So, does it make any difference cognitively if people don't read?
I think it does. At least, as far as I can tell from what I've seen, there are noteworthy differences between the readers and non-readers as far as common arguing styles, comprehension and even emotive responses in the world outside the book.
Books train the reader to think in a specific way. They cause us to follow an extended argument over several pages, and often ask the reader to find implicit meaning. They train the reader to recognize various rhetorical styles, even in fiction. Often, they introduce the reader to nuance, ambiguity and various shades of meaning. They are not always easy, and often they require great patience. More importantly, they require the reader to "fill in" many spaces with their own cognition. Nobody has the same reading of a book. Book-reading is private and internal. It is quiet and patient. And, as such, it teaches these behaviors.
What I see quite often with my non-reading acquaintances and students are the following traits, which you'll notice are also very widespread:
1. Fairly shallow and emotive arguments. A statement like "George Bush doesn't care about black people" is, cognitively, very much of this era because it's more an emotive statement than a logical argument. It's hard to respond to in any way, whether you agree or disagree. As people's arguments become more shallow, they seem to become more angry or emotive because it's much harder to respond to "You hate America!" than it is to respond to an actual argument. When people complain about the "polarization" of our society, I wonder if communication mediums don't foster this.
2. An inability to understand other people's arguments. With some exaggeration, what I see happen quite often is something like this:
Mr. Brown: I believe that people who walk their dogs should have to have the dog on a leash at all times.
Mr. Green: So, you're saying that people should be forced to own dogs?!?!
The shocked outrage is also quite common. In general, when a person doesn't understand arguments in print, it seems to me that they're not terribly good at understanding them in oral form. (Although of course, books are an extension of the oral form anyway)
3. A sort of low-level floating hostility and inability to understand humor. I don't know if this is related to non-reading or something to do with the stress of living in a sped up world, but I see it most often in my non-reading acquaintances and very rarely in my frequently-reading colleagues.
4. What Bill Maher once said of Americans in general: They don't do nuance.
5. Flattening of affect.
6. Inability to see others as fully human.
7. And most noticably, a general lazy cynicism about the world as such. "People are all corrupt, the government is crooks, the opposite sex is heartless, work is miserable, and everyone is out to get theirs." Is this attitude related to reading? Maybe not. But, for me, books have taught me to pay attention to the world and to others- that there is more than just surfaces to the world around me. I've said before that life rewards close readings, and I think that books teach us this. Good books teach us to be mindful, just in order to read them, and they transform the way that we see the world, allowing us to see it for the first time in a new way. For many people I meet, there really is little more to the world aside from struggle and suffering. Life is something they carry. Books suggest that life doesn't have to be this way. Writers like Blake, or even someone like Henry Miller (corny though he is) force us to confront lives that are no better than our own, but lived more exuberantly. The sort of cynicism and malaise I see is widespread, but it is anything but learned cynicism.