Thursday, March 3, 2011

Reading machine. Especially about PVT studies.

Been reading a lot of papers. Here is a thing I'd be interested to know: academic folks, when reading academic papers, how fast do you read them? I've done 4 so far today, total of about 55 pages, but there are days I've knocked out 8. I guess it all depends on the paper: some of these are easy reading because they're grounded in reality and not mathy. Probably also depends on how well you need to know it: some papers I skim because I think I won't be able to use it for much, but I just want to get the general idea.

Anyway! What am I reading about? Mostly still "how to tell how awake or sleepy you are." The PVT (Psychomotor Vigilance Test) has caught my attention. It's pretty simple: when you see a signal, press a button. The signal happens randomly every 2-10 seconds for 20 minutes. This tells some measure of "how sleepy" you are.

Here's a long book chapter about it. In short:

- it's easy to learn (after 1-3 trials, you're as good at it as you'll ever be, so no need to worry about learning effects) and easy to do
- it gets a lot of data
- it's reliable within each person
- it reflects some real brain function loss

Why it's interesting to me:
- nowadays, with smart phones, it could potentially be used by an average person to test his/her wakefulness at any time. Indeed, it has been implemented on Palm devices in 2005, and is being implemented at Intel on Android (I'm assuming. Search for "PVT" in that doc. Those look like Nexuses One, no?)
- it measures attention. (for some value of "attention"... hope I'm not totally squashing together meanings of "attention" here.) This sounds like a link between sleep and attention. Because (as I like to say) your attention is your life, that means more sleep = more attention = more life.

Other things:
- self-reported sleepiness has 2 or 3 parts: how tired you feel, and how likely you are to fall asleep. (kinda interesting correlations there: women and young people feel more tired, men and old people are more likely to fall asleep.)
- instead of the SSS, you could try this 13-item "VAS-F" visual self-reported sleepiness test. They showed that it correlates with the SSS and parts of the POMS (mood test), but I didn't see any reason to use it over the SSS, besides hand-wavey "one-item tests are unreliable" arguments. Interestingly, though, they too split this into two parts: fatigue and vigor.

A conclusion that's brewing in my head:
There are roughly 2 things to measure: let's call them the "sleep drive" and the "wake drive". They're different. When I say "how tired are you?" that's a measure of your wake drive. (It's pretty easy to manipulate that one: drink coffee or get surprised. Or get bored.) Your sleep drive is homeostatic and circadian: sleepdrive = time you've been awake * N + sin(time of day). When you try to fall asleep, that's a measure of your sleep drive minus your wake drive. And your wake drive becomes more erratic: now it's on, now it's off.

Just conjecture for now, but it fits pretty nicely with all of these studies. If it's true at all, though, where does that leave us? Can we measure sleep drive AND wake drive quickly on your cell phone? OR: can we assume sleep drive grows according to time of day (and how long you've been awake) and just measure wake drive? Hmm...

EDIT: check it out shut up, here is the coolest PVT paper! Meditation improves your PVT times. Whoa. Not expecting that. Also, experienced meditators in India can sleep a lot less.

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