“…Early findings from studies on bilingual acquisition were interpreted as evidence that, although children are exposed to distinct sets of input, they go through an initial stage in which their two languages are represented in a unitary or fused system (UNITARY LANGUAGE SYSTEM hypothesis, Genesee, 1989), at the phonological (Schnitzer & Krasinski, 1994 ;Vogel, 1975), lexical (Clark, 1987 ;Volterra & Taeschner, 1978) and syntactic level (Murrell, 1966 ;Redlinger & Park, 1980;Volterra & Taeschner, 1978). Starting from the 1980s, an increasingly large number of investigators have indeed turned to the study of bilingual first language acquisition, focusing on whether bilingual children can differentiate their languages in production early on and whether they acquire languagespecific constraints at the same age as monolinguals.…”