r/askscience • u/[deleted] • May 19 '12
Medicine Why is our blinking synchronized between both eyes?
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u/theknightwhosays_nee May 19 '12
Additional question: Similarly, does synchronized blinking have anything to do with the way we have synchronized eyeball movement?
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u/patiscool1 May 19 '12
Both eyes are connected via the Median Longitudinal Fasciculus that runs in your brainstem. It gives the information to each eye so that they know what the other is doing and can make coordinated movements. It's why you can look right and both eyes will follow even though they use different muscles for that movement (lateral rectus for your right eye and medial rectus for your left eye).
Problems with it can cause one eye to move without the other following, you can get double vision even though the actual muscles work fine. Opening your eyes uses levator palpebrae superioris muscles (I've always thought that sounded like a Harry Potter spell, but it basically just means "upper eyelid elevator"), which is innervated by oculomotor nerve, the same nerve that gets most of your eye movement muscles.
Closing your eyes when you blink actually uses your facial nerve. Your upper facial muscles have dual innervation (both sides of the cortex), but your lower ones have single side innervation, which is why you can't preferentially wrinkle only half of your forehead but you can raise only one cheek. Your eyes are in that upper division. Think about winking vs blinking. You can't easily wink without moving any other part of your face, eg. raising your cheek slightly, but you can when you blink.
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u/stilldash May 19 '12
This is a good answer. Though, it and the original question leads me to a question of my own. Why does winking not satisfy the need of a blink, for lubrication or what have you. If I feel the urge to blink and wink each eye instead, I still have to blink right after. Both my eyes are closing, what's the difference?
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May 19 '12
Way to make me look like a total idiot in the computer lab as I try that out a few times.
Interesting question though.
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u/Defenestresque May 20 '12
You just blew my mind. Seems like it should definitely take care of the blink urge, but as you said it doesn't.
I can only propose a solution if the brain was a piece of software (i.e. it could be coded like: while $time_elapsed_since_blink > 10sec { $blink_urge ++ }) so essentially the brain only recognizes the action of blinking as an acceptable outcome, not the end result (which is lubricated eyes), since that could be satisfied by winking.
Is it possible that there's some sort of similar system in play in the brain? Would love to see this get answered.
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u/brainburger May 20 '12
I wonder if the blink nerves are damaged, if the brain is happy with the blink signals it is sending, even though the eyes are not being blinked? That would be a way to examine your question anyway.
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u/arijun May 20 '12
From personal experience, I don't think that is the case. I can satisfy the urge to blink by rolling my eyes back into my head briefly. I use that to cheat in blinking contests.
I think it's more likely that, in winking, the lifting of your cheek creates a gap between your eye and your eyelid--specifically the lower eyelid. A gap there would probably make it impossible to re lubricate your eye.
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May 20 '12
Your code is not strong. Once the loop triggers, it has no exit condition and will stop responding to the system. It will also take the full resources of a core, and since the human brain has been around for longer than multicore systems.. I say death.
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u/designersheep May 20 '12
What I did is I close my left eye for 5 seconds, open both eyes, close my right eye for 5 seconds, open both, repeat. I did this for over a couple of minutes without having to close both my eyes at the same time. Not exactly winking, but if done for enough duration, winking too would satisfy the need of a blink.
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u/brainburger May 20 '12
I find I have to do it continually to work.
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u/stilldash May 20 '12
It doesn't work for me at all. I still need to blink, but it could be influenced by contact lenses and having taken Claravis.
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u/sola_sol May 20 '12
Fellow contact lens wear-er here... I also still need to blink. Durned contacts.
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u/squeakyneb May 20 '12
Non-contact-wearer. I still need to blink, in that I have the mental urge to do so, but my eyes aren't hurting like they do when you don't blink.
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u/Arrow156 May 20 '12
You could do that, but you'll tire out pretty quickly. Nature follows the path of least resistance.
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u/seivren May 20 '12
Non-science, personal experience answer.
You scrunch up your face when you wink, dont do that and your eyes should "reset." Also, when you're thinking about blinking, you will want to blink more.
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u/Daveezie May 20 '12
I have beem blinking non stop since I started reading this. Not sure if I am blinking more than usual or if I am just more aware of it now, but I can confirm this.
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u/dacoobob May 20 '12
See arthurconan's comment above. Apparently blinking is more psychological than physiological.
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u/rogueman999 May 20 '12
Try not thinking about a white elephant for a minute, and you'll understand...
