Magazine article Volta Voices

A Discriminating Audience: Babies and Speech Perception

Magazine article Volta Voices

A Discriminating Audience: Babies and Speech Perception

Article excerpt

If you want to study how a baby's experiences influence his or her speech perception, the city of Vancouver in British Columbia, Canada, is a good place to start. An increasing proportion of the population there speaks English as a second language.

Many children are raised in homes where two or more languages are spoken, and an estimated 67 different languages are used with some level of frequency in the local schools. For Dr. Janet Werker, a leader in developmental cross-language and speech research, Vancouver offers a rich natural research environment in which she can study the speech perception and language learning abilities of young children.

A prolific author and fellow of both the Royal Society of Canada and the American Association for the Advancement of Science, Werker is consumed with questions about how and when young children develop the skills to differentiate environmental sounds from meaningful speech.

"Children [with typical hearing] rapidly acquire language, and children with exposure rapidly acquire the Ianguage or languages in their environment," she said at the 2007 Talk for a Lifetime Summer Conference. "One of the mysteries that keeps me jumping out of bed every morning is how does this happen so quickly?"

A theory that Werker shares with many of her fellow researchers is that babies' language learning is supported by the development of perceptual systems that integrate listening and the visual cues offered by the speakers around them. At one time, researchers thought that babies developed speech perception in a sequential process, Werker explained. Now, the research community is relatively confident that babies are listening at multiple levels, even very early in life.

What does listening at multiple levels entail, exactly? In brief, babies are learning the properties of a language - rhythm, acceptable sound sequences, language categorization and visual cues such as lip movements and hand gestures - simultaneously. In turn, those skills set the stage for language acquisition with a focus on word learning.

Despite the seeming complexity of this developmental process, most babies get a natural head start to listening in utero so that, by the time they are born, they already show a predisposition for their native language. Babies even have the ability to use the acoustic and phonological cues in words to discriminate between content words (such as nouns, verbs and adjectives) and function words, said Werker.

"Ultimately, by age 6 months, [babies] prefer content words. By 8 months, they hear a function word and know to expect a content word to come," Werker explained. "It allows them to learn when to listen for meaning, when to listen for structure. It's a kind of boot-strapping mechanism for learning the native language."

Speech Versus Nonspeech

Let's return to the concept of infant preferences at birth. In research published in Developmental Science. Werker and doctoral candidate Athena Vouloumanos outlined an experiment that gave babies the choice of listening to speech versus nonspeech. Babies were laid in a bassinette and given a pacifier connected to a system that enabled the researchers to measure the baby's sucking pattern. After establishing a baseline, the researchers "rewarded" babies with a speech or nonspeech sound for each high-amplitude sucking motion. The study showed that babies delivered more sucking sounds in order to hear speech.

The team's research is corroborated by studies of adults that show how certain parts of the brain are selectively activated when hearing speech. In addition, brain imaging research conducted on newborn babies by Marcela Peña, Jacques Mehler and colleagues at the International School for Advanced Studies in Trieste, Italy, shows greater activation in the form of oxygenated blood flow to the language areas of the brain's left hemisphere in response to speech.

Werker and colleagues have gone on to explore whether babies listen selectively to some languages over others. …

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