Thursday, February 24, 2011

Measuring how awake you are

It'd be nice if you could have an instant thermometer for "awakeness". Then you could just "take your temperature" a few times a day, average them out, and say "I was 83 awake today" or "I've been only 34 awake for the past week; I ought to sleep more."

One measure we can use is self-report: how awake do you feel? This is nice for people who want to feel more awake. It's not necessarily awesome if you're trying to gauge whether a truck driver should be driving. I'd like to get an objective, as well as a subjective, component to awakeness measurement. So let's see what other people have used to measure awakeness.

First, we should define awakeness. This is surprisingly difficult. It looks like there's subjective feeling of tiredness, sleep propensity (how likely you are to fall asleep), and reaction time, and these three measures are not the same. One paper hypothesizes that there's a "sleep drive" and a "wake drive", and how sleepy you feel is some function of the two. For example, if you haven't slept in a while, but you are excited about something, your sleep drive and wake drive might both be very high. You could be very tired and very awake. (I like this hypothesis; it's kind of like how happy and sad moods are not opposites; you could feel both.)

So I guess I will wave hands a little bit and just point out some things other people have used to measure sleepiness:

Things you can do in a lab:

Multiple Sleep Latency Test (MSLT). You go to a lab and try to nap every 2 hours. They measure how long it takes for you to fall asleep. Normally takes about 7 hours. Here's a big paper (Carskadon and Dement, 1987) about how the MSLT has been used in many studies. I... think it might be a bit impractical for anything I want to do. (I'd add a smiley but this is a serious research blog)
Maintenance of Wakefulness Test (MWT). Same as the MSLT except you have to stay awake instead of fall asleep. Also not really relevant to me.

OSLER test- like a shorter, easier MWT, with less human intervention; you have to hit a button every time a light flashes; when you miss for 21 seconds, it knows you're asleep. Apparently it works pretty well.

- Sleep-Wake Activity Inventory (SWAI). Questionnaire, 59 items, takes about 15 minutes, provides 6 subscores: Excessive Daytime Sleepiness, Nocturnal Sleep, Ability to Relax, Energy Level, Social Desirability, and Psychic Distress.
- Epworth Sleepiness Scale (ESS). Questionnaire, 8 items, only a few minutes, asks you to rate how likely you are to fall asleep in a few situations. Probably good for a pre-screening to tell if people have sleep disorders, as shown by this study; it accurately differentiates normal people from people with narcolepsy, sleep apnea, hypersomnia, or PLMD, and almost idiopathic insomnia. (not snoring, though.) They draw a distinction between sleep propensity (how likely you are to fall asleep) and how tired you feel.
- Stanford Sleepiness Scale (SSS). One question, 7 options. Now this is more like it! (here's the paper if I want it later.)
- Karolinska Sleepiness Scale (KSS). One question, 10 options. These are both basically "how awake are you?" and yet, they correlate well with EEG data.

- Psychomotor Vigilance Task (PVT)- give people an electronic reaction time test. Here's a study that tried to use PVT to replace driving simulators to tell when you're too tired to drive. They found that they measured fatigue pretty well, but they didn't correlate well enough with the driving simulators to replace them. I am interested in this. Perhaps it could be pretty quick.

TODO still: investigate the Optalert device, pupillometry (although not investigate too hard because it involves measuring pupils, so probably not an at-home task)

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