WASHINGTON -- It is called the "word spurt," that magical time when a toddler's vocabulary explodes, seemingly overnight.
New research offers a decidedly unmagical explanation: Babies start really jabbering after they have mastered enough easy words to tackle more of the harder ones. It is essentially a snowball effect.
That explanation, published in today's edition of the journal Science, is far simpler than scientists' assumptions that some special brain mechanisms must click to trigger the word boom.
Instead, University of Iowa psychology professor Bob McMurray contends that what astonishes parents is the fairly guaranteed outcome of a lot of under-the-radar work by toddlers as they start their journey to learn 60,000 words by adulthood.
If McMurray is right, it could have implications for parents bombarded with technological gimmicks that claim to boost language.
McMurray said talking and reading a lot to a child is the key.
"Children are soaking up everything," he said.
"You might use 'serendipity' to a child," he continued. "It will take that child maybe hundreds of exposures, or thousands, to learn what 'serendipity' means. So why not start early?"
Sometime before the first birthday comes that first word, perhaps "mama." A month or so later comes "da-da."
Now, it may seem like it took the child almost a year to learn the first word and a month to learn the second.
Not so. The child had been working on both the whole time, something scientists call parallel learning.
Up to age 14 months, on average -- and how soon children speak is hugely variable -- words pop out here and there. Then comes an acceleration, and after they can say 50 or so words, there is often a language explosion, sometime around 18 months, McMurray said.
What sparks the spurt?
There are numerous theories centering on the idea that a toddler brain must first develop specialized learning tools, such as the ability to recognize that objects have names.
The new research doesn't negate those theories, but it suggests "we might be missing the big picture," said McMurray, who developed a computer model to simulate the speed at which 10,000 words could be learned.