Browsing by Author "Dobbins, Ian G"

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    Functional Neuroimaging Investigations of Human Memory: Comparisons of Successful Encoding and Retrieval for Relational and Item Information
    (2007-05-10T14:55:10Z) Prince, Steven Eric
    Memory is a complex and multifaceted entity. Cognitive psychology has adopted terminology to help simplify the study of memory. For example, one can consider the cognitive process the brain is engaged in, such as encoding versus retrieval. Similarly, one can consider the content of information, such as words, faces, or scenes. Content and process can also interact such as with instructions to view a face that happens to be situated next to a house (item memory) versus instructions to evaluate whether the face 'belongs' in the house (relational memory). Although neuropsychology, animal lesion studies, and cognitive neuroscience have identified brain structures that are consistently associated with memory performance, such as the medial temporal lobes (MTL) and prefrontal cortex (PFC), the specifics of when and why such regions participate in memory is still largely unexplored. Theoretical standpoints are often at odds about whether regions such as the MTL operate as a functional unit, supporting memory in general, or whether subregions within the MTL support specific types of memory (e.g. item versus relational memory). To investigate how memory processes might recruit unique and common brain regions, three functional magnetic resonance imaging (fMRI) studies were conducted. Each study involved comparisons of successful encoding (trials later remembered versus forgotten) and successful retrieval (hits versus misses). Experiment 1, using semantic and perceptual word pairs, found unique contributions for subregions in the MTL and PFC, dependent on memory phase and stimulus class. One region in the left hippocampus was associated with memory success, regardless of either memory phase or stimulus class. Experiment 2, using faces and scenes, found unique contributions for 'stimulus sensitive' subregions of the fusiform gyrus and parahippocampal gyrus, as well as for the PFC, and MTL that were dependent on content-process interactions, or independent of content and process. Experiment 3, using faces, scenes, and face-scene pairings, found unique contributions for subregions of the MTL and PFC based on item versus relational processing and memory phase. Together, the results of the three experiments provide support for dichotomies in brain structures based on specific processes, specific content, or process-content interactions.
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    The Characteristics and Neural Substrates of Feedback-based Decision Process in Recognition Memory
    (2008-04-10) Han, Sanghoon
    The judgment of prior stimulus occurrence, generally referred to as item recognition, is perhaps the most heavily studied of all memory skills. A skilled recognition observer not only recovers high fidelity memory evidence, he or she is also able to flexibly modify how much evidence is required for affirmative responding (the decision criterion) depending upon whether the context calls for a cautious or liberal task approach. The ability to adaptively adjust the decision criterion is a relatively understudied recognition skill, and the goal of this thesis is to examine reinforcement learning mechanisms contributing to recognition criterion adaptability. In Chapter 1, I review a measurement model whose theoretical framework has been successfully applied to recognition memory research (i.e., Signal Detection Theory). I also review major findings in the recognition literature examining the adaptive flexibility of criteria. Chapter 2 reports behavioral experiments that examine the sensitivity of decision criteria to trial-by-trial feedback by manipulating feedback validity in a potentially covert manner. Chapter 3 presents another series of behavioral experiments that used even subtler feedback manipulations based on predictions from reinforcement learning and category learning literatures. The findings suggested that feedback induced criterion shifts may rely upon procedural learning mechanisms that are largely implicit. The data also revealed that the magnitudes of induced criterion shifts were significantly correlated with personality measures linked to reward seeking outside the laboratory. In Chapter 4 functional magnetic resonance imaging (fMRI) was used to explore possible neurobiological links between brain regions traditionally linked to reinforcement processing, and recognition decisions. Prominent activations in striatum tracked the intrinsic goals of the subjects with greater activation for correct responding to old items compared to correct responding to new items during standard recognition testing. Furthermore, the pattern was amplified and reversed by the addition of extrinsic rewards. Finally, activation in ventral striatum tracked individual differences in personality reward seeking measures. Together, the findings further support the idea that a reinforcement learning system contributes to recognition decision-making. In the final chapter, I review the main implications arising from the research and suggest future research that could bolster the current results and implications.