Whom to Believe? Children Find Out Early

Beware a puppet who tells you that a ball is a book, or that you tie your shoe with a spoon. That, at any rate, is the message of a study that looked at how 3- and 4-year-olds evaluate the trustworthiness of others.

Puppets that had spun such fanciful tales were no longer believed when they tried to teach the children words for unfamiliar objects and actions. But faced with puppets who had given them reliable information — calling a cup a cup, for example — the children were much more accepting.

“Humans make mistakes,” Susan A. J. Birch of the University of British Columbia and colleagues write in the current issue of the journal Cognition. “They trick; they lie; they have different levels of knowledge and different areas of expertise; and they offer information even when they are uncertain.”

The challenge for the child is figuring out whom to believe, and the study suggests that this process starts early and without prompting by adults.

For the study, two puppets gave the children accurate or inaccurate information about everyday objects the children already knew. When the children were then shown objects they did not recognize and given different made-up names for them or explanations for their use, they responded to the names used by the puppet who had been right earlier.

By ERIC NAGOURNEY

Go Ahead, Put the Water Bottle Down

Drinking a lot of water is supposed to be healthy, but there is apparently little scientific support for the belief. A review of clinical studies has found no evidence that drinking eight glasses of water a day, the usual recommendation, is beneficial to a healthy person.

Numerous claims have been made about water — that it prevents headaches, removes dangerous “poisons,” improves the function of various organs and is associated with reduced risk for various diseases. But none of these is supported by scientific evidence. The authors were not even able to find a study leading to the “eight glasses a day” rule, whose origin remains unknown.

The researchers, in the June issue of The Journal of the American Society of Nephrology, say some studies have found evidence that drinking extra water helps the kidneys clear sodium, and long-term sodium retention might increase the risk of hypertension, but no clinical significance for the phenomenon has been established. Water also helps clear urea, but urea is not a toxin.

There is “intriguing” evidence that water might help decrease appetite and control weight gain, write the authors, who say this might be worth more research.

“Under normal circumstances,” said Dr. Stanley Goldfarb, a co-author and a professor of medicine at the University of Pennsylvania, “drinking extra water is unnecessary. I want to relieve people of the burden of schlepping water bottles around all day long.”

By NICHOLAS BAKALAR