Rats abstract rules from a response series lacking a consistent motor pattern

Two experiments examined whether rats could learn a rule-based response sequence when prevented from performing a consistent motor pattern. In a serial multiple-choice procedure, rats chose from an 8-lever array mounted on the walls of an octagonal operant chamber. In Experiment 1, rats learned to choose levers in proper order according to one of two patterns, a structured pattern, 1-2-3-4-5-6-7-8, or an unstructured pattern, 1-7-3-5-6-4-2-8, where digits indicate the clockwise position of correct levers in the circular array. These patterns were interleaved with random elements consisting of levers drawn from the set of all 8 possible positions in the array. Rats in the structured group learned their pattern, indicating that they were not limited to learning response sequences based on a consistent motor pattern. Furthermore, rats learned the structured pattern much faster than the unstructured pattern, indicating that pattern structure facilitated learning. To test the notion that the random elements of Experiment 1 may have slowed learning by creating structural ambiguity caused by irrelevant structural relations, in Experiment 2 irrelevant relations were minimized by ensuring that the correct pattern- and random-element responses were spatially distant from one another. Rats again learned the structured pattern faster than the unstructured pattern and, additionally, faster than the structured pattern in Experiment 1. The results of both experiments indicate that even when prevented from performing a consistent motor pattern and irrelevant relationships are present between pattern elements, rats abstract and encode rules describing structured sequential patterns.