The dissertation research described herein examined several facets of pattern separation (conceptualized as an encoding process whereby two very similar stimuli are stored as discrete representations). Previous research has conceptualized pattern separation as a discrete, high threshold process and has relied upon performance measures that are derived from that theory. More recently, it has been suggested that pattern separation may be better fit by a continuous, signal-detection-based model. Should that be the case, it would mean that previous work examining pattern separation in aging and dementia has relied upon potentially misleading dependent measures.

The current project had three goals: 1) to determine the most appropriate cognitive modeling for pattern separation, 2) to examine whether or not pattern separation is selectively impaired in aging and dementia populations, and 3) to compare biomarkers of preclinical impairment with performance on behavioral recognition memory and pattern separation tasks. In Chapter 1, ROC and d’ analyses showed that pattern separation is indeed best conceptualized as a continuous signal detection process. In Chapters 2 and 3, we took the framework for pattern separation identified in Chapter 1 and applied it to a population consisting of young adults, older adults, individuals with amnestic mild cognitive impairment (aMCI), and Alzheimer’s disease. The general approach was to first try to equate performance across groups on a recognition memory task and then compare group performance on the pattern separation task. Taken together, Chapters 2 and 3 provided evidence that pattern separation is selectively impaired in aMCI and possibly in healthy older adults as well, and this deficit is not explained by a recognition deficit alone. In Chapter 4 we measured the relationship between behavioral performance measures (on both the recognition memory tasks and pattern separation tasks) and cerebrospinal fluid biomarkers (Aβ42 and tau levels) in healthy aging participants. We found a significant positive correlation between performance on both the recognition memory task and the pattern separation task, but only for pictures of everyday objects. Thus, these biomarkers are predictive of general memory performance for objects but do not selectively predict pattern separation performance.

This dissertation contributes to a growing body of research that attempts to bridge the chasm between basic and applied memory research. Its basic approach is to use signal detection theory to analyze higher-level cognitive components that influence recognition memory. The work consists of three research papers that examine the effects of internal and external sources of memory on discriminability and response bias in order to better understand memory in the real world. Paper one provides new evidence supporting a basic assumption of reality-monitoring theory that certain cognitive operations are important for knowing whether or not a memory comes from an internal source. This research demonstrates that people are more susceptible to false memories after completing mindfulness training because their reality-monitoring accuracy is reduced. Paper two examines the verbal overshadowing effect (where people are worse at correctly identifying someone from a police lineup after providing a verbal description of a face) with receiver operating characteristic (ROC) analysis to determine if that well-known effect is due to differences in actual memorability rather than differences in response bias. This research indicates that internally- generated information can be confused with an external memory source when the internally-generated information is not sufficiently detailed. Paper three examines the cross-race effect wherein memory is worse for a person of a different race than a person of the same race. This research indicates that although memory is worse in terms of discriminability, high-confidence identifications are just as reliable for a cross-race face as for a same-race face.

As time passes after learning, connections between the hippocampus and neocortex gradually change. The exact time course of these changes is not well established and competing theories of memory consolidation debate if the role of the hippocampus in memory retrieval changes with the age of the memory. Functional magnetic resonance imaging (fMRI) can measure changes in retrieval-related brain function associated with the age of the memory to characterize the roles of the hippocampus and neocortex in memory consolidation. This dissertation aims to identify common functional brain networks associated with long-term memory consolidation by examining how these networks change with the age of the memory. Three fMRI studies in healthy adults were conducted to examine changes in retrieval-related brain function associated with different memory ages and types of memoranda. Each study measured whole-brain changes in retrieval-related brain activity, hippocampal functional connectivity, and ventromedial prefrontal cortex connectivity. In Chapter 1, I examine changes in brain function during retrieval of natural scenes learned 1 month to 1 hour prior to test. I demonstrate changes consistent with systems consolidation theory can be detected across short time periods. In Chapter 2, I examine changes in brain function during retrieval of three-word sentences learned 1 month to 1 hour prior to test. I similarly demonstrate changes consistent with systems consolidation theory can be detected across short time periods. In Chapter 3, I examine changes in brain function during retrieval of news events learned 1 year to 30 years prior to test. I demonstrate changes both consistent and inconsistent with memory consolidation theories are observed across long time periods. In the discussion, I compare commonalities between the brain networks identified in Chapters 1 and 2 which similarly change across short time periods but for different types of memoranda. I also compare the commonalities between the brain networks identified in Chapters 2 and 3 which change across both short and long time periods for similar memoranda. In sum, common changes in the functional roles of the hippocampus and neocortex consistent with memory consolidation can be detected across different types of memoranda and memory ages.

This dissertation builds upon our existing understanding of confidence, uncertainty, and their relationship to recognition memory accuracy. Its basic approach is to measure overt expressions of confidence in children and adults and to examine both the development of confidence and its relationship to memory accuracy. The work consists primarily of one review paper (Chapter 2) and three research papers (Chapters 3, 4 and 5) that each seek to deepen our understanding of confidence in a unique way. Chapter 2 reviews the existing literature on the confidence-accuracy relationship in children, both in developmental and eyewitness contexts. Chapter 3 provides new evidence for the emergence of a relationship between confidence and recognition memory accuracy during the preschool years. Chapter 4 tests for a confidence-accuracy relationship in adults using an eyewitness memory paradigm developed for children. Chapter 5 introduces a novel paradigm that uses disconfirming evidence (e.g. evidence that disconfirms a previously held hypothesis about the state of the world) to improve confidence scale use in preschool-aged children. This research expands our knowledge of how confidence develops, as well as how the relationship between confidence and memory accuracy changes between early childhood and adulthood.

A meta-analysis of the distributed practice effect was performed to illuminate the effects of temporal variables that have been neglected in previous reviews. This review found 839 assessments of distributed practice in 317 experiments located in 184 articles. Effects of spacing (consecutive massed presentations vs. spaced learning episodes) and lag (less spaced vs. more spaced learning episodes) were examined, as were expanding inter-study interval effects. Analyses suggest that inter-study interval (ISI) and retention interval operate jointly to affect final test retention; specifically, the ISI producing maximal retention increased as retention interval increased. Areas needing future research and theoretical implications are discussed.