Sequence-specific delayed gains in motor fluency evolve after movement observation training in the absence of early sleep

Abstract

Following physical practice, delayed, consolidation-phase, gains in the performance of the trained finger-to-thumb opposition sequence (FOS) can be expressed, in young adults, only after a sleep interval is afforded. These delayed gains are order-of-movements specific. However, in several perceptual learning tasks, time post-learning, rather than an interval of sleep, may suffice for the expression of delayed performance gains. Here we tested whether the affordance of a sleep interval is necessary for the expression of delayed performance gains after FOS training by repeated observation. Participants were trained by observing videos displaying a left hand repeatedly performing a 5-element FOS. To assess post-session observation-related learning and delayed gains participants were tested in performing the observed (trained) and an unobserved (new, the 5-elements mirror-reversed) FOS sequences. Repeated observation of a FOS conferred no advantage to its performance, compared to the unobserved FOS, immediately after practice. However, a clear advantage for the observed FOS emerged by 12 h post-training, irrespective of whether this interval included sleep or not; the largest gains appeared by 24 h post-training. These results indicate that time-dependent, offline consolidation processes take place after observation training even in the absence of sleep; akin to perceptual learning rather than physical FOS practice.

Figure 1

The finger-to-thumb opposition sequence (FOS) task (A), the training protocol (B) and the overall study design (groups-conditions) (C). (A) Two five-element sequences, each the mirror-reverse of the other, were used. (B) The training protocol consisted of viewing 160 repetitions of the assigned FOS (10 video-clips with 16 FOS repetitions in each) tapped by a person’s left hand. (C) Three groups observed the to-be-learned FOS (O-FOS) in a morning session: (a) group Obs_T_Imm was tested immediately after the training session; (b) group Obs_T_24h was tested 24 h after the session, overnight; (c) group Obs_T_day was tested 12 h after the session. Group Obs_T_night observed the to-be-learned FOS in the evening and was tested 12 h later, overnight (d). In all 4 groups, participants were first tested on the observed sequence (O-FOS) and immediately after on the untrained (mirror-reversed) movement sequence (U-FOS).

Figure 2

Participants’ mean speed (A) and accuracy (B) in executing the O-FOS and U-FOS in the immediate (Obs_T_Imm) and overnight (Obs_T_24h) tests. Bars represent standard error of the mean.

Figure 3

Group and individual performance on the O-FOS compared to the U-FOS after the two 12-h intervals (groups Obs_T_day; Obs_T_night). (A, B) Speed and accuracy after a delay interval of 12 h, with and without sleep. Bars represent the standard error of the mean. (C) Individual data, the difference (delta) in performance speed for the O-FOS versus U-FOS; the results of the two 12-h interval groups (Obs_T_day; Obs_T_night) are shown in comparison to the results of the 24-h interval group (Obs_T_24h).