It is here that he starts to run into problems. There is little doubt that the Internet is changing our brain. Everything changes our brain. What Carr neglects to mention, however, is that the preponderance of scientific evidence suggests that the Internet and related technologies are actually good for the mind. For instance, a comprehensive 2009 review of studies published on the cognitive effects of video games found that gaming led to significant improvements in performance on various cognitive tasks, from visual perception to sustained attention. This surprising result led the scientists to propose that even simple computer games like Tetris can lead to “marked increases in the speed of information processing.” One particularly influential study, published in Nature in 2003, demonstrated that after just 10 days of playing Medal of Honor, a violent first-person shooter game, subjects showed dramatic increases in ­visual attention and memory.

Carr’s argument also breaks down when it comes to idle Web surfing. A 2009 study by neuroscientists at the University of California, Los Angeles, found that performing Google searches led to increased activity in the dorsolateral prefrontal cortex, at least when compared with reading a “book-like text.” Interestingly, this brain area underlies the precise talents, like selective attention and deliberate analysis, that Carr says have vanished in the age of the Internet. Google, in other words, isn’t making us stupid — it’s exercising the very mental muscles that make us smarter.

This doesn’t mean that the rise of the Internet won’t lead to loss of important mental talents; every technology comes with trade-offs. Look, for instance, at literacy itself: when children learn to decode letters, they usurp large chunks of the visual cortex previously devoted to object recognition. The end result is that literate humans are less able to “read” the details of the natural world.

While Carr tries to ground his argument in the details of modern neuroscience, his most powerful points have nothing do with our plastic cortex. Instead, “The Shallows” is most successful when Carr sticks to cultural criticism, as he documents the losses that accompany the arrival of new technologies. The rise of the written text led to the decline of oral poetry; the invention of movable type wiped out the market for illuminated manuscripts; the television show obliterated the radio play (if hardly radio itself). Similarly, numerous surveys suggest that the Internet has diminished our interest in reading books. Carr quotes Wallace Stevens’s poem “The House Was Quiet and the World Was Calm,” in which stillness allows the reader to “become a book.” The incessant noise of the Internet, Carr concludes, has turned the difficult text into an obsolete relic.

Or maybe even these worries are mistaken; it can be hard to predict the future through the haze of nostalgia. In 1916, T. S. Eliot wrote to a friend about his recent experiments with composing poetry on the typewriter. The machine “makes for lucidity,” he said, “but I am not sure that it encourages subtlety.” A few years later, Eliot presented Ezra Pound with a first draft of “The Waste Land.” Some of it had been composed on the typewriter.