Towards the Neurocognitive Mechanisms Underlying Semantic Feature Generation in Individuals With Aphasia
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| Izdano u: | ProQuest Dissertations and Theses (2025) |
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| Online pristup: | Citation/Abstract Full Text - PDF |
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| Sažetak: | This dissertation investigates the neural and cognitive mechanisms underlying Semantic Feature Analysis (SFA), a prominent word-production therapy for aphasia. While SFA effectively improves naming accuracy, treatment response remains variable, and the underlying neural mechanisms are poorly understood. This work applies representational similarity analysis (RSA) and representational similarity decoding (RSD) to better understand how the brain encodes and decodes semantic representations during feature generation, the hypothesized active ingredient of SFA, in both healthy adults and people with aphasia.Using RSA, Study 1 compared neural activation patterns to five semantic models (taxonomic, experiential, and distributional) during a covert semantic feature generation task. Experiential semantic features derived from sensory, motor, and affective dimensions demonstrated the strongest neural alignment within semantic network and anatomically defined left-hemisphere regions previously associated with semantic processing, underscoring their central role in conceptual encoding. This experiential dominance persisted after controlling for shared variance with other models and was evident even in participants with aphasia, suggesting preserved experiential semantic processing.Study 2 extended these findings by employing RSD to assess whether the identity of individual concepts could be decoded from neural patterns. Decoding accuracy was robust but varied across individuals, averaging 67.5% for healthy controls and 64.3% for people with aphasia, confirming that experiential semantics strongly influence neural representation. However, contrary to prior research, decoding accuracy showed considerable variability, reflecting methodological differences and participant-specific neural representational stability.Study 3 was exploratory in nature and investigated behavioral and neurobiological correlates of individual differences in decoding accuracy among participants with aphasia. Strong positive correlations emerged between decoding accuracy and conceptual-semantic abilities, including semantic error profiles (s-weight) and performance on semantic judgment tasks. Conversely, phonological abilities and data-quality metrics were weakly associated or unrelated to decoding accuracy, emphasizing the specificity of semantic processing integrity in determining representational robustness.Collectively, these findings indicate that experiential semantic features play a central role in shaping neural representations during feature generation. This pattern is consistent with the hypothesized mechanism of spreading activation in SFA, suggesting that activation may, at least in part, be grounded in experiential information. By linking neural representational structure to individual differences in semantic processing, this dissertation offers a foundational neurocognitive framework for refining therapeutic strategies—such as incorporating experiential prompts—and demonstrates the promise of representational decoding as a potential biomarker of semantic system integrity in aphasia. |
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| ISBN: | 9798291597729 |
| Izvor: | ProQuest Dissertations & Theses Global |