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A Watched Clock Never Moves
August 16, 2012 2:50 PM   Subscribe

Have you ever wondered why you don't see motion blur when your eyes flick to a new position? Why, if you sit in front of a mirror and watch yourself, you never see your eyes move? That is saccadic masking, one of the lies your brain tells to avoid confusing you. Have you noticed that the first tick after glancing at a clock with a second hand can take more than one second? No, it's not just you! That's a related phenomenon called chronostasis, or more commonly the stopped clock illusion.
posted by gilrain (46 comments total) 49 users marked this as a favorite

 
Tripping a few stray balls
posted by theodolite at 2:57 PM on August 16, 2012 [6 favorites]


I think "lie" is an unfair pejorative given that without it I'd pretty much spend my days puking my guts up from motion sickness.
posted by Kid Charlemagne at 3:05 PM on August 16, 2012 [1 favorite]


Beware - your brain may no longer be the boss! If you are beginning to doubt what I am saying, you are probably hallucinating.
posted by tommasz at 3:06 PM on August 16, 2012 [2 favorites]


I had to look up saccade from the saccadic masking link, and when I read the following it tripped my brain up and I couldn't read any more!

"When scanning the scene in front of you or reading these words right now, your eyes make jerky saccadic movements and your eyes stop several times, moving very quickly between each stop. We can not consciously control the speed of movement between stops and during each saccade
posted by marienbad at 3:06 PM on August 16, 2012 [1 favorite]


Is it also related to the phenomenon of waking up in the morning, looking at the wine bottle, and swearing that you didn't drink that much the previous night?
posted by perhapses at 3:07 PM on August 16, 2012 [3 favorites]


And:

   Paris
  in the
the spring


is not Paris in the spring.
posted by weapons-grade pandemonium at 3:15 PM on August 16, 2012 [3 favorites]


Why Do We See Things Upright When the Images Formed on Our Retinas are Upside Down?

We watched a film made in the 1960s demonstrating the malleability of this effect in my 1970s elementary school science class.

The man in the film donned a special pair of glasses that inverted everything. For a few hours (days?) he stumbled around until his brain flipped the world right side up for him again. He "proved" it by climbing behind the controls of a little Cessna and going for a flight, landing safely.

After he removed the special glasses, he bumbled around for a little while again until his brain once again righted the world.
posted by notyou at 3:21 PM on August 16, 2012 [5 favorites]


Well, now I just want to re-read Peter Watts' Blindsight.

Hooray, I can!

(and so can you)
posted by Earthtopus at 3:26 PM on August 16, 2012 [12 favorites]


Is there a name for that thing that happens with electric hair clippers where after you use them for a few minutes everything sounds buzzy? It's like staring at a lightbulb with your ears.
posted by Sys Rq at 4:24 PM on August 16, 2012


It's the Silence.
posted by Renoroc at 4:29 PM on August 16, 2012


Cool! Thanks!
posted by davidjmcgee at 4:34 PM on August 16, 2012


According to...a friend, ketamine interferes with saccadic eye movement, which can defeat the illusion. This leads to an experience wherein whenever you turn your head, you find you're still perceiving your previous view, and waiting a beat for the image to pan and show you the things that your face is actually facing.
posted by evidenceofabsence at 4:46 PM on August 16, 2012 [2 favorites]


"Have you noticed that the first tick after glancing at a clock with a second hand can take more than one second?"

Yeah, when it's the Windows system clock.

What a shitty clock.
posted by colinshark at 5:16 PM on August 16, 2012 [2 favorites]


"Brains are liars." -- some scientists' brains.
posted by straight at 5:25 PM on August 16, 2012


Motion blur when you move your eyes can sometimes happen when you try out a new prescription for bifocal spectacles. Then it goes away by itself after a while. If you don't have bifocals, just wait long enough, and eventually you'll get the chance to test it out.
posted by ovvl at 5:39 PM on August 16, 2012 [4 favorites]


I had always noticed that effect with the second hand on a clock, but didn't know it was a "thing."

