February 17, 2009

Will you perceive the event that kills you?

David Eagleman is guest blogging this week.

When light strikes your eyes, it takes some hundreds of milliseconds before you become conscious of the event. As a consequence, you are always living in the past. This strange fact of our existence is well known is neuroscience, but there’s an interesting, underappreciated consequence: you may not ever become aware of the thing that kills you.

Cormac McCarthy addresses this point in his post-apocalyptic novel The Road, in a scene in which the main character has his pistol leveled on a miscreant. The malefactor challenges: “you won't shoot....they [my companions] will hear the shot.”

The protagonist replies, “Yes they will. But you won’t.”

“How do you figure that?”

“Because the bullet travels faster than sound. It will be in your brain before you can hear it. To hear it you will need a frontal lobe and things with names like colliculus and temporal gyrus and you won't have them anymore. They’ll just be soup.”

One way to appreciate the slowness of your perception is to compare it to the speed of mechanical devices. Take this incredible, sobering "anatomy of a crash," as described in an Australian magazine and echoed on Tom Vanderbilt’s blog. With fine-grained temporal resolution, it analyzes what happens when a stationary Ford Falcon XT sedan is struck in the driver’s door by another vehicle traveling at 50 kilometers per hour:

0 milliseconds - An external object touches the driver’s door.
1 ms - The car’s door pressure sensor detects a pressure wave.
2 ms - An acceleration sensor in the C-pillar behind the rear door also detects a crash event.
2.5 ms - A sensor in the car’s centre detects crash vibrations.
5 ms - Car’s crash computer checks for insignificant crash events, such as a shopping trolley impact or incidental contact. It is still working out the severity of the crash. Door intrusion structure begins to absorb energy.
6.5 ms - Door pressure sensor registers peak pressures.
7 ms - Crash computer confirms a serious crash and calculates its actions.
8 ms - Computer sends a “fire” signal to side airbag. Meanwhile, B-pillar begins to crumple inwards and energy begins to transfer into cross-car load path beneath the occupant.
8.5 ms - Side airbag system fires.
15 ms - Roof begins to absorb part of the impact. Airbag bursts through seat foam and begins to fill.
17 ms - Cross-car load path and structure under rear seat reach maximum load.
Airbag covers occupant’s chest and begins to push the shoulder away from impact zone.
20 ms - Door and B-pillar begin to push on front seat. Airbag begins to push occupant’s chest away from the impact.
27 ms - Impact velocity has halved from 50 km/h to 23.5 km/h. A “pusher block” in the seat moves occupant’s pelvis away from impact zone. Airbag starts controlled deflation.
30 ms - The Falcon has absorbed all crash energy. Airbag remains in place. For a brief moment, occupant experiences maximum force equal to 12 times the force of gravity.
45 ms - Occupant and airbag move together with deforming side structure.
50 ms - Crash computer unlocks car’s doors. Passenger safety cell begins to rebound, pushing doors away from occupant.
70 ms - Airbag continues to deflate. Occupant moves back towards middle of car.
Engineers classify crash as “complete”.
150-300 ms - Occupant becomes aware of collision.

The last line is the zinger. Early studies by Benjamin Libet suggest that the last line should perhaps read as high as 500 ms, although others, such as Daniel Dennett, have correctly pointed out that it is impossible to measure the moment of onset of conscious experience, so the exact timing will never be known.

Just as the explorer David Livingstone appreciated the biological kindness of stress-induced analgesia, there may an equivalent kindness in the slowness of perception.

David Eagleman is a neuroscientist and a writer. His book of literary fiction, Sum, debuted internationally this month.


  1. A small quibble: I think Dennett's point might more precisely be that there's no sharp and non-arbitrary dividing line between cognitive processing that precedes consciousness and veridical consciousness, so there could not be an exact timing even in principle. That said, one could investigate when humans become conscious of something for a particular purpose, say, of storage to long-term memory, or for particular kinds of deliberative processing. I suspect that's where the really interesting discoveries are to be made.

  2. Anonymous8:11 PM

    Brilliant. The reason we need science is the fallibility of our senses, which this post so viscerally describes.

  3. Anonymous3:30 AM

    It's very likely that you become aware of the crash after only 50ms. All of the measures of reaction time involve both an input and output of signals (for example, see a light, press a button). Accounting for the fact that we can't instantaneously push a button, the signal to push takes time to travel, measured reaction times of 120ms imply a time-to-awareness of much less.