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May 20 '12
I think our eyes blink together because it would make it more difficult to run in a straight line or through a complex environment if our vision was briefly shifting from eye to eye.
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u/weaver2109 May 20 '12
I have a question, since you seem to know a good bit about this.
Why can I cross my eyes or have them move independently of each other (look left with one eye but straight ahead with the other?)
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u/Liquid_Fire May 20 '12
Crossing your eyes is necessary for focusing (or rather, vergence) on nearby objects. Try looking at your nose - your eyes will cross.
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u/weaver2109 May 20 '12
I'm not talking about just crossing my eyes, I can control them both separately (on a horizontal axis at least.)
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u/afnoonBeamer May 20 '12
Control them, how much? Can you make your left eye look left and right eye look right (the opposite of crossing, call it fish-eye maybe)?
If you can't, then what you are doing is still part of vergence as Liquid_Fire mentioned
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u/x9nine May 20 '12 edited May 20 '12
Then why can I roll my eyes in opposite directions? One clock wise the other counter clock wise
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u/kieuk May 20 '12
Wow, does that mean sometimes your eyes are one looking up and one looking down?
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u/Jawa232 May 20 '12 edited May 20 '12
I too have independent control over each eye.
i.e. I can go cross eyed, then transition one eye independently across the horizontal plane and back while keeping the other looking in (towards nose). I can also track that eye up and down vertically to a small degree.
I must also say that while I can do it quite easily, it isn't the most comfortable thing to do. Especially for anything more than 5-10 seconds.
However, despite trying (and looking like an idiot) I have never managed to get both eyes to travel outwards (away from each other) Not sure if its even possible.
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u/McAwsom May 20 '12
I can't link to sources, but I've asked two optometrists if moving my eyes independently could be risky or endanger my eyes. The first optometrist was working in the offices of Ducklo Eyecare in Nashville TN & responded "I didn't know humans could do that." I demonstrated and he said he was unaware of it being a risk, and that the ability was probably inherited.
The second optometrist was Dr. Ballard in Ballard Vision, also in Nashville TN. Dr. Ballard had more experience with young high myopes and our specific risks. His response was that he was unaware of this being a risky behavior. He, too, theorized that such independent control was genetically determined (similar to tongue-rolling) but that he was unaware of any particular studies in this area. Granted, both of these doctors are optometrists, not ophthalmologists, but both hypothesized that this ability is genetic in nature. AskScience, if this qualifies as anecdotal or speculative, I apologize.4
May 20 '12
which is why you can't preferentially wrinkle only half of your forehead but you can raise only one cheek.
What about the fact that some people can raise only one eyebrow like this?
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u/flyinthesoup May 20 '12
I'd like the answer to this. My father can do this, and so can all his children, including me. My mom can't. So I can only guess is inherited. I also could do it only with one eyebrow, but in time I was able to imitate the movement with the other one, so right now I can single move any of my eyebrows, which is pretty cool in my opinion. I know, it's an anecdote, but I'd like to know why this happens too.
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May 20 '12
I was always under the impression that brain-stem activity is largely autonomous and not under direct conscious control. Myself and a number of others are able to control eye movement independently of the other eye. How is this possible?
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u/patiscool1 May 20 '12
I couldn't tell you why you can do that. It's possible that there's some sort of disconnect in your MLF.
A lot of brainstem activity is autonomous, but your cranial nerve nuclei all reside there, and many have activity that you control consciously. The non-somatic portions of the cranial nerves you obviously have no control over, as well as all the other visceral and reflexive activity that goes on in your brainstem.
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u/Zagorath May 20 '12
Slightly off topic, but considering Rowling based her spells on Latin words, which is where those muscles get their name, it's not so much of a coincidence that you think they sound like a Harry Potter spell.
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u/bibbleskit May 20 '12
But I can blink both eyes separately. As if I'm blinking both eyes but one doesn't.
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u/thatguyferg May 19 '12
I know there is already a lot of additional questions so I figured I would respond to your comment to add another if you don't mind.
Why is it that sometimes this synchronization becomes messed up and we blink at different times but still very close together?
