Effects of bilingualism on cognitive-linguistic abilities

This thesis examines the effects of bilingalism on three key areas of cognition and language - cognitive control, sentence recognition and word learning. The first study investigated the effect of socio-economic status on bilingual cognitive control. Previous studies have suggested that the advantages shown by bilinguals on some cognitive tasks may be associated with higher socio-economic status. We therefore explored this issue in bilingual and monolingual illterates of lower socio-economic status. We administered two cognitive control tasks: the Simon task and the Attentional Network task. The results showed that bilinguals were faster overall than monolinguals for both tasks : a global bilingual advantage. The finding of a bilingual advantage even for individuals of comparable lower socio-economic status confirms that these advantages are not due to a confound with higher socio-economic status. In the second study, we examined the effect of bilingualism in linguistic domain. More specifically, we explored whether bilingualism is associated with a sentence recognition cost in even the native language. We tested sentence recognition abilities in bilinguals and monolinguals in the presence of a non-linguistic distractor (background noise). Our results indicated similar sentence recognition accuracy for bilinguals and monolinguals when the sentences were presented in quiet conditions and even when presented in noise. The final two studies in the thesis examined whether the positive effects of bilingualism extend to benefit language learning. We investigated language learning using a novel word learning task. In the third study, novel word learning abilities in late bilinguals were compared with early bilinguals and monolinguals to see if a delayed onset age of second language acquisition also results in a bilingual advantage. Although we found an overall advantage for early bilinguals, critically, we also found a learning advantage for late bilinguals compared to monolinguals. This suggests that although age of acquisition of a second langauge has an impact on word learning abilities, second language acquisition also seems to modulate the late bilinguals' ability for word learning. In the final study, we examined the specific mechanisms that drive the advantages of bilingual speakers for novel word learning. We specifically manipulated the phonotactic probability and phonological neighbourhood density of the novel words to see if bilingual advantages are influenced by these properties. We found a biligual advantage for learning novel words regardless of phonotactic probability and neighbourhood density effects indicating that mechanisms underlying bilingual word learning advantages are not constrained by the phonological and lexical features of the novel words. The evidence from all four studies is summarised in the final chapter and current models of bilingualism are used to inform our understanding of the patterns observed. Finally, this thesis highlights that the positive consequences of bilingualism are not confined to cognitive control mechanisms, and bilingualism exerts unique effects in other domains such as novel word learning.