Spurred by unlimited texting plans, American teenagers sent and received an average of 2,272 text messages per month in the fourth quarter of 2008–nearly 80 messages a day, more than double the average of a year earlier. And the phenomenon is beginning to worry physicians and psychologists, who say it is leading to anxiety, distraction in school, falling grades, repetitive stress injury, and sleep deprivation, reports the New York Times. The rise in texting is too recent to have produced any conclusive data on health effects. But Sherry Turkle, a psychologist who is director of the Initiative on Technology and Self at the Massachusetts Institute of Technology and who has studied texting among teenagers in the Boston area for three years, said it might be causing a shift in the way adolescents develop. "Among the jobs of adolescence are to separate from your parents, and to find the peace and quiet to become the person you decide you want to be," she said. "Texting hits directly at both those jobs."