Theoretical Implications of the Spacing Effect 1

Interest in the effects on memory of the temporal distribution of study trials goes back to some of the very first memory experiments. Jost (1897) noted a facilitative effect of the spacing of learning trials in Ebbinghaus’s data, and set out to study it systematically. More than sixty years later, Underwood (1961) was compelled by a large body of experimental evidence to conclude that “Facilitation by distributed practice in verbal learning occurs only under a highly specific set of conditions, and the magnitude of the effect when it does occur is relatively small [p. 230] .” Today, with interest focused more on the learning of individual items than on the acquisition of multi-item lists, and with study and…