Professor Werker is an organizer and speaker for the AAAS symposium The Effects of Early Experience on Lifelong Functioning: Commitment and Resilience, Friday, Feb. 17, 1:30 – 4:30 p.m.
One of the greatest joys for new parents is to hear their baby utter that first word. “Mama,” “Dada,” or even “juju” (the name of the family dog) are each greeted with enthusiasm and pride. These first spoken words were already preceded by understanding. For example, by six months babies recognize highly frequent words such as their name. But even the achievement of word recognition is not the beginning of language acquisition; it has begun several months earlier, even in the womb.
Language acquisition begins in the womb
Human infants are born with a predisposition to listen to human speech, and to watch the faces of people when they are talking. Although the preparedness for acquiring language is deeply engrained in our biology, it is not ‘language writ large’ that the child has to acquire, but rather the particular language they experience. The perceptual systems are the child’s first entry into acquisition of the native language. They are able to hear native speech beginning at around 26 weeks gestation. By this time the peripheral auditory system has developed, and speech spoken by the mother – and also in the world outside the womb – causes vibrations in the amniotic fluid that displace the eardrum, and hence conduct ‘sound’ to the brain.
Infants do learn about their native language in utero. At birth they show a preference not only for their mother’s voice, but also for the native language. Babies who were exposed to two languages in utero show a preference for both of their native languages. These preferences highlight attention in the neonate to the speech of their native language, and this in turn is thought to help them learn more about the properties of that native language.
Watching talking faces plays a role
Over the next several months of life, infants learn more and more about the properties of the native language. Much of this learning involves attuning, or reorganizing sensitivities that were present at birth. For example, young infants can discriminate many more speech sound differences than they will need in any particular language, and gradually narrow their discrimination sensitivities to just native language sounds. The most famous example here is that young Japanese-learning infants are better able than their parents to respond to the difference between ‘ra’ and ‘la.’ Watching talking faces also plays a role: while a young infant can discriminate French from English just by watching silent talking faces, by the time they are eight months old, infants no longer do so unless they are growing up bilingual. In addition to tuning to the speech sound differences used in their native language, babies also tune to the rhythm and melody of the native language, and learn the sound sequences that occur within words versus those that might signal a boundary between two words.
The perceptual tuning that takes place during the first months of life enable the infant to pull out individual words from the speech stream they hear around them, a skill needed to eventually attach meaning to those words. Thus prior to understanding and speaking that first word, an enormous amount of development has already occurred. By charting when speech-processing changes occur, and how they relate to other abilities that are emerging in the child, we have a far better understanding of how language development unfolds. This positions us to better understand what might happen when there are perturbations in the timing of any particular part of the system, and how to intervene to ensure language development gets back on course.
