Has any real, scientific research done on the subject? Specifically, do cats instinctively understand where people are paying attention to, like dogs instinctively understand when people point? Or, is it simply behavioral conditioning, as they learn that sitting on open books gets them attention?
Or are books just that comfy?
There have been studies that prove that cats are really bad at figuring out what pointing means, and that they aren’t so hot at gaze-tracking either. (Dogs on the other hand are really quite good at it. Better than kids sometimes.)
That said, it doesn’t take a mental genius to put together the following two observations:
that your person is not paying attention to you.
your person is instead paying rapt attention to something that crinkles at regular intervals.
Therefore, obvious solution is to put self on crinkly thing - you now are on top of a crinkly thing (good thing 1) AND your person is paying attention to the space you are in - therefore paying attention to you (good thing 2).
Also, in my experience, cats want to sit on anything that’s not just the ground itself. If I have a book in the middle of an empty room with nobody paying attention to the book, my cats will gravitate towards sitting on the book.
So, I think it’s a combination of (a) it’s a book and (b) it’s what you’re looking at.
I find that cats just really like paper and cardboard and will always try to sit or lay on it. I think it reminds them of leaves, which when they rustle means there’s something to eat under there. So a little bit of the motivation is an instinct to sit and wait for prey to show up. Plus, they don’t know we’re reading. As far as they know, we’re doing the equivalent to them staring at the wall at nothing.
My cat just wants to be part of everything. Like when I get a package delivered and I’m trying to cut it open, she’ll come over and stick her head right where the scissors are. One day I’m going to accidentally snip a whisker off and she’ll have no one to blame but herself.
I’ve noticed, though, that she doesn’t care when we’re reading books; it’s only if we have a newspaper on the floor that she’ll come and sit on it.
The comic strip “Rhymes With Orange” addressed this issue. One cat said, “The newsprint takes me back to the box of my birth.”
Paper and cardboard are insulators, meaning, they’ll be warmer ‘to the touch’ than tile floor.
Although, if your position reading is seated, I can’t imagine a cat choosing the book you’re reading rather than the warmth of your lap.
They like warm things. A lot.
Most dogs I have known, when you point, look at the end of your finger.
That’s been my experience as well. One sock lying on the entire floor will likely have a cat lying on it.
My guess as to the cat psychology is also that they want attention, so they go put themselves where you’re looking. As has been mentioned, if that’s a laptop computer, even better, since it is also warm. 
Or maybe they have to get close to hear you because you’re whispering to them all the goddamned time. Speak up, dammit! 
(+1 to all the posts here, I’ve noticed the same things)
Has anyone here read “How to tell if your cat is plotting to kill you”, written by the guy who does “The Oatmeal” comic strip? My favorite panel is in the section where the car is trying to get his owner to pet him, and he brings out an easel that says:
But if they aren’t completely obtuse, they can be trained otherwise. I got my black lab to find hidden treats by pointing to where they were located.
I’ve heard of two stroke engines, but…
Hey, when my cat purrs, I describe it as “her motor is running”.
That’s how cats read.
Seconding the “it’s not floor, it’s crinkly, and it gets attention” answers (see also: “if it fits, I sits”). It’s especially funny to see my feline overlords trying to sit on a tiny square of paper and curling their tail around themselves so that none of their body parts are on the floor (which must be made of lava in their little kitty minds or something).
As no less an authority than Mike Rowe has pointed out, cats love that crinkling sound.
And, as many in this thread have observed, to a cat, the best place to sit is on a thing that is on top of another thing.
Beat me to it.
Yes, they have tiny light receptors in their anuses. And they’re very near-sighted. And if they’re sitting on something with texture, they use feline braille.
Yep. Whenever I come home from the grocery store, I’ll set the bags down on the kitchen floor; the cats are there in short order to inspect the new inventory.
Also, my cats don’t care for people food but that doesn’t stop them from sniffing around my plate every damn time I sit down to eat. I guess they fancy themselves food inspectors too.
I think our cat just likes to be the center of attention, so if we are looking at something, that’s where she goes. A few weeks ago, my dad was helping my husband with something around the house. They were bending over a spot on the wall where they were taking a measurement, so the cat walked over and stood right in that exact spot. 
She doesn’t usually hang around us at meal times because we eat at the countertop in our kitchen, and I think she just can’t be bothered to jump up and look. But for Valentine’s Day I made a nice dinner and wanted to eat in the dining room. So we are sitting down eating filet mignon, and suddenly she jumps on one of the chairs. This cat is normally fairly expressionless - she always seems to have the same look on her face all the time. But suddenly, when there was tasty food involved, she somehow got her eyes to look twice as big. So during the meal, we’re sitting there looking at this.
