Rats' use of hierarchical organization in serial pattern learning

Many organisms show aptitude for learning and performing patterned sequences. However, we do not yet have a complete account of how they accomplish this. One of the most successful is Restle's hierarchical model, which supposes organisms represent sequences using the simplest form available through using hierarchies to organize the sequences' elements. In two experiments, we evaluated if Restle's model accurately accounted for rats' patterned sequence learning. First, we compared rats' learning of a runs pattern with three levels of hierarchical organization with no violations of pattern structure to learning of the same pattern with one violation of pattern structure in the pattern's second half. Restle's model predicts rats should have more difficulty learning the violation pattern and that rats learning the pattern with the violation in the second half of the pattern should attempt to reflect that violation to the first half. The results indicated that rats had more difficulty learning the violation pattern and that inserting a violation in the second half of the pattern led rats to make significantly more errors on the second half of the pattern relative to the first half of the pattern. Rats did not insert the violation from the second half of the pattern into the first half of the pattern. In a second experiment, we continued to explore if Restle's model accurately accounted for rats' pattern learning using more complex patterns. The present results of both experiments and prior work with humans were inconsistent with Restle's model, suggesting more work is needed to develop a model that accurately accounts for rats' learning of complex patterned sequences.