How is language acquired in case of bilingualism. Sometimes a learner is exposed to two languages simultaneously, sometimes one language comes earlier than the other. It is observed that language development happens at different rates in different learners in case of bilingualism. We look at the issue from the perspective of Phonology in this essay.
Issues in Phonology
It is observed that bilingual learners have a problem in picking up accent of the second language. Learning a second language is problematic for a bilingual just as for everyone else. This is because one language already has a dominance in the learner's system. Even if bilingualism is simultaneous, that is, both the languages are given at the same time in early infancy, one of the languages become the dominant language. If this doesn't happen, the child will be confused about the codes of language. This can result in latent language development in children. The gist is, that one language has to be the dominant language.
How does the proficiency of the second language get affected by various factors like time of exposure, age of exposure, etc.? It is observed that children exposed to a second at the earliest age acquire the language better. The earlier the better. Second factor is exposure. The more the exposure, the better the rate of acquiring the second language. Here, exposure includes both reception and production of language. This is related to brain plasticity. Brain plasticity is explained in two ways. The first is about evolution: as human race advances through centuries in time, the brain becomes more adaptive and more capable of handling more complex data. Thus today's human brain might be a raw material for what might come a century or two later. The second way brain plasticity can be looked at is at a micro level: an individual's brain changes over time, and becomes more adaptive and complex with exposure. In the case of bilingual, this plasticity of brain is lost as age advances. So, if the child is exposed to a second language at a very early age, the child would pick up that language in a better fashion.
Becoming a Bilingual
In order to be called a bilingual, one should be able to handle two languages. This involves various levels of language. The very first is the sound system of a language, because phonemes are the basic building blocks of a language. A bilingual child should be able to distinguish between the sound systems of the two languages.
Experiments have proved that new born babies can differentiate between some pairs of languages that share a common sound system, but have sufficient differences in their rhythmic pattern/structure and prosody. (Prosody is the way you say things / the emotional signature on utterances.) So, of languages have same prosody, children cannot distinguish between languages. This implies that in the very early stages of language development, children develop prosody and rhythmic features. That is, children differentiate between speech sounds and non-speech sounds. At such early age, prosodic bootstrapping happens in children. This is why the age of exposure is said to be very important. Prosody gives children the basic data that is used for the rest of their lives.
After bootstrapping happens, the child starts picking up recursive parameters with which it can generate new structures using the available bits of language. That is, children distinguish between speech sounds and non-speech sounds and then, start differentiating between sounds of different languages. So, already a system is built up as the default system. If infants are exposed to two languages, prosody helps separating and building up two separate systems. This is because, once a child is first exposed to its first language, it acts as a reference point for later language acquisition. Infants exposed to Spanish and Catalan were able to distinguish between these languages at an early age of 4.5 months! 5 month olds can distinguish between two languages which are within the same native rhythmic class. For example, American and Australian English can be distinguished between by babies. But they cannot differentiate between Dutch and German (Dutch is a stress based language, while German is not). All this can be related to the idea that a child learns languages with reference to its first language.
Segmental Information
After picking up the phonemes in the language, children go on to acquire other features of language. Vowels are next in line. How are vowels distinguished by children? There are experiment based evidences that say that 4.5-6 month old babies can distinguish between mother tongue and a second language. Usually bilingual kids get confused regarding two language inputs that they receive. But if there are cues like prosody available for the child, this is overcome by the child. Even here, for different pairs of languages, the mental processes will be different.
In syllable detection tasks, french speakers were found to distinguish /ba/ in the given words because they were familiar to them in their first language. But when they were asked to identify /bal/ it took time/found it difficult because their first language doesn't process syllables that way. This is evidence to different parsing techniques used by different individuals.
Another test using time-compressed language: Anyone can adapt to time-compressed language. But if you remove the features of language that determine boundary features, like the space between words, etc., it becomes difficult. When such language bits were given to learners, it was found that they were able to transfer adaptation to the second languages that were in the same rhythmic group, and they found it difficult to transfer adaptation to languages that were not within their rhythmic group. Between Spanish and Catalan, learners could transfer their adaptation, but between English and French, they couldn't.
Phonemes
6 month old infants can identify native language phonemes. This is a developmental change. First the child learns to distinguish between speech and non-speech sounds, then it moves to identifying phonemes of its native language, and differentiates them from those of other languages.
There is a decline in sensitivity to non-native phonemes as the child grows up. That is, language specific system builds up in early childhood. After a few months of age, children can't distinguish between different phonemes (10-12 months). This is a complex task that the brain does by fixing one system as the dominant system.
Perceptual re-organization: sensitivity to consonants also decline by the end of the first year of a child's life. English speaking children distinguished between English and Zulu clicks (consonants). This did not depend on exposure since these subject did not have exposure to Zulu. So, by the end of first year of its life, a child already knows that its primary language is different from other languages.
EEG done on learners gives mismatch negativity. Mismatch negativity is obtained when a difference is identified by the subject. for example, /b/, /b/, /b/, /b/, /d/ should generate a mismatch negativity since the last phoneme is different from the previous ones. In Learners' EEG, mismatch graph amplitude increased showing discrimination of sounds between two languages when exposed.
Monolingual children have to handle only one language data. In bilingualism, children have double task. All the processes discussed above happen doubly for a bilingual child. It has to identify and distinguish between two sets of phonemes simultaneously. As children grow, they can't distinguish between all the sounds from other languages if they are similar. Bilinguals distinguish between similar sounds a much later stage than monolinguals (probably because they have to handle much more data).
Notes from : Handbook of Bilingualism: Psycholinguistic Approaches Edited by Judith F Kroll and Annette MB De Groot
