Learning Mechanisms in Early Vocal Development

点击翻译按钮获取中文摘要

Achievement of the canonical babbling stage (on average at 7 months) is an important milestone: at this age the infant begins to produce consonant-vowel syllables that are the fundamental building blocks of spoken language. Research from my lab, involving infants with varying levels of hearing loss, shows that hearing speech from adult talkers is essential to achieving speech-like babble in the first year of life. Furthermore, babies learning English, French, and Arabic, learn to babble in subtly different ways. How do babies learn to babble with native language sound characteristics? I propose to test a model of speech motor learning in which the infant learns to perceive speech categories from heard speech and attempts to produce those categories when babbling. The baby is motivated to reduce errors in the match between internalized perceptual categories and speech produced during babble. Speech input from adult caregivers (a) provides information about native-language speech categories, (b) encourages vocal exploration, and (c) reinforces speech practice. This model can be contrasted with an alternative model in which speech-like infant utterances are reinforced when adults mimic infant speech that is similar to speech categories in the adult language. One aim of this research program is to describe patterns of mimicry between adults and their infants in three contexts: (1) normal hearing infants and their English-speaking mothers; (2) normal hearing infants and their Arabic speaking mothers; (3) hearing impaired infants, with cochlear implants, in interaction with their Arabic speaking mothers. We expect that maternal mimicry will occur much less frequently than is predicted by some current computer models of speech development and to find that mothers adjust their speech responses to the meaningfulness of their infant's outputs. In a second study we will teach infants to produce foreign language vowels by providing exposure to the foreign language, but without imitating or expanding infant utterances. Changes in the infants' perception and production of foreign language sound categories will be described in comparison to a control group. We hypothesize that the results will support intrinsic motivation and self-supervised learning as mechanisms that support speech learning. Understanding how speech production develops has always had important applications in fields such as speech therapy and accent reduction. More recently, infant speech production research has been applied in the areas of speech recognition and synthesis, machine learning and robotics. Theoretical accounts are currently being tested via machine learning models without the benefit of sufficient human data to guide their implementation or validate their outputs. This research program will produce large samples of detailed phonetic and acoustic data describing infant vocal output under varying conditions.