Episodic memory, the ability to store and retrieve information from our past, is at the very heart of human experience, underpinning our identity and relationship with the world. Episodic memory is not a unitary phenomenon: in dual-process theory, researchers draw a distinction between familiarity, a rapid and automatic sense of oldness to a previously encountered stimulus ("I know that face"), and recollection, the reactivation of additional context from a particular episode ("We met at the York conference"). A fundamental objective in the study of human memory is to ground recollection and familiarity in neural terms. This requires accurately measuring the contribution of each from behavioural data, which in turn relies on an accurate characterisation of recollection. This thesis introduces a novel source retrieval task to demonstrate that recollection has two critical, and fiercely contested, properties: it is thresholded, i.e. it can fail completely, and successful recollection is graded, i.e. it varies in strength. The consequences of this characterisation are explored. Firstly, familiarity and recollection are functionally separable retrieval mechanisms. Secondly, the models currently used to measure the contribution of each are generally flawed, and a corrected model is described which better fits, and explains, the extant data. Finally, the frequency of recollection is shown to be dissociable from its strength, a result which links behavioural data more strongly than before to a neurocomputational account of episodic memory, and which suggests a relationship between the representational overlap of memory traces and their retrieval. This thesis necessitates a change in the way behavioural memory data is modelled, and consequently the interpretation of evidence underpinning neuroanatomical accounts of memory experience. Significantly, however, it also moves the field beyond a long-running debate and provides a deeper dual-process framework with which to address outstanding questions about the relationship between, and neural basis of, episodic memory processes.

From an adaptive perspective human memory ought to be strategically attuned towards information deemed to be of value according to nature's criterion; i.e. that which promotes individual survival and reproduction. The experiments in this thesis represent an interdisciplinary venture to merge cognitive psychology with social perception research in order to study how sociosexual pressures may have shaped women's episodic memory systems. A vast literature has validated sexual dimorphism as a cue by which women comparatively judge the value of potential mates in terms of their perceived biological and behavioural characteristics (e.g. heightened sexual dimorphism in men correlates with positive biological attributes but also negative behavioural traits). The first 5 experiments extend this work by focusing on the functional contribution women's episodic memory systems may play in constraining generalisations. Experiments 1 and 2 reveal a mnemonic bias in women's memory for contents of encounters with men who have (attractive) masculinised low vs. (less attractive) feminised high pitch. Experiment 3 finds a similar memory benefit for information associated either with masculinised or feminised men's faces, depending on whether women prefer masculinised or feminised characteristics in men. Data from Experiments 6 and 7 reveal further evidence of sociosexual adaptation in women's episodic memory. Memory appears to be biased towards remembering the location of women with feminised (highly attractive) facial features, i.e. high-value competitors for potential mates. While no sociosexual bias was found in women's location memory for attractive male faces, a sociosexual bias was present in women's location memory for men with attractive, low-pitch voices. Considered along with other recent adaptive memory research, the data in this thesis further erode the idea of episodic memory as a general purpose mechanism.

The goal of the experiments was to evaluate an explanation of set-alternation costs based on episodic memory principles. The assumption is that performance of any task is a consequence of memory retrieval processes that involve representations of specific prior experiences (Kolers, 1976; Leboe, Whittlesea, & Milliken, 2005; Neill & Mathis, 1998; Tenpenny, 1995; Whittlesea, 1997; Whittlesea & Jacoby, 1990). When the Event 1 and 3 targets mismatch the retrieval of the Event 1 memory episode is not entirely appropriate for performing the Event 3 task. The interference due to a partial match between Events 1 and 3 might be the source of set-alternation costs. Results of Experiment 1 revealed larger costs in the high probability set-alternation condition. The high probability set-alternation condition encouraged retrieval of Event 1. However, because the targets of Event 1 and 3 mismatched the retrieval of Event 1 interfered with the processing of Event 3’s task-set. In other words, the interference due to a match in task-sets but a mismatch in targets generated costs. If set-alternations costs originate from a partial match between Events 1 and 3, increasing the amount of overlapping information between these events should reduce costs. The findings of Experiments 2 and 3 showed reduced set-alternation costs when there was a target identity match between Events 1 and 3. Lastly, Experiment 4 showed that set-alternation costs are larger when the retrieval of the Event 1 memory episode is obstructed. That is, costs were larger when there was a combination of obstructed Event 1 retrieval and a partial match between Events 1 and 3.

The goal of the experiments was to evaluate an explanation of set-alternation costs based on episodic memory principles. The assumption is that performance of any task is a consequence of memory retrieval processes that involve representations of specific prior experiences (Kolers, 1976; Leboe, Whittlesea, & Milliken, 2005; Neill & Mathis, 1998; Tenpenny, 1995; Whittlesea, 1997; Whittlesea & Jacoby, 1990). When the Event 1 and 3 targets mismatch the retrieval of the Event 1 memory episode is not entirely appropriate for performing the Event 3 task. The interference due to a partial match between Events 1 and 3 might be the source of set-alternation costs. Results of Experiment 1 revealed larger costs in the high probability set-alternation condition. The high probability set-alternation condition encouraged retrieval of Event 1. However, because the targets of Event 1 and 3 mismatched the retrieval of Event 1 interfered with the processing of Event 3’s task-set. In other words, the interference due to a match in task-sets but a mismatch in targets generated costs. If set-alternations costs originate from a partial match between Events 1 and 3, increasing the amount of overlapping information between these events should reduce costs. The findings of Experiments 2 and 3 showed reduced set-alternation costs when there was a target identity match between Events 1 and 3. Lastly, Experiment 4 showed that set-alternation costs are larger when the retrieval of the Event 1 memory episode is obstructed. That is, costs were larger when there was a combination of obstructed Event 1 retrieval and a partial match between Events 1 and 3.

