- selective exposure: This is the idea that people seek out and consume information that pleases them, avoiding data that contradicts our own beliefs while simultaneously surrounding ourselves with voices that reinforce our beliefs. (The increased number of specialized news channels made available by the proliferation of cable news, talk radio, and blogs has made it easier for people to indulge this behavior by simply ignoring the channels they don't like.)
- selective perception: Individuals interpret documentary evidence through the lens of their own previously held beliefs, such that two people with opposing ideologies watching the same newscast dealing with a topic connected to those ideologies will not merely interpret what that newscast says differently, they will literally see and hear the news different, selectively editing their perceptions on an unconscious level to match their prior views. (This is most easily seen with sporting events but also occurs commonly with film footage of events like riots or wars.)
- peripheral processing: In a world in which individuals are bombarded with more and more information every day, often involving complex concepts and/or data, people come to rely to a greater degree on the advice and opinions of experts rather than taking the time and energy to learn about topics directly. This is a problem because we don't know how to properly categorize who is an expert and who is not and are often fooled by false or inflated claims to specialized knowledge of a field because we buy into fancy titles or incorrectly assume that expertise in one area of study translates equally into mastery of even vaguely related areas. (Such as assuming that anyone with a math background can correctly analyze polling data without any special knowledge of politics or regional voting trends.)
- hostile media phenomenon: Both liberals and conservatives perceive a bias in the news against their own point of view because they focus on the arguments and facts presented in the news that are hostile to their perspective. They remember them more strongly afterward and so are left with the impression of bias. (The classic example being people watching a political debate. Each person is likely to report that their candidate won the debate, but if asked will say that anyone watching the news coverage of the debate will think that their candidate lost due to the biased presentation of the debate by the news.)
- video news releases: Companies produce a lot of faux-news reports, presented to look like actual news programming, and give them away for free to local television news stations. Strapped for cash and stories to fill their time slots, these stations often run these news programs without proper attribution, so the viewer has no idea that the product placements in the news stories are all forms of advertising.
- particularized trust: As opposed to generalized trust, which describes the degree to which people are trusting of strangers, particularized trust deals with how we view people who we think are just like us.
In a sense, he's saying that instead of the Internet and other means of digital communication producing networks that connect people, these technologies have made it possible for many segments of society to exist in worlds that are parallel to each other, intersecting rarely if at all.
It's not a particularly happy book to read, but it is well-written and provides a lot of food for thought.