An Investigation of Inhibitory Control in Bilingual Aphasia
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Speaking involves selecting words and syntactic structures from among numerous competing options. It has been suggested that constant practice in using inhibitory control (IC) to limit within and cross-language competition may be associated with better lexical-semantic IC in proficient bilingual speakers relative to monolingual speakers. This advantage is also theorized to generalize to IC advantages in non-linguistic tasks (bilingual advantage hypothesis; BAH; Bialystok, 2001). However, conflicting evidence with regard to bilingual IC advantages abound, and the nature of relationship between linguistic and domain-general inhibitory control abilities is poorly understood. Since IC is proposed to be critical for lexical retrieval, it is important to understand the nature of IC engaged in individuals with lexical retrieval deficits (aphasia). Bilingual speakers with aphasia provide an ideal platform to examine the relationship between language processing and IC because there are seemingly contradictory effects at play: while bilingualism may render an IC advantage, acquired brain injury may be associated with less efficient IC. These contrasting effects allow one to tease apart the effects of bilingualism on IC, the domain generality of the bilingual IC advantage, and relationship between bilingualism, IC and lexical selection. It is important to examine these effects relative to matched monolingual controls to understand (i) if there is a bilingual advantage in lexically based IC and, (ii) the domain generality of any bilingual IC advantage. To address these aims, IC engaged in (i) lexical retrieval (semantically blocked cyclic naming task), (ii) linguistic processing (Stroop task), and (iii) non-linguistic processing (flanker task) was compared in ten each of bilingual (Tamil-English) and monolingual (English) neurologically healthy speakers and participants with aphasia. Results from neurologically healthy participants revealed a bilingual advantage in the blocked cyclic naming task (lexical IC) but no advantages in the non-lexical Stroop and flanker tasks. Results from participants with aphasia revealed no support for the proposed bilingual advantages in all three experiments. Furthermore, there was no significant association between inhibitory control measures in the three experimental tasks for all participants. Contrary to the predictions of the BAH, the collective results of this study indicate that there is insufficient evidence for the role of bilingualism in modulating non-lexical IC advantages. This lack of consistent support for BAH questions the influence of bilingual experience in modulating non-linguistic inhibitory control. These findings also reveal that the relationship between inhibitory control and lexical retrieval is not influenced by language background (monolingual versus bilingual) in persons with aphasia.