Time for Considering the Possibility That Sleep Plays No Unique Role in Motor Memory Consolidation: Reply to Adi-Japha and Karni (2016)
The hypothesis that sleep makes a unique contribution to motor memory consolidation has been debated in recent years. In the target article (Pan & Rickard, 2015), we reported results of a comprehensive meta-analysis of the explicit motor sequence learning literature in which evidence was evaluated for both enhanced performance after sleep and stabilization after sleep. After accounting for confounding variables, we found no compelling evidence for either empirical phenomenon, and hence no compelling evidence for sleep-specific consolidation. In their comment, Adi-Japha and Karni (2016) critiqued the target article on three primary grounds: (a) our unrealistic (in their view) assumption that, if sleep-specific consolidation occurs, it is mechanistically unitary across all variants of the motor sequence experiments included in the meta-analysis, (b) our inclusion of child groups, which they believe may have resulted in an underestimation of sleep effects among adult groups, and (c) our inclusion of several experiments with atypical experimental designs, which may have introduced unaccounted for heterogeneity. In this reply we address each of those potentially legitimate concerns. We show that the metaregression allowed for tests of multiple candidate variables that could engender separate consolidation mechanisms, yielding no behavioral evidence for it. We also show through reanalysis that the inclusion of child groups had virtually no impact on the parameter estimates among adults, and that the inclusion of experiments with atypical designs did not materially influence parameter estimates.