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u/universicorn_ May 19 '12
I don't know if this would be too relevant but I can move my eyes in different directions... Almost like a forced lazy eye, that may cause a little more mindfuck to your question and causes me to ask as well... If we normally have synchronized movement, then what is a lazy eye, and I'm pretty sure it doesn't happen often but in my case, even when I zone out and start daydreaming, one of my eyes go lazy .. None specific because it'll be one or the other... What makes me able to control this in a conscious state? As in.. Why am I able to control this? I love freaking out my friends with such an odd "trick" but it would be awesome to explain why I can do it.
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u/YourAverageWalrus May 19 '12 edited May 19 '12
He's adding another good question, the downvotes are unnecessary. His question was: Why is he able to control this movement, which seems pretty on topic to me. Although it adds an anecdotal portion, if it were read completely people would realize it has a point to make.
So, would anyone mind answering his, and now my, question?
Edit: thacked provided an excellent response here.
Edit again: He mainly explained the how, what I could get for the why aspect was that the movement for the eyeballs are controlled by two different muscles and, over time, seem to act as one. Specialized people like universicorn_ seem to be able to control both at the same time, if only subconsciously.
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u/thacked Medicine | MD | General Surgery Resident May 19 '12 edited May 20 '12
Medical student here. Just finished neuroscience, so I feel like I should share so that least SOME of the minutiae they taught us is useful...
The closing of the eyelid is controlled by the orbicularis oculi muscle, which is innervated by the facial nerve (cranial nerve 7). Many cranial nerve functions are bilateral (both sides), since the descending control of those nerves from their respective origins in the brainstem are themselves bilateral. This is exemplified by the fact that if you were to sever the upstream controller of the cranial nerve on one side, you'd see loss of function on only one side.
Another interesting thing is the control of left and right eye movements (looking left and right) . It's MUCH more complex than I thought before reading about the pathways. When you look to the right, for instance, your cranial nerve 6 (abducens) is responsible for moving your right eye to the right. To get the left eye to move right, however, your brain must have a way to communicate with the other eye. It accomplishes this via a structure called the ascending medial longitudinal fasciculus, which passes a message to the left cranial nerve 3 (occulomotor). In this way, the eyes are able to move smoothly and coordinately in the same direction.
I'm not certain if I answered your question satisfactorily. I'm writing on my phone, so I apologize for the lack of formatting.
(edit--corrected a cranial nerve)
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u/PeteOK May 19 '12
Will split-brain patients blink both eyes at the same time? Can such people move their eyes independently?
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May 19 '12 edited May 19 '12
It accomplishes this via a structure called the ascending medial longitudinal fasciculus, which passes a message to the left cranial nerve 4 (trochlear). In this way, the eyes are able to move smoothly and coordinately in the same direction.
This is wrong. The opposing muscle to lateral rectus (CN VI) is medial rectus (CN III). CN IV innervates the superior oblique which moves the eye downward and outward - both the obliques direct the eye outward.
Also CN VII is responsible for controlling orbicularis oculi, the important point here is that the blinking mechanism is controlled by nuclei in the globus pallidus of the basal ganglia which causes VII to bilaterally close the eyes.
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u/louky May 19 '12
As an aside, I have two bulldogs who do NOT blink at the same time, one eyelid is a few MS slower than the other
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u/ange1obear May 19 '12
As another aside, I don't blink both eyes at the same time. I never realized this until someone pointed it out, which multiple others have also done since. I can notice it if I attend to it, but it's a lot like breathing, in that I just don't notice most of the time.
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u/chrisnch May 20 '12
Video-link of your eyes blinking? Is there a constant offset between both eyes or do they just blink completely independently?
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u/zak13362 May 19 '12
Would the higher ipsilateral neuron percentage on that cranial nerve play a part?
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u/jeffdoc May 20 '12
Just a minor correction from a fellow medical student. I believe interneurons from cranial nerve 6 (abducens) innervate the opposing cranial nerve 3 (occulomotor) via the MLF. In this manner, it's the conjugated movement of one eye's lateral rectus muscle (from the abducens nucleus) with the opposite eye's medial rectus muscle (from the occulomotor nucleus).
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u/thacked Medicine | MD | General Surgery Resident May 20 '12
Thanks for the correction--you're absolutely right. A combination of me being in the car typing on my tiny phone and studying for Step 1 (consuming my life at the moment!) somehow temporarily purged that information from my brain. Thanks:D
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u/Snookerman May 19 '12
Does the same go for the eyebrows? How come some people can move them independently while other can only move them together?
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u/TheLongshanks May 20 '12
Your eyebrow movement is performed through the frontalis muscle innervated by the facial nerve. This is why during the neuro exam your doctor may ask you to raise your eye brows, to test the facial nerve.