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  5. Anonymous10:49 AM

    Fantastic article. Something that occurred to me was that the driver in that car (unless they were in full sensory deprivation gear) would be aware of the event much sooner than that - subconsciously at least. They would have a head start over the car because they would see the other car coming. Or hear it coming. And those things might not have time to be consciously noted, but they sure as heck would have been processed before the car struck. One could argue that prediction is in a sense a kind of perception. When the man points the gun to my head, I instantly predict the bang, the flare, the speeding bullet. The human brain is constantly trying to stay one step ahead of events, so does this counteract the fact that our perceptions are a step behind?

  6. Anonymous2:00 PM

    I've been in a couple of car accidents where the air bag deployed and this fits with experience. You never see the air bag deploy. You're driving along and the next thing you know there's an air bag in your face, and the odd smell of nitrates. It happens too fast to be conscious of it.

    Also, I used to work in a lab where we used a PVT to measure response times. It's basically a box with an LED display and a single button. You watch for numbers to start scrolling on the LED and click the button as soon as you see them. My typical response times were around 200 ms. The signal travels at ~100 m/s from the cell bodies of motor nerves in the brain to their axon terminals in the finger, a distance of 1 meter, which means it should take ~10 ms. Perhaps a similar length of time is needed to transmit the sensory signal from photoreceptors in the eye to the relevant visual processing areas. So you know ~180 ms of that response time was internal brain processing and becoming aware of the numbers on the LED.

  7. Anonymous1:30 AM

    Just remember we haven't yet evolved past the hunter/gatherer period. 500ms is plenty fast enough to register a her of gazelle, or even a lion charging at you! Maybe in a few hundred thousand years our brains will have evolved to react fast enough to deal with cars!

  8. Anonymous5:30 AM

    Good stuff! Here's a question: If your perception of the passage of time is frozen in that final moment before everything becomes soup, wouldn't it follow that you'll spend an eternity in that final thought? I don't think it is in fact frozen so abruptly. He may not hear the gun-shot, but it seems unlikely his conscious experience will simply end like that. Rather, his final experience would probably be a deaf dull pain - as introspection slowly dissipates - and then: end. So what's the best way to commit suicide?

  9. "Curious the small and lesser fates that join to lead a man to this. The thousand brawls and stoven jaws, the clubbings and the broken bottles and the little knives that come from nowhere. For him perhaps it was all done in silence, or how would it sound, the shot that fired the bullet that lay already in his brain? These small enigmas of time and space and death."

    Cormac McCarthy, Suttree, pp. 374-375.

  10. Anonymous2:28 PM

    ...sure in a car crash you wouldn't experience your death but if someone raises a gun in a threatening way you will be aware of your impending death before it happens... you may even see their finger contract on the trigger. There is pretty much no doubt what is happening.

    I think it likely that you would retain consciousness after beheading too... although surely it would be a matter of seconds... and not 15 seconds... before blood loss caused you to black out.

    The phantom limb pain phenomenon suggests that you might continue to experience your body even after it had been severed from your head as your head fell into a basket or rolled down the stairs.

    You would have experienced the event that led to your death, and even had a moment to think "oh damn"... or "so you really do retain consciousness after a beheading... I wish I could tell someone" before all faded to black.

  11. As a rather grisly comment, I'd like to point out that when "modern" takfiri terrorists behead a victim, they start at the throat so that blood pressure in the victim's brain drops to zero and ends consciousness immediately. This is, I think, something they consider merciful.

  12. Anonymous12:43 AM

    That's creepy, but really interesting. It's cool to know how much faster our machines are at responding to events than we are.

  13. A fascinating post. So interesting the man made machines are so much more efficient at sensing and recording.

  14. This fails to take into consideration Einstein's Theory of Special Relativity. Time slows down for the person experiencing such an event... it's likely that they experience it in a matter of time outside of the measurable milliseconds expressed in this article.

    Of course, I could be wrong. I don't pretend to know the intricacies of the theory or it's application.

  15. Anonymous8:51 AM

    @Ron Coy
    I believe this is in fact questioning Einstein.

    The problem with the 150-300ms 'Occupant becomes aware of collision' statement is that it's overly generic from a non-engineering point of view. Is this talking about becoming aware of the fact of collision occuring, aware of the experience during the collision, or aware of the physical (both vehicular and bodily) consequences of the collision (ie injuries)?

