In today's fast-paced, multitasking world, it's easy to get hooked on technology that's always online, delivering a steady stream of texts and tweets.

But some mental health experts fear that a growing technology addiction, perhaps accelerated by the popularity of smart phones and social networks, will lead to a breakdown of interpersonal relationships and an increase in attention deficit disorder.

"If our attention span constricts to the point where we can only take information in 140-character sentences, then that doesn't bode too well for our future," said Dr. Elias Aboujaoude, director of Stanford University's Impulse Control Disorders Clinic at Stanford University.

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"The more we become used to just sound bites and tweets," Aboujaoude said, "the less patient we will be with more complex, more meaningful information. And I do think we might lose the ability to analyze things with any depth and nuance. Like any skill, if you don't use it, you lose it."

Dr. John Ratey, an associate clinical professor of psychiatry at Harvard Medical School, uses the term "acquired attention deficit disorder" to describe the way technology is rewiring the modern brain.

He noted that reliance on even the simplest programs - such as a spell-checker in a word-processing program or a contact list that memorizes all your phone numbers for you - are short-circuiting the brain's ability to process details.

"My favorite example is when I type the word 'tomorrow,' " Ratey said. "I know spell-check will get it right. It would take 30 milliseconds for me to make sure in my mind. But we depend on that (spell-check). Even when we take the time to write, we don't have the patience to give that a consideration."

To be sure, the digital revolution has increased productivity and opened vast new worlds of information and discourse. Some mental health experts say there's still not enough research to determine whether heavy use of computers, the Internet or video games is an unhealthy condition by itself or merely a symptom of recognized problems such as depression.

'This little appendage'

But experts such as Ratey and Aboujaoude say they are already seeing cases that go beyond addiction to the Internet, especially with the growing popularity of portable devices that make it harder to walk away from technology.

The signs are everywhere - college students texting as their professors lecture, pedestrians crossing the street with their heads down checking messages on a BlackBerry, and BART riders reaching furtively into their pockets thinking their iPhone has vibrated - even if it hasn't.

One of the firms generating the biggest buzz in technology, Twitter, caters to short attention spans with its text messages of 140 characters or less. Another new San Francisco company called Particle recently started Robo.to, which offers video updates no longer than four seconds. Pop star Justin Timberlake is the lead investor.

"We are definitely an addicted society," said Dr. Kimberly Young, the founder and director of the Center for Internet Addiction Recovery of Bradford, Pa., and author of a series of books on Web addiction. "EBay goes down for a day, and everybody has a fit. It's like this little appendage that people have."

It even reaches into the bedroom. In a September survey, 36 percent of the people ages 35 and younger said they often used Facebook or Twitter after having sex. Men were twice as likely to tweet or post status updates after sex.

"It's the new cigarette," said Manish Rathi, co-founder of Retrevo.com, a Sunnyvale consumer electronics shopping site that commissioned the survey.

Separation anxiety

Software engineer Jeanine Swatton of Dublin said that when she goes to lunch or dinner with someone, she eats "fairly quickly" to get back to her computer and tends "to check my e-mail messages on my iPhone throughout the meal. Luckily, my friends understand."

Swatton, 37, believes her attention span has shortened.

"If I do not have access to a computer, I will check my iPhone or will have a glass of wine to reduce the anxiety of being away from a computer," she said.

Indeed, technology has elevated the ability to multitask to a higher level. But a study published in August by researchers at Stanford University's Communication Between Humans and Interactive Media Lab found multitaskers were more distracted by irrelevant details and didn't do as well as people who completed one job at a time.

Harvard's Ratey, author of the new book "Spark: The Revolutionary New Science of Exercise and the Brain," said he fears today's tech-savvy generation is evolving away from the "genetic roots" of humankind, which used to have time for deep contemplation about complex problems without "being bombarded from stimuli from the outside."

"It's a challenge for many kids just to sit silently for a few minutes without moving around, looking for some kind of stimulation," he said. "We need that ability to center ourselves."

"A bigger portion are not learning to be more resilient, and we're going to have a lot of kids who are just not used to the challenges of defeat," he said. "It's just part of society that we're multitasking all the time. We can't stop to think, and if we have to stop and consider something, we get frustrated."

Writing habits change

Aboujaoude, assistant director of the Stanford School of Medicine's Obsessive-Compulsive Disorder Clinic, said a few studies indicate a link between excessive Internet use and attention-deficit-hyperactivity disorder in children and some adults, which could impair academic performance and social development.

The Internet, though, is only part of "one big virtual addiction," he said.

"One reason that ADD is on the rise is that our attention span is similar to our attention span on Facebook," Aboujaoude said. "Look at language. People are writing the way that they text. Anything complex that takes several paragraphs to develop is information overload at this point.

"I think of it as regressive. I don't think of it as progressive. It's becoming so normalized in our culture, it becomes hard to catch while it's happening."