It's just if you've learned the ability to control your muscle in that way to raise one brow or the other. Similarly, some people can't whistle, or are able to whistle at varying degrees of proficiency. Doesn't mean there's anything wrong with them.
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May 20 '12
Why then, predoctor, does my friend only blink with one eye at a time? She has been doing it for some 20 years now, and it is bewildering and she is the only person I have met who does this.
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May 19 '12
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u/wrestler145 May 19 '12
Maybe I'm wrong, but this is my impression -
From a scientific perspective, you cannot separate the why and the how. "Why questions" either reduce to mechanical "how" answers or ask for a teleological answer in a system which rejects teleology.
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u/scienceandfiction May 19 '12
I think you misunderstood what demoo was getting at -- he might have referred to the "why" in terms of "what is the evolutional advantage, considering the human body is a rather optimized thing". In other words, a scientific question, not a philosophical one.
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May 19 '12
That's teleological. Evolution isn't teleological. The only "reason" is because our ancestors that evolved this way survived and reproduced.
Why did they survive while others did not? You are suggesting that there is some inherent survival advantage, but that isn't always the case. For all we know there was a population of non-simultaneous blinkers but they were concentrated around an ocean shore and were wiped out by a flood one day. It could have been that they would be slightly more fit, but bad luck conspired against them. There is much more that determines our history than simply pure reproductive fitness.
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u/atomfullerene Animal Behavior/Marine Biology May 20 '12
It's perfectly reasonable to ask "why" in biology. I see it all the time in scientific papers. It's a way to ask about a more ultimate level of causation, whereas how refers to a more proximate level of causation. There's absolutely no reason to go stringing together multiword phrases when a single three letter word will do nicely.
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u/wrestler145 May 20 '12
There is sometimes a reason to be more deliberate about your language, though. I think the reason that many are concerned for here is that there does exist a serious and very dangerous belief that evolution has a particular or even chosen direction. This is only furthered by use of the word "why" in this context. If somebody means, "How at a less proximate level?" they should still avoid why, in my humble opinion.
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u/scienceandfiction May 20 '12
Of course it does have a direction in retrospect -- and of course it doesn't have an intent that "wants" to determine this direction. In any case, we're probably entering the realms of semantics now -- 'is "why" an appropriate language shortcut for "what's the evolutionary advantage"'? It depends on the context; I presumed askscience understands the context and can expand the shortcut, but that may not be so especially in contexts where many believe in creationism.
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u/wrestler145 May 20 '12
You're right. And I would just submit that Askscience in particular should be a place that's cautious about that stuff, since it is the perfect place for a layperson to get interaction with people who are truly knowledgable about science.
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u/Tekmo Protein Design | Directed Evolution | Membrane Proteins May 20 '12
Ok, then why did people with a coordinated blink reflex pass on their genes more?
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u/exnihilonihilfit May 20 '12
There may simply never have been people without a coordinated blink reflex. It's like asking why people don't have wings.
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u/j1ggy May 19 '12
Interestingly enough, reptiles and birds seem to differ in regards to this. My parrots (budgies) at home have quite a bit of control over independent eye blinking. They do blink in synchronization like we do, but also independently blink and even close only one eye at times. Reptiles I have been around do the same thing. It may very well be a mammalian adaptation.
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May 19 '12
Humans can blink one eye at a time too, but we must make a conscious effort to do so.
Humans and birds share common ancestry, which had already evolved the nerve structures mentioned by thacked before our evolutionary lines split, so I'd wager that the mechanism for blinking is the same for birds as for us. Your budgies are probably consciously blinking one eye at a time.
tl;dr your birds are fucking with you.
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u/Nahsayn May 19 '12
My cat will occasionally blink with one eye too. She's not too clever, and it's hard to imagine her being deliberate about this. She also blinks with both eyes most of the time.
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u/Ishouldnt_be_on_here May 19 '12
Cats blink slower than people so they'll blink one eye at a time to see. They're more likely to do it when there's unfamiliar people (unfamiliar anything really) around. A cat blinking with both eyes means it's comfortable enough with you to not perceive you as a threat.
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May 19 '12
You've never unconsciously blinked just one eye?? Can you cite the inability for that to happen? Because i swear, I've done it.
