At an age when "ba-ba" and "da-da" may be their only utterances, infants nevertheless comprehend words for many common objects, according to a new study.
In research focused on 6-to-9-month-old babies, psychologists Elika Bergelson and Daniel Swingley demonstrated that the infants learned the meanings of words for foods and body parts through their daily experience with language.
These findings unseat a previously held consensus about infant learning.
It was widely believed that infants between six and nine months, while able to perceive and understand elements of the sounds of their native language, did not yet possess the ability to grasp the meanings Comprehension though speech.
Most psychologists believed word comprehension didn't emerge until closer to a child's first birthday.
In fact, infants are often referred to as "pre-linguistic," according to Bergelson. But there have been few attempts to determine just when infants begin understanding what is meant by specific words. The belief that infants do not comprehend language for most of the first year is easy to understand, given that infants do not often speak in words, or even gesture meaningfully, before 10 or 11 months.
To test this belief, the researchers recruited caregivers to bring their children to a lab to complete two different kinds of test. In the first, a child sat on the caregiver's lap facing a screen on which there were images of one food item and one body part.
The caregiver wore headphones and heard a statement such as, "Look at the apple," or, "Where's the apple?" and then repeated it to the child. The caregiver also wore a visor to avoid seeing the screen. An eye-tracking device, which can distinguish precisely where a child is looking and when, then followed the child's gaze.
The second kind of test had the same set-up, except that, instead of the screen displaying a food item and a body part, it displayed objects in natural contexts, such as a few foods laid out on a table, or a human figure. For both kinds of test, the question was whether hearing a word for something on the screen would lead children to look at that object more, indicating that they understood the word. In total, 33 6-to-9-month olds were tested. The researchers also had 50 children from 10 to 20 months complete the same tests to see how their abilities compared with the younger group. As part of their analysis, the researchers corrected for eye movements not related to caregivers' speech.
"So if you have a boring cup and a really colourful cup, they're going to look at the more interesting thing, all else being equal."
To eliminate this potential source of error, the researchers subtracted the amount of time that the babies gazed at a given object when it was not being named from the time they looked when it was named.
In both the two-picture and scene tests, the researchers found that the 6- to 9-month-old babies fixed their gaze more on the picture that was named than on the other image or images, indicating that they understood that the word was associated with the appropriate object.
This is the first demonstration that children of this age can understand such words.
"There had been a few demonstrations of understanding before, involving words such as mommy and daddy," Swingley said. "Our study is different in looking at more generic words, words that refer to categories."
"We're testing things that look different every time you see them," Bergelson said. "There's some variety in apples and noses, and 'nose' doesn't just mean your nose; it could mean anybody's nose. This is one of the things that makes word learning complicated: words often refer to categories, not just individuals."The researchers were also curious to know whether they could observe a pattern of learning during the months from 6 to 9.
But, when they compared the performance of 6 and 7-month-old babies with that of 8- and 9-month olds, they found no improvements. Factoring in the results of the older babies, the researchers found little improvement until the children reached roughly 14 months, at which point word recognition jumped markedly.
The study's novel results contribute to an ongoing debate about infant language acquisition and cognitive development.