Response sequence difficulty in an incremental repeated acquisition (learning) procedure.

Incremental repeated acquisition (IRA) procedures require subjects to learn a different sequence of behavioral responses during each experimental session with required response sequences increasing incrementally in length as subjects demonstrate mastery of shorter response chains. The purpose of this study was to investigate whether some response sequences are more or less difficult to acquire than others. If true, then sequence difficulty must be considered as a potential confound when attempting to assess the effects of drugs and other experimental manipulations on learning. Accuracy for each response sequence was assessed using control data from two large rodent studies, and each sequence was classified as easy, moderate or hard. Sequences that required responses on adjacent levers were easier (characterized by higher accuracies) to acquire than those that required responses on non-adjacent levers. In addition, sequences that required responses on only two of three response levers were easier to acquire than those that required responses on all three levers. These results provide strong evidence for differing levels of response sequence difficulty in IRA procedures with sequence difficulty seeming to be dependent on whether or not responses are required on adjacent levers.