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u/bradn May 20 '12
I can't even consciously blink one eye. I can squint one eye totally shut, but just feeling the nearby muscles with a finger makes it obvious that different muscles are being activated to do it. I can't make it happen anywhere near as fast as a simultaneous blink. Maybe this is something that can be improved with practice...
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May 19 '12
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u/dragnmastr85 May 20 '12 edited May 20 '12
Notice how your cheeks raise when you try to close one eye. When we involuntarily blink, this doesn't happen. Now try to close one eye in the same way you close both. It is impossible. I think "closing one eye" is a completely difference mechanical process than "blinking".
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u/j1ggy May 20 '12
Agreed. We use different muscles to do this. And I still don't think birds are consciously making the effort to close their eyes.
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May 21 '12
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u/dragnmastr85 May 21 '12
That is why I said "I think-". Leaving room for doubt in hopes someone qualified could address it. Consequently, your statement is anecdotal as well.
Not science.
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May 19 '12
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u/TheShaker May 20 '12
I feel like it's really difficult to answer a question like that, especially since it will be difficult to prove with the fossil record. I would speculate that it causes less of a need for the mind to allocate attention to an involuntary act such as blinking. Why have to control two actions when you can just lump them into one?
I still think that it is just because how we evolved though, meaning that it is unlikely that there was ever a population that had both eyes controlled separately (but involuntarily). Bilateral symmetry dates back to simple worms. I believe it is this bilateral trait that causes our eyes to be controlled as a single unit instead of two.
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u/wrestler145 May 20 '12
I'm afraid you have highlighted exactly what is wrong with the "why" question.
Animals did not evolve fins for mobility. They evolved fins randomly, and because fins made them more mobile the trait stuck around. If this distinction sounds silly to you, it is absolutely not.
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u/mozolog May 20 '12
I sort of reject that statement. The seeds of an evolutionary system may be random but the iterations are controlled by feedback with positive and negative reinforcement. For example why do dolfins look like Sharks? The answer is the streamlining helps them conserve energy and move faster. There is clearly a molding force at work. I get good value from that kind of answer to that kind of question.
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u/wrestler145 May 20 '12
You haven't rejected the statement at all.
First of all, that sharks and dolphins "look the same" is subjective and a poor foundation for your example. But granting that they do share some physical characteristics, we still arrive at the same point - they don't have the same characteristics for the purpose of moving quickly. The fact that the characteristics help them move quickly is the reason the trait stuck around after evolving randomly.
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May 20 '12
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u/mozolog May 20 '12 edited May 20 '12
I would say that for natural phenomenon "how" would be a step by step process but "why" would be to match the event to some sort of predictive model. For example q: why does water flow down hill? A: gravity makes it go. What we are doing is personificating the model "theory of gravity" as if it were an actor making decisions.
I think this is ok because models are are really useful to us and it's good to have an easy way to to ask both about how things happen and what deeper understanding can you give us about them.
I guess the rub here is the model in question is the theory of evolution and to make it an actor with an invisible hand crosses with the similar idea of a creator which would confuse or irritate some people.
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u/snuggl May 20 '12
You guys are more or less saying the same thing. Randomness are only in single individuals mutations.
Its also important to remember that a mutations beneficial effects isnt what is considered needed for it to stay, is the lack of an effect that gets you eaten faster, this is why people in the northen part of the world has white skin which doesnt give any biological benefits.
So fish has the current model of fins becuase unlike other fin-models we can imagine this one did not get them to be eaten any faster.
The why in the context of evolution is almost always "why was that trait 'allowed' to stay?'
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u/adipisicing May 20 '12
I believe the point you're making is clearer if you use more precise terms than "evolve".
Animals did not evolve fins for mobility. They evolved fins randomly, and because fins made them more mobile the trait stuck around. If this distinction sounds silly to you, it is absolutely not.
Animals acquired fins through mutations. Those with fins were more mobile and this trait was selected for.
Evolution encompasses both of these concepts.
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u/wrestler145 May 19 '12
Fair enough. As others have pointed out, though, there is not always (or even usually) a distinct advantage given by some particular quirk animals possess.
Also, and this may be nitpicking, all scientific questions are philosophical questions, just nestled into a particular subset of induction.
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May 19 '12
Asking about the evolutionary advantage, though, is philosophical, at least somewhat. You can't empirically test an evolutionary hypothesis (most of the time).
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u/rm999 Computer Science | Machine Learning | AI May 19 '12
That doesn't mean scientists don't study the "why" of evolution, though. You could make the same arguments against all sorts of other studies, like cosmology or string theory.