Also, with regard to "bypassing" the effect of not seeing motion blur or whatever, there used to be (probably still are) these LED strips that were 1 pixel wide, and about 100 pixels tall. They flicked out a pattern of lights (at about 60hz, I assume) such that if you looked at the strip directly, it just looked like a red line, but if you flicked your eyes past it quickly, you would see a hidden message or picture. It never seemed to work well if you did it "straight on", but if you kinda did it out of the corner of your eye, you'd see it.
posted by ShutterBun at 5:44 PM on August 16, 2012


"Why Do We See Things Upright When the Images Formed on Our Retinas are Upside Down?"

Yeah, this is a pretty common supposed insight, but it actually signifies a deep confusion, probably involving what Dennett termed the cartesian theater. The illustration on that Wikipedia page is, I think, surprisingly helpful in this specific context because it implies the absurdity of assuming that there's a "right-side-up" orientation of the image. The assumption in your question is that the orientation is "wrong" and that the brain "fixes" it...but there is no "wrong". It just matters that the mapping of those nerves in the back of the eye and the objects in the physical world which emit/reflect light that strikes those nerves have some sort of predictable relationship.

And there is, really, a relationship to the fallacy of the cartesian theater and many or most of the examples in the cracked.com article. The best example is probably the last one in the list, the one that talks about the subconscious and specifically about evidence that we make decisions some moments before we consciously believe we've made decisions.

In a way, all of these examples demonstrate that memory and consciousness together (if they're separate things, which they arguably are not) is synthetic and quite unlike what we intuitively believe it to be. The synthesized result is an experience of self and sensation in the now with a strong sense of a relationship of the now balanced between past and future. But that's as artificial as a fictional narrative, where inconsistencies and the unimportant are largely elided, where the past is altered to make it more meaningful from the context of the present. What we do in our storytelling is qualitatively exactly what we do in our consciousness itself. We create subjective and objective viewpoints which don't exist independently of the narrative. Our consciousness, our self is just as much a useful "lie" as is a fictional character. And just as true.

Which isn't to say that I'm asserting a strong philosophical relativism. I'm a materialist; I think the evidence that the physical universe exists and has the properties we think it has is very strong.

What isn't very strong, what is weak on evidence, is that we ourselves are what we believe ourselves to be. That's a statement that is meaningful primarily only in the context in which I made it — that's the problem with Descartes dualism. It both asserts a material, objectively comprehensible universe but also places an integral observer within it which experiences it directly. There's hundreds of years of important philosophy devoted to these issues and I won't recapitulate them. However, from a scientific standpoint, the assumption that the self is a homunculus in the brain is both almost universal and wholly unsupported by evidence. All of these sorts of things described in these links undermine that assumption, cast very strong doubt on it. Accumulating evidence is that the self is not integral, it's not a viewpoint that exists in the now and perceives the universe directly. It's synthetic. It's an illusion ... but ironically only within the context of the assumptions that assert that it's not an illusion.

Because while on its own terms it's not what it thinks it is, in a functional and practical sense it is exactly what it thinks it is. In this Descartes was quite right.

If my comprehension of myself as a self existing in a moment in time and having a past is all synthesized and the result of an ongoing process, if my memory of both what I've experienced of the external world and what I've experienced of my internal self is not a perfect representation of exactly what happened, and in what order it happened, according to some external observer, that doesn't mean that it's all one big, useless lie. It's at the very least a very useful lie and, really, it's quite closer to a useful truth and not much a lie at all. Only in the most specific and contrived context will we call it a lie.
posted by Ivan Fyodorovich at 5:54 PM on August 16, 2012 [16 favorites]


I ran into saccade in a biomedical design course in college, of course I didn't know about it then. My lab group and I had built an eye motion tracking system to control a mouse cursor and couldn't figure out why we had to have such a large weighed average of the input signals. It wasn't until I took a human factors design course that someone mentioned the natural, rapid eye movements everyone has.

