He found that as long as toddlers are working to decipher many words at once — that parallel learning — and they're being exposed to more difficult words than easy ones, the word spurt is guaranteed.
Consider: Scientists know children learn through the process of elimination. If Mom asks, "Please pass me the plate," and the child sees a fork, a spoon and some round thing, by age 2 most will match the new word to the unknown object.
That fits with McMurray's model. As you acquire many words, the process of elimination for new ones becomes easier so that vocabulary accelerates.
Then he compared easy words parents use with babies to more sophisticated adult speech. There was faster early learning with exposure to simple words, but then new vocabulary slowed — only to speed up again with exposure to harder words.
"The work is extremely creative," said Dr. Janet Werker, a language development specialist at the University of British Columbia.
Her own research shows that some words are particularly difficult for toddlers, including rhyming words such as "bin" and "din." The new work shows that trouble won't stall overall learning.
"It suggests the fact that some words are more difficult to learn than others is part of what propels the vocabulary explosion," Werker said. "That's really insightful."
