Running head: Language Acquisition in Infants
Language Acquisition in Infants
University of California, Los Angeles
Language Acquisition in Infants
The unknown has always puzzled the human brain. When marvelous scientific technologies were unavailable to solve the mystery of human intelligence, scientists made numerous guesses as to which processes might underlie the smooth and complex functioning of the brain; modern technologies made it possible to look inside the human scalp and start decoding Nature’s most complex creation – the human mind. Language is an extremely essential attribute of human beings, which distinguishes them from the rest of the animals. However, its mystery started to be unwound only recently.
How humans acquire ability to separate and construct words is one of the central questions of the modern research in the field of language acquisition. It has been proposed that to construct words, human infants use sequential probabilities; that is, they are innate mathematicians and use simple statistics to perceptually categorize particular sound groups, calculate their frequency in the ambient stream of sounds, and predict which group of sound should follow the certain other one. For example, Japanese, Swedish, and English infants (i.e., representatives of different types of languages) demonstrate increased sensitivity to the phonemes and prototype vowels specific to their language, and do not respond as highly when hearing phonemes and vowels pertaining to languages, other than their native one. The experiment on eight-months-old infants also showed that when discriminating a change from a particular syllabus to another one in the string of syllabi (i.e., “de” to “ti”), infants who succeed the most are the ones who learn a pattern of syllabi in the sequence (i.e., perceive combinations of certain syllabi as words) by learning that the sequential probability of a certain syllabi given a certain other syllable is one; that is, the syllable will undoubtedly occur. As hypothesized, learning to chunk certain syllabi into words on the basis of statistical frequency reduced perceptual demands of the lingual task for the infants, and made it easier for them to fulfill the task of distinguishing one syllable from another. Another experiment on infants, based on the fact that infants pay more attention to novel stimuli, demonstrated that once having heard the two-minute strings of invariantly repeated syllabi (their order was not changed), infants showed novelty preference when they heard an unexpected order of syllabi when tested by listening to three-syllabi chops of the two-minute sequence. Since the pure statistical frequency of occurrence of all of the three syllabi was the same, it was the sequential probability of occurrence of a certain syllabus that made the infants heighten their attention to the crossing-word-boundaries combinations. In addition, even younger infants are able to discern the prosodic pattern (trochaic, with the stress on the first syllable of the word, or iambic, with the stress on the second one) of the native language, based on the sequential computations.
Sequential probabilities are definitely important to acquisition of language skills in infants, but they are not the only mechanism of mastering a language. Rigid neural networks, produced in the first year of life, encode the patterns of native language and interfere with the ones of foreign languages. This way, it is easier for the infant to keep learning the native language as more and more neural paths and connections are created in the brain; growing number of these native connections interferes with creating different ones for foreign languages. When adults are subjected to hearing foreign speech, larger areas of their brains are illuminated for longer times during magnetoencephalography as compared to when they hear native speech, which indicates that more effort is required on the part of the adult to process the speech sounds. Similarly, infants’ language skills at an older age strongly correlate with their speech discrimination skills later in development. A longitudinal research on seven- and eleven-months old infants showed that at the age of seven months, infants still discriminate between native and non-native consonant combinations, whereas at the age of eleven months this discrimination is almost absent. This distinction illustrates the fact that with age, neural networks underlying acquisition of language strengthen and filter out foreign sound combinations more effectively. If it were not for neural commitment of neural networks, infants should have reacted to combinations in each language equally strongly. Neural commitment is also said to be responsible for the “sensitive period” during language acquisition, during which, according to the NLNC (Neural Language Neural Commitment) model, brain networks solidify and become more sensitive to the patterns of native language. Sensitive period closes, when neural networks stabilize (i.e., become neurally committed).
As suggested in the article, neural networks stabilize when they stop being sensitive to speakers’ individual differences in pronunciation of various speech sounds; that is, when infants’ representations of sound distributions become stable and rigid. In this regard, bilingual children’s neural networks should take longer to stabilize since there is simply more of them (at least, two systems instead of one), and the perceptual load on a bilingual individual’s brain is much greater. A longitudinal quasi-experiment could be performed to test this hypothesis. Participants in this experiment - bilingual and monolingual infants at ages of six, nine, twelve, fifteen, eighteen, twenty one, and twenty four months – will be subjected to hearing series of computer-generated sounds, demonstrating different pronunciations of the same vowel. Each vowel will play for about two or three minutes in order to give infant enough time to familiarize with the task; about five vowels will be tested with the order of their appearance counterbalanced, as to control for the order effects. Some distracter sounds will be played between the presentations of the vowel, so that the infant does not get used to the simply presence of a monotonous sound from the source. The dependent variable in this experiment – the sensitivity of an infant to different pronunciations of the same vowel – will be tested by observing infants’ instances of behaviors caused by distracting novelty (turning of the head towards the sound source, interrupting the on-going activity, etc.) while the sound is playing. The more distracting behaviors observed, the more sensitive the infant is to the differences in presentation of the same sound. Any extraneous variables that might interfere with the results will be kept roughly constant: participant infants will be taken from families of similar socio-economic status and will be of similar health conditions, sounds played will be the same throughout the whole experiment, infants will be tested on the day when they reach the next appropriate age for testing, lab conditions will be kept constant for all of the infants and throughout the length of the experiment. The experimenters will make sure that for the bilingual group of children, they will be exposed to the non-English language equally often as to the English language throughout the whole experiment; for the monolingual group of infants, they will not be exposed to any language, other than English.
The results of this experiment, if consistent with the hypothesis, will show that more distractive behaviors will be observed in bilingual infants because of higher perceptual load of two languages on their brain. For the monolingual group, less distractive behaviors due to novelty stimulation will be observed. If, for example, for monolingual children, neural networks will stabilize by the age of one year, then, for bilingual children, the neural networks will be committed at the age of about fifteen months; that is, later (these ages are hypothetical).
Language acquisition in human infants is a starting-to-be-resolved mystery to the mankind; its resolution will help to treat children with linguistic problems and ameliorate language learning in healthy children.