On Rest-from-Deliberate-Learning as a Mechanism for the Spacing Effect: Commentary on Chen et al. (2021)

In their recent paper, Chen et al. (Educational Psychology Review, 2021) propose that rest periods between deliberate learning characterize the spacing effect and the alternation between skills without rest characterizes the interleaving effect. In this commentary, we show that this theory is inadequate in two aspects. First, the operationalization of their constructs are problematic—their mechanism of rest-from-deliberate-learning mismatches their operationalization (e.g., they code deliberate learning activities that should not allow for working memory recovery as rest-from-deliberate-learning), and their definition of whether stimuli require discriminative contrast appears to depend on the study outcome. Second, their systematic review neglects a large body of literature that is incompatible with their theory. For example, they neglect classic spacing studies on vocabulary learning, and their theory of spacing effects as being a result of working memory recovery cannot account for lag effects or interactions found in the literature. We conclude that there are almost certainly mechanistic differences between spacing and interleaving effects, but the mechanisms are likely not mutually exclusive, as defined by Chen and colleagues.