For decades, bilingualism has resisted definition. If bilingualism is defined as habitual, fluent, correct and accent-free use of two languages, few individuals would qualify as bilinguals. A more viable approach may be to concede that 'bilingual' can be seen instead as a range of points on a continuum that allows for differences. The psychological study of bilingualism encompasses a wide range of phenomena including the organization and representation of the grammar, the perception and production of language mixing, cerebral lateralization of language functions, and patterns of recovery...