Empirical evidence suggesting colour influences object recognition is mixed; leading to conclusions that colour may not always be represented in object memory. Positive evidence for the representation of colour in episodic object memory is often complicated by the possibility that encoding specificity may be responsible for such observations. The current thesis examined whether colour is represented and makes an independent contribution of shape in episodic memory for familiar and novel objects, using a modified paradigm based on the typical retrieval- practice task (e.g., Anderson, Bjork, & Bjork, 1994). Participants studied pictures of objects, presented one at a time. In a subsequent practice phase, participants either performed Old/New recognition with a subset of the studied objects and their distractors (Experiments 1-7), or they rated a subset of the studied objects for attractiveness, complexity, and usefulness (Experiments 8 and 9). The critical manipulation concerned the nature of unpracticed objects. Unpracticed objects shared either shape only (Rp- Shape), colour only (Rp-Colour), both shape and colour (Rp-Both), or neither shape nor colour (Rp-Neither), with the practiced objects. Interference effects in memory between practiced and unpracticed items are revealed m the forgetting of related unpracticed items - retrieval-induced forgetting (RIF). If both shape and colour information is explicit in the object representations in episodic memory, then there would be significant RIF for unpracticed objects sharing shape only and colour only with the practiced objects. RIF was significant for Rp-Shape and Rp-Colour objects, suggesting that shape and colour are represented and independently drive competition effects in episodic object memory. The use of RIF to probe those representations improves on previous evidence, because it bypasses alternative encoding specificity explanations. The current work provides proof of concept for a modified retrieval-practice paradigm and establishes it as a tool to probe feature- based representations that do not easily lend themselves to retrieval practice.

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Emerging evidence suggests that hippocampal memory processing is modulated by midbrain regions under conditions of reward, resulting in enhanced encoding of episodic information—long-term memory for events. Current theories further suggest that hippocampal subregions may have distinct roles in episodic memory formation, and may be differentially influenced by dopaminergic midbrain inputs. Using high-resolution functional magnetic resonance imaging (fMRI), the present study investigated hippocampal subregional function as well as activation in surrounding medial temporal lobe (MTL) cortex, midbrain, and nucleus accumbens during associative encoding and cued recall under varying conditions of reward. A high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association. At test, participants performed cued recall followed by match (correct association) or mismatch (incorrect association) probe decisions and received feedback on their performance. Behaviorally, cued recall performance was superior for pairs preceded by high reward cues at encoding relative to pairs preceded by low reward cues. FMRI analysis revealed regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showing subsequent memory effects (greater encoding activation for remembered, compared to forgotten associations) and reward effects (greater activation for high-value, compared to low-value associations) during stimulus encoding. Within several of these regions, individual differences in reward-related encoding activation were correlated with the degree of the behavioral reward effect (better memory for high-value compared to low-value object pairs). At retrieval, regions in midbrain and subiculum predicted successful associative recall, and regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showed reward effects in the absence of explicit reward cues. Within several MTL regions, activation was greater for match than mismatch probes. These findings are consistent with theories suggesting that reward-based motivation influences memory formation through interactions between dopaminergic midbrain and hippocampus. / text

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Research conducted over the past two decades has contributed a wealth of new knowledge to the field's understanding of stress effects on memory. It has been widely demonstrated that stress can either facilitate or impair memory, depending on 1) the phase of memory processing influenced by stress hormones and 2) the valence or arousing nature of the encoded information. It has also been reported that, when stress levels are significantly elevated at encoding, emotional memory is preserved (or enhanced) while memory for non-emotional information is impaired. These effects have been discussed at the neurobiological level with respect to the stress hormone, cortisol, and the impairing and facilitating modulatory effects it has on regions of the brain involved in emotional learning and memory. Whether diurnal shifts in basal levels of cortisol modulate these effects remains unknown. Additionally, it remains unknown whether enhancing and impairing effects of stress on memory result in memory traces that are more or less open to alteration by subsequent experiences, such as observed in the so-called "misinformation" effect.The current dissertation aimed to investigate the effects of stress on encoding of thematically negatively arousing and non-emotional events, composed of negatively arousing and neutral stimuli. Our goal in using more complex materials, in lieu of stimuli (e.g. word lists, images) traditionally used in studies of emotion and memory, was to examine the effects of stress on encoding of information more representative of a real-world event. Within this framework we examined 1) the effects of basal cortisol levels on stress modulation of memory encoding, and 2) the integration of subsequent misinformation on memory for negatively arousing versus non-arousing events encoded under stress. The research included in this dissertation aims to further the field's current understanding of the effects of stress on memory processes. Findings are relevant to the literature on traumatic memory, eyewitness testimony, and the effects of moderate to severe emotion on long-term episodic memory.