Developmental contributions to motor sequence learning.

Little is known about how children acquire new motor sequences. In particular, it is not clear if the same learning progression observed in adults is also present in childhood nor whether motor skills are acquired in a similar fashion across development. In the present study we used the multi-finger sequencing task (MFST), a variant of the serial reaction time (SRT) task, to study motor sequence learning, across two consecutive days, in three cross-sectional samples of children aged 6, 8, and 10 years, and a control sample of adults. In the MFST, participants reproduced 10-element sequences of key presses on an electronic keyboard, using four fingers of the right hand. Each block of practice included 10 intermixed trials of a Repeated (REP) sequence and four trials of Random (RAN) sequences. Performance was assessed by examining changes in accuracy, a component of the task that requires the association of the visual stimulus with the motor response, and response synchronization, a component that requires fine-grained sensorimotor integration and timing. Additionally, participants completed Recognition and Recall tests, to assess explicit knowledge of the repeated sequence. Overall, results showed a developmental progression in motor sequence learning within and across days of practice. Interestingly, the two behavioral measures showed different developmental trajectories. For accuracy, differences were greatest for the two youngest groups early in learning, and these groups also showed the greatest rate of improvement. However, by the end of Day 2, only the 6-year-olds still lagged behind all other groups. For response synchronization, all child groups differed from adults early in learning, but both child and adult groups showed similar rates of improvement across blocks of practice. By the end of Day 2, 10-year-olds reached adult levels of performance, whereas 6- and 8-year-olds did not. Taken together, the dissociation observed with our two behavioral measures of sequence learning is consistent with the hypothesis that accuracy or finger-stimulus association may rely on cortical pathways that show the greatest maturation between ages 6 and 10; whereas motor timing and sensorimotor integration may rely on subcortical pathways that continue to develop into young adulthood. Despite developmental differences across blocks of practice on both behavioral measures, there were no significant group differences for either the Recognition or Recall tests. We suggest that explicit knowledge of the MFST is not directly linked to task performance, thus challenging the implicit-explicit distinction in pediatric SRT studies assessing the developmental invariance model.