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From Wikipedia (emphasis mine):

When experiencing microsleeps while driving an automobile, from the perspective of the driver, he or she drives a car, and then suddenly realizes that several seconds have passed by unnoticed. It is not obvious to the driver that he or she was asleep during those missing seconds, although this is in fact what happened.

It references this, which also claims:

Microsleep episodes last from a few seconds to two minutes, and often the person is not aware that a microsleep has occurred. In fact, microsleeps often occur when a person's eyes are open.

[...] selective loss of awareness without the person feeling he or she has been asleep.

That second link acknowledges the difficulty in quantifying microsleep, but its references are 6 years out-of-date.

Is it true that people are unaware that they have experienced a microsleep episode?

I could say that I have always been aware of microsleeps, but somebody could pull a "no true scotsman" fallacy and say, "then you haven't really experienced microsleep". Or maybe I'm pulling the "toupeé fallacy" by just saying "I've never been asleep without knowing it".

(Related, but not essential: do they happen while driving?)

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    From unfortunate personal experience, I'm entirely aware of those missing seconds. Usually because I'm now drifting and jerk awake. Estimating how long would be hard, though. – Bobson May 30 '14 at 18:28
  • FYI: Gladly will give the bounty to one of the current answers if edited to give extra detail about the awareness aspect of the claim. – user5582 Jun 1 '14 at 19:39
  • I added an anecdotal answer which got deleted for being, well, anecdotal. But my brother used to be prone to falling asleep while driving for a few seconds at a time (he's since been diagnosed with sleep apnea and doesn't fall asleep while driving). I've seen his eyes close and his head dip slightly, and then wake up a few seconds ago, hands remaining steady on the wheel but obviously unseeing. He was unaware that he was doing it until I asked. It's probably linked to a combination of loss of short term memory while falling asleep and dreams supplying the missing details of lost time. – Sean Duggan Jun 2 '14 at 16:28
  • Once I had a rather long (a minute or two perhaps) microsleep while walking. On a building site! Unless a microsleep is something different, but then I don't see why someone would be unaware of it. – Markus von Broady Jun 2 '14 at 19:09
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+150

Yes micro-sleep (or microsleep) is a real phenomenon that is well documented in both the mainstream and scientific literature and can be verified by EEG. There is also evidence to support that people are sometimes not aware when this happens.

With regards to the phenomenon itself, the BBC said that,

Of 1,000 drivers it interviewed, 45% of men admitted to micro-sleeping while driving, as did 22% of women. But what does this mean?

Micro-sleep is an episode of light sleep lasting five to 10 seconds. The brain goes to sleep involuntarily and it is more likely to happen in a monotonous situation. People wake suddenly, often with a sharp jerk of the head.

"Your eyelids start drooping and you start to lose contact with reality," says Prof Jim Horne, director of Loughborough University's Sleep Research Centre. "You're asleep for a few second, then wake up, often with a jolt."

Which is similar to a report by ABC News,

Sleep researchers at the Liberty Mutual Research Institute in Hopkinton, Mass., estimate that every day 250,000 Americans drive while sleep-deprived.

According to National Highway Traffic Safety Administration figures, more than 6,000 people are killed every year in vehicle accidents blamed on an exhausted driver behind the wheel. That's second only to drunk-driving fatal accidents and ahead of those attributed to driver distraction, which includes texting.

These figures are also reported by highway safety administrations and researchers such as those in Texas, during symposiums, and finally the NHSTA reports their research on this topic under the heading "Drowsy Driving" which encompass micro-sleeps.

To further complicate the matter, there has been recent research into local sleep that can occur during period of wakefulness, as summarized by Science Daily,

Researchers at the University of Wisconsin-Madison have a new explanation. They've found that some nerve cells in a sleep-deprived yet awake brain can briefly go "off line," into a sleep-like state, while the rest of the brain appears awake.

"Even before you feel fatigued, there are signs in the brain that you should stop certain activities that may require alertness," says Dr. Chiara Cirelli, professor of psychiatry at the School of Medicine and Public Health. "Specific groups of neurons may be falling asleep, with negative consequences on performance."

Until now, scientists thought that sleep deprivation generally affected the entire brain. Electroencephalograms (EEGs) show network brain-wave patterns typical of either being asleep or awake.

Most of these articles and research indicate that those surveyed are either unaware or deny the extent of their fatigue so it is reasonable to conclude that those experiencing it are unaware of the event. Furthermore, the research cited into local sleep demonstrates that in rats it can occur even when the subject appears awake.

To further expound upon the question of if people are aware of micro-sleep episodes, the following discussion was found:

Most drivers involved in sleep-related vehicle crashes usually deny having fallen asleep, with evidence pointing to the crash being sleep-related coming from other sources. Possible reasons for the denial could include fear of procession and loss of insurance indemnity. It is possible, however, that the person genuinely had no memory of having fallen asleep, with studies showing that drives who fall asleep typically deny having been asleep if awoken within a minute or two (30). It is very likely, however, that drivers falling asleep at the wheel were aware of the precursory feeling of sleepiness even though they may not remember this after the crash (30).

