Just joining the chorus of "me toos"... Didn't think it was that prevalent, I wonder where the instinct comes from? Anyone have any fun pseudo-scientific theories?
I think it's just that highlighting is neat. Some portion of my brain is pleased by the flashing/changing colors (different than a flashing ad, etc., since I'm controlling the action).
Maybe it's the equivalent of sliding your finger under the line of text you are reading? Like they teach small kids in school.
That is a nice theory, but I don't do that when reading. Why would I highlight on screen, but not use a ruler edge when reading?
What if it's not to help follow the line for reading, but to "feel" the page as you read it? A proxy for dealing with immaterial bits on a screen instead of holding and feeling the paper of a book or magazine? Showing you have some sort of control over it.