The Influence of Aging and Neurological Impairment on Bilingual Lexical-Semantic Representation and Processing

Samantha Siyambalapitiya (2010). The Influence of Aging and Neurological Impairment on Bilingual Lexical-Semantic Representation and Processing PhD Thesis, School of Health & Rehabilitation Sciences, The University of Queensland.

       
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Author Samantha Siyambalapitiya
Thesis Title The Influence of Aging and Neurological Impairment on Bilingual Lexical-Semantic Representation and Processing
School, Centre or Institute School of Health & Rehabilitation Sciences
Institution The University of Queensland
Publication date 2010-12
Thesis type PhD Thesis
Supervisor David Copland
Helen Chenery
Total pages 158
Total black and white pages 158
Subjects 11 Medical and Health Sciences
Abstract/Summary While there is a growing body of research investigating bilingual lexical-semantic representation and processing in younger adults, few studies have employed on-line experimental methods to examine lexical-semantic representation and processing in older bilingual adults or bilingual speakers with acquired neurological impairment. Understanding the nature of bilingual language processing in older adults will provide a platform from which to better understand acquired language impairments in bilinguals, such as dementia and aphasia, and will enhance understanding of changes potentially associated with cognitive aging. Investigation of lexical-semantic processing in bilingual adults with acquired neurological injuries will improve the knowledge base from which to develop effective cognitive neuropsychological language intervention approaches for bilingual aphasia, and will further inform understanding of the neural underpinnings and functional architecture of bilingual language in healthy speakers. Thus, the aims of this thesis were to employ on-line experimental techniques to determine whether there were differences in lexical-semantic representation and processing between healthy younger and older bilingual adults, and to examine lexical-semantic processing in bilingual individuals with acquired neurological impairments. Specifically, this thesis employed a semantic priming experiment to investigate whether semantic representation is shared or separate; a cognate repetition priming experiment to explore the cross-linguistic connections between cognates and noncognates; and a synonym judgement task to compare the processing of within- and cross-language synonyms in bilingual adults. The first study in this thesis (chapter 2) employed a semantic priming paradigm to investigate whether semantic representation is shared or separate in younger bilingual adults. Although the participants showed no cross-linguistic priming, the finding of solely within-language priming (within the speaker’s dominant language) was deemed to be indicative of shared semantic representation in a group of less-proficient bilinguals, and lent support to the revised hierarchical model (RHM: Kroll & Stewart, 1994). In the second study (chapter 3), this same paradigm was employed with a group of older bilingual adults who showed priming both within and across languages, providing further support for the RHM and suggesting that the basic integrity of semantic representation is maintained in older bilingual adults. The third and fourth studies (reported in chapter 4) investigated the representation and cross-linguistic connections between cognates in comparison to noncognates using a repetition priming paradigm. The younger bilingual adults produced the anticipated cognate advantage for same language repetitions and a language-specific cognate advantage for different language repetitions. The older bilingual adults, however, showed a language-specific cognate advantage for same language repetitions but produced faster reaction times for noncognates for different language repetitions. The reversal of the cognate advantage was attributed to poorer inhibitory mechanisms in older adults, causing difficulties in selecting between form-similar lexical competitors. The fifth study (chapter 5) compared within-language and cross-language connections using a synonym judgement task with both younger and older healthy bilingual adults. Both groups showed faster processing of translation equivalents over within-language synonyms, confirming the notion that translation equivalents are more closely connected than within-language synonyms. The older bilingual adults showed a greater discrepancy between processing times for translation equivalents and within-language synonyms, suggesting that there are subtle changes in lexical-semantic connections with increased age. Chapter 6 reports the performance of two bilingual adults with neurological injury, on the semantic priming and cognate repetition priming experiments. The participant with bilingual aphasia produced semantic priming effects in only three of four conditions, suggesting a weaker connection between the English lexicon and semantic system, possibly as a result of both premorbid proficiency and postmorbid impairment. In the cognate repetition priming experiment, this participant produced results that generally mirrored those of the older bilingual adults. The participant with a cerebellar lesion only produced semantic priming effects in two conditions (one within-language and one cross-language), suggesting impaired lexical access mechanisms. On the cognate repetition priming experiment, this participant produced similar results to those of the older adults. The results from this participant lend further support to the role of the cerebellum in language processing. In summary, the findings of this thesis suggest that the general integrity of bilingual lexical-semantic representations are maintained and accessible with increased age, in relation to the representation of semantic meaning, cognates and noncognates, and cross-linguistic connections between within-language synonyms and translation equivalents. There are, however, subtle changes that occur in relation to bilingual lexical access in older bilingual adults, particularly for lexical items that are similar in form. The bilingual individuals with neurological impairment showed changes in accessing lexical-semantic representations that were over and above those that can be attributed to normal aging processes. It is anticipated that these findings will enhance our understanding of language processing mechanisms in older bilingual adults and bilinguals with neurological impairment, and can potentially be used to inform the development of impairment-level treatment methods for bilingual aphasia.
Keyword Bilingual language
lexical-semantic organisation
aging
bilingual aphasia
cerebellar language
Additional Notes Landscape pages: 110, 111, 117

 
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