Distributed practice (also known as spaced repetition, the spacing effect, or spaced practice) is a learning strategy, where practice is broken up into a number of short sessions over a longer period of time. Humans and other animals learn items in a list more effectively when they are studied in several sessions spread out over a long period of time, rather than studied repeatedly in a short period of time, a phenomenon called the spacing effect. The opposite, massed practice, consists of fewer, longer training sessions and is generally a less effective method of learning. For example, when studying for an exam, dispersing your studying more frequently over a larger period of time will result in more effective learning than intense study the night before.
History
Influential German psychologist Hermann Ebbinghaus first observed the effect of distributed learning, and published his findings in Memory: A Contribution to Experimental Psychology. Using himself as a subject, Ebbinghaus studied lists of nonsense syllables to control for confounding variables such as prior knowledge, allowing him to discover the spacing effect and serial position effect.Ebbinghaus, H., Ruger, H.A., Bussenius, C.E. (1913) Memory: A contribution to experimental psychology
A more recent study that researched the effects of distributed practice was done by Alan Baddeley and Longman in 1978. They researched the effectiveness of distributed practice by teaching postmen how to type using a new system on a typewriter and comparing massed and spaced learning schedules. Baddeley found that although massed practice would seem a more effective learning method because the participants would be able to learn the material in fewer days, the postmen who were taught using shorter sessions stretched over multiple days learned the material better than those who had the longer training sessions. Those who learned how to type with shorter learning sessions, spaced over more days ended up with more accurate and quicker typing.Baddeley, A.D., Longman, D. J. A., (1978) "The Influence of Length and Frequency of Training Sessions on the Rate of Learning to Type." Ergonomics V21 No8, 627-635.
Methodology Multiple psychological functions are responsible for the beneficial effects of distributed practice. The most prevalent of these are procedural learning, priming effects, and expanding retrieval.
Procedural learning Procedural learning is the act of repeating a complex activity over and over again, until all of the relevant neural systems work together to automatically produce the activity.Zimbardo, P. G., and Gerring, R. J. (1999). Psychology and life. (15th ed.).New York: Longman. Distributed practice is the most efficient method of procedural learning. By equally distributing the amount of practice of a given activity over a period of time, you will increase the efficiency of learning that skill.
Priming Priming is an effect where an initial (often brief) exposure to a stimulus influences its subsequent recall or perception. This effect is most notable when dealing with semantic knowledge, but is also applicable to the acquisition of general skills.Tulving, Endel; Daniel L. Schacter; Heather A. Stark (1982). "Priming Effects in Word Fragment Completion are independent of Recognition Memory". Journal of Experimental Psychology: Learning, Memory, and Cognition 8 (4). With regards to distributed practice, increasing the amount of practice when learning will result in an increased priming effect for subsequent practice sessions. This causes an increase in memory recall, which is equivalent to an increase in learning. This helps explain why equally distributing your practice sessions, rather than massing them into one session, allows for greater learning.
Expanding rehearsal Expanding rehearsal refers to a learning schedule wherein items are initially tested after a short delay, with pre-test delay gradually increasing across subsequent trials.Baddeley, A. D., Human Memory: Theory and Practice", 1997 This phenomenon relies on the strength of the consolidated memory in order to efficiently increase success and learning. Memories that were poorly consolidated through inefficient means of practice will be harder to recall, and will reduce the learning achieved through expanding retrieval. Distributed practice directly influences the efficiency of expanding recall, as it provides the strongest basis for memory consolidation, from which to draw needed information.
Theories
Free recall and cued-memory tasks Different theories explain the spacing effect in free recall and in explicit cued-memory tasks. Robert GreeneGreene, Robert L.. Spacing effects in memory: Evidence for a two process account. Journal of Experimental Psychology: Learning, Memory, and Cognition15. 3 (May 1989): 371-377 proposed a two-factor account of the spacing effect. The spacing effect in free recall tasks is accounted for by the study-phase retrieval account. Because free recall is sensitive to contextual associations, spaced items benefit from additional encoding of contextual information. Thus, the second occurrence of an item in a list reminds the learner of the first occurrence of the same item and of the contextual features surrounding that item. When items are distributed, different contextual information is encoded with each presentation, whereas for massed items, the difference in context is relatively small. This leads to more retrieval cues being encoded with spaced than with massed items, leading to improved recall.
Cued-memory tasks (for example, recognition memory, and frequency estimation tasks) rely more on item information and less on contextual information. Greene proposed that the spacing effect is due to the increased amount of voluntary rehearsal of spaced items. This is supported by findings that the spacing effect is not found when items are studied through incidental learning.
