Event-related potentials and semantic processing in Alzheimer's patients and normal controls.
Item
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Title
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Event-related potentials and semantic processing in Alzheimer's patients and normal controls.
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Identifier
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AAI9218237
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identifier
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9218237
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Creator
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Hamberger, Marla Jill.
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Contributor
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Adviser: Jeffrey Rosen
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Date
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1992
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Experimental | Psychology, Physiological
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Abstract
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Based on behavioral measures generated by young adults during semantic processing tasks, semantic memory has been conceptualized as a network organized according to semantic relationships. Additionally, in young adults, the N400 component of the event-related brain potential (ERP) is also responsive to semantic relationships. Under certain conditions, N400 amplitude varies inversely with the extent to which a word has been primed by its preceding semantic context, reflecting a gradient of semantic relatedness within the semantic network. Based on their behavioral performance on a wide range of tasks, patients with Probable Alzheimer's disease (PAD) show a collapsing of the semantic gradient, such that items within a category lose their distinction, whereas superordinate information remains relatively intact. Given that N400 provides an index of the gradient of semantic relatedness in normal young adults, and that according to behavioral measures, PAD patients show a collapsing of this gradient, the present study examined whether this collapse would also be reflected in the N400 pattern of PAD patients.;Ten normal young adults, 10 normal elderly, and 6 "mild" PAD patients made speeded (but accurate) sense/nonsense decisions to the final word of a series of highly constrained sentence contexts in which final words belonged to one of four types: (1) best completion/sensical, (2) related to best completion/sensical, (3) related to best completion/nonsensical and (4) unrelated to best completion/nonsensical. Behavioral and ERP responses were recorded only to terminal words.;In contrast to the behavioral data, PAD patients demonstrated an orderly gradient as a function of semantic relatedness (i.e., N400 was smallest to best completions, and largest to unrelated/nonsensical stimuli). However, as predicted, they committed a disproportionate number of errors (i.e., "sense" responses) to nonsensical sentences terminating in words related to the sentences' best completions. It was speculated that this disruption in semantic processing occurs at some point between the elicitation of N400 and the emission of a behavioral response. Although normal elderly showed an unexpected N400 pattern, this appeared to be associated with strategic processing superimposed upon an intact semantic network.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