    One's perception of the crash can be predictive due to environmental signs before the moment of impact; all of the crash avoidance/preparation techniques one puts into play pre-collision (eg braking, bracing, blinking).

    "Will you perceive the event that kills you?" - my interpretation is generally yes, but it depends largely on the state of our senses, and on the type of event that occurs.

    As Eagleman et al conveyed in a nutshell, the perceived time duration of a high intensity event expands upon it’s recollection (http://tinyurl.com/36g2t3).

    High intensity events are where there is an acceleration of stimuli due to the reduction of safety buffers, ie getting closer to danger. Such an ecstatic moment increases adrenaline and heightens the senses, allowing any memory to be much more vivid than a memory made in a low intensity event.

    If I'm in a low intensity event when I die, I might not perceive or predict it. However, if I'm in a high intensity event, full of danger and ecstasy of motion, I may indeed predict and perceive the event that kills me.

    Glad to see you blogging, David!

  16. Anonymous2:11 AM

    Nato makes a valid point, especially considering that consciousness of an event is not absolutely necessary for the body to make at least rudimentary reactions toward the event. If you reach out and touch something that is, unbeknownst to you, extremely hot, your hand will pull away before your conscious mind acknowledges the heat. Preconscious reactions like this might not be helpful in vital situations like these, but they show that the body is capable of some sort of reaction before the time lapse that conscious processing entails.

  17. Anonymous1:41 AM

    "If you reach out and touch something that is, unbeknownst to you, extremely hot, your hand will pull away before your conscious mind acknowledges the heat."

    I would not strictly agree with this..

    When I touch something that I do not know is hot I don't pull away before I know it's hot, no, not at all though, my hand does pull away before I have a chance to think "Oh, this hurts, I should move my hand." I would call this "instinct" or some kind of automatic muscle spasm.

    I'm no expert and it's not such a big deal and you may have even worded it wrong, just saying what I think.

  18. Anonymous11:28 AM

    At point blank range or even at a considerable distance, you can hear the shot before the bullet arrives. I've stood behind the wall that absorbs the bullets at a shooting range near my house and you hear the gunshot before the impact of the bullet, not long before though.

  19. Anonymous3:14 PM

    I was involved in a near head-on collision when an approaching car lost control and I certainly DID perceive the entire sequence, my still vivid memory of it is of a high detail slow motion inflation of the bag, the almost simultaneous firing and tightening of the belts and a drawn out impact while continuously attempting to position the car and myself into the safest position. My explanation for this is when you have some time (a couple of seconds) to assess the likely severity of the event, i.e is it life threatening? before it happens, your brain can switch into an emergency survival mode, probably triggered by adrenalin, that allows us to suspend all trivial brain function for a few seconds and concentrate massively on the critical event.

    In the 2-3 seconds following the impact I checked occupantants (family) and assessed immediate internal surroundings for anything that was life threatening i.e. obvious body injury - this was an automatic thing, I certainly didnt "think" about it.

    I am sure there is an extreme survival instinct mode that our brains can call upon to speed perception and decision making.

    However it probably needs to be triggered first by "risk assesment" logic.

  20. Anonymous12:48 AM

    interesting conflict between the assertion of Daniel Dennett and Charles Darwin's quote at the top of the page.

  21. I was rear ended a few years back as a rear seat passenger and only realised it had happened when i picked myself off of the floor and thought the car was on fire with smoke from the air bags and picking glass out of my clothing.

  22. Anonymous7:08 PM

    I'll keep that in mind... the good news being IF I am ever shot in the head, I won't know!

  23. Anonymous4:14 AM

    I am a man in mid-life. Older than 40 but less than 60. I have 'almost died' at least 20 times so far (it's been a tremendously exciting life). Having seen death coming so many times, the experience has so much variability to it. It definitely depends on the context of the situation, and your 'situational awareness'.

    There were times where I was totally clueless as to what was about to transpire, and thankful to survive ..

    I compare that to other situations where I knew I was in danger (had a heightened sense of awareness) and literally watched everything unfold *microsecond* by *microsecond* and cognitively realized as each millisecond clicked by that "oh nO!! - I think I am about to .." - WhACk !!!

    So a bullet coming at you from close range - you might see that, you might not.

    The impact would certainly scramble any cognitive thoughts you had. I would think there probably would not be much pain ..

    Interesting topic. Then there's the experience of watching your life pass before your eyes ..


  24. Anonymous7:03 AM

    In many of the above comments, I think there is danger that our conscious perception of time is accurate. I think you would have to admit that the complex processing required for recognitions takes longer than the simple sensory perceptions, yet our (or at least my) conscious experience is that they occur simultaneously. When someone speaks, do we not seem to be conscious of the sounds at the same time as the words? But I'm sure it takes the brain much longer to recognize the words after the sounds are perceived. What I am saying is that consciousness backtracks the timecode so that the sounds and the words seem to be simultaneous, when obviously, they are not.

    I've had the experience where a person's speech was difficult to decipher, due to mumbling or interference, so that at first, all I heard were the unintelligible sounds without most of the words. In that instance, it seemed to take much longer than normal to recognize the words. I actually heard the sounds replay in my head a second time, but with words that didn't quite make sense. I started to ask the speaker to repeat what he said, when I heard the sounds replay in my head a third time, as words that made sense.

    I think that normally, the processing of the sounds into recognized words occurs quickly enough, that it happens before we are entirely consious of it, and the timecodes of the sounds and recongnized words are adjusted so they seem to be simultanious. But if takes long enough to recognize the words, then it is outside of the "window" that the timecode adjustment is possible, and it seemed as if I consciously heard the speech replay itself in my mind.

    So I am saying that the conscious perception of the timing of mental events (not just our perceptions, but also our reactions) is subject to adjustment before we become aware of it, but only within a window of about 300ms or less. The mental processes that seem to make up our consciousness can occur at different points in time, some almost immediate to the sensory stimulus, and some rather delayed, yet our consciousness has the illusion that they are all simultaneous. I think this is what makes it difficult to determine when consciousness actually occurs. It doesn't really occur at one point in time, even though it seems to.

  25. Anonymous3:42 AM

    Interesting stuff. I went back this evening and re-read my post. I also re-read other's posts, experiences, and postulates; and watched the U-Tube video - something I didn't do before.

    The brain is obviously a very complex machine. The researcher (what's-his-name) talks about the lag between vision and sound, and sound processing being quicker; how the brain does 'editing' and stitching together of imagery and sound to arrive at what 'makes sense', also he covers the 'flash-lag' effect.

    I agree with all that - there are all sorts of visual perception 'tests' that illustrate to a casual user the brains ability to stitch something together.

    I think too that those examples fall apart rapidly, in direct correlation to ascending levels of perceived danger.

    Out of my ~20 events (after 10 - who counts) there were possibly only two (maybe 3) events where I was in a heightened state of awareness and watched as things unfolded. It's interesting to note (for me anyway) in each of those situations there was *no* sound.

    Absolutely nothing. Zero, Zilch, Nada. Only intense microsecond by microsecond visuals.

    Perhaps my noggin re-routed itself to process only visuals in 'extreme survival mode'.

    OOOoooo oo ..

    Tantalizing possibility.

    All other ~17 incidents were a mix of sound and visuals. Several times I heard danger coming before I ever saw it, and logically it should have been at the same time. Hey !! - maybe that's why we 'jerk' involuntarily during many perceived instances of danger. OOOoooooo .. another tantalizing possibility.

    So 'flash-lag' (see the video) may apply when you are in a steady state 'pick-your-nose' and watch the computer mode.. the brain then rewires itself to deal with higher perceptions of danger in 'fight-or-flight' mode (involuntary jerk followed or interwoven with the visual 'what the heck was that !!') ..

    .. and in those unusual moments when you are aware you are in total danger and can't escape, all auditory shuts down, and brain processing power is re-routed to parse visual images. Not that you can do much about it .. cause your muscles can't react fast enough to get you significantly out of the way.

    That's of course, unless your name happens to be Neo, Morpheus, or Agent Smith.

    With so many Anon's out there, it would be interesting to hear from Anon at 3:14pm to know whether he heard any sound to go along with his 'Matrix slo-mo' visual experience during his automobile accident.

    Sean O'H (alias Neo)

    Trinity sure was hot wasn't she?

  26. @Ron Coy, August Bohem

    This has almost nothing to do with Einstein. The rate of passage of time does not change simply because an individual happens to be experiencing something that happens quickly.

    The confusing arises from the difference in the passage of time between an observer O in a frame of reference K and another observer O' in a frame of reference K' that is undergoing uniform translational motion relative to K.

    In other words, if I get on a spaceship with a clock, and take off at near light speed, I will see no change in the rate at which the clock moves. If you stay behind in mission control, you will see no change at the speed at which the clock in mission control moves. However, if you could look into the spaceship and see my clock, it would be running much slower than the one in mission control.

    This seems to agree with the statement that since the people involved in a car crash are moving fast, time is running slightly slower for them, and in fact, it is.

    However, the difference is so small that it is swamped by other effects, and the entire system can be treated as a single frame of reference. In order for a speeding car to be considered a measurably different frame of reference, it would have to be going a significant portion of the speed of light.

    Also, this doesn't cover cases like the guillotine or getting shot while standing still, where the person who is doing the dying is not moving at all relative to the thing that killed them. This is actually a bit of handwaving, since under special relativity there is no absolute frame of reference, so everything is moving relative to everything else. However, as pointed out earlier, the effects don't become apparent at a scale humans can perceive until at least one of the reference frames involves something moving very fast (or being very dense. Black holes are a special case).

  27. Anonymous7:45 PM

    Coming in a bit late on the conversation... Got here via StumbleUpon

    So, upon reviewing the initial posts along with *robust, spirited, and intelligent* comments, I declare this is one of the better debates that I've seen in a while!

    Break It Down
    What are the positions:

    *Debate 1: Do you perceive the event that kills you?

    *Debate 2 (condensed): "Does our consciousness work as a construct of our physiological self, i.e., the consciousness is an operating system running at the top of a stack of machine language-esque biological processes that work at some intensity(Einstein popped into the conversation here. in relative terms.) speed relative to light, the senses, and each other in order to make who who we, as humans, are?

    *Debate 3 (condensed): What is the deal with "fast" events? Like, it seems with some much occurring in terms of milliseconds, I don't have a snowball's chance in hell to actually perceive a HUGE amount of stuff that occurs in the world because at the end of the day, I'm just the evolved decent of a common ape ancestor who was catching his lunch with a spear with a sharp stone tip only thousands of years ago.... you need Matrix-like computer skillz just to BEGIN to manipulate the world at such a tiny fraction in time.

    *Debate Four: "Can't win. Don't try." -Homer Simpson

    This debate centers on no matter what, you're gonna die somehow, so might as well measure and examine the moment prior to death to try and figure out the LEAST sucky way to die.

    That's a pretty solid final four match up of good questions about time, perception, motion, and the end of life.

    I'll take a swing at a single synthesis in hope that the debate gets picked up again:

    Could this debate about time really be about speed?

    Are, events really just as fast or as slow as they can be?

    So, if you look at how the repeating fractal-esque dendrites grow inside the physical brain as input from the senses travels through the neveruos system into the crebral cortex and all of it's substructures, you can imagine how the "robust-ness" of those pathways would lead to faster overall processing of sensory input.

    *That*, means that if your focusing on the "world ahead of you" like when you are going through an intersection, information from the other 270 degrees is absent.

    SO, when you get hit by a car that blew a red light, of course it feels like it was instantaneous, the pathway for "side angle and periphery vision vision" is MUCH smaller that input coming in from the front.

    To better understand take the opponent position: If we, humans, had evolved with 4 eyes, each at 90 degrees, we wouldn't even be having this conversation because we'd have a perfect 360 degrees of vision, kinda like a spider...why do you think they are so damn good at catching things? They see more of the world."

    So, it's all about speed. unexpected *fast* events , if perceived front on SLOW DOWN and event that happen from the side SPEED UP.

    Why do you think it's cowardly to attack a man from behind? Because then they never even know it's coming. *instant* lights out.

    That's my theory about it. It's actually pretty simple! :)

    Invent some type of "built in side and back vision" to the human skull and we've got ourselves a person that really can see the big picture


    Make a man with microscopes for eyes and tell him to solve quantum physics by Friday.

    Now that's debate!

    Thanks so much for reading if your did!

    Madison, WI

  28. Anonymous7:10 AM

    This can be They would have a head start over the car because they would see the other car coming. Or hear it coming. And those things might not have time to be consciously noted, but they sure as heck would have been processed before the car struck. One could argue that prediction is in a sense a kind of perception ReebokShoess.com

  29. Anonymous5:38 AM

    (⊙o⊙)… i have no idea about this!!

  30. I enjoyed this posting very much and just put it out for my Twitter and FaceBook friends to enjoy.

    Ironically, though, based on reading and anecdotal evidence, people dying from events other than just extremely sudden or explosive events, e.g. in a hospital bed, can be aware that something is happening and they are dying.

    All I can pray is, may our final moment(s) be of peace and no pain.


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