Development of precursors to speech in infants exposed to two languages

The study of bilingualism has often focused on two contradictory possibilities: that the learning of two languages may produce deficits of performance in each language by comparison with performance of monolingual individuals, or on the contrary, that the learning of two languages may produce linguistic or cognitive advantages with regard to the monolingual learning experience. The work reported here addressed the possibility that the very early bilingual experience of infancy may affect the unfolding of vocal precursors to speech. The results of longitudinal research with 73 infants aged 0;4 to 1;6 in monolingual and bilingual environments provided no support for either a bilingual deficit hypothesis nor for its opposite, a bilingual advantage hypothesis. Infants reared in bilingual and monolingual environments manifested similar ages of onset for canonical babbling (production of well-formed syllables), an event known to be fundamentally related to speech development. Further, quantitative measures of vocal performance (proportion of usage of well-formed syllables and vowel-like sounds) showed additional similarities between monolingual and bilingual infants. The similarities applied to infants of middle and low socio-economic status and to infants that were born at term or prematurely. The results suggest that vocal development in the first year of life is robust with respect to conditions of rearing. The biological foundations of speech appear to be such as to resist modifications in the natural schedule of vocal development.