An ERP Investigation of the Effects of Bilingualism on Working Memory and Age-Related Cognitive Decline
Creators: name: Morrison, Cassandra
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2020
Subjects: Bilingualism
Working memory
Event-related potentials
Aging

description: Being bilingual appears to afford benefits to cognitive functioning relative to being monolingual. Bilingual advantages have been observed in several areas of cognitive functioning such as task switching, inhibition, and cognitive control. Many studies, however, have been unable to replicate findings of a bilingual advantage. Inconsistencies in these findings may result from methodological differences and limitations within and across studies. Thus, the purpose of the present thesis was to examine if working memory capacity and processing differ between monolinguals and bilinguals using electroencephalography (EEG) to measure event-related potentials (ERPs). While several studies have observed differences in working memory capacity between monolinguals and bilinguals, these studies have often been limited to behavioral measures. Therefore, it remains unknown if the neural processes differ between monolinguals and bilinguals during working memory. Part 1 of the present thesis examines whether brain activity differs in English monolinguals compared to English-French bilinguals during working memory tasks. Part 1 comprised two paradigms. In Paradigm 1, participants completed an n-back working memory task while EEG was recorded. Results of this study revealed that monolinguals exhibited smaller P3b amplitudes compared to bilinguals. Paradigm 2 employed a delayed matching-to-sample task while EEG was recorded. In both paradigms, monolinguals displayed smaller P3b amplitudes than bilinguals. In Paradigm 2, monolinguals also displayed larger negative slow waves and N2b amplitudes than bilinguals. Both Paradigms found ERP differences in the absence of any behavioral advantage in bilinguals. These findings suggest that bilinguals may have more cognitive resources available in working memory to allocate to task completion than monolinguals. Part 2 was designed to determine whether bilingual ERP differences translated to a cognitive advantage in healthy older adult English-French bilinguals. Because older adults experience age-related cognitive decline, any advantages offered by bilingualism may be more pronounced in older adults compared to young adults. As in Part 1, we employed the same two paradigms, (the n-back working memory task; Study 3 and the delayed matching-to-sample task; Study 4). Similar to the results found in young adults, Studies 3 and 4 both revealed that bilinguals exhibited larger P3b amplitudes in the absence of behavioral and neuropsychological differences. Additionally, young and older adults exhibited different patterns of activation during the task, consistent with the compensation utilization of neural circuits hypothesis (CRUNCH). Part 3 (Study 5) examined whether linguistic distance between the L1 and L2 of bilinguals affects ERPs. Many studies compare participants proficient in Indo-European languages such as English and French. The purpose of Study 5 was to compare the processes associated with working memory processing (using ERPs) in Arabic-English bilinguals to English-French bilinguals. EEG was recorded while participants completed the n-back and delayed matching-to-sample task. In the delayed matching-to-sample task, monolinguals exhibited smaller N2 amplitudes compared to both bilingual groups, and smaller P3b amplitudes compared to English-French bilinguals. In the n-back, English-French bilinguals displayed larger P3b amplitudes than both English monolinguals and Arabic-English bilinguals. P3b amplitude did not differ between Arabic-English bilinguals and monolinguals in either task. The present work demonstrates that working memory functioning (as indexed by ERPs) may differ between monolinguals and bilinguals in the absence of a behavioral advantage. These findings also suggest that bilingual advantages in working memory are not more pronounced in older adults despite ERP differences. Finally, these results show that ERP differences between Arabic-English bilinguals compared to English monolinguals and English-French bilinguals will vary depending on the component of working memory that the task examines.