It was a fun project, but we got really annoyed with the cursor jumping all over the screen and finally just split the screen in to quadrants and brute forced a solution.
posted by highway40 at 6:35 PM on August 16, 2012


I wonder if saccadic masking operates differently in the visually oriented autistic savants, where if I understand/remember correctly, they perceive images as a whole rather than as parts, and can replicate large amounts of image data correctly from memory. Do their eyes move differently to accommodate the brain, or does the brain accommodate the eye movements differently while processing? Forgive my clunky understanding of autistic savants; I am only speaking of the subset that is unusually masterful at replicating images they have seen.

Also, to awkwardly step into weirdville, if one were able to somehow influence saccadic masking to the point where you could extend the 'blank space', perhaps you could 'freeze' a persons mind for a limited amount of time, move them, and then 'unfreeze' them, and they would feel like they just teleported there. It would make riding a cross-country flight more tolerable, for example.
posted by chambers at 6:55 PM on August 16, 2012


"Forgive my clunky understanding of autistic savants; I am only speaking of the subset that is unusually masterful at replicating images they have seen."

It's been a good long while since I read on this topic (well more than ten years), but the last I did it was my understanding that such savants have never been demonstrated to do anything qualitatively differently than non-savants — usually, just more quickly or simply with much more focus. Most of the popular portrayals of so-called idiot savants are about as factual as portrayals of multiple personality disorder. That is to say, almost not at all.
posted by Ivan Fyodorovich at 7:23 PM on August 16, 2012


The way to see a smooth pan with your eyes without the saccade is to lock your eyes all the way to one side or the other so they cannot move and then move your head in the opposite direction. Voila! No saccade and a smooth, motion-blurry (or juddery) camera-like pan result.
posted by bz at 7:33 PM on August 16, 2012 [6 favorites]


Also, to awkwardly step into weirdville, if one were able to somehow influence saccadic masking to the point where you could extend the 'blank space', perhaps you could 'freeze' a persons mind for a limited amount of time, move them, and then 'unfreeze' them, and they would feel like they just teleported there. It would make riding a cross-country flight more tolerable, for example.

I believe there's been cases where brain damage causes a person to have like <1 frame per second vision, which is sort of like what you describe. I can't remember the name of the condition but I'm pretty sure it's a thing.

Also, if we don't actually experience motion blur then how come it (presumably) works as an effect in video games and such to make the graphics seem more real? Do movies condition us to expect it even though we don't experience it naturally?
posted by passerby at 7:40 PM on August 16, 2012


Earthtopus: "Well, now I just want to re-read Peter Watts' Blindsight. Hooray, I can! (and so can you)"

That was much better than expected.
posted by Memo at 7:41 PM on August 16, 2012 [1 favorite]


The way to see a smooth pan with your eyes without the saccade is to lock your eyes all the way to one side or the other so they cannot move and then move your head in the opposite direction.

Is that even possible? I thought saccades were involuntary. Can you consciously keep your eyeballs from moving?
posted by straight at 7:47 PM on August 16, 2012


"I'm saying these things can see your nerves firing from across the room, and integrate that into a crypsis strategy, and then send motor commands to act on that strategy, and then send other commands to stop the motion before your eyes come back online. All in the time it would take a mammalian nerve impulse to make it halfway from your shoulder to your elbow. These things are fast, Keeton.

Wheee Nightmare fuel.
posted by Lemurrhea at 7:47 PM on August 16, 2012


We see motion blur just fine but that is when something else is moving and our eyes are stationary (waving your hand in front of your face really fast, for example). This is talking about the motion blur that we would see when everything else is stationary but our eyes move.

If you want to know what it would be like not to have the saccade masking, play and FPS and pan the camera back and forth quickly and really concentrate on the screen. You might start to feel a little queasy though. It's also really hard for me to pick out any details while doing this.
posted by VTX at 7:49 PM on August 16, 2012


straight: "Is that even possible? I thought saccades were involuntary. Can you consciously keep your eyeballs from moving?"

