Ning that the experience given during early childhood are capable of effecting the physiological and psychological development. During that period, it is capable to learn certain kind of knowledge in a short span of time and last for a long term. After those critical periods, it becomes difficult or impossible to imprint information, like how a baby chic recognizes the first thing they see as their mother, and they will not react to their actual parents if they meet later. This idea is known as critical period hypothesis. Regard to Language acquisition, linguist and neurologist Lenneberg (1968) suggests that critical period exist around the age of two, when the brain function has developed and the brain’s lateralization as well as differentiation finish. Beyond that, he estimates that the brain will lose flexibility and plasticity, and language acquisition will become difficult to succeed.
In addition, according to Anu Sharma, an auditory neuroscientist at University of Colorado, brains start to differentiate and limit the sound according to necessity, making it harder to recognize the sound of the new language at the age of around seven. This means early age learning provides fluent and native like pronunciation, and it gets stronger if the language is studied continuously. However, skills like grammar and spelling can be studied at later age; there is difficulty in achieving pronunciation compared to early childhood. Based on that, babies may be the most intelligent in terms of pronunciation. Babies start with zero, capable of corresponding to any language, and eventually speaks the language or languages they hear their parents talk.
Trying to learn a language as an adult is much different. Since the critical period has ended, they have to take a different approach. Adult learners, compared with early language learners are mature, have more experience and background knowledges, meaning that their brain is much more developed. Their ability to understand is predominant over child. They use both of their cognitive skills and analysis ability which allows the adults to learn efficiently. Adults have more source to connect the new language with one’s mother tongue, and find better strategies to learn that best fits each individual. In spite of that, the fact that they have many background information can become a burden at the same time. Flege, Munro, and MacKay (1995) focused on the second language learners’ balance of the usage of the two languages. Since adults have a language that they are much more familiar with, they tend to use it in their daily life more often.
Based on that, as age gets higher and the use of mother tongue increase, it has the possibility of effecting the quality of pronunciation, gradually fall in accuracy, ending with incomplete and non-native like language. Adding to that, there is the Affective Filter Hypothesis suggested by Krashen. Affective filter works when the learners are in an anxious state. As people get older, they tend to care about what other people think, and become nervous about being humiliated when making a mistake. This psychological factor limit the amount of source successfully taken in, and stops the learner to acquire a language smoothly. However, once this uneasiness disappear, the act of affective filter is restricted. From these points about age factors, it can be said that all age bracket have the potential to learn a language. The difference is the advantages from the capability of each age group.