The spacing of lists in free recall

Spaced presentations of 12- and 15-word lists were better recalled when no task or an easy task, rather than a demanding task, intervened between the presentations, contrary to the results of Bjork and Allen (1970). When no task intervened between spaced presentations, recall was better than when presentations were massed (Experiment I). These results are important because (a) they indicate a lack of generality of Bjork and Allen's findings, often considered crucial to general understanding of spacing effects; (b) they indicate a need for (at least) a two-factor theory of the spacing effect; and (c) they are the first evidence for a spacing effect when lists are considered as the unit of repetition.