Project Summary The dominant method for measuring short- and long-term memory in the laboratory is a straightforward recognition memory test in which people are presented with a single item and asked whether the item was or was not seen during the experiment. Recent work in the eyewitness domain suggests, however, that when people are presented with multiple similar items at test —instead of a single item at test— their memory performance is facilitated. However, currently there is no mechanistic explanation regarding how presenting similar items at test may improve memory. Furthermore, the formal study of this effect of similar items has not been extended outside of the context of eyewitness memory. It is virtually unexamined in the context of other memory systems, particularly, long- versus short-term memory, or stimuli that are similar in different ways (i.e., across visual versus semantic dimensions). The aim of this proposal is thus two-fold. The overarching aim is theoretical: To develop and test a theoretical framework for how correlations amongst memory signals at test may arise from shared neural populations representing items, and may facilitate memory. Not only will the project ask how generalizable previous work from the eyewitness domain is, but a major novel aspect of the project approach to this problem is that it will leverage computational modeling to develop an integrative theoretical framework that helps address the question of how, specifically, similarity between items presented at test facilitate memory. The second aim is empirical: To examine how generalizable the finding is that similarity amongst stimuli presented at test affects memory, across the long- and short-term memory systems, and for stimuli that are related on visual and semantic dimensions. Thus, the project will be the first to test these effects across the study of different memory systems, and across the study of items that are related based on their semantic or visual similarity. Regardless of what empirical results are obtained, this line of work will have broad implications for memory researchers and practitioners because it will, for the first time, provide insight into the generality or boundary conditions for the effects of similar items in memory test; furthermore, the current work will equip cognitive neural researchers with the conceptual and computational tools to examine the neural signatures of these effects.