Speech‐Sign Bilingualism: A Unique Window into the Multilingual Brain

Bilingualism provides a unique window into language processing and its underlying neurocognitive mechanisms. This chapter focuses on bilinguals who know both a signed and spoken language (speech-sign bilinguals). It compiles and interprets the findings that relate to speech-sign bilingualism in the brain. The chapter provides an overview of the relevant research to date placed in a wider language context by extending the study of bilingualism to languages in two different sensorimotor modalities, but at the same time focusing on results that provide critical insight into multilingualism more broadly. The cognitive demands on lexical processing may be higher for speech-sign bilinguals compared with monolinguals as, similarly to spoken-language bilinguals, speech-sign bilinguals must represent two sets of lexical items. Finally, long-term cognitive benefits in terms of grey matter volume have been attributed to bilinguals. Specifically, an increased grey matter volume in brain areas underpinning executive control has been identified as a beneficial neural change of bilingualism.