Semantic analysis and priming Research has also shown reliable spacing effects in cued recall tasks under incidental learning conditions, where semantic analysis is encouraged through orienting tasks.Challis, Bradford H.. (Mar 1993). Spacing effects on cued-memory tests depend on level of processing. Journal of Experimental Psychology: Learning, Memory, and Cognition 19. 2, 389-396.Russo, Riccardo; Mammarella, Nicola; Avons, S E. Toward a Unified Account of Spacing Effects in Explicit Cued-Memory Tasks. Journal of Experimental Psychology: Learning, Memory, and Cognition28. 5 (2002 Sept): 819-829. Bradford Challis found a spacing effect for target words after the words were incidentally analyzed semantically. However, no spacing effect was found when the target words were shallowly encoded using a graphemic study task. This suggests that semantic priming underlies the spacing effect in cued-memory tasks.
When items are presented in a massed fashion, the first occurrence of the target to be memorized, semantically primes the mental representation of that target, such that when the second occurrence appears directly after the first, there is a reduction in its semantic processing. Semantic priming wears off after a period of time,Kirsner, Kim; Smith, Marilyn C; Lockhart, R S; King, M L; Jain, M. The Bilingual Lexicon: Language-Specific Units in an Integrated NetworkJournal of Verbal Learning and Verbal Behavior23. 4 (1984 Aug.): 519-539. which is why there is less semantic priming of the second occurrence of a spaced item. Thus, on the semantic priming account, the second presentation is more strongly primed, and receives less semantic processing when the repetitions are massed, compared to when presentations are spaced over short lags. This semantic priming mechanism provides spaced words with more extensive processing than massed words, producing the spacing effect.
Implications with nonsense stimuli From this explanation of the spacing effect, it follows that this effect should not occur with nonsense stimuli that do not have a semantic representation in memory. A number of studies have demonstrated that the semantically based, repetition priming approach cannot explain spacing effects in recognition memory for stimuli, such as unfamiliar faces, and non-words that are not amenable to semantic analysis.Russo, Riccardo; Parkin, Alan J.; Taylor, Sandra R.; Wilks, Jacqueline. Revising current two-process accounts of spacing effects in memory. Journal of Experimental Psychology: Learning, Memory, and Cognition24. 1 (Jan 1998): 161-172. Cornoldi and Longoni have even found a significant spacing effect in a forced-choice recognition memory task when nonsense shapes were used as target stimuli.Cornoldi, C., Longoni, A., (1997). The MP-DP effect and the influence of distinct repetitions on recognition of random shapes. Italian Journal of Psychology, 4(1),65-76. Russo proposed that with cued memory of unfamiliar stimuli, a short-term perceptually based repetition priming mechanism supports the spacing effect. When unfamiliar stimuli are used as targets in a cued-memory task, memory relies on the retrieval of structural-perceptual information about the targets. When the items are presented in a massed fashion, the first occurrence primes its second occurrence, leading to reduced perceptual processing of the second presentation. Short-term repetition-priming effects for nonwords are reduced when the lag between prime and target trials is reduced,McKone, E (1995). Short-term implicit memory for words and nonwords. Journal of Experimental Psychology: Learning, Memory, and Cognition 21(5). thus it follows that more extensive perceptual processing is given to the second occurrence of spaced items relative to that given to massed items. Hence, nonsense items with massed presentation receive less extensive perceptual processing than spaced items; thus, the retrieval of those items is impaired in cued-memory tasks.
Congruent with this view, Russo also demonstrated that changing the font in which repeated presentations of nonwords were presented reduced the short-term perceptual priming of those stimuli, especially for massed items. Upon a recognition memory test, there was no spacing effect found for the nonwords presented in different fonts during study. These results support the hypothesis that short-term perceptual priming is the mechanism that supports the spacing effects in cued-memory tasks when unfamiliar stimuli are used as targets.
Furthermore, when the font was changed between repeated presentations of words in the study phase, there was no reduction of the spacing effect. This resistance to the font manipulation is expected with this two-factor account, as semantic processing of words at study determines performance on a later memory test, and the font manipulation is irrelevant to this form of processing.
Mammarella, Russo, & AvonsMammarella, N., Russo, R., & Avons, S. E. (2002). Spacing effects in cued-memory tasks for unfamiliar faces and nonwords. Memory & cognition, 30, 1238-1251. also demonstrated that changing the orientation of faces between repeated presentations served to eliminate the spacing effect. Unfamiliar faces do not have stored representations in memory, thus the spacing effect for these stimuli would be a result of perceptual priming. Changing orientation served to alter the physical appearance of the stimuli, thus reducing the perceptual priming at the second occurrence of the face when presented in a massed fashion. This led to equal memory for faces presented in massed and spaced fashions, hence eliminating the spacing effect.
Encoding variability Encoding variability and assumes the benefits of spacing appear because spaced presentations lead to a wider variety of encoded contextual elements. Additionally, the variable encodings are thought to be a direct result of contextual variations which are not present in massed repetitions.