The lasting benefits of the spacing effect on recall despite compromised hippocampal and episodic memory development

The spacing effect is a robust memory phenomenon where items reviewed after a spaced interval of time are remembered better than items reviewed immediately. Evidence reported by Cermak and colleagues (1996) suggests that spaced review is a successful memory strategy for patients of adult-onset amnesia. However, it is unclear whether the spacing effect exhibited by these patients was the result of an uncontrolled retention interval (timing between the second presentation of an item and the item at test). Moreover, these patients would have had pre-morbidly intact episodic memory. Experience with episodic memory and prior intact hippocampal function may be a necessary foundation for spacing effect benefits even after the onset of amnesia. To investigate these questions, we examined the spacing effect in a developmental amnesiac patient, an individual with impaired episodic memory in relation to underdeveloped hippocampi from birth. The results of two experiments confirmed the patient's superior memory recall for items reviewed by spacing, both in a single-session paradigm where we properly controlled the retention interval, and in a multi-day paradigm where we assessed the patient's memory after one week. These results suggest that there may be alternate routes to the spacing effect that circumvent the use of episodic memory. Theoretical considerations are discussed.