Still, Gallagher deserves credit for calling our attention to attention itself, specifically to the way it works neurologically. In essence, attention is the faculty by which the mind selects and then zeroes in on the most “salient” aspect of any situation. The problem is that the brain is not a unified whole, but a collection of “systems” that often come into conflict with each other. When that happens, the more primitive, stimulus-driven, unconscious systems (the “reactive” and “behavioral” components of our brains) will usually override the consciously controlled “reflective” mind.

There are excellent reasons for this. In the conditions under which humanity evolved, threats had the greatest salience; individuals who spotted and eluded dangers before they went chasing after rewards tended to live long enough to pass on their traits to future generations. As a result, we inherited from our distant ancestors the tendency to pay greater attention to the unpleasant and troublesome elements of our surroundings, even when those elements have evolved from real menaces, like a crocodile in the reeds, to largely insignificant ones like nasty anonymous postings in a Web discussion.

Likewise, our interest is grabbed by movement, bright colors, loud noises and novelty — all qualities associated with potential meals or threats in a natural setting; we are hard-wired to like the shiny. The attention we bring to bear on less exciting objects and activities, where the payoff may be long-term rather than immediate, requires a conscious choice. This is the kind of attention that opens into complex, nuanced and creative thought, but it tends to get swamped by the more urgent demands of the reactive system unless we exert ourselves to overcome our instincts. The reflective system flourishes best when the environment is relatively free of bells and whistles screaming “Delicious fruit up here!” or “Large animal approaching over there!”

The conditions conducive to deep thought have become increasingly rare in our highly mediated lives. When the physical limitations on print and broadcast media kept the number of competitors for our attention relatively few, some candidates could afford to appeal to our reflective side. Now we live in an attention economy, where the most in-demand commodity is “eyeballs.” As more options crowd the menu, direct appeals to the reactive mind in the form of bright colors or allusions to sex, aggression, tasty foods and so on, take over.

The machinations of late capitalism aren’t the only things driving the incessant pinging on our reactive attention systems, either. If you’re like most people, you will keep checking for new e-mail despite the unresolved messages that await in your inbox. The already-read messages may even deal with urgent matters like an impatient question from your boss or appealing subjects like possible vacation rentals, yet there’s something lackluster about them compared to what might be wending its way to you over the Internet right this minute. Despite the fact that the incoming messages are probably not any more compelling than the ones you’ve already received, they’re more attention-grabbing simply by virtue of being new. When Carr complains of the compulsion to skim and move on that possesses readers of online media, a major culprit is this instinct-driven craving for the novelties that lurk a mere mouse-click away.

The fact that sensationalism sells is hardly news, but less well-known is the fact that a constant diet of reactive-system stimuli has the potential to alter our very brains. The plasticity of the brain, scientists concur, is much greater than was once thought. New brain-imaging technologies have demonstrated that people consistently called upon to use one aspect of their mental toolbox — the famously well-oriented London cabbies, for example — show enhanced blood flow to and development of those parts of the brain devoted to, say, spatial cognition. In “The Overflowing Brain: Information Overload and the Limits of Working Memory,” Torkel Klingberg, a Swedish professor of cognitive neuroscience, argues that careful management and training of our working memory (which deals with immediate tasks and the information pertaining to them) can increase its capacity — that your data-crammed noggin can essentially build itself an annex.

But while it’s one thing to accommodate more information, it’s another to engage with it fundamentally, in a way that allows us to perceive underlying patterns and to take concepts apart so that we can put them back together in new and constructive ways. The early human who was constantly fending off leopards or plucking low-hanging mangoes never got around to figuring out how to build a house. Because leopards and mangoes were for the most part relatively few and far between, most of our ancestors found it easier to summon the kind of attention conducive to completing projects that, in the long term, make life measurably better. Ironically, while immediate threats and fleeting treats are comparatively much rarer in our complex social world, the attention system designed to deal with them has been kept on perpetual alert by both design and happenstance.

As long as we remain only dimly aware of the dueling attention systems within us, the reactive will continue to win out over the reflective. We’ll focus on discussion-board trolls, dancing refinancing ads, Hollywood gossip and tweets rather than on that enlightening but lengthy article about the economy or the novel or film that has the potential to ravish our souls. Tracking the shiny is so much easier than digging for gold! Over time, our brains will adapt themselves to these activities and find it more and more difficult to switch gears. Gallagher’s exhortations to scrutinize and redirect our attention could not be more timely, but actually accomplishing such a feat increasingly feels beyond our control. I can’t speak personally to the effectiveness of meditation, Gallagher’s recommended remedy for chronic distraction, but the effectiveness of meditative practices (religious or secular) in reshaping the brain have also been abundantly demonstrated.

Knee-jerk Internet boosters like to argue that the old ways of thinking are both obsolete and less wondrous than fuddy-duddies make them out to be. The next generation of citizens, they insist, will happily inhabit a culture composed of millions of small, spinning, sparkly bits and, what’s more, they will thrive in it. Tell that to the kids who spent all weekend holed up with the last Harry Potter book. As exhausting as it can be to fight off the siren call of the reactive attention system, some part of us will always yearn to be immersed, captivated and entranced by just one thing, to the point that the world and all its dancing diversions grows dim, fades and falls away.