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Babies in Tokyo lose "ra" and "la"
The head-turn test
The test is simple. A baby sits on a parent's lap and turns their head when a sound changes, such as from "ah" to "ee." If the head turn comes at the right moment, a black box lights up and a panda bear pounds a drum. Six-month-olds love it.
Run in labs all over the world, the task shows that young babies are citizens of the world. They can tell apart the sounds of every language, which adults cannot do. Adults are culture-bound listeners, able to separate the sounds of their own language but not those of foreign ones.
How sounds get tallied
The change happens before the first birthday. "Ra" and "la" matter in English but not in Japanese, so the American babies keep getting better at hearing them while the Japanese babies get worse. Both groups are preparing for the language they will actually learn.
The mechanism is statistics. Babies listen intently to the speech around them, including the exaggerated motherese adults use with children, and tally how often each sound occurs. English has plenty of Rs and Ls, while Japanese has a cluster of intermediate sounds known as the Japanese R. That tally reshapes the baby's brain.
How does the Japanese R differ from English R and L?
The Japanese R is usually a quick tap of the tongue tip against the ridge behind the upper teeth. English speakers make R and L with quite different tongue shapes, and the sounds land in separate categories. The Japanese tap falls in an acoustic range somewhere between the two. A 1975 study by Miyawaki and colleagues found that Japanese adults had much more trouble than American adults telling English R from L.
How do babies tally sounds without knowing any words?
A 2002 experiment by Maye, Werker, and Gerken tested this directly. Infants of six to eight months heard a series of syllables that fell along a continuum between two sounds. Those who heard most of the examples clustered at two ends later distinguished the two sounds better than those who heard most of them clustered in the middle. The result showed that infants can respond to how often sounds occur, with no meanings attached.
When does hearing narrow to the native language?
The narrowing was documented in a 1984 study by Janet Werker and Richard Tees. English-learning infants at six to eight months could tell apart sounds from Hindi and from the Salish language Nlaka'pamux, which English speakers cannot normally separate. By ten to twelve months, those infants had lost most of that ability. Infants raised in Hindi-speaking homes kept it.
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