This 2014 Montreal study provided more evidence of critical periods during human development:

“Clearly illustrates that early acquired information is maintained in the brain and that early experiences unconsciously influence neural processing for years, if not indefinitely.“

YES! GIVE US MORE STUDIES LIKE THIS ONE!

“We show that internationally adopted children (aged 9–17 years) from China, exposed exclusively to French since adoption (mean age of adoption, 12.8 mo), maintained neural representations of their birth language despite functionally losing that language and having no conscious recollection of it.

We show that neural representations are not overwritten and suggest a special status for language input obtained during the first year of development.”

http://www.pnas.org/content/111/48/17314.full “Mapping the unconscious maintenance of a lost first language”