Give it a try, and you'll see. If you look all the way to the left, and then turn your head to the right, you'll get saccade-less panning, because your body wants to keep your eyes trained on whatever is in front of them. Since you're moving your head to the right, it will want to track whatever you're looking at by moving your eyes to the left...but they're already as far left as can go. So they'll next lock onto whatever is now in front of them, and try to track to the left...but still fail to do so. And on and on. And thus, you'll get smooth panning.

It is also physically painful.
posted by Bugbread at 7:54 PM on August 16, 2012


"Is that even possible? I thought saccades were involuntary. Can you consciously keep your eyeballs from moving?"

Try it. Just look all the way over with your eyeballs. You can prevent the saccade by "locking" them to one side. Now, get the smooth panning view by rotating your head in the opposite direction. It's easy to hold the eyes against their rotation limit.
posted by bz at 7:58 PM on August 16, 2012 [2 favorites]


The way to see a smooth pan with your eyes without the saccade is to lock your eyes all the way to one side or the other so they cannot move and then move your head in the opposite direction. Voila! No saccade and a smooth, motion-blurry (or juddery) camera-like pan result.

Augh. My eyes.

...

It is also physically painful.

You don't say.

Actually it's not so much 'painful' as much as 'uncomfortable and unsettling'.
posted by CrystalDave at 8:02 PM on August 16, 2012


Speaking of Dennett, when I first read Dennett's discussion of saccadic masking in the 90s, I thought he had gotten it totally wrong. The eyes clearly do not shut off due to the eye motion itself, as he claimed, because I could see otherwise: Many the time I had been staring up at ceiling fan daydreaming and suddenly, out of the blur of the blades, a single blade would leap into clarity, and then quickly disappear. As a kid I had wondered what was going on, but it soon became clear to me that it was because the jump of my eye just happened to give it a velocity equal to the fan blade, causing it to snap into focus even though the eye was in mid saccade. I was too young to write to Dennett at the time to quibble, but in any case it seems from the wikipedia article that this has been known for a long time. But it's still shows that it requires *both* the jump and the blur for the blindness to kick in -- plus it's a neat way to see fast-moving stuff that you otherwise can't track.
posted by chortly at 9:19 PM on August 16, 2012 [1 favorite]


While saccades are one way of moving the eyes, smooth pursuit is another. One can voluntarily engage in smooth pursuit, although some people need a slowly moving target to initiate smooth pursuit. During this time, however, AFAIK there is no loss/blanking of information.

Then, there is the microsaccade which is a miniature version of a saccade, also involuntary. The microsaccade is believed to introduce a slight jerkiness so that the retinal image doesn't fade away. Personally I have tried to hold my eye stationary, and after several seconds my vision starts becoming gray gradually. I am not sure if it is because I am stopping microsaccades or if it is because I am applying pressure on my eye (lack of sleep may have been an issue too, when I tested this :-O ).

I don't know if eye movements influence how autistic persons display savant qualities or not, but there is a strong correlation with sensory processing disorders and autism. Specifically, some autistics don't have the vestibulo-ocular reflex (VOR, which is generated in the vestibular system, next to your ears) which along with efference copy ( I don't know if efference copy is still the dominant idea in explaining space constancy, I only learnt about it in non-human species) informs the visual system to fixate accurately. This also means that they can get a lot of vestibular input like spinning without getting dizzy or nauseated and they also crave that input (others end up being dizzy more often and quicker because we do utilize the sensory input via the VOR).

Basically, efference copy is a copy of the signal that the motor fibers receive from the brain about the movement that is going to be made. It is also why we find it difficult to tickle ourselves. This signal sent to the ocular muscles (in the case of eye movements) is incorporated in the internal visual model of preserving the relative invariance of the map when we move our eyes, which is also why we know that it is our eye that is moving and not the world. Of course, there will be drift and errors which are corrected with external visual input.

