The time between to learnign events when those learning events share a knowledge component. A vast literature shows that the temporal spacing of practice improves learning and especially long-term retention.
- Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed Practice in Verbal Recall Tasks: A Review and Quantitative Synthesis. Psychological Bulletin, 132(3), 354-380.
- Ebbinghaus, H. (1913). Memory: A contribution to experimental psychology (translated by Henry A. Ruger & Clara E. Bussenius; original German work published 1885). New York: Teachers College, Columbia University.
- Pavlik Jr., P. I., & Anderson, J. R. (2005). Practice and forgetting effects on vocabulary memory: An activation-based model of the spacing effect. Cognitive Science, 29(4), 559-586.