Did you ever wonder how media draw your attention, then sell it?

Six years ago, when I reviewed Tim Wu’s previous book, “The Master Switch,’’ I was given nearly 1,100 words in which to do it. This time, I get around 800.

This should tell you something about the shrinkage of the modern newspaper and also about our diminished ability to pay attention to the old-school written word. Who’s got time to read 1,100 of them? There are e-mails to check, Facebook notes to post, and YouTube videos to snicker over.

There’s never been a limit to the stuff we can choose to focus on and think about. But in the past couple of centuries people have made a science of cultivating and harvesting our attention like a Kansas farmer’s wheat crop.

Wu’s “Master Switch’’ showed how alliances and conflicts between corporations and government regulators played at least as great a role in the rise of modern telecommunications as the inventions of Bell or Edison. In his vigorous, entertaining new book, Wu describes how the rise of electronic media established human attention as perhaps the world’s most valuable commodity.

The process began, not with websites or radio waves, but with the printed word. It was the early newspaper publishers who first realized that the big money wasn’t to be made by selling information to readers but by selling readers’s attention to advertisers. The pioneering New York Sun cost readers next to nothing, but it made a fortune from the ads that ran alongside its stories.

The success of the Sun established a pattern for the media industries spawned by electronics. Radio pioneers, once they learned how to attract large audiences, packaged and sold the listeners’s attention to commercial sponsors. Television would follow, with video versions of programs invented for radio — the sitcom, the soap opera, live play-by-play sports broadcasts.

For a few decades, radio and TV networks created a new kind of audience. The most popular shows — “Amos ‘n’ Andy’’ for example, or “I Love Lucy’’ — would reliably attract a large percentage of the entire US population. A single commercial could reach tens of millions. It was an oceanic pool of human awareness that Wu calls “peak attention.”

Tyrants like Adolf Hitler could now inject poisonous ideas into millions of brains at a time. More benevolent broadcasters, like Britain’s BBC, delivered upscale dramas, music, and news programs in a bid to uplift the tastes and values of listeners.

American broadcasters, especially CBS founder William Paley, tried a blend of crowd-pleasing entertainment, high-end experimental dramas, and hard-hitting news shows. But the silliest and most trivial programs proved best at delivering audiences in bulk.

The empire of peak attention was washed away by a tsunami of innovation. Cable television allowed for hundreds of channels catering to specific tastes and interests; the Internet-connected personal computer made possible a groaning variety of distractions; and now our smartphones allow us to dig in anytime, anywhere.

The age of peak attention is now gone forever. The Super Bowl is about the only American media product that attracts a large percentage of the entire nation. Nearly everything else we read or view is aimed at smaller, profitable niches — news junkies, video-game buffs, gossip mavens, cat lovers. Wu reminds us how it all happened — the rise of reality TV and the cult of celebrity; the birth of the blogosphere; the astonishing success of Facebook, which went from a Harvard dorm room project to the world’s most powerful media company in about a decade.

These innovations demolished the old strategies of the attention merchants, who could no longer count on finding tens of millions of us at a handful of media watering holes. Now the brand managers and political propagandists hunt for us. The same digital technologies that ravaged their old business model has enabled them to track our tastes and interests with remarkable precision through our online activities, then pitch products at us. Armed with the tools of “big data” analysis, the advertisers now know each of us — where and how we live, what we like and dislike, and believe and desire.

Millions of us dread these intrusions. Wu claims to see signs of a backlash, but they’re very tenuous ones — a slight decline in cable TV subscribers, for instance, or hints that some of us regularly disconnect from the Internet and take a “digital Sabbath.”

Hardly the makings of a mass uprising. But as the attention merchants insert themselves into every vacant corner of our individual lives, our privacy and peace of mind will only be preserved by our individual choices. Wu’s new book is right about that, and about a great deal more.

THE ATTENTION MERCHANTS:

The Epic Scramble to Get Inside Our Heads

By Tim Wu

Knopf, 403 pp., $29.95