Babies may start to learn their mother tongues even before seeing their mothers’ faces. Newborns react differently to native and foreign vowel sounds, suggesting that language learning begins in the womb, researchers say.
Infants tested seven to 75 hours after birth treated spoken variants of a vowel sound in their home language as similar, evidence that newborns regard these sounds as members of a common category, say psychologist Christine Moon of Pacific Lutheran University in Tacoma, Wash., and her colleagues. Newborns deemed different versions of a foreign vowel sound to be dissimilar and unfamiliar, the scientists report in an upcoming Acta Paediatrica.
“It seems that there is some prenatal learning of speech sounds, but we do not yet know how much,” Moon says.
Fetuses can hear outside sounds by about 10 weeks before birth. Until now, evidence suggested that prenatal learning was restricted to the melody, rhythm and loudness of voices (SN: 12/5/09, p. 14). Earlier investigations established that 6-month-olds group native but not foreign vowel sounds into categories.
Moon and colleagues propose that, in the last couple months of gestation, babies monitor at least some vowels — the loudest and most expressive speech sounds — uttered by their mothers.
Any vowel tracking before birth demonstrates that fetuses hear surprisingly well despite being immersed in amniotic fluid inside cramped quarters, remarks psychologist Minna Huotilainen of the Finnish Institute of Occupational Health in Helsinki. The new study “implies that the fetal brain close to birth can perceive and learn most of the key aspects of speech,” Huotilainen says.
Moon’s team studied 80 healthy newborns, half in U.S. hospitals and half in Swedish hospitals. Each infant lay in a crib in a quiet room with soft headphones placed next to his or her ears. By sucking on a pacifier connected to a computer, babies triggered the presentation of vowel sounds for five minutes.
Utterances consisted of 17 variants of an English hard e, as in the word fee, and 17 variants of a Swedish vowel which sounds roughly like yeh and is made with compressed lips. Each set of vowels included one that had been rated as the best example of that sound by native speakers.
A vowel sound was played until a newborn stopped sucking for at least one second. A new vowel was presented when sucking resumed. Longer bouts of sucking denoted greater interest in a sound, the researchers say.
On average, newborns sucked their bugged binkies more times upon hearing foreign vowels than native vowels. This finding held regardless of time since birth. Pacifiers got the biggest workout when babies heard the best example of the foreign vowel.
All versions of the native vowel sound elicited about the same rate of pacifier sucking, indicating that newborns already perceived these speech sounds as part of a single category, Moon says.