One way to experience blur is to close one eye and move the other eyeball with a finger (from under or above, by pushing on the eyelid, in jerky steps). This bypasses the efference copy mechanism hence there is no correction applied to the visual signal and no saccadic blanking either, which result in the effect that the world is totally shaking around you. It feels weird.
posted by ssri at 9:55 PM on August 16, 2012 [7 favorites]


So, that crappy 50ms my brain needs to process visual information is way slower than sound from up to 10 meters away. Does that mean if I learned echolocation and walked around with my eyes closed I could have faster reflexes, i.e. superpowers?
posted by speicus at 10:22 PM on August 16, 2012 [1 favorite]


speicus- are you comparing apples to apples there? Auditory processing is also subject to latency over and above the time it takes sound to get to you.
posted by Jpfed at 10:38 PM on August 16, 2012


However, from a scientific standpoint, the assumption that the self is a homunculus in the brain is both almost universal and wholly unsupported by evidence.

You take that back.
posted by homunculus at 10:39 PM on August 16, 2012 [4 favorites]


Auditory processing is also subject to latency over and above the time it takes sound to get to you.

Auditory processing is orders of magnitude faster than visual processing (cf. North 2010, other sources I'm too lazy to look up).
posted by speicus at 11:02 PM on August 16, 2012 [2 favorites]


Auditory processing is orders of magnitude faster than visual processing (cf. North 2010, other sources I'm too lazy to look up).

This is mostly true. It depends on what we mean by processing. Complex sound processing happens as early as at the level of the brain stem (by about 5-10 ms after the sound reaches our ears) and different aspects such as pitch, timbre, localization, object recognition processing all take place at the brain stem or even lower.
The complexity of the stimulus determines how much time it takes for the percept to be recognized.

Auditory "objects" are likelier less complex than visual "objects". But scene analysis (audio and visual) works in such a way that percepts processed within a certain time interval of each other are perceived as happening simultaneously consciously (say, at the cortex) . For example, for objects that are about 15 m away, the sound from them reaches us ~50 ms later than the visual signal. To preserve subjective simultaneity (which presumably has ecological meaning, as in the object I see may be the same object making the sound), the auditory neural processing pathway is about as much quicker than the visual processing pathway. The brain allows audiovisual integration over intervals as large as 100-150 ms. Sights and sounds can be separated by this much temporal distance and still be perceived as from a single object or as being simultaneous (depending on the circumstances such as object distance etc..).
posted by ssri at 12:11 AM on August 17, 2012 [1 favorite]


Soooo, if we could skip the audiovisual integration step (by closing your eyes for example) could you react to certain things faster? Or does consciousness not work that way?
posted by speicus at 1:18 AM on August 17, 2012


The results suggest that ADHD participants have reduced ability to suppress unwanted saccades and control their fixation behavior voluntarily...
I did see something shiny after all!
posted by mimi at 6:42 AM on August 17, 2012 [1 favorite]


However, from a scientific standpoint, the assumption that the self is a homunculus in the brain is both almost universal and wholly unsupported by evidence.

But there's still little people in our sperm cells, right?
posted by straight at 7:20 AM on August 17, 2012


Soooo, if we could skip the audiovisual integration step (by closing your eyes for example) could you react to certain things faster? Or does consciousness not work that way?

Yes, the auditory reaction time is known to be quicker than the visual reaction time. So you could, in theory, react faster to auditory stimuli, if you "learnt" the world around you in that sense. I don't know how long that would take or how much effort it would take to override the visual sense (because the visual system is much more salient than the auditory system, in humans).

AFAIK consciousness (as proposed by Ned Block) is believed to have a phenomenal and an access part to it. The conscious part that comes to the fore, is the access part, as in, you have access to it to influence rational thought and action. The phenomenal part being the response of the brain to stimuli. I believe this is the part you are referring to here. Daniel Dennett appears to think that the difference between the two is more in degree of richness and content.

I think that learning a skill like echolocation (either in addition or in place of vision), would give different texture to objects, say, a different qualia indeed.
posted by ssri at 8:14 AM on August 17, 2012 [1 favorite]


We are fast and slow in the visual sense itself depending on the stimulus. When a brick is thrown at you, you don't consciously duck your head. You just do it. Here, the visual signal doesn't even reach the primary visual cortex for recognition and decision making (well it reaches, and you know it after the fact, but a decision is already made by using an alternate parallel motion detection pathway).

