Until about 30 years ago, language researchers focused their studies on infants who had already begun to babble, according to Jusczyk, who has written a book on how children acquire language titled The Discovery of Spoken．Language．Babies start to vocalize at around four months of age, and to babble in strings of words at around six or seven months.
'Theories around at that time said that infants perceived speech sounds by producing them,' says Jusczyk．In other words, by listening to themselves babble, babies learned to tell one sound from another．Mom, Dad, or the babysitter would reinforce these sounds by repeating their utterances like, 'Baba! That's bottle.'
Researchers, however, had not developed methods of deciphering what went through a baby's mind before baby uttered his first 'Ma' or 'Papa'．So Jusczyk and other experimentalists devised techniques that allow them to study the pre-babbler．They have demonstrated that speech is the culmination of a tremendous amount of learning．Long before a baby utters his first 'baba', the researchers discovered, his mind is furiously sorting out the sounds and shapes of words and sentences.
Colleagues credit Jusczyk for being one of the key experimentalists to bridge the gap between the study of infant speech perception and language development．'Peter is the father of a lot of this work,' says Robin Cooper, an associate professor of psychology, who studies infant language acquisition.
In their decades-long search for the universal truths about language acquisition, Jusczyk and collaborators around the world have found that at every stage of development, babies know a lot more than they'd been given credit for．The very seeds of language learning, in fact, start to develop in the womb (子宫).
Researchers cannot easily investigate language perception in the womb, however．So they study newborn babies' reactions to sounds that mimic the muffled language that penetrates the womb．In this technique, newborn babies listen to filtered recordings of a woman (the baby's mother or another mother) speaking, while ing on a pacifier (婴儿用的橡皮) that is attached to a pressure transducer (传感器)．Filtering erases the crisp edges of words, while leaving intact other features such as rhythm, melody, pitch, and intonation—similar to what a fetus (胎儿) hears in the womb．'It's kind of like listening to a stereo next door,' says William Fifer, an associate professor of developmental psychobiology at Columbia University．'You hear a lot of bass, but not the crisp, clear high frequencies.'
Using this technique, Fifer and his colleagues found that newborns harder on the pacifier when listening to filtered recordings of their own mother's voice in comparison to another mother's．The newborns thus recognize and prefer their own mother's voice, concludes Fifer.
In further studies, Jusczyk and postdoc Thierry Nazzi found that newborns prefer filtered recordings of their own native language over that of a foreign language．'Babies like what they know,' says Jusczyk．'Newborns,' he says, 'apparently learn the rhythm of their native language and of their mother's voice while in the womb.'
How do babies recognize different sounds?