Inner speech and bilingualism: A scoping review with clinical implications

IntroductionBackground: Inner speech, or the “little voice in the head,” is implicated in many cognitive functions and is gaining interest in interdisciplinary research. Inner speech in bilinguals, people who speak more than one language proficiently, may shed a light on the underlying mechanisms of language and cognitive function in the brain. Objectives: We aim to examine the research on inner speech in bilingual adults and the methods used in this research to characterize how bilingual adults use inner speech. We further focus on the factors which influence language choice for inner speech. Finally, we aim to relate this research to future research on inner speech in bilingual adults with aphasia and its clinical implications. MethodWe conducted a scoping review of inner speech in bilingual adults and used a specific search strategy on five databases. Using the software Covidence, we reviewed the titles and abstracts, then completed a full text review. We extracted the relevant data and charted them based on pre-defined variables. ResultsInner speech is bilingual, but many factors influence which language is used, including age and context of acquisition, social environment, and emotionality. The most common methods used to evaluate inner speech in bilingual adults are questionnaires and interviews, and we critically examine these methods and suggest possible improvements in the discussion. ConclusionExamining how inner speech is used by bilingual adults can help researchers understand the phenomenon of inner speech, language organization in the brain, cognitive functions, and the importance of context and experience. This review helps to inform researchers and clinicians who work with bilingual adults with aphasia, as we must ensure that our work is based on accurate assumptions of these individuals rather than extending the knowledge from research with monolinguals without regard for the additional complexity of navigating multiple languages.