Cognitive Daily

ResearchBlogging.orgThis morning I went into the darkest room in our house (the kids’ bathroom), closed the door, and turned off the lights for 5 minutes. There was enough light coming in through the crack in the door that after a minute or two I could begin to make out shapes in the room: A towel rack, the shower curtain. My eyes had adapted to the dark condition. Then I closed my right eye and covered it with my hand. I turned the lights back on, for a minute, until my left eye had adapted to the light. Then I turned the lights off.

I could still see the towel rack and shower curtain with my right eye, which remained adapted to darkness. But my left eye could see nothing. In fact, my left eye felt as if it was closed. I made every effort to open the eye, but it seemed that some unstoppable force was keeping it closed. The only way to make my eye feel as if it was open was to cover it with my hand. I still couldn’t see anything with the eye, but at least I could convince myself it was open.

What I was experiencing was a fascinating illusion discovered by Uta Wolfe and her colleagues. When one eye is adapted to darkness and the other is not, then in a dark room, the light-adapted eye will feel as if it is at least partially closed. You can try it out for yourself, just as I did (You might want to bring an iPod [with screen dimmed] or some other form of non-visual entertainment — five minutes in the dark is a long time!). I’ll include a poll later on so we can see if our readers experienced the effect.

Although I experienced the effect after just 5 minutes, Wolfe’s team actually asked student volunteers to adapt to darkness for 30 minutes. A key to the experiment is that the room should not be completely dark. They used adjustable fluorescent lights to dim the room to 0.005 fc (footcandles — compare to about 30 fc in typical indoor lighting). Then the students closed one eye and covered it with their hand while the experimenter increased the lighting to 2 fc for one minute. The lights were dimmed again and the students uncovered their eyes. Then they rated the sensation in the light-adapted eye (the one that had NOT been covered and therefore was no longer adapted to darkness). Here are the results:


Thirteen of the fourteen students tested experienced the illusion, saying that the eye that had adapted to light felt like it was sagging, closed, and “droopy,” compared to the other eye. So what’s going on here?

Wolfe et al. say that the effect is related to other somatosensory illusions, such as the “phantom leg” effect that amputees feel. A milder version of this effect can be experienced by most people: if you see a rubber hand in a spot where your hand could be (e.g. in front of a screen that hides your hand), then if someone scratches the rubber hand, you feel your own hand being scratched. In fact, for a wide variety of physical sensations, when the visual sense contradicts the touch sense, usually vision will win out.

That appears to be what is going on in Wolfe’s team’s illusion. You don’t normally see your eyelid, so the only visual confirmation you get that your eye is closed is that things appear darker. The illusion takes advantage of the fact that everything appears darker when you first enter a darkened room. After a few minutes, your eyes adjust and you can see again. In the illusion, only one eye is adapted to the dark, and so while one eye sees normally in the darkened room, everything seems dark in the other eye. Even though our tactile sense tells us the eye is open, vision trumps touch, and we experience the illusion of the eye being closed.

In a second experiment, people who experienced the illusion covered up the light-adapted eye. The illusion disappeared, and the eye felt as if it was open again. Covering the dark-adapted eye also caused the illusion to disappear. Why?

Now the sense of touch and vision were aligned again. We expect to not be able to see when our eye is covered, so it makes sense that the eye could be open. When the dark-adapted eye was covered, neither eye could see anything, so visual and somatosensory systems were again aligned.

In a final experiment, people experiencing the illusion covered the light-adapted eye with a clear disk (they were unaware the disk was clear). The illusion disappeared, even though the visual input didn’t change at all. But when the dark-adapted eye was covered with a clear disk, the illusion did not disappear: at this point, the participants could still see out of the dark-adapted eye, and could not see out of the light-adapted eye, so the illusion persisted, as before. Fascinating stuff.

So, let’s see how many of our readers are willing to try this effect on themselves. It’s important to not be in a completely dark room, and not to look directly at light sources (even faint ones) while adapting to darkness. If you have five minutes to try this out, you’ll experience a truly extraordinary sensation. You can report your results in the poll below.

Wolfe, U., Comee, J.A., Sherman, B.S. (2007). Feeling darkness: A visually induced somatosensory illusion. Perception & Psychophysics, 69(6), 879-886.


  1. #1 marciepooh
    May 15, 2008

    In the interest of full disclosure, I checked definitely even though I didn’t do the experiment. I experience this all the time when I have to turn on a light in the middle of the night. I close one eye when I turn on the light so I’ll be able to see when I turn it off again.

  2. #2 dean
    May 15, 2008

    I think this is why sailors were known to wear eye-patches, so that they could easily see when going below deck.

  3. #3 Dave Munger
    May 15, 2008


    I think you’re right about that, but whether they actually experienced the illusion would depend on their behavior. I’ve read some accounts suggesting that they switched the patch from eye to eye, so that when they went below deck, they covered the light-adapted eye. In this case, they would not have experienced the illusion.

    But they might have just flipped up the eyepatch below deck. Then the light-adapted eye should have experienced the sensation of being at least partially closed.

  4. #4 Marty
    May 15, 2008

    On an episode of Mythbusters The team examines this possibility. They concluded that the Eye-patch might actually have been used for “instant night-vision” When going below decks during the day, or above at night.

  5. #5 Felstatsu
    May 15, 2008

    This is rather interesting, and an illusion I’d not heard about before. Going to have to try this out as soon as I can figure out how to set it up in my house, and should I be able to set it up I’ll be sure to post back with the results.

  6. #6 Jefrir
    May 15, 2008

    I get a version of this