The first two sections of Nicholas Carr's The Shallows can be summed up with the following two major ideas:
1. The content of the Internet cannot be separated from the medium of the Internet, in true McLuhan fashion; and
2. The Internet (and computers generally) exerts influences upon its users which affect how our minds work.
In particular, I found the following sentences poignant: "The computer, I began to sense, was more than just a simple tool that did what you told it to do. It was a machine that, in subtle but unmistakable ways, exerted an influence over you. The more I used it, the more it altered the way I worked. ... In using the word procesor, I had become something of a word processor myself" (p. 13).
Carr refers to the pre-computer mind of the Rennaissance and the Enlightenment as linear, contrasted with the disjointed mind of the Internet, and explains that as our minds change through computer interaction, we have a harder time performing traditional, linear tasks (like reading a book, etc.) and that there are mind-altering consequences that come from using the Internet.
I'm not sure, however, that 'linear' vs. 'disjointed' is the best way of describing this difference between the minds of pre-Internet and Internet users. One useful way of thinking about this concept might be to remember the old adage that 'to a hammer, everything looks like a nail.' In using computers and the Internet, we begin to see data and information in the way that computers do: decontextualized, sporadic, lacking cohesion, truthless, manipulable, etc. And, as a result, we begin to see information in the same way that computers do and have difficulty thinking in ways that a computer cannot.
Thus, the difference between the pre-Internet mind and the Internet mind might have less to do with linear vs. disjointed, because a computer can think linearly, and have more to do with a computer's inability to contextualize information in a way that makes sense to native human