“The Effect of Overlearning on Retention”, 1929 (; backlinks):
This experiment is concerned with the following problems, (1) As the degree of learning is varied 100%–200%, will the degree of retention vary proportionally, i.e. will 50% overlearning increase the amount retained by 50% or by some other proportion? (2) Will the relation between the degree of retention and the degree of learning vary with the interval between learning and recall? For example, if 50% overlearning increases retention by 40% after a one-day interval, will this latter percentage increase or decrease with the length of the interval?…1922 obtained results bearing upon these problems…the present experiment was designed to supplement and to extend Luh’s work by employing two degrees of overlearning and a wider range of intervals.
…50% overlearning is highly economical from the standpoint of retention for intervals of 2–28 days for lists of nonsense syllables, and the larger the interval, the greater is the economy.
Further increases of overlearning, however, proved to be uneconomical for most intervals.
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