“My guest tonight wrote a book about how the Internet is making us dumb,” said Stephen Colbert when he introduced author Nicholas Carr on “The Colbert Report” recently. “I certainly hope his book isn’t more than 140 characters long.”

At more than 200 pages, “The Shallows: What the Internet Is Doing to our Brains” ($26.95, W.W. Norton) isn’t exactly a Twitter message. It’s an intriguing look at the impact the Web may be having not only on how we read, but how we think.

Carr’s book is an expansion of his 2008 “Is Google Making Us Stupid?” article for the Atlantic. In the first chapter, he describes his impressions of how the Internet has changed him.

“Whether I’m online or not, my mind now expects to take in information the way the Net distributes it: in a swiftly moving stream of particles. Once I was a scuba diver in the sea of words. Now I zip along the surface like a guy on a Jet Ski,” he writes.

Referring to recent scientific studies and the history of everything from the alphabet to the printed word, Carr explores the differences between the sort of distraction-free reading you can have with a book and the typical experience of online reading, where frequent interruptions are part of the process.

He compares the intellectual environment of the Internet — with its hyperlinks, videos, e-mail alerts and so on — to trying to read a book while you do a crossword puzzle.

Of course, multitasking is nothing new for baby boomers and Gen Xers, who’ve been attempting to read and watch TV at the same time for decades now. But Carr thinks the Web bombards us with more distractions than we’ve ever had to deal with before.

Carr’s book doesn’t ignore the value of the Web. But his argument might encourage readers to think about how they use the technology and consider the importance of reading the old-fashioned way — where the words are on paper instead of a screen.

“I think there needs to be balance and there needs to be a realization that you shouldn’t be spending all your time online and you shouldn’t be getting texts every five minutes and sending texts every five minutes, because you’ll never experience more attentive ways of thinking,” he says in a phone interview.

Has anyone else been feeling online fatigue? I’m sure there’ll be a blog item about it soon. I better check my e-mail.