An older text on the "Neurobiology of Sleep and Memory" contains a discussion about micro-sleep in the broader context of amnesia that can point to the biological explanation for the denial,

Another question concerns what happens to the information during this abnormal state and why patients deny any memory trace of the events. During micro-sleep episodes a lack of perception may exist, which is responsible for a non-acquisition of information. The results from the LSVT seem to confirm this assumption. But micro-sleeps are very short events and the absence of perception during these periods can only account for a small amount of the total amnesic period. Another component must also play a role in the existence of the amnesia. Our patients obviously present a retrograde amnesia and if we combine the results of our pilot study on students with the finding on our patient population, one could suggest that a certain amount of information stored in the "short-term" memory pool cannot be switched to the long-term pool because of successive micro-sleep events.

  • Thanks! Could you perhaps focus this answer more on the question of whether subjects are aware that they had microslept? The question presumes the phenomenon exists (and your answer does a good job of establishing that as well). I'd be interested in more detail behind the sentence "Most of these articles and research indicate that those surveyed are either unaware or deny the extent of their fatigue so it is reasonable to conclude that those experiencing it are unaware of the event." – user5582 May 30 '14 at 19:24
  • @Articuno Updated. – rjzii Jun 6 '14 at 14:38
  • So researchers conclude that subjects can be not aware that they experienced microsleep based on self-reporting, but the denials of microsleep during self reporting may be due to incentives to not disclose that they were actually sleeping? Is that how you understand it? – user5582 Jun 8 '14 at 23:38
  • @Articuno That's my understanding. From what I have been able to find, baring having some way of verifying micro-sleep (i.e. EEG) self-reporting is relied upon; however, people may or may not report accurately depending on the situation. Also, they also might deny micro-sleep just because of how memory works since they might not remember actually falling asleep. Some of the articles also referenced highway hypnosis as potentially being related to micro-sleep and not remembering what you did afterwards with regards to long term memory. – rjzii Jun 9 '14 at 1:01
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Looks like to answer this question regarding the awareness or lack thereof of microsleeps, we are going to have to rely on expert testimony as to why some people lack awareness of this phenomenon.

Dr. Katherine Sharkey, an assistant professor of medicine and psychiatry and human behavior at Brown University is quoted as saying,

Some people aren’t aware of falling into microsleeps, and about half of those who drop off into the first stages of sleep in a sleep lab will not say they had fallen asleep. “When people are sleepy, they are impaired and bad at judging their own sleepiness,” she says. And whether it’s three-second microsleeps or deeper sleep in which all of our senses are shut down, our brains aren’t as aware or able to pay attention to what’s happening around us.

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To directly answer the question of whether people can be unaware of microsleeps happening (while driving), here's a quote from a journalist participating in a study:

I asked about the episode when I had run off the road.

"Yes," he said. "We could see it coming in your brain wave recoding."

He said I was asleep five or six seconds. But what truly shocked me was when he told me that I'd micro-slept a total of 22 times. I had only remembered dosing off twice.

Personally, I don't find it hard to believe at all. The times you remember it happening are probably the times you were drifting out-of-lane. You then snap back to awareness and recover, so you're bound to be aware of it. In other episodes where you stay in-lane and nothing "bad" happens, there's not much of a frame of reference to say "This is not the situation I was just in, what happened to those seconds?"

  • Brain waves accurately report the state of microsleep? How do they rule out the possibility that their brain wave criteria isn't overcounting the instances of microsleep? – user5582 May 30 '14 at 19:16
  • They're what is measured in the majority of microsleep studies (rob's answer has links to several). Otherwise I think you're not going to find anything meaningful anywhere. – Is Begot May 30 '14 at 19:17
  • Okay, so they're defining mircosleep to be that which exhibits some characteristic features in brain wave observations. Is that correct? – user5582 May 30 '14 at 19:21
  • Also, the test for subject awareness of the event is based on self-reporting? It's okay if it is, but it would be good to know if that is the current standard of evidence accepted by the experts. – user5582 May 30 '14 at 19:33
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    The American Academy of Sleep Medicine defines NREM Stage 1 sleep (the transition from awake to sleeping) as having a brainwave frequency of <=7Hz. So, while it appears that the study does define microsleep as periods of characteristic brainwave activity, that is in line with other modern sleep studies. – Is Begot May 30 '14 at 19:35
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Yes, microsleep is real. It manifests either as a momentary lapse of attention, or sometimes an actual 'micro' nap, which the subject is usually unaware of. This is a well known phenomenon, which is one of the reasons freeways are bordered with rumble strips, or also known as singing strips.

Rumble strips seem to originate from an idea called SNAP, or Sonic Nap Alert Pattern. There have been studies that show microsleep could result due to fatigue, sleep disturbances, and many other reasons. The microsleep episodes, though are a few seconds long, they can result in major accidents.

  • Is the person that experiences microsleep unaware that they experienced it? – user5582 Jun 5 '14 at 2:45

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