mi·cro·sleep
[mahy-kroh-sleep] noun Psychology .
a moment of
sleep followed by disorientation, experienced especially by persons suffering from narcolepsy or
sleep deprivation.
(From Wikipedia.org) A microsleep is an episode of
sleep which may last for a fraction of a second or up to thirty seconds.
[1] Often, it is the result of
sleep deprivation, mental
fatigue, depression,
sleep apnea,
hypoxia,
narcolepsy, or
idiopathic hypersomnia. For the sleep-deprived, microsleeping can occur at any time, typically without substantial warning.
Microsleeps (or microsleep episodes) become extremely dangerous when they occur in situations which demand constant alertness, such as
driving a motor vehicle or working with heavy machinery. People who experience microsleeps usually remain unaware of them, instead believing themselves to have been awake the whole time, or to have temporarily lost focus.
[2]
There is little agreement on how best to identify microsleep episodes. Some experts define microsleep according to behavioral criteria (head nods, drooping eyelids, etc.),
[3] while others rely on
EEG markers. One study at the
University of Iowa defined EEG-monitored microsleeps in driving simulation as "a 3–14 second episode during which 4–7 Hz (theta) activity replaced the waking 8–13 Hz (alpha) background rhythm."
[4]
Driver fatigue is particularly dangerous because one of the symptoms is decreased ability to judge your own level of tiredness. It reasonable to assume this applies equally to aircraft operation.
In my present position, I run a small manufacturing company. The hours tend to be long, but when you run a business, you have a tiger by the tail and cannot let go. I calculate that if I can bag 5 hours sleep per night 5 days a week, then I can still function during the week and recuperate satisfactorily on the weekend.
Unfortunately, sometimes the demands of business result in considerably less than 5 hours sleep>> resulting in close acquaintance with extreme fatigue/ sleep deprivation. This is critical since I face a ~1 hour night drive home.
We are all probably familiar with fatigue resulting in that mental “wading through sand” feeling as we attempt to accomplish a mental task. I see that often. For me, it is an indicator that , I should just take a short nap to regain performance. Trying to bull through these situations just results in inefficient staring at a screen.
Perhaps you remember suddenly realizing that you have driven a number of miles and have no memory of the process. (This is not necessarily microsleep induced, but can be the result of a loss in focus on the driving process.) It is a warning that you are excessively fatigued.
Recently I encountered a repeated microsleep situation on one drive home and came to the realization that this is an especially hazardous situation to be avoided at all costs. I had seen this microsleep effect before but had attributed it to “getting old.” Remember, microsleeps occur without warning and you may not recognize you have been sleeping after the event.
What I experienced was finding myself on the road without a picture of what I was doing. (But even that description is inadequate.)
In vehicle control, be it aircraft or automobile, there is a continuity of navigation that the mind must engage in. In simple terms, you correlate your position with regard to landmarks and plan your actions to most effectively execute your navigational plan. Your mind notices deviations from the plan due to distraction or inattention/loss of focus and you make corrections.
What I discovered first hand that was most alarming was that following a microsleep episode, the entire navigation plan was gone from my memory and had to be recreated. This is the source of the confusion associated with microsleep!
Judging from my lane alignment while driving, the microsleeps were very short, however it takes several seconds to recognize your surroundings (on a familiar route) and restart your navigation plan (ie. To begin thinking ahead of present position.)
What was exceptionally disconcerting were the turns into the neighborhood around my house. When reawakening into the need for an immediate turn, all you can do is react in an appropriate manner and then determine if you made a correct turn.
Since microsleep events occur without warning, and are generally not recognized by the participant as a sleep event, the best method of detecting one is by detecting the resulting confusion that results from loss of the plan. This is the news that I hope you can use.
In the process of writing this report, I found an excellent paper published by the NZ CAA:
http://www.caa.govt.nz/Publications/...un03Vector.pdf