 In psychology and in psycholinguistics the label "code-mixing" is used in theories that draw on studies of language alternation or code-switching to describe the cognitive structures underlying bilingualism.During the 1950s and 1960s, psychologists and linguists treated bilingual speakers as, in Grosjean's term, "two monolinguals in one person".This "fractional view" supposed that a bilingual speaker carried two separate mental grammars that were more or less identical to the mental grammars of monolinguals and that were ideally kept separate and used separately.