Preserved Implicit Semantic Differentiation in an Alexic Wernicke's Aphasic
Fernandes, Leyan Oi Lin
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https://hdl.handle.net/2142/82285
Description
Title
Preserved Implicit Semantic Differentiation in an Alexic Wernicke's Aphasic
Author(s)
Fernandes, Leyan Oi Lin
Issue Date
1999
Doctoral Committee Chair(s)
Miller, Gregory A.
Department of Study
Psychology
Discipline
Psychology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Psychology, Cognitive
Language
eng
Abstract
Lesions of Wernicke's area are typically associated with functional impairments in word comprehension. These impairments are traditionally assessed with neuropsychological measures that examine overt behavioral responses. The aspects or stages of semantic categorization processes that are disrupted, however, are unknown. These were probed with event-related brain potentials in a case of alexic Wernicke's aphasia. At 10 weeks post-infarct, the patient performed 3 tasks: a 2-category, non-semantic visual oddball; a 3-category, semantic visual oddball; and a word-to-picture card-sorting task. ERPs collected during the oddball tasks were analyzed using the bootstrap method, a non-parametric technique for estimating a population distribution from a single sample's data. In the non-semantic oddball paradigm, which served as a baseline for the semantic oddball paradigm, a classic P300 probability effect was obtained. In the semantic oddball paradigm, where the subject was asked to decide whether words were animals, N400 was larger for semantically anomalous fish words than for frequent mammal words. Evidence for P300 enhancement for rare, semantically distinct musical instrument words was not decisive. Response accuracy revealed no misclassifications of stimuli during the non-semantic task, but overt performance approximated chance for the semantic oddball and card-sorting tasks. The dissociation of N400 and overt performance reveals that implicit semantic differentiation can be preserved in alexic Wernicke's aphasia.
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