Age-related Impairments in Implicit Recall Depend on What You Are Remembering

The hippocampus is one of the first brain regions to deteriorate with age, accounting for some forms of memory loss in older adults, akin to a mild form of hippocampal amnesia. Hippocampal impairment entails the loss of explicit memory (e.g., source recognition) despite preservation of implicit memory (e.g., priming, as observed in word-stem completion paradigms). Many have argued that the crucial factor differentiating between implicit/explicit memory tasks is whether retrieval is automatic or whether it intentionally references a specific episode. We tested an alternative explanation of the implicit/explicit dissociation based on the content of memory rather than different retrieval processes. Under this view, memory for complex, associative items (e.g., scenes) should be impaired by aging, regardless of retrieval mode (i.e., for both implicit and explicit tasks), whereas memory for simpler items (e.g., individual objects) should not. We tested implicit retrieval of objects and scenes in younger and older adults, cueing memory with a partial “patch view” of the images, analogous to word-stem completion; our findings supported the content-based explanation.