WASHINGTON, Aug 3 (Reuters) Parents know that at about 18 months of age, toddlers start talking up a storm -- a vocabulary surge dubbed a ''word spurt'' -- and some scientists have credited complex brain mechanisms.

But a simpler explanation may suffice, University of Iowa psychology professor Bob McMurray proposed in research appearing in the journal Science yesterday.

Using computer simulations and mathematical analysis, McMurray suggested that learning sufficient numbers of simple words paves the way for the seemingly sudden escalation in vocabulary.

McMurray emphasized the importance of word repetition, variations in word difficulty and learning multiple words at the same time in helping these toddlers turn loquacious.

''So in the 'word spurt,' it's not that children are learning words faster, it's that they've reached a point in development where there's lots of words that they can master,'' McMurray said in a telephone interview.

Between birth and adulthood, children learn about 60,000 words on average, amounting to eight to 10 words a day, McMurray said.

''Most parents and most development psychologists are aware of the fact that at around 18 months or so, children go crazy learning new words,'' McMurray said.

He said some experts had assumed that important physiological or psychological changes in the child must be unfolding.

''People have posited lots and lots of different mechanisms that might happen. One idea might be that those first 50 words force the brain to reorganize to be a little more efficient,'' McMurray said.

But he said that as long as children are learning more than one word at a time and learning a greater number of difficult or moderate words than easy ones, his analysis showed that a vocabulary explosion will result.

REUTERS SG BD0854