When do infants make this connection? Earlier than most people think, says psychologist Amanda Woodward. She has shown that children comprehend words equally well at 13 months an age when they use just five to ten words as at 18 months, when their vocabulary is about 100 words and the pace of word learning suddenly zooms upward.
This change called the naming explosion or vocabulary spurt is a key stage in development. Woodward, who came to Chicago last fall as an associate professor, has recently broken with the phenomenon's traditional explanations, which propose various progressions in conceptual development to explain 18-month-olds' new understanding that words are symbols. Before then, the theory goes, a child laboriously learns words through association, almost as a dog might link the sound of a bell with food.
Working from that theory, Woodward along with colleagues Colleen Fitzsimmons and Ellen Markman of Stanford University tried to measure how much better an older baby could learn new words, hoping to correlate that skill with other abilities. They exposed 13- and 18-month-old infants to unfamiliar objects like a big plastic paper clip and a plastic strainer, calling one of them by a made-up name, toma. After one person repeated the word nine times in different situations, another unaware which object was the toma tested the child's comprehension through a play activity, such as presenting two objects on a tray and asking the child to "put the toma in the box." They adjusted these verbal instructions so as not to unfairly confuse 13-month-olds.
Surprisingly, the researchers found little difference in rates of word learning and retention between the two groups of infants. Babies at both ages even remembered the new word after a 24-hour delay.
"It was a very unexpected finding," says Woodward. "It's one of those results that really goes against some people's intuition, and goes against a good number of theories." In an article to be published in Developopmental Psychology, she and her colleagues conclude that the vocabulary spurt probably isn't the result of broad changes in comprehension. Instead, factors related to the production of words, such as babies' improved memory or the ability to articulate successfully, may account for the quick advance.
As a result, Woodward says, "I'm less interested in the naming explosion now." She's currently using her Beecher Hall laboratory where video equipment shares space with a basket of toys, and colorful paper shapes and posters decorate the walls to test younger infants, pushing back to the origins of language ability. She wonders, "When it is that children understand that language is a symbolic system?" In one study, she's finding evidence that even 1-year-olds are beyond associative learning. Their performance in linking a new object to a nonlinguistic sound, like a whistle, is poor compared to when the object is called by a name.
Soon she'd like to explore a related idea: that language learning requires an ability to reason about human actions. When, for instance, do infants know that, if a person looks at an object while talking, he or she is probably talking about that object? In this way, Woodward hopes to link language development with another of her interests the distinctions babies make between animate and inanimate objects. It's a subject she likens to infant physics": Babies appear surprised, for instance, when a ball begins to roll for no visible reason, but unimpressed when people cause others to move simply by pointing or talking.
Her insights may have applications to developmental disorders like autism, which is marked by poor language skills and a difficulty in grasping human intentions, perceptions, and goals. With a four-year grant from the John Merck Fund, part of its program to boost research on the underlying neurobiology of developmental disabilities, Woodward plans to test her ideas about language learning and infants' understanding of other people using autistic children. "This will fill in the picture of what specific abilities autistic children lack," she says, "and how these deficiencies affect later development."
Working with babies is fun, of course, but Woodward's motivation has another source. "I'm interested in how things begin, how things get started," she says. "Every time I hear about something interesting in [human] development, I say, 'That's great, but how did it start?' If you have that bent, you end up looking at infants."
Written and compiled by Andrew Campbell.