The 800 phonemes of the tiniest linguists

New research helps explain how infants acquire language skills – by losing their ability to discriminate sounds they don’t need.

Verbal Energy

Searching for videos of parents baby-talking to their little ones may sound only marginally more respectable than checking out cat videos as a workday pursuit.

But I had to go looking after reading a recent piece in Scientific American by Patricia K. Kuhl called “Baby Talk,” about how infants learn to talk – “a mastery,” she notes, “that occurs more quickly than any complex skill acquired during the course of a lifetime.” 

She discusses fascinating new research into the “sensitive period” of just a few months, beginning at age 6 months, when infants are “most open to learning the sounds of a native tongue,” as Professor Kuhl, of the University of Washington, explains it. Vowels come first; consonants follow some three months later. By the time the window closes, infants have “acquired” the phonemes of their mother tongue. The window stays open longer for infants exposed to two languages.

Phonemes are the building blocks of a language. The sound of “b” in “baby” is a phoneme in English; ditto the hard consonant at the beginning of “cat” or “kitten.” So is each of the “long vowels,” plus their “short” counterparts, and a handful of diphthongs, such as the “ou” of “couch.”

Merriam-Webster explains a phoneme as “the smallest unit of speech that can be used to make one word different from another word.”

A child who can tell a “lake” from a “rake,” or a pork “chop” from a potato “chip,” shows mastery of phonemes.

Linguists estimate that the world’s languages use 800-plus phonemes. Any given language will use only a subset of these, typically a few dozen.

But in their sensitive period, infants are “citizens of the world,” as Kuhl calls them, able to “discriminate” all 800 phonemes. As they listen to the world around them, they track, like tiny statisticians, the sounds they hear. 

Kuhl writes, “Children between eight and 10 months of age still do not understand spoken words. Yet they are highly sensitive to how often phonemes occur – what statisticians call distributional frequencies. The most important phonemes in a given language are the ones spoken most.” 

This is where “parentese” comes in – that high-pitched, singsong patter sometimes simply called “baby talk.” Yes, it sounds silly, but it furnishes “daily lessons in the intonations and cadences of the baby’s native tongue,” Kuhl writes. 

It goes across cultures, but content varies. English-speakers expose their infants to lots of “r’s” and “l’s,” for instance; Japanese parents, not so much, because those sounds matter less in Japanese. And Kuhl’s lab has found that, at age 6 to 8 months, Japanese and American infants are about equal in ability to discriminate “la” from “ra”; four months later, Japanese babies lose their ability to make this distinction, but Americans gain.

This transformation of “citizens of the world” into what Kuhl calls “language-bound listeners” is a bit of a downer: It involves letting go of literally hundreds of possibilities. But it anchors children to the sounds of their mother tongue.