In the early nineteen fifties, researchers found that people scored lower on intelligence tests if they spoke more than one language. Research in the sixties found the opposite. Bilingual people scored higher than monolinguals, people who speak only one language. So which is it?

Researchers presented their newest studies last month at a meeting of the American Association for the Advancement of Science. The latest evidence shows that being bilingual does not necessarily make people smarter. But researcher Ellen Bialystok says it probably does make you better at certain skills.

"Imagine driving down the highway. There’s many things that could capture your attention and you really need to be able to monitor all of them. Why would bilingualism make you any better at that?"

And the answer, she says, is that bilingual people are often better at controlling their attention -- a function called the executive control system.

"It’s quite possibly the most important cognitive system we have because it's where all of your decisions about what to attend to, what to ignore, what to process are made."

Ms. Bialystok is a psychology professor at York University in Toronto, Canada. She says the best method to measure the executive control system is called the Stroop Test. A person is shown words in different colors. The person has to ignore the word but say the color. The problem is that the words are all names of colors.

"So you would have the word blue written in red, but you have to say red. But blue is so salient, it's just lighting up all these circuits in your brain, and you really want to say blue. So you need a mechanism to override that so that you can say red. That’s the executive control system."

Her work shows that bilingual people continually practice this function. They have to, because both languages are active in their brain at the same time. They need to suppress one to be able to speak in the other.

This mental exercise might help in other ways, too. Researchers say bilingual children are better able to separate a word from its meaning, and more likely to have friends from different cultures. Bilingual adults are often four to five years later than others in developing dementia or Alzheimer's disease.

Foreign language study has increased in the United States. But linguist Alison Mackey at Georgetown University points out that English-speaking countries are still far behind the rest of the world.

"In England, like in the United States, bilingualism is seen as something special and unique and something to be commented on and perhaps work towards, whereas in many other parts of the world being bilingual is just seen as a natural part of life."