Time for Considering Constraints on Procedural Memory Consolidation Processes: Comment on Pan and Rickard (2015) With Specific Reference to Developmental Changes

In the acquisition of some motor skills, sleep may be necessary for the completion of procedural memory consolidation processes, as expressed in delayed "offline" performance gains. Pan and Rickard (2015) conducted an original meta-analysis of the literature on performing an explicitly instructed finger movement sequence and tested the role of sleep versus wake in the enhancement of performance over posttraining delay periods. In this comment we propose that a more-biological, process-oriented framework is needed, allowing for more than a yes-no answer to the question addressed, and suggest methodological issues that may affect the target meta-analysis. We argue that different task demands, task conditions, and developmental differences should be considered a priori rather than expected to emerge from pooled data. For example, several recent studies have indicated that there is a qualitative change in the time course of procedural memory consolidation processes at puberty, between the ages of 12 and 17. Before puberty, consolidation processes are reflected in enhancement of task performance over sleep and wake periods alike. In their extensive set of relevant empirical data the authors included a number of developmental studies comparing children with adults (expecting "child status" effects) but did not fully consider developmental changes. We show that the inclusion of the 6 studies of childhood, comprising 13 groups, biases the meta-analysis toward the conclusion that skill enhancement is similar across wake and sleep periods.