How speech sounds convey meaning

Dan Swingley, Department of Psychology
Photo credit: Candace diCarlo

Researchers have known for years that young children begin acquiring language-learning abilities from a very early age. The outstanding question has always been: How early?

A new Penn study is finally supplying the answer: Research from one Penn psychologist has shown toddlers as young as 18 months have learned to ignore subtle speech distinctions not native to their own language. This sophisticated skill enables them to recognize how their parents use sounds to convey meaning. Previously, scientists had speculated children did this later in life, only after amassing a large vocabulary.

“The failure to discriminate sounds your language doesn’t use begins very early in life, probably before your first birthday. This knowledge helps children interpret other sounds they encounter,” says Daniel Swingley, an assistant professor in the Department of Psychology.

The idea for the study came to Swingley while he was living in Netherlands and learning to speak Dutch. There, he discovered there are important differences in the sound structure of the two languages, especially in the way adults talk to young children.

“We love this baby talk. It happens in the Netherlands too, but it takes slightly different forms,” he says.

One way Dutch speakers convey word meaning is by alternately elongating and shortening vowel sounds. That’s not the case with most English words.

“To a baby, we might say, ‘Where is the maaan’ or, ‘Show me the man.’ In English, we’re still talking about the same man. But they have to figure this out.”

In Dutch, those two pronunciations of “man” mean completely different things (man and moon). Thus, the vowel lengthening characteristic of American English baby talk only results in confusion.

“The question is: What do children know about this and when do they know it? Our evidence shows that 18-month-olds have already learned this and apply that knowledge when learning new words,” Swingley says.
To find out, Swingley and his colleagues colleagues from the University of British Columbia and the Max-Planck-Institute for Psycholinguistics tested vowel duration in three experiments comparing Dutch- and English-learning 18-month-olds.

Children were shown two different toys. With one toy, researchers repeated a word dozens of times, naming it a “tam.” The other toy was named too, with the same label, only the vowel’s duration was lengthened to “taam.”

When the researchers switched the labels, Dutch children showed increased attention, indicating they learned which word goes with each object.

“They recognize that something new has happened here and they’re wondering how you got it wrong,” Swingley says. “It suggests Dutch children conduct a sophisticated analysis of the speech signal they hear, and that analysis tells them there are two categories – the long and short ones. They guessed correctly that the long and the short signify different things.”

English learners could hear the difference between the words, but did not differentiate between the distributions of long and short sounds. Rather, they concluded there is one word, with many variables.

“It’s not a perceptual problem. … We’re confident they can both hear the difference. By 18 months, they are considering whether it’s relevant for deciding the identity of the word,” Swingley says.

The study, which appeared in the Oct. 1 issue of the Proceedings of the National Academy of Sciences, reinforces earlier research that demonstrates the importance a child’s first year is in acquiring language.
“The more we can find out how this process works in childhood development, the better we will be able to figure out the timing of interventions for hearing impairment,” Swingley says.

Originally published on November 1, 2007