Characteristics of sequential movements during early learning period in monkeys

We previously demonstrated that the organization of a learned sequential mo vement, after long-term practice, is based on the entire sequence and that the information pertaining to the sequence is largely specific to the hand used for practice. However, it remained unknown whether these characteristi cs are present from the beginning of learning. To answer the question, we e xamined the performance of four monkeys for the same sequential procedure i n the early stage of learning. The monkeys' task was to press five consecut ive pairs of buttons (which were illuminated), in a correct order for every pair, which they had to find by trial-and-error during a block of trials. We first examined whether the memory of a sequential procedure that was lea rned once was specific to the hand used for practice. The second time that the monkeys attempted to learn a novel sequence, they were required to use either the same hand they used the first time or the opposite hand. The num ber of errors decreased to a similar degree in the same-hand condition and in the opposite-hand condition. The performance time decreased in the same- hand condition, but not in the opposite-hand condition. The results suggest that, in the early stage of learning, memory of the correct performance of a sequential procedure is not specific to the hand originally used to perf orm the sequence (unlike the well-learned stage, where the transfer was inc omplete), whereas memory of the fast performance of a sequential procedure is relatively specific to the hand used for practice (like the well-learned stage). We then examined whether memory of a sequential procedure depends on the entire sequence, not individual stimulus sets. For the second learni ng block, we had the monkey learn the sequence in the same or reversed orde r. In the reversed order, the order within each set was identical, but the order of sets was reversed. The number of errors decreased in both the same -order and reversed-order conditions to a similar degree for two out of fou r monkeys; the decrease was larger in the same-order condition for the othe r two monkeys. For all monkeys, the performance time decreased in the same- order condition, but not in the reversed-order condition. The results sugge st that the memory structure for correct performance varies among monkeys i n the early stage of learning (unlike the well-learned stage, where the mem ory of individual sets was consistently absent). On the other hand, memory of the fast performance of a sequential procedure is relatively specific to the learned order used for practice (like the well-learned stage). (C) Spr inger-Verlag 2000.