The effect of element interactivity and mental rehearsal on working memory resource depletion and the spacing effect

•The resting effect is another version of the spacing effect, which is explained by the working memory resource depletion.•Under different conditions, the spacing effect can be explained by both working memory resource depletion and by mental rehearsal.•Working memory resource depletion is more sensitive to materials high in element interactivity.•For low element interactivity information, mental rehearsal is likely to happen automatically during wakeful resting.•Measures of working memory resource depletion can be used to determine whether it is a relevant cause. The spacing effect occurs when learning with rest periods is superior to learning without rest periods. Cognitive load theory has explained this superiority by working memory resource depletion, under which resources are depleted during cognitive activity but restored with rest. In a series of four experiments involving 341 participants, we explored the relationships between the spacing effect, depletion of working memory resources, and mental rehearsal, particularly focusing on how these dynamics are influenced by task complexity as defined by element interactivity. Experiment 1 showed that materials with higher element interactivity had a greater impact on working memory resource depletion. In Experiment 2, using materials low in element interactivity, a spacing effect was obtained with no evidence of working memory resource depletion. Instead, results suggested that the effect might be due to mental rehearsal occurring during rest periods. Experiment 3, using more complex information, obtained both the spacing and working memory resource depletion effects for less knowledgeable learners for whom the information was high in element interactivity. In Experiment 4, testing more knowledgeable learners for whom the same information was lower in element interactivity, both effects disappeared. The results indicated that working memory resource depletion and recovery may be more sensitive to materials high in element interactivity and suggest that it is only one of multiple causes of the spacing effect.