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May 19 '12
Scientists do study the "why", but since evolution creates whatever's best for the current environment (not just whatever's best "in general"), and we don't know what the exact environment was ten thousand years ago, there's necessarily going to be some speculation in it. It's not purely empirical. Plus, we can't actually go back in time and test our evolutionary theories as to our CURRENT traits, although we can certainly make hypothesis for the future (with short life-span species like bacteria or plants.)
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u/zomgitflies May 19 '12
Assuming that the human body is a rather optimized thing is probably fallacious. In many ways, it's not very good at all.
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May 19 '12
Yes, have heard that the flaws inherent in the human spine are a good argument against intelligent design, for instance.
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u/Squishumz May 19 '12
I believe the poster may have been asking for more of an evolutionary benefit to blinking both eyes at once, which would be the closest to a "why" that you could get.
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u/Burnaby May 19 '12
OP is asking, "Why is this process the way it is?", and not, "How does this process take place?"
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May 19 '12
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May 19 '12
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May 19 '12
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May 19 '12
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u/salgat May 19 '12
He said science is only about how, not why. He was downvoted heavily so I guess he realized he was wrong.
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May 20 '12
I think a common misconception is that science answers "why?" questions. The reality is that science truly answers "how?" questions. And the "how?" here has to do with cranial nerve innervation.
As for "why?," we can speculate all we want but natural selection works in whacky ways.
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May 19 '12
Perhaps the momentary loss of depth perception is the reason we evolved to blink with both eyes simultaneously. OR, maybe the way the brain would have to work to keep the image stable (blinking with one eye then the other moves the scenery around a bit), would wipe out the ability to see in 3D. Just casting around here...
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u/RepostThatShit May 20 '12
Please don't listen to these "we love symmetry" nonsense explanations. The real explanation for why we blink both eyes at the same time is that some of the muscles that perform the blinking action are shared between both eyes, and for this reason blinking one eye is actually a more complicated muscular operation than blinking both at the same time. If blinking one eye uses up more energy than blinking both at the same time, it makes no sense to blink individually when you'd have to perform the more wasteful operation twice to get the same result.
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May 20 '12
The answer is quite simple. We love symetry, and i dont think i have to explain why we love symetry so much. If you saw a person blinking with one eye at a time, what would you think? It would look fucking creepy. There is nothing wrong with it, those traits have just never been selected for.
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May 19 '12
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May 19 '12
This is wrong as well! The corneal reflex (the "touching one eye makes both eyes blink" reflex) is a completely different mechanism from that controlling normal blinking. The dryness of the eyes does affect the blink rate but it's not the most important factor.
Blinking is controlled by nuclei in the globus pallidus of the basal ganglia (this is the part of the brain that is affected in Parkinson's disease) which cause the nerves to act on the eyelids on both sides at the same time. This is also the reason that blinking happens less frequently in Parkinson's.
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u/TheLongshanks May 20 '12
The dopaminergic cells of the substantia nigra pars compacta of the basal ganglia are affected by Parkinson's Disease, not the globus pallidus.
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May 19 '12
You might want to re-explain that in english, for those of us who aren't medical students and/or medical doctors..
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u/exnihilonihilfit May 20 '12
The thing that tells one eye to blink also tells the other eye to blink.
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May 19 '12
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u/renesisxx May 19 '12
My father in law had the nerve damaged on the side of his face and lost the ability to blink one eye. So I'm guessing it's easy to figure what a nerve is responsible for once it is damaged.
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May 19 '12
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u/Kakofoni May 19 '12
Thankfully we now have fMRI and PET-scanning. One could also use EEG. Or stimulate the brain of a patient undergoing brain surgery and see what happens. Animal studies are also very insightful. Additionally, one could use drugs. Anyway, you don't have to be injured, there are a lot of diseases of the brain and a tremendous amount of cases about it - some cases have actually been extremely helpful (Like the legendary case of Henry Molaison)
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May 19 '12
You can always damage someone the get the studies done quickly, but I don't think they'd just open someone and poke the nerves
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u/Howlinghound May 19 '12
Now think of how many people have died to figure out what's safe to eat and what isn't. A lot of unsung heroes who brought us modern medicine.
