Infants Show Keen Ear for Speech Sounds

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Infants show keen ear for speech sounds

Six-month-olds may not utter an articulate word, but a new study indicates they already organize adult vowel sounds into distinct categories and perceive some sounds as better examples of a particular vowel than others. Specific speech sounds apparently serve as "perceptual anchors" from infancy onward, crucially influencing the ability to speak and understand language, say psychologists Di-Anne Grieser and Patricia K. Kuhl of the University of Washington in Seattle.

Grieser and Kuhl base their work on the notion that human perception -- the operation of senses such as seeing and hearing -- sorts diverse incoming stimuli into meaningful categories. Certain stimuli, according to the theory, constitute the best instances, or prototypes, of their particular category. When new stimuli are encountered, the brain assigns them to a perceptual category based on how closely they resemble a category's prototype.

For example, people in a broad array of cultures agree on color prototypes -- say, the hue that best represents the color green. These preferences are thought to be inherently defined by the visual system.

Over the past decade, researchers have found that adults group the smallest units of language -- consonant and vowel sounds -- into acoustic categories and that they perceive some sounds as better examples of a category than others.

Reports also indicate that 6-month-old infants can distinguish between prototypical vowel sounds made by adults and recognize novel variations of the sounds. Grieser and Kuhl, who describe their study in the July DEVELOPMENTAL PSYCHOLOGY, examined how infants accomplish this complex feat.

In their first experiment, the researchers conditioned 16 infants to turn their heads toward a loudspeaker when the prototype for one vowel category (the long "e" in the word "peep") changed to another vowel prototype (the short "e" in the word "pep"). …