Science: Researcher Decodes the Toddler Language Explosion

The astonishing speed at which toddlers learn new words may relate to the distribution of easy and complex words in a language, not some specialized part of the toddler brain becoming active, according to new research published in the 3 August issue of Science.

As young children begin to acquire the more than 60,000 words an average adult uses, they first learn the very easiest words. But there are not that many of these, said Bob McMurray, a professor of psychology at the University of Iowa at the paper's sole author.

After they have grasped basic words, toddlers begin to acquire words that are more difficult. There are many more of these.

With very few very simple words and very complex words, most fall somewhere in between, creating a bell curve of word difficulty.

"[T]he difficulty of learning words is distributed such that there are few words that can be acquired quickly and a greater number that can take longer," McMurray wrote.

It is believed that the vocabulary explosion takes place once toddlers have progressed to the steeply rising stretch of the bell curve.

McMurray's hypothesis contrasts previous theories because it shows how language acquisition could rapidly increase without a specialized part of the toddler brain becoming more active at around 18 months.

Although his research shows that a specialized part of the toddler brain isn't necessary to explain the vocabulary explosion, McMurray said he cannot rule out the possibility that such a mechanism might exist.

Kathy Wren and Benjamin Somers

3 August 2007