Spacing and Lag Effects in Free Recall of Pure Lists

Article excerpt

Repeating list items leads to better recall when the repetitions are separated by several unique items than when they are presented successively; the spacing effect refers to improved recall for spaced versus successive repetition (lag > 0 vs. lag = 0); the lag effect refers to improved recall for long lags versus short lags. Previous demonstrations of the lag effect have utilized lists containing a mixture of items with varying degrees of spacing. Because differential rehearsal of items in mixed lists may exaggerate any effects of spacing, it is important to demonstrate these effects in pure lists. As in Toppino and Schneider (1999), we found an overall advantage for recall of spaced lists. We further report the first demonstration of a lag effect in pure lists, with significantly better recall for lists with widely spaced repetitions than for those with moderately spaced repetitions.

Repeating items within a list leads to an increase in the probability of their being recalled, with the beneficial effects of repetition being greatest when the repetitions are spaced (separated by other unique items). The finding of improved memory for spaced repetitions-the spacing effect-has been found in a broad range of memory tasks with many different types of study materials (Greene, 1992). In some experiments, the probability of recalling repeated items has increased monotonically with the distance, or lag, between the repetitions (Glenberg, 1976, 1977; Madigan, 1969; Melton, 1970; Underwood, 1969). The latter finding is termed the lag effect (Murdock, 1974).

A number of theoretical constructs have been proposed to account for the beneficial effects of spacing on memory for repeated items. One popular account sees subjects as devoting less attention or rehearsal to successively repeated, or massed, items (Greene, 1989; Hintzman, 1976; Rundus, 1971). This could be either a consciously controlled strategy of allocating more rehearsal to weaker items or an automatic process that responds to the novelty of a just-presented item. The possibility that rehearsal may partially explain the large spacing and lag effects typically found in free recall was supported by an early study in which the overt rehearsal technique was used (Rundus, 1971). Rundus showed that the total number of rehearsals was a strong predictor of later recall and that spaced items were rehearsed more than massed items. Thus, whatever process leads to the greater rehearsal of spaced items may account for some or all of the spacing effect in free recall.

A concern arises, however, due to the nature of the lists employed in studies of the spacing effect. In these studies, lists comprising a random mixture of items repeated with varying lags have typically been used. Consequently, spaced list items have inherently occupied more early list positions. At early positions, rehearsal time is distributed among the current list item and the last few items, whereas in later list positions, rehearsal time is distributed among items throughout the list (Modigliani & Hedges, 1987; Murdock & Metcalfe, 1978). Thus, it is possible that the higher level of recall observed for spaced items results from their having more rehearsal opportunities (Crowder, 1976).

Although many studies of the spacing effect have included additional, once-presented items at the beginning and end of the list to buffer recency and primacy effects, the primacy effect for rehearsal frequency persists well beyond the first few list positions (Brodie & Murdock, 1977; Tan & Ward, 2000). Even if serial position confoundings could be completely controlled, rehearsal can amplify any effects caused by the spacing of the nominal positions of the list items. Suppose, for example, that subjects attend more fully to the third repetition of a spaced item than to the third repetition of a massed item. They can use the extra time available during the presentation of the massed item to rehearse other items from the list, and these could be other massed items or spaced items. …