The phenomenon was first identified by Hermann Ebbinghaus, and his detailed study of it was published in the 1885 book Über das Gedächtnis.
Untersuchungen zur experimentellen Psychologie (Memory: A Contribution to Experimental Psychology), which suggests that active recall with increasing time intervals reduces the probability of forgetting information.
This robust finding has been supported by studies of many explicit memory tasks such as free recall, recognition, cued-recall, and frequency estimation (for reviews see Crowder 1976; Greene, 1989).
In spite of these findings, the robustness of this phenomenon and its resistance to experimental manipulation have made empirical testing of its parameters difficult.
The result was interesting because other studies using only twice-presented items have shown a strong spacing effect, although the lag between learning and testing was longer.
Cornoldi and Longoni (1977) have even found a significant spacing effect in a forced-choice recognition memory task when nonsense shapes were used as target stimuli.
Russo et al. (1998) proposed that with cued memory of unfamiliar stimuli, a short-term perceptually-based repetition priming mechanism supports the spacing effect.
Upon a recognition memory test, there was no spacing effect found for the nonwords presented in different fonts during study.
Mammarella, Russo, & Avons (2002) 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.
[3] According to this view, spaced repetition typically entails some variability in presentation contexts, resulting in a greater number of retrieval cues.
[4] To test the encoding variability theory, Bird, Nicholson, and Ringer (1978)[5] presented subjects with word lists that either had massed or spaced repetitions.
[7] If encoding variability is an important mechanism of the spacing effect, then a good advertising strategy might include a distributed presentation of different versions of the same ad.
They also found that at long intervals, varying the presentation of a given ad is not effective in producing higher recall rates among subjects (as predicted by variable encoding).
[9] Although it is accepted that spacing is beneficial in learning a subject well and previous units should be revisited and practiced, textbooks are written in discrete chapters that do not support these findings.
There is conclusive evidence that cumulative final exams promote long-term retention by forcing spaced learning to occur.
Bahrick et al. (1993)[11] examined the retention of newly learned foreign vocabulary words as a function of relearning sessions and intersession spacing over a nine-year period.
Current school and university curricula rarely provide students with opportunities for periodic retrieval of previously acquired knowledge.
[13] Michael Kahana's study showed strong evidence that the lag effect is present when recalling word lists.
In 2008, Kornell and Bjork published a study[14] that suggested inductive learning is more effective when spaced than massed.