The Empirical Study Of Infant Speech Perception And Its Underlying Mechanism

In this thesis,a Visual Fixation procedure is used to test infants' ability of speech sounds discrimination,and then the internal mechanism of infant phonetic perception ability is discussed by comparing two well-known theories:the congenital theory and the statistical learning(SL) theory.It is found that each theory has its advantages and deficiency to explain the underling mechanism of infants' remarkable performances on sound discrimination.However,according to the test results,it finds that the congenital theory is more powerful to cover infants developmental changes in speech perception.A fixed trial VF procedure is applied to test 2-10 months old Mandarin infants.It has shown that Mandarin infants as young as 2-9 month old could well discriminate the sound contrasts[pa]&[pha]in Chinese phonetic system.And,such ability is not limited to Mandarin.They can also distinguish English sound contrasts[(?)a] and[?a] without prior language experience.However,such capacity has its limitations.A 10-month old infant can not discriminate the English sound contrast[(?)a] and[?a] like 2-9 months old infants do.He can only discriminate[(?)a]&[pha] which is within the realm of Mandarin phonetic system.That is to say that infants' discriminative ability gradually disappear as they age.Comparative discussion has been done to see how congenital theory and statistical learning theory explain for such results.Under statistical learning theory,it is suggested that a distributional learning mechanism exist for newborn infants to set up native phonological catesories.As infants are,their discrimination of speech sounds is affected by the phonetic distribution in their native language because they are gradually exposed to more native language input.That is why infants' sensitivity to non-native sound differences decreases and even disappears while native sounds discrimination ability increases.Under the SL theory,language experience takes a huge part in speech perception and language acquisition.However,the language input around infants are too limited to cover the whole language system.The congenital account assumes infants have a universal innate faculty to acquire language and this ability is innately constrained.The nativists try to use Universal Grammar and LAD to explain such phenomena.Primary linguistic data comes into play as infants age.The environment is mainly taken as a trigger rather than a tutor for language acquisition.As infants access to more language input,the LAD will tune to the settings of one language and turn them away from others.The congenital theory sets a general frame for infancy speech perception while the statistical learning theory is rather concrete to explain how language information is computed into a language system.