How Zeo scores short term awakenings

Jay Aitchsee · Post by **Jay Aitchsee** » Wed Oct 17, 2012 6:36 am

This question comes up a lot. Usually in the form of, " I looked at my Zeo and it said I was asleep. What gives?" So, here is what the Zeo folks say:

http://blog.myzeo.com/how-does-zeo-scor ... utes-long/

During sleep, the brain transitions from state to state rather quickly; so quickly in fact that in a sleep lab, they score little awakenings (micro-arousals) lasting only three seconds! Since we wanted to give you an overview of your whole night, we stuck to scoring sleep every 30 seconds.
Here’s how it works:
1. Zeo calculates a sleep phase every two seconds.
2. Those two second answers are averaged to create a more stable answer every thirty seconds. However, this interval still has a lot of phase transitions, so…
3. Zeo uses information from the surrounding minutes to make the call for that new, thirty second interval.
4. Now Zeo has to decide what to tell you at the bedside, which displays five minute intervals. The thirty second intervals vote and the winner take all.
Of course, there are exceptions to these rules; for example, if one of the intervals was Wake, it trumps the rest.
Now, to answer this question more specifically, it really all depends on the signal quality and brain activity at that given time. In addition to larger brain activity,we also have to deal with noisy bits of signal, such as disturbances due to movement, micro-arousal, and other things.
If we assume a perfect on/off signal for wake, we would get something like this, with each letter representing a 30 second period of sleep:
Your Brain : SSSSSSSSWWWSSSSSSSSSS
Zeo Reports: SSSSSSSSSSWWWSSSSSSSS
But a 30 second wake period would get completely smoothed over.
Your Brain : SSSSSSSSWSSSSSSSSSSSS
Zeo Reports: SSSSSSSSSSSSSSSSSSSSS
In reality, of course, sleep is a bit more complicated.
When we consider a situation more true to life–where the line between sleep and wake is fuzzy–that same 1.5 minute as represented by Zeo looks more like the example below. Note that “U” is for unknown, when there is too much artifact or disturbance to report on that period.
Your Brain : SSSSSSSSWWWSSSSSSSSSS
Zeo Actually Sees: SSSSSSUUWSUWWSSSSSSSS
Zeo Reports : SSSSSSSSSSSSSSSSSSSSS
As you can see, both sleep and sleep scoring is more nuanced. Depending on the exact situation, a 1.5 minute awakening could be reported perfectly, strangely (a bit of Wake here and there in the 30 second sleep graph), or not at all. As such, the rule of thumb is that it generally takes two minutes of Wake to be noticed, though we may sometimes report awakenings that are a bit shorter than 2 minutes.