Isolation of massed- and distributed-practice items

In four experiments, massed-practice (MP) or distributed-practice (DP) items were isolated from other items in a list presented either visually or auditorially for free recall. For three independent groups, the first, second, or both presentations of an item were isolated. Locus of isolation had a marginal influence on recall. When MP items were isolated, they were recalled better than DP items. Isolating the DP items enhanced the MP-DP effect. The results are congruent with the idea that the MP-DP effect in free recall results, in part, from differential rehearsal.