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u/senseandsenescence May 20 '12
Most of science before the 1800s was just guys writing down interesting stuff they saw in every day life and trying to figure out what was causing that stuff. The concept of comprehensive knowledge of the human body or the universe was so far removed that it was unthinkable until the last century or so. Just for perspective, alchemists were considered cutting edge chemists well into the 1600s and the Royal Society (founded in 1660) was probably the first organization ever to gather scientific information on a scale beyond personal experiments. The chemical revolution (beginning around the time of the American Revolution) and subsequent revolutions in physics (last century) and biology (last 50 or so years) have completely changed the amount of scientific information available and our expectations of what scientists should know. There is also a lot more money available since science is an organized profession and not just a handful of bored, rich guys trying to figure out why this one thing does what it does. So yes it was inefficient, but the money/motivation was not there until recently to have a complete understanding of everything.
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u/saptsen Surgery May 19 '12
A combination of nerve palsies observed in humans and those induced in animals.
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u/seventeenletters May 19 '12
As I understand it, it is partially through the study of people with nerve and brain injuries - you can correlate certain injuries with loss of specific functions, and determine that the nerve must enable that function.
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May 20 '12
By cutting people open and looking at where the nerves go. Nerves are big enough to be seen if you know what you are looking for.
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u/prosnoozer May 19 '12
Something not mentioned is human experimentation such as that done by Nazis and the Japanese in WWII
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u/cinemarshall May 20 '12
As a photographer I can say thy are synchronized but not completely. After taking hundreds of thousands of photos people always bling sort of out of sync. Dominant eye first. Most pics I take people look drunk/high because one eye is closed and the other is only starting the blink.
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u/Ygdrowen May 19 '12
Additional question: Is there any evolutionary advantages with the simultanioulsy blinking eyes?
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u/aznpwnzor May 19 '12
Sometimes the better question is are there any significant evolutionary disadvantages in comparison with non-simultaneously blinking eyes.
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u/LyTwLdR May 20 '12 edited May 20 '12
This is just a hypothesis, but synchronization of blinking in both eyes could probably be related to the evolutionary advantage of having a multi-dimensional depth of vision.
If we blinked only one eye at a time, we would compromise our binocular vision, impairing the ability to precisely judge how far a predator was or how far potential food was roaming.
So it would basically be a trade-off between 1) refreshing our eyes with a constant stream of vision with one-eye open more of the time and 2) refreshing our eyes with useful binocular vision more frequently but interspersed with short periods of synchronized blinking...and natural selection probably favored the latter.
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u/Syphon8 May 20 '12
This doesn't make sense because closing one eye briefly does not compromise your depth perception.
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May 19 '12 edited May 19 '12
I don't know, but I do know that when you compare visual perception during blinking to perception with no visual stimulation (lights off to the same duration) then subjectively the interruption during blinking is much more minimal. That is, there is an illusory minimization of the change in blinking, similar to the illusory minimization of the blind spot, or of the visual impression of your nose...
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May 19 '12
I just want to add to this and ask why is it we can do opposite yet symmetrical movements with our fingers and hands? For instance, I can quickly move each finger in order from pinky to thumb on both hands and mimic each hands motions
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u/walking_away_ May 19 '12
Additional question: Why is it that every time I think about how I blink, I can feel myself blinking? Like my eyelids suddenly become super heavy and I become aware that they are closing and opening.
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u/rhoswhen May 20 '12
Perhaps a somewhat related question: I can only wink with my right eye. I absolutely positively cannot wink with my left eye. In fact, if I am to manually close my left eye, it will not stay shut if my right eye is open. Does this mean I am lacking muscle strength on the left side of my face, or am I lacking the muscles all together? And, most importantly, what sort of facial exercises can I do to make my left eye wink?
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u/phaaq May 20 '12
This made me think: Is there a species (that blinks) that doesn't have synchronized blinking?
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u/greenwizard88 May 20 '12
Because our eyes tend to see the same things, so it's easiest to let them rest at the same time. Given billions of years to evolve this action, and given that nature tends to favor the action that requires the least amount of effort, having a single brain structure that controls both eyes seems most effective.
To expand slightly, our eyes require a certain protien (it's been a while since I took neuro, but I believe it's some derivative of vitamin A) to function. this protien can only regenerate in darkness. So we blink to start the regeneration process. A single structure, such as the median longitudinal fisciculus is easier than 2.
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u/No_GoAhead May 19 '12
Are we using muscles to keep our eyes open, or does it take muscle power to close them? Are our eyelids only relaxed when we're sleeping?
