While "The Shallows" does contain significant chunks of the Atlantic essay, this isn't one of those all-too-familiar annoyances, the book that should have remained an article. In the brief period between the writing of the original piece and the publication of "The Shallows,"
neuroscientists have performed and reviewed important studies on the effects of multitasking, hyperlinks, multimedia and other information-age innovations on human brain function, all of which add empirical heft to Carr's arguments.
The results are not cheering, and the two chapters in which Carr details them are, to my mind, the book's payload. This evidence --
that even the microseconds of decision-making attention demanded by hyperlinks saps cognitive power from the reading process, that multiple sensory inputs severely degrade memory retention, that overloading the limited capacity of our short-term memory hampers our ability to lay down long-term memories -- is enough to make you want to run right out and buy Internet-blocking software.
Above all, Carr points to the past 20-some years of neurological research indicating that the human brain is, in the words of one scientific pioneer, "massively plastic" -- that is, much like our muscles, it can be substantially changed and developed by what we do with it. In a study that is quickly becoming as popular a touchstone as the Milgram experiment, the brains of London cab drivers were discovered to be much larger in the posterior hippocampus (the part of the brain devoted to spatial representations of one's surroundings) than was the case with a control group. These masses of neurons are the physiological manifestation of "the Knowledge," the cabbies' legendary mastery of the city's geography. The drivers' anterior hippocampus, which manages certain memory tasks, is correspondingly smaller. There's only so much space inside a skull, after all.
References to the cabbie study don't often mention this evidence that cognitive development may be a zero-sum game. The more of your brain you allocate to browsing, skimming, surfing and the incessant, low-grade decision-making characteristic of using the Web, the more puny and flaccid become the sectors devoted to "deep" thought. Furthermore, as Carr recently explained in a talk at the Los Angeles Times Festival of Books, distractibility is part of our genetic inheritance, a survival trait in the wild: "It's hard for us to pay attention," he said. "It goes against the native orientation of our minds."
Concentrated, linear thought doesn't come naturally to us, and the Web, with its countless spinning, dancing, blinking, multicolored and goodie-filled margins, tempts us away from it. (E-mail, that constant influx of the social acknowledgment craved by our monkey brains, may pose an even more potent diversion.) "It's possible to think deeply while surfing the Net," Carr writes, "but that's not the type of thinking the technology encourages or rewards." Instead, it tends to transform us into "lab rats constantly pressing levers to get tiny pellets of social or intellectual nourishment."