CHARACTERISTICS OF A LONG-TERM PROCEDURAL SKILL IN THE MONKEY

The purpose of this study was to characterize the nature and structure of procedural memory. We have previously studied the process of learn ing sequential behavioral procedures using monkeys. The monkey's task was to press five consecutive pairs of buttons (indicated by illuminat ion) in the correct order for every pair, which he had to find by tria l-and-error in a block of trials. The whole sequence was called a ''hy perset''; each pair was called a ''set''. We first examined whether mo nkeys learned to perform a hyperset as a single sequence or learned th e order of button-presses individually for each set. To answer this qu estion, we generated hypersets that were the same as the hypersets tha t had been extensively learned except that the order of the sets was r eversed. The performance of these ''reversed hypersets'' was much wors e than the performance of the original learned hypersets and was simil ar to the performance of new hypersets, as regards both the number of errors and the performance time. The result suggests that monkeys lear ned a hyperset as a sequence, To examine whether the learned performan ce was specific to the hand used for practice, we had monkeys use the same hand throughout the long-term practice of each hyperset, and then tested the opposite hand. The performance using the opposite hand was worse than the performance using the trained hand, but was better tha n the performance for new hypersets. This indicates that the memory fo r the sequential procedure is only partially accessible to the hand th at was not used for the practice.