I've been reading a lot over the past few months, both online and in book form. Not unusual, but I've noticed that I retain a lot more from my online reading than from the offline. My recall of names, facts, circumstances, themes, and lessons from articles I've read online is excellent, but not so good when it comes to books. Part of it is that I approach book reading as a leisure activity and not as work or study, although I'm not sure the opposite is necessarily true for Web reading (partially perhaps, because I do use the web to brush up on design and programming issues -- work stuff). But the bigger reason for the difference is probably due to the nature of what the task of reading entails in those two media.
Books are self-contained. There are 332 pages in my copy of The Selfish Gene (incl. endnotes). There might be a bibliography, but unless you're in the library, reading up on any of the 200 or so references contained therein would prove challenging. Everything you get with a book is in between its front and back covers.**
With the web, you're always in the library. It's not always a proper library (some of the "reference" materials can be a little sketchy), but it's better than nothing. And the materials you want are very often hyperlinked right in the material you're reading for instant research gratification. Web reading is a deeper and more active type of reading. I can completely research a particularly interesting topic, jumping from site to site to Google to site and back to Google, hunting down exactly what my brain is jonsing for, and skim over the stuff I'm not so keen on. I'm not dependent on the author of the book to give me exactly what I want; I can "write" my own book of sorts, editing the subject matter as I see fit. It's this active reading -- researching really -- that I think is responsible for the much higher rate of retention with online reading.
** "Ha ha, not quite!" you're rightly saying to yourself. You've got your whole lifetime of experience and a healthy imagination to draw upon. Two covers my ass, books are as full as you want to make them. That's one of the drawbacks of reading on the web for me. My recall is excellent, but I typically don't stop to ponder like I do with books. There's always that next thing to click on or research. I don't have to work out for myself on which points Dawkins disagrees with Stephen J. Gould...I can just go and read for myself. I might recall more from web reading, but I think I get more from books. (Although, online research while reading a book is a very potent combination...if you remember to ponder before scurrying off to the web for easy answers.)
See also:
The internet is shit (seemingly arguing for libraries instead of the internet...like we should have either one or the other, but not both or the universe will explode)
The Lure of Data: Is It Addictive? (NY Times)
Faster: The Acceleration of Just About Everything (James Gleick)
Project Gutenberg (reading books on the web)
Report: Online Training 'Boring' (Wired News, "Studies have shown that onscreen reading retention is 30 percent lower than with printed material.")
Digital Divide (pbs.org)
As We May Think (Vannevar Bush, Atlantic Monthly)
Oh, and that "The internet is shit" thing... well, that's dumb. Both are useful for many different uses.
I've learned a lot from the internet, but it's mostly facts, not ideas, and that's an important distinction.
As for the basic paper versus pixels thing, the one thing that nags me about reading online is the tendency to distraction. With a book, sure, I'll occasionally get up to hit the encyclopedia, a dictionary, some other work for reference, but it's otherwise pretty straight going. The web, on the other hand, is a multimedia Times Square, and all that hypertextual neon can really blur your vision.
That's just the economics of books, etc., at work, but I can't read Phillips himself or know anything beyond reportage -- a.k.a., his ideas -- without reading the books themselves. It's alos just because books are really long and complex things take a long while to communicate. The big exception to this are 'journals,' like Foreign Affairs, which are online and filled with idea-laden articles. Mmmmm.
I definitely prefer news online, however.
But when it is time to read that pile of 800-page monographs, well, who wants to do that onscreen anyway?! You'd need to keep an ophthalmologist on call.
The Internet is generally a two-way, discussion-oriented communications structure. Books are one-way lectures tossed at you in an authoritative manner. Neither is inherently bad. Neither is great, either; you have to work up a reputation system on both to figure out who to believe and who to ignore.
The web is great for lite research and learning more about personal interests and news-y topics, it's bad for doing thorough research that needs to stand up to scrutiny unless you are in one of a small subset of fields. More online databases, available with library cards or at an academic library, are narrowing this gap, but people being unable to use them effectively muddles this issue. It's sad to see peopel in the library with Lexis-Nexis or fulltext New York Times databases come to the reference desk and say "there's nothing available about my topic"
My tendency is to read the book and then learn more about the topic in the particular areas that interest me online. Sort of like how I watch a movie [this week, The Messenger] and then go learn more by heading to the library to read a proper book on the subject.
Plus, as much as everyone seems to think the contrary, it's tougher than you'd think to find a true range of opposing viewpoints online, especially for older political topics. A lot of radical and fringe-y political information and discussion are still only available in paper form. This is largely an issue of money: it's less likely to be online if you can't attach a "buy me" or "fund my digitzing project" label onto it.
The book is also a slow medium. By the time a person buys, borrows or finds another book that has the answer to a question, he or she also has had the time to think about it more thoroughly and perhaps even refine the question. The time spent in thought will in many instances enable a person to generate an answer to the question that aroused his or her curiosity in the first place.
I usually print out things to read if I need to ponder from site like this one:
http://www.soilandhealth.org/
Cheers,
Avi
ebook readers are rather blah now, but in 5 or 10 years they may really change how with think about a book, the new ebooks may be just as usuable as print, and be able to hold an entire library. maybe...
This thread is closed to new comments. Thanks to everyone who responded.

