Multiple shifts in the representation of a motor sequence during the acquisition of skilled performance

Abstract

When do learning-related changes in performance occur? Here we show that the knowledge of a sequence of movements evolves through several distinctive phases that depend on two critical factors: the amount of practice as well as the passage of time. Our results show the following. (i) Within a given session, large performance gains constituted a signature for motor novelty. Such gains occurred only for newly introduced conditions irrespective of the absolute level of performance. (ii) A single training session resulted in both immediate but also time-dependent, latent learning hours after the termination of practice. Time in sleep determined the time of expression of these delayed gains. Moreover, the delayed gains were sequence-specific, indicating a qualitative change in the representation of the task within 24 h posttraining. (iii) Prolonged training resulted in additional between-session gains that, unlike the effects of a single training session, were confined to the trained hand. Thus, the effects of multisession training were qualitatively different than the immediate and time-dependent effects of a single session. Altogether, our results indicate multiple time-dependent shifts in the representation of motor experience during the acquisition of skilled performance.

Fig. 1.

The finger-to-thumb opposition task. The two sequences were matched for number of movements per digit and mirror-reversed in relation to each other (in terms of order).

Fig. 2.

Fast (within-session) and slow (posttraining) gains (experiment 1a). Two indices of performance are plotted for the first 48 h after a single training session: speed, mean number of correct sequences (Upper), and accuracy, mean number of errors (Lower). Each data point depicts performance in a 30-sec test block. Baseline, immediately after training, and 24- and 48-h posttraining scores for LtT and the three transfer conditions tested 48 h post-training: LtR sequence, RtR sequence, and RtT. ▴, mean performance 5 h posttraining (n = 8); arrow, training interval. (Bars, SEM.)

Fig. 3.

Immediate posttraining performance (experiment 2). Baseline and immediate posttraining scores for LtT and the three transfer conditions (LtR, RtR, and RtT). Arrow, the training interval. Speed (Upper) and accuracy (Lower) are shown as described for Fig. 2. (Bars, SEM.)

Fig. 4.

Contributions of time and time in sleep to motor performance during the first 24 h posttraining (experiment 3). (Upper) ON group. (Lower) OD group. Baseline, immediately, and 12- and 48-h posttraining scores for the trained condition. Arrow, the training interval; ^*, P < 0.05. (Bars, SEM.)

Fig. 5.

Long-term retention after a single training session (experiment 1a). Shown is performance 48 h posttraining and the retention (Re) test. The retention intervals were 5 and 8 months for participants HD and DI, respectively. T, trained; LR, left reversed; RR, right reversed; RT, right trained.

Fig. 6.

Single versus multisession training (experiment 1b). Performance 48 h after a single training session compared with performance after five additional training sessions. Arrows, training sessions. Speed (Upper) and accuracy (Lower) are shown as described for Fig. 2. (Bars, SEM.)

Fig. 7.

Block-by-block changes in performance (novelty effect). Data points are the mean slopes of linear regression lines fitted to the four blocks of each test condition (experiment 1b). Novel, all conditions in which no specific training was given (from left to right: LtT at baseline, LtR, RtR, and RtT 48 h after a single training session, and LtR, RtR, and RtT after prolonged training); Trained, trained condition immediately and 24 and 48 h posttraining after a single session and after prolonged training. (Bars, SEM.)