“Attention is the holy grail,” Mr. Strayer says.

“Everything that you’re conscious of, everything you let in, everything you remember and you forget, depends on it.”

Echoing other researchers, Mr. Strayer says that understanding how attention works could help in the treatment of a host of maladies, like attention deficit disorder, schizophrenia and depression. And he says that on a day-to-day basis, too much digital stimulation can “take people who would be functioning O.K. and put them in a range where they’re not psychologically healthy.”

The quest to understand the impact on the brain of heavy technology use — at a time when such use is exploding — is still in its early stages. To Mr. Strayer, it is no less significant than when scientists investigated the effects of consuming too much meat or alcohol.

Liza Colburn uses her cellphone constantly.

She taps out her grocery lists, records voice memos, listens to music at the gym, tracks her caloric intake and posts frequent updates to her Twitter and Facebook accounts.

The one thing she doesn’t use her cellphone for? Making calls.

At the end of 2007, text messaging had just overtaken voice calls 218 to 213. But by the end of the second quarter of this year, an average mobile phone subscriber placed or received 204 calls, compared with sending or receiving 357 text messages.

Teens between the ages of 13 and 17 now send or receive 1,742 messages per month, compared to the second-highest age group, 18 to 24 year olds, who send and receive about 790 messages.

Read the story in Wired News or New York Times.