The first reason is that the plasticity of the brain is lost and various functions of the parts of the brain cannot be reorganized. The second reason is the lateralization of language functions in the left hemisphere which is regarded to be perfect after puberty. So the learning of L1 and L2 becomes difficult. Another observation is interesting to quote here is by, Lenneberg, (1967) who asserts that the children who suffered a brain damage before the age of 9 to 12 recover language learning. While those children who suffered brain damage after puberty faced difficulty in language acquisition. Another researcher, Genesee, (1988) describes that after the critical period is complete, native-like competence of languages L1 or L2 is difficult and unlikely. Penfield and Roberts (1959) published a book entitled “Speech and Brain Mechanism”, and from their book the idea of the CPH entered the field of linguistics. Then later in 1967, Lenneberg studied the CPH in more detail and wrote “Biological Foundation of Language”. In recent years there have been many studies which have tried to find out the relationship between language acquisition and the CPH. The principal concern of the CPH is the assumption that this period plays a crucial role in the learning of both L1 and L2Moreover, with the increment of age, this ability of language acquisition decreases. Therefore, CPH for language learning is well acknowledged and has been studied by many researchers, Penfield & Roberts (1959); Birdsong, 1999; Singleton, 2001). Some researchers, (Penfield & Roberts, 1959) agreed that human brain at the age of nine gets rigid and stiff for language learning. There are many studies which show the existence of the CPH. …show more content…
All these studies establish the idea that young language learners perform far better than older learners. To investigate whether during the critical period a child remains able to acquire language or not, one needs to do some experiments on actual children. This means that they should not be given any linguistic input at all. Such experiments are forbidden, therefore never conducted. There are some case studies, where few unfortunate children remained unable to receive proper linguistic input during the critical period. As a result their language ability was highly affected, or even they remain unable to produce a single word. There are some examples, where unfortunate