"It started happening about three years ago, when I first got a cellphone," says Canadian Steven Garrity, 28, of Charlottetown, Prince Edward Island. "I'd be sitting on the couch and feel my phone start to vibrate, so I'd reach down and pull it out of my pocket. But the only thing ringing was my thigh."

Though no known studies have analyzed what may cause spontaneous buzzing, anecdotes such as Garrity's ring true with the public.

Spurred by curiosity, Garrity, a Web developer, described the recurring false alarms on his blog. The response was not imaginary: More than 30 cellphone users reported that they, too, experienced phantom vibrations.

"I ended up hearing from a lot of people who said, 'Hey, the exact same thing happens to me,' " Garrity says. "And it was somewhat comforting, because it made me think I wasn't insane, after all."

Some who experienced recurring phantom vibrations wondered whether the phenomenon had physical roots: Was it caused by nerve damage or muscle memory?

But experts say the false alarms simply demonstrate how easily habits are developed.

Psychologically, the key to deciphering phantom vibrations is "hypothesis-guided search," a theory that describes the selective monitoring of physical sensations, says Jeffrey Janata, director of the behavioral medicine program at University Hospitals in Cleveland. It suggests that when cellphone users are alert to vibrations, they are likely to experience sporadic false alarms, he says.

"You come armed with this template that leads you to be attentive to sensations that represent a cellphone vibrating," Janata says. "And it leads you to over-incorporate non-vibratory sensations and attribute them to the idea that you're receiving a phone call."

Alejandro Lleras, a sensation and perception professor at the University of Illinois at Urbana-Champaign, adds that learning to detect rings and vibrations is part of a perceptual learning process.

"When we learn to respond to a cellphone, we're setting perceptual filters so that we can pick out that (ring or vibration), even under noisy conditions," Lleras says. "As the filter is created, it is imperfect, and false alarms will occur. Random noise is interpreted as a real signal, when in fact, it isn't."

Phantom cellphone vibrations also can be explained by neuroplasticity — the brain's ability to form new connections in response to changes in the environment.

When cellphone users regularly experience sensations, such as vibrating, their brains become wired to those sensations, Janata says.

"Neurological connections that have been used or formed by the sensation of vibrating are easily activated," he says. "They're over-solidified, and similar sensations are incorporated into that template. They become a habit of the brain."

Cellphone company spokesmen, meanwhile, say they are not aware of any consumer complaints about phantom vibrations. Cellphones cannot sporadically vibrate on their own, says Mark Siegel of AT&T, formerly Cingular Wireless.

"Perhaps in the mind of the cellphone user only," he says.

But Rob Whitehouse, vice president of communications at University Hospitals, insists the phantom vibrations he experiences each day are simply proof of how important constant communication is.

"It's some psychological expression of my need to always be connected," he says. "It's like when e-mail first came out, and we constantly checked our inboxes, because getting a new message was so exciting.

"I like that better than 'I'm crazy,' anyway."