelevant relationships retarded learning more when at the beginning versus the end of the pattern, suggesting that, like humans, rats processed patterns from beginning to end. In Experiment 1, all groups were presented with the entire pattern throughout training. In Experiment 2, I explored the effect of irrelevant relations on learning following initial pattern induction. In this experiment, I trained subjects on only half the interleaved pattern (which either did/did not contain irrelevant relations) in Phase 1. Then, I added the second half (which also either did/did not contain irrelevant relations) in Phase 2. Results indicated that for rats, like humans, once pattern structure was induced irrelevant relations were not impairing. Experiment 3 explored rats' ability to learn a patterned sequence when it could not be performed correctly using an identical set of motor responses. In this experiment, rats learned a structured subpattern (12345678) interleaved with randomly extended levers. Results indicated rats were not limited to using an identical set of motor responses, suggesting their representations were more cognitive in nature. The three experiments provide further evidence that rats' representations of patterns are flexible and akin to those of humans.