The 'Critical' Period
Researchers and instructors training foreign language teachers often discuss the "Critical Period." It can be counterproductive to overemphasize this period because children and adults CAN learn later in life as well. It is fascinating, however, to see the effects of early bilingualism.
Studies support the importance of the first nine months because infants have an amazing ability to distinguish between sounds. Doctors at Madison Memorial Hospital note, “Studies of babbling in five-month-old infants show that, rather than being random, the sounds are speechlike and rhythmic.”  CGJ 09:56, 19 January 2006 (MST)
Internationally renowned brain and learning specialist, Dr. Patricia Kuhl, conducted a well known study on Japanese babies. She found that they could distinguish between the “l” and “r” sound up, until they turned around 10 months. Researchers have used her study and others on children's brains to say then, that by one year of age, children have lost the ability to distinguish between the sounds of their home language and those of another language . The argument being that their brains, from then on, only hone in on sounds in their own language and battle against pronunciations of a new language. CGJ 10:00, 19 January 2006 (MST)
Counter Arguments: Adults Can Learn Another Language
Even given the critical period research, it cannot be said with certainty that someone's ability to distinguish between foreign sounds and their own language's sound cannot be learned later in life. How can one prove an adult learner cannot learn certain sounds? So much is dependent on affective factors such as the learner's motivation for learning the language, does (s)he think it is possible to learn to distinguish between sounds? Is (s)he being well-taught by a trained instructor. Is (s)he getting enough input hearing the sound? CGJ 10:03, 20 January 2006 (MST)
To say that one cannot learn to diferentiate between sounds is simply not supported by what we do know about the brain. Human Devolpment Specialist at the Department of Child and Family Development, Dr. Diane Bales, in her collaboration with Better Brains for Babies, feels that learning a language and its sounds may be more taxing on an adult and may require more time to learn, but the adult mind is capable of learning another language and its pronunciation. . CGJ 09:56, 19 January 2006 (MST)
1. Madison Memorial Hospital (accessed 2006). Talk to Your Baby and She’ll Talk Back, Madison Memorial Hospital, Rexburg, ID, http://www.madisonhospital.org
2. Edwin Kiester, J. c. P. K. (2001). "Accents are Forever." Smithsonian Magazine (January, 2001, Issue 1), http://www.smithsonianmag.com
3. Diane Bales, Ph.D. "Better Brains for Babies" Collaboration. Supported by the University of Georgia College of Family and Consumer Sciences, Athens, Georgia http://www.fcs.uga.edu.