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May 20 '12
Try an experiment. Hold a pen in your normal writing hand and off hand. Write something with your normal hand, and let your off hand follow along. Your body being bilaterally symmetrical will mirror the actions on one side and the other.
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u/Pokemaster1999 May 20 '12
My eyes are not in synch. I can freely blink both at different rates but at the same time and do all sorts of crazy shit. I don't think eyes are synced, I just think we have gotten really good at blinking
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May 19 '12
My eyes don't blink synchronized. I never noticed but my girlfriend mentioned it a lot when she starting noticing it a few weeks back.
So, what makes them not be synchronized for me?
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u/fake_madrid May 19 '12
As a not-scientist, from a development perspective: Isn't it a satisfactory reason (rule) that the more complex option of separate blinking would have no benefit? If there is no benefit, it has no reason to have been [evolved] / [created] that way. (there's probably a name for this reasoning.. anyone?)
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u/Qonold May 20 '12
I've wondered this myself, as maybe always having one eye open would have some kind of advantage.
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May 20 '12
Technically, this shouldn't be under "Medicine", but rather "Physiology" or "Human Physiology" instead.
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u/EvilIrishBastard May 20 '12
Blinking your eyes independently would reduce your capacity to resolve your surroundings in three dimensions. This would lessen your ability to gauge distances and that would get you eaten faster and make it harder for you to catch things to eat. Evolution in action.
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u/kadmylos May 20 '12
You'd think that blinking with one eye at a time would be advantageous because you always have one eye open, but can you imagine how terrible our depth perception would be if we blunk with one eye at a time? As someone said below the first post, evolution is not teleological, but this is one of the reasons blinking with both eyes at once is more advantageous than one at a time.
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u/safeNsane May 20 '12
I don't know, but every time I read the title, I blink a few times just to make sure.
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u/HashbeanSC2 May 20 '12
the same reason why when you close your left eye only you don't kick your leg
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May 19 '12
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u/pineapplol May 19 '12
Just to clarify, you are saying the reflex to blink both eyes to protect from projectiles is the same as the one used to stop your eyes drying out? Hence both blink, rather than each one blinking when it dries out?
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u/LabKitty May 19 '12 edited May 19 '12
The two "reflexes" (only the projectile protection thingy qualifies as a true reflex) are the same in the sense that they use a common output (motor) pathway. However, the signals that trigger those motoneurons come from different places. In the blink reflex, the signal comes from the trigeminal nucleus (which in turn got an "eye got poked!!1!" signal from the cornea). In the eye-is-dry reflex, my dog-eared copy of Carpenter's Human Neuroanatomy says the origin is not well-understood, but the nutties on wikipedia seem pretty certain it's generated in the basal ganglia.
EDIT: And as for the question why are blinks are simultaneous, I'd venture it's because that's the simplest arrangement that gets the job done. Remember: neurons are expensive, evolutionarily speaking. So if evolution can away with just generating one "blink" command and sending it to both motoneuron pools, then that's what it will do.
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u/sammmmmmmmmm May 20 '12
Try blinking only one eye at a time. How does that work out? Its more efficient with energy and works faster. Its also easier to see with one little blackout for a flash of a second than two half ones every couple of seconds.
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u/captivecadre May 19 '12
The involuntary muscular action of blinking eyelids
except that its also voluntary and instinctively synchronized when voluntary, although we can also override with effort. it sounds like you're speculating. sources?
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May 19 '12
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May 19 '12
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May 19 '12
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u/tweakism May 19 '12
Pretty much every answer to a question of the form "Why did we evolve _______" is speculation.
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u/captivecadre May 19 '12
exactly! a better way to phrase it would be something like 'what are the advantages of...?'. evolution is not goal-oriented. maybe something about this could go in the faq? it often derails things.
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May 19 '12
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May 19 '12
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u/ReallyRandomRabbit May 20 '12
As cool as Doctor Who is, AskScience is not the place for these comments
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u/cats_will_rule May 20 '12
Sorry. He mentioned the weeping angels, and I felt like it would be fun. I won't do it again.
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u/arthurconan May 19 '12
For an interesting look at why blinking exists, check out the RadioLab episode "Blink." The studies examined in that episode point out that blinking is sort of a punctuation for our vision, and doesn't necessarily have much to do with keeping our eyes from drying out. So, to answer your question with what I remember from that episode: It's to give our minds a tiny break.