Sleep

Disruptions of sleep due to external stimuli

The ideal environment for sleep is a dark and quiet place. But in most situations, the sleep environment is not perfect. There may be lights coming from the street, from electronic devices, etc. One may live with someone that makes noise, alarms going off, sound from the street, etc. This acoustic perturbations can have negative consequences for quality of sleep, causing tiredness, negative effects on mood, headaches and "nervous stomach" in sensitive individuals. [1]
The source of the noises can be difficult or impossible to eliminate, but there are simple solutions that can be applied in almost all situations.

Blocking light

Light is the easier to deal with than sound. The simplest solution is to use a headband covering your eyes. You can also put tape over the LEDs in electronic devices. Darker curtains tend to work better for blocking light.

Blocking sound

There are basically three possible approaches to this:

Passive noise supression

With this I mean the normal ear plugs you can get anywhere. They work well for blocking loud noises. This is the most simple and low tech solution.

Masking noises with white noise

This solution involves using white noise to mask other more disruptive noises. The theory behind this is that the when sleeping, sleep is only disrupted by the difference between peaks and background noise. Theres some evidence for that.[3]
But the problem is that white noise itself has negative effects on sleep. It increases light sleep and waking time and decreases deep and REM sleep. [2] So it isn't clear if using white noise to mask other non uniform noises is better than only hearing those noises. One thing is clear though: complete silence is better.
If you decide to use this, there are headbands that include comfortable headphones specifically designed for sleeping with them (even when sleeping on the side) and also block light.

Active noise control

This means using ANC headphones. that take the ambient noise and feed it to your ears with an inverted phase, thus canceling it. They should work in theory, but there aren't any earphones of this type specifically designed for sleep an thus you could only use them comfortably when sleeping on your back.

How to measure quality of sleep

The best method for measuring sleep quality, characteristics and disorders that exists is the polysomnography. That includes EEG, eye movement, EMG, ECG, breathing parameters, and a few others.
But that's hard or impossible to get for most people, and can't be used in daily life. The cheaper alternative is actigraphy, which is basically an accelerometer worn on the wrist of the non dominant arm that records movement. The actigraphy measures are highly correlated with those of the polysomnography, except for sleep onset delay[4] (actigraphy underestimates it, which makes sense because in the minutes when you are trying to sleep you generally don't move).
There are also EEG products for consumer use designed specifically to measuring sleep, like the Zeo.
Then you have apps which use the accelerometer in a smartphone placed close to the pillow to determine movement. They seem to work reasonably. [5]

Polyphasic sleep

Polyphasic sleep involves splitting total sleeping time in two (biphasic) or more parts (polyphasic). Basically everyone agrees that biphasic works. Opinions about Polyphasic are much more diverse.

Polyphasic Sleep: Facts and Myths
(counter arguments, anyone?)

Discussion on polyphasic sleep

Possibly useful papers

google scholar results for "polyphasic sleep" that may be relevant up to 4th page

  • Forty-eight days on the “Leonardo da Vinci” strategy for sleep reduction: Performance behaviour with three hours polyphasic sleep per day (no link)
  • Leonardo da Vinci's polyphasic ultrashort sleep: A strategy for sleep reduction? (no link)

Gen.lib links when searching "polyphasic" (apparently there are only 2 with that keyword)

other random papers

External links

Good sleep, good learning, good life: Interesting article by Piotr Wozniak (creator of Supermemo) about getting quality sleep time

Bibliography
1. Effects of night time road traffic noise—an overview of laboratory and field studies on noise dose and subjective noise sensitivity http://www.sciencedirect.com/science/article/pii/0022460X88903689
2. Modifications of sleep structure induced by increasing levels of acoustic perturbation in normal subjects http://www.sciencedirect.com/science/article/pii/001346949090055O
3. The influence of white noise on sleep in subjects exposed to ICU noise http://www.sciencedirect.com/science/article/pii/S1389945704002242
4. http://www.ncbi.nlm.nih.gov/pubmed/24179309 Measuring sleep: accuracy, sensitivity, and specificity of wrist actigraphy compared to polysomnography.
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