There is also a degree of reaction too, depending on whether it is a simple detection, a recognition reaction or a choice reaction. That would affect how fast or slow we are.
posted by ssri at 8:31 AM on August 17, 2012


Sights and sounds can be separated by this much temporal distance and still be perceived as from a single object or as being simultaneous (depending on the circumstances such as object distance etc..).

Wait, are you saying that our brains' judgment of simultaniety is dependent on

1. actual object distances (which determine the time difference in the availability of different channels of information)
2. our brains attempting to take into account temporal disparities using an estimated object distance?

Of course #1 plays a part, but if #2 also played a part that would be trippy.
posted by Jpfed at 10:28 AM on August 17, 2012


The conscious part that comes to the fore, is the access part, as in, you have access to it to influence rational thought and action. The phenomenal part being the response of the brain to stimuli. I believe this is the part you are referring to here. Daniel Dennett appears to think that the difference between the two is more in degree of richness and content.

This is what interests me. Obviously we often react to things before we consciously know what's happening, but I'm wondering how much this is affected by what stimuli we're responding to. Could we train ourselves to respond more consciously to auditory stimuli, and if so, could this speed up our conscious reaction times? Or would the integration step happen anyway, with the access part of consciousness simply bottlenecked at 50ms?
posted by speicus at 1:30 PM on August 17, 2012


Wait, are you saying that our brains' judgment of simultaniety is dependent on

1. actual object distances (which determine the time difference in the availability of different channels of information)
2. our brains attempting to take into account temporal disparities using an estimated object distance?

Of course #1 plays a part, but if #2 also played a part that would be trippy.


Rather than thinking in terms of estimating object distance, which is quite difficult to implement, an easier way would be to allow for robust detection across a large interval of asynchronous arrival of auditory and visual stimuli.

The brain has evolved to allow for temporal asynchronies in perceiving simultaneity. In speech perception (which is an audiovisual percept, at least), the sound can lag as much as 150-200 ms behind the visual signal of lip movement or lead as much as 40 ms for the event to be perceived simultaneously. Reported lags and leads vary depending on study differences and stimuli differences. The McGurk effect is usually used to study this. When incongruent visual and auditory speech stimuli are presented, we perceive a sound different than what is presented. This effect is used to determine at which point in time we start losing simultaneity.

What is really interesting is training for a short while (just for a few minutes) with temporally asynchronous, but otherwise congruent audiovisual stimuli results in temporal recalibration and we start perceiving events with asynchronies of even 300 ms as simultaneous.

The adaptability and fuzzy nature of the mechanism makes it possible to even preserve simultaneity in an unnatural situation (where vision trails the audio, although not as much asynchrony as in the other way). One theory is that there is some sort of temporal ventriloquism where the visual event is synced with the appropriate auditory event.
posted by ssri at 3:32 PM on August 17, 2012


Could we train ourselves to respond more consciously to auditory stimuli, and if so, could this speed up our conscious reaction times? Or would the integration step happen anyway, with the access part of consciousness simply bottlenecked at 50ms?

This is an interesting question. I don't know if we could train ourselves to do this. Our visual system is much better equipped than the auditory system. The auditory system usually ends up taking a backseat to the visual system. For example, when we hear an unexpected sound, our natural response is to orient our gaze in that direction. We then use the visual system to better respond to that stimulus. Even in a predominantly auditory signal such as speech, the visual system (in cases where we do we vision present) has a large influence on what is perceived.

Maybe, if we had visual sensory deprivation during the critical development period, the other senses might become dominant and one could train to better respond to auditory stimuli. This would be really awful though, sewing kittens' eyes shut was bad enough.
posted by ssri at 3:53 PM on August 17, 2012


I'm not a science fella at all, so could someone tell me if this chronostasis thing applies equally to the rapid eye movement of dream sleep, and if so, if this is why a dream that lasts five minutes in awake-time seems to last hours in dreamland?
posted by thisclickableme at 6:02 PM on August 17, 2012


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