THE PLACE OF PHONETICS IN LANGUAGE LEARNING
Infant’s speech perception skills show a dual change towards the end of the first year of life. Not only does non-native speech perception decline, as often shown, but native language speech perception skills show improvement, reflecting a facilitative effect of experience with native language. The mechanisms underlying change at this point in development, and the relationship between the change in native and non-native speech perception, is of theoretical interest. As shown in new data presented her, at the cusp of this developmental change, infants’ native and non-native phonetic perception sills predict later language ability, but in opposite directions. Better native language skill at 1.5 months of age predicts faster language advancement, whereas better non-native language skill predicts slower advancement. We suggest that native language phonetic performance is indicative of neural commitment to the native language, while non-native phonetic performance reveals uncommitted neural circuitry.
Keywords: Theories of speech perception, language development, event-related potentials, effect of linguistic experience neural commitment.
How infants accomplish the task has become the focus of debate on the nature and origins of language, from babbling at six months of age to full sentences by the age of 3, young children learn their mother tongue rapidly and effortlessly, following similar developmental path regardless of culture. Research and theory are now aimed at elucidating the mechanisms underlying developmental change in infant’s perception of speech, and the emerging picture in complex. Young infants learn statistically at many levels, including phonetic and syntactic. However, learning requires more than computation. In experimental interventions mimicking natural language learning situations, social factors play an important role when expose to new language for the first time at nine month of age, for example, infants learn phonetically from a live interacting human being, but not from a disembodied source, even though the acoustic information remains the same in the two situations while social factors may play in speech perception development has only recently been explored.
Non-linguistic cognitive factors also appear to play a role in phonetic learning.
Previous research (Lalonde and Werker 1995) suggested a link between general cognitive perceptions towards the end of the first year. These findings along with research showing that children raised bilingually from birth have an advantage on non-linguistic tasks requiring control of attention.
THE DEVELOPMENTAL PROBLEM AND EARLY THEORY
To acquire a language, infants have to discover which phonetic distinctions will be utilized in the language of their culture.
For example, English is different from Japanese,; the phonemes /r/ and /i/ create different words in English (‘rake’ and ‘lake’), but do not change the meaning of the work in Japanese. Our understanding of this process is anchored b =y two well-established fats. Early in life, infants discriminate among virtually all the phonetic units of the world’s languages. By adulthood, this universal phonetic capacity is no longer in place and non-native mechanism underlying this developmental transition.
Historical models of developmental speech perception were based on selection. Infants’ phonetic abilities were argued to stem from an innate specification of all possible phonetic units, which were subsequently maintained or lost as a function of linguistic experience. Eimas phonetic feature detector account and Liberman’s motor theory are classic examples. The primitives differ in the two accounts- Eoimas’ phonetic feature detectors were responsive to the acoustic events underlying phonetic distinctions, whereas Lieberman’s motor theory held that infants initially detect all phonetically relevant gestures but both views were based on selection and the maintenance loss view. Early data on developmental change in infant’s perception of speech supported this view; native abilities appeared to be maintained and non-native abilities lost.
In the 1970s, the discovery of ‘categorical perception’ for speech in non-human animals and demonstrations of categorical perception for non-speech stimuli in infants, undermined the selection model and provided an alternative explanation for infants’ abilities which was rooted in neurobiology and evolution. The argument was that phonetic contrast in speech capitalized on existing, more general properties o auditory perceptual mechanisms rather than specially evolve phonetic feature detectors. These data suggested that infants’ initial abilities were more primitive-the base on which language builds-rather than domain-specific mechanisms evolved for language. Additional comparative studies subsequently revealed many more similarities in human-animal speech perception and of equal importance, differences between human and animal perceptionand of equal importance, differences between human and animal perception and learning.
The idea that infants began life with phonetic feature detectors that were either maintained or lost was further undermined by adult and infant results. Both show that we remain capable of discriminating non-native phonetic contrasts, thoug at a reduced level wen compared with native contrasts.
However, the idea that more than selection is involved in developmental phonetic perception was most clearly demonstrated by experimental findings, showing that native language phonetic perception shows a significant improvement between 6 and 12 months of age. American infants tested on the English /r-i/ contrast showed a statistically significant improvement between 6 and 12 months of age. Also, both Mandarin-learning and English-learning infants showed native language phonetic improvement on affricate fricative contrasts between 6 and 12 months of age. Brain measure in the form of electrophysiological ERPs in response to syllable changes between 6 and 12 months of age also showed an increase in native consonant perception; the same pattern in ERP data has been shown for vowels. Previous studies had shown native language improvement after 12 months of age and before adulthood, but the new studies establish a pattern of improvement in native language phonetic perception in the first year, which we consider significant
SOCIAL INTERACTION INFLUENCES EARLY LANGUAGE LEARNING AT THE PHONETIC LEVEL
Current studies shows that young infants have computational skills that assist language acquisition; simple laboratory experiments indicate that statistical learning can occur with just 2 min exposure to novel speech material. Nevertheless, social influences on computational learning were recently shown in a study investigating whether infants are capable of phonetic learning at nine months of age at natural first-time exposure to a foreign language.
Mandarin Chinese, a language with prosodic and phonetic structure very different from those in English, was used in a foreign language intervention experiment. Infants heard four native speakers of Mandarin (both male and female) during twelve 25 min sessions of book reading and play during a four to six week period. A control group of infants also came into the laboratory for the same number and variety and play session, but heard only English. On average, infants heard approximately 33000 Mandarin syllables during the course of the 12 language-exposure sessions, including approximately 1000 instances of each of the two Mandarin syllables (an affricate fricate contrast not phonemic in English) that were used to test infants after exposure.
EARLY SPEECH PERCEPTION PREDICTS LANGUAGE GROWTH
NLM-e predicts and association between infants’ early perception of native language phonetic units and later language development, an association that differs for native and non-native perception. Retrospective studies suggested a connection between early speech perception and later language, but prospective studies measuring some aspect of early speech processing in typically developing infants and its relationship to language have appeared only recently.
We conducted the first prospective studies investigating the relationship between early phonetic perception and later language. Tested 6-months-old infants’ performance on a behavioural measure of speech perception using a simple vowel contrast (the vowel in ‘tea’ an ‘two’) and showed that infants performance measure on the task at six months of age were significantly correlated with their language abilities measured t 13, 16, and 24 months of age. The findings demonstrated that a standard measure of native language speech perception at six months of age prospectively predicted language outcomes in typically developing infants over the next 18 months. As discussed by the authors, Tsao et al’s result could be explained by infants’ basic auditory or cognitive abilities. Infants with better auditory skills might perform better in test of phonetic perception as well as in later language, the same could be argued for infants’ cognitive skills-clever infants might respond more readily in the head-turn task and also acquire language more quickly.
The findings of this study is consistent with the view that age-related changes in non-native speech discrimination are influenced by broad, domain-general cognitive processes. We also come to know that young children learn their mother’s tongue very rapidly and effortlessly.
A recent study with 11-month-old infants indicates that reduction in non-native discrimination skills at this age is linked to better performance on a detour-reaching task that requires inhibition of proponent responses and more goal-directed behaviours on a mean-end task. Finding that native language perceptual abilities are not associated with non-linguistic skills in either study suggests that cognitive control abilities may play a specific role in the ability to disregard irrelevant phonetic information while maintaining attention to relevant information.
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