Research from the University of Washington suggests that babies lose their bilingual ability as early as their first birthday if they are not exposed to different sounds.
The study suggests that introducing two languages before the child can speak seems to be the best way to raise bilingual babies. By around a year old, the monolingual babies in the study appeared to only respond to an English distinguishing sound, whereas bilingual babies still responded to both the English and Spanish sounds.
“This difference in development suggests that the bilingual babies “may have a different timetable for neurally committing to a language” compared with monolingual babies, said lead author Adrian Garcia-Sierra.
“When the brain is exposed to two languages rather than only one, the most adaptive response is to stay open longer before showing the perceptual narrowing that monolingual infants typically show at the end of the first year of life,” Garcia-Sierra said.” (Source: Wired)