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The Spacing Effect

As a rule, repetitions of an experience farther apart in time will have greater effect in improving memory than repetitions close together in time. The spacing effect is a powerful and well-documented effect on memory. It is robust, meaning (1) it applies to many situations and types of learning, and (2) it is dependable. It always seems to make a difference.

What is the spacing effect? Why was Dempster exasperated?

The spacing effect has been known for more than a century. Dempster (1988) expressed exasperation that it was not used more often in schools. He wrote, "The spacing effect would appear to have considerable potential for improving classroom learning, yet there is no evidence of its widespread application." The title of his article was, "The Spacing Effect: A Case Study in the Failure to Apply the Results of Psychological Research."

How did researchers study massed vs. distributed practice in language learning?

In one practical demonstration of the spacing effect, Bahrick, Bahrick, Bahrick, & Bahrick (1993) showed that retention of foreign language vocabulary was greatly enhanced if practice sessions were spaced far apart. For example, "Thirteen retraining sessions spaced at 56 days yielded retention comparable to 26 sessions spaced at 14 days." In other words, subjects could use half as many study sessions, if the study sessions were spread over a time period four times as long.

What is the simple principle that predicts the effectiveness of a "spaced" repetition?

Hundreds of experiments on the spacing effect reveal a simple underlying principle. The closer you are to forgetting something, the more a fresh exposure to it helps. Banaji and Crowder (1989) put it this way:

As an empirical rule, the generalization seems to be that a repetition will help most if the material had been in storage long enough to be just on the verge of being forgotten. (p.49)

Why does the spacing effect work? How does it focus attention?

Why does the spacing effect work? There must be some underlying mechanism involving the basic operations of nerve cells, because the spacing effect works with all species, not just humans rehearsing verbal material. But for students who are studying, there is another common-sense reason why spaced repetitions may be beneficial. They focus attention on weakly learned material. A second study session allows special emphasis to be put on information that was not well learned in the first study session. In a single session one never finds out which material is easily forgotten.

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