Objective: The spacing effect describes the typical finding that repeated items are remembered best when additional items are introduced between each repetition than when the repetitions occur in immediate succession. In this study, we investigated the nature and limits of the spacing effect in the developmental amnesic case H.C. Method: In Experiment 1, we compared the performance of H.C. to that of controls on a short-term, free recall, verbal learning spacing paradigm while controlling for retention interval (timing of item review and recall). In Experiment 2, we compared the performance of H.C. to that of controls on a multiday, cued recall, verbal learning spacing paradigm, in which memory was assessed after 1 week. Results: In both experiments, H.C. demonstrated a spacing effect comparable to the effect exhibited by controls. In Experiment 1, her final recall memory for long-lag (spaced) items was better than recall for no-lag (massed) items t(23) = 10.99, p < .001, d = 2.5. In Experiment 2, her final cued recall memory for next-day-reviewed (spaced) items was better than cued recall for same-day-reviewed (massed) items, t(20) = 17.6, p < .001, d = 4.1. Conclusions: This study demonstrates the spacing effect in a person with impaired episodic memory development and is the first to show long-term benefits of spacing in amnesia. Substantially slower learning-to-criterion suggests an alternate mechanism supporting the spacing effect, perhaps independent of the hippocampus. Spacing should be considered as a candidate memory intervention technique given its effectiveness in both short- and long-term learning settings.
