Secret to Toddler Vocabulary Explosion Revealed

Learning 10 new words a day may seem daunting, but it's actually fairly simple for toddlers, who must tackle this vocabulary milestone to eventually talk like the rest of us, a new study suggests.

At about the age of 18 months, children experience a "vocabulary explosion" that suddenly involves learning new words, left and right. Many parents likely remember being amazed by how smart their child seemed during this stretch.

Researchers have previously thought complex mechanisms must govern this voracious rate of word-learning.

"The field of developmental psychology and language development has always assumed that something happens at that point to account for this word spurt: kids discover things have names, they switch to using more efficient mechanisms and they use their first words to help discover new ones," said study author Bob McMurray of the University of Iowa. "Many such mechanisms have been proposed."

But these mechanisms aren’t necessary, according to McMurray, whose study of a mathematical model to describe the vocabulary explosion is detailed in the Aug. 3 issue of the journal Science.

While children may engage those types of specialized mechanisms to help them learn new words, McMurray says, computational simulations he conducted suggest that simpler mechanisms—such as word repetition and learning multiple words at once—can explain the vocabulary explosion.

"Children are going to get that word spurt guaranteed, mathematically, as long as a couple of conditions hold," McMurray said. "They have to be learning more than one word at a time, and they must be learning a greater number of difficult or moderate words than easy words. Using computer simulations and mathematical analysis, I found that if these two conditions are true, you always get a vocabulary explosion."

McMurray likens the word-learning process to filling up jars, with jar size increasing with the difficulty of the word.

Experts previously suggested that when a child learned a word, it was easier for him or her to learn more words, analogous to shrinking the jar size. But McMurray's model found that even if jar size is increased, the vocabulary explosion still occurs.

The key is the relative number of small jars to big jars (or easy words to difficult words)—as long as there are more difficult words than easy words, which is generally the case with languages, the vocabulary explosion will happen.

"Clearly, the specialized mechanisms aren't necessary," McMurray said. "Our general abilities can take us a lot farther than we thought."