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Abstract■ Episodic memory relies on both recollection and familiarity; why these processes are differentially engaged during retrieval remains unclear. Traditionally, recollection has been considered necessary for tasks requiring associative retrieval, whereas familiarity supports recognition of items. Recently, however, familiarity has been shown to contribute to associative recognition if stimuli are "unitized" at encoding (a single representation is created from multiple elements)-the "benefit" of unitization. Here, we ask if there is also a "cost" of unitization; are the elements of unitized representations less accessible via familiarity? We manipulated unitization during encoding and used ERPs to index familiarity and recollection at retrieval. The data revealed a selective reduction in the neural correlate of familiarity for individual words originally encoded in unitized compared with nonunitized word pairs. This finding reveals a measurable cost of unitization, suggesting that the nature of to-be-remembered stimuli is critical in determining whether familiarity contributes to episodic memory. ■

Although the neural mechanism supporting episodic recollection has been well characterized in younger adults, exactly how recollection is supported in older adults remains unclear. The electrophysiological correlate of recollection—the parietal retrieval success effect—for example, has been shown to be sensitive to both the amount of information recollected and the accuracy of remembered information in younger adults. To date, there is mixed evidence that parietal effect also scales with the amount of information remembered in older adults whilst there is little evidence that the same mechanism is sensitive to the accuracy of recollected information. Here, we address one potential concern when investigating Event Related Potentials (ERPs) among older adults—namely, the greater potential for single-trial latency variability to smear and reduces the amplitudes of averaged ERPs. We apply a well-established algorithm for correcting single-trial latency variability, Residual Iteration Decomposition Analysis (RIDE), to investigate whether the parietal retrieval success effect among older adults is sensitive to retrieval accuracy. Our results reveal that similar to younger adults, older adult parietal retrieval success effects scale with the accuracy of recollected information—i.e., is greater in magnitude when recollected information is of high accuracy, reduced in magnitude when accuracy is low, and entirely absent when guessing. The results help clarify the functional significance of the neural mechanism supporting recollection in older adults whilst also highlighting the potential issues with interpreting average ERPs in older adult populations.

Healthy aging leads to a significant decline in episodic memory, producing a reduction in thelikelihood of successful recollection, such that older adults remember less than younger adults.Emerging evidence from behavioral and neuroimaging studies demonstrate that recollectedinformation can also be more or less precise, highlighting a source of variability in memoryperformance not typically considered in studies of aging. Consequently, it is unknown whetherolder adults, compared to younger adults, only show a significant reduction in recollection rate or also exhibit a decline in recollection precision. Here, we provide new insight into age-relatedmemory decline by employing a novel source task that allows us to examine both the quantity(rate) and quality (precision) of episodic memory retrieval. First, we validated our task,demonstrating that it can effectively capture variability in both the rate and precision in olderadults. Second, we directly compared younger and older adults’ performance as a function ofstudy-test delay, showing significant reductions in both the rate and precision of recollectionwith age. Finally, we asked whether age-related changes in recollection can be accounted for bya reduction in attention, revealing that the division of attention in young adults results in areduction in rate but shows little evidence for a change in precision. Our results raise questionsabout the nature of age-related memory decline, highlighting the importance of measuring boththe quality and quantity of memory, and suggest new routes to achieve the early detection anddiagnosis of abnormal aging deficits.