If you're trying to read a person's mind, watching how often he blinks can be a good place to start, according to an article published last month in Psychology Today.

People blink more when they are angry, excited or bored, and they blink less when they are taking in information or actively concentrating, the March issue said, citing research by John Stern of Washington University in St. Louis."Using everything from electrodes to infrared cameras, researchers have shown that the frequency, duration and timing of blinks are influenced by a wide range of physical and mental states," the article said.

Babies blink only once every couple of minutes, to moisten their eyes. But the rate of blinking steadily increases until puberty, when it reaches about 15 blinks per minute a level usually maintained for life.

Most of that blinking serves no particular function, but is a result of mental processes, according to Stern.

People who are undergoing physical or psychological stress blink more, Stern said, noting that he first became interested in blinking at the time of the Watergate hearings.

"President Nixon's blink rate markedly increased when he was asked a question he was not prepared to answer," Stern said. "His speech was well-controlled and did not manifest other symptoms of anxiety, but you could see it in his eyes. Most politicians have learned to disguise feelings except in ways they cannot inhibit."

Research is also under way on what longer and shorter blinks tell. The Air Force is using blink tests to indicate how tired pilots and flight controllers are. One test with pilots deprived of sleep showed that the more often a pilot blinked, and the longer a blink lasted, the more mistakes were likely. Tests with car drivers showed similar results.

"I want a light on the top of every car and truck that will indicate when a driver is not performing safely," said Stern. Blink monitors could also serve as checks for boredom, a dangerous condition in demanding jobs, he suggested.