Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Psychology

Date of Defense

4-6-2017

Graduate Advisor

Suzanne E. Welcome

Committee

Robert Paul

Michael Griffin

Carmen Russell

Abstract

Language tasks are typically lateralized to the language dominant left hemisphere in healthy right-handed adults. Additionally, lesions in left frontotemporal areas typically result in a variety of language impairments called aphasia. Interestingly, increased activation in right cerebral regions homologous to left side lesions has been observed in patients with aphasia during word-finding tasks. The neural mechanism and the impact on word-finding remain unclear. There are two competing theories concerning compensatory right hemisphere activation. One view is that the right hemisphere plays a supportive role, taking over functions of the damaged left hemisphere. The other perspective is that rightward laterality is maladaptive and leads to some of the word-finding error patterns observed in aphasia. It may be possible to reconcile the discrepancy in the literature when considering a third view. I propose that while the right hemisphere may in fact be able to assist in language processes when the dominant left hemisphere is damaged, its capabilities are limited. Word-finding errors may result when this process is overgeneralized beyond the capacities of the right hemisphere. The aim of the present study is to examine how laterality is affected by word-finding difficulty in patients with chronic aphasia and in healthy adults. I used event-related potentials (ERP) to record neural activity that was time-locked to the cognitive events of interest among 10 participants with chronic aphasia secondary to single cerebrovascular accidents and 10, healthy age-matched control participants. Specifically, I compared ERP signatures between the two groups, during word-stem completion and picture naming. ERPs can reveal temporal dynamics and general spatial location of neural activity underlying word-finding processes. The outcomes of this study will provide key insights into the qualitative and quantitative contributions of the right hemisphere for word-finding in both healthy adults and individuals with aphasia and may help inform intervention practices that aim to enhance or suppress bilateral activation.

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