What makes distributed practice effective?

Abstract

The advantages provided to memory by the distribution of multiple practice or study opportunities are among the most powerful effects in memory research. In this paper, we critically review the class of theories that presume contextual or encoding variability as the sole basis for the advantages of distributed practice, and recommend an alternative approach based on the idea that some study events remind learners of other study events. Encoding variability theory encounters serious challenges in two important phenomena that we review here: superadditivity and nonmonotonicity. The bottleneck in such theories lies in the assumption that mnemonic benefits arise from the increasing independence, rather than interdependence, of study opportunities. The reminding model accounts for many basic results in the literature on distributed practice, readily handles data that are problematic for encoding variability theories, including superadditivity and nonmonotonicity, and provides a unified theoretical framework for understanding the effects of repetition and the effects of associative relationships on memory.

Figure 1

Actual (diamonds) and predicted (black line) performance as a function of performance on items studied once for all conditions in the data set for which lag was precisely specified. Longer lags are indicated by darker shading of the diamonds.

Figure 2

Mean actual (black circles) and mean predicted (open circles) performance as a function of the lag bands used in Figure 2. Asterisks indicate that performance is higher than predicted by the independence baseline (p < .001).

Figure 3

Actual (diamonds) and predicted (black line) performance as a function of performance on items studied once for all conditions in the data set for which a cued-recall test was administered. Longer lags are indicated by darker shading of the diamonds.

Figure 4

Demonstration of superadditivity by the reminding model. Solid lines indicate performance on twice-presented items, with darker lines indicating faster forgetting. The dashed lines indicate the independence baseline. Two different levels of p₁ performance are displayed.

Figure 5

Top panel: The effects of reminding on repeated items (darkest line), high-associate pairs (next darkest shade), and nonassociates (lightest shade). The superadditivity baseline is indicated by the dashed line. Bottom panel: Data reproduced from Hintzman et al. (1975) comparing recognition of repetitions and associate pairs.

Figure 6

Simulation of the interaction between lag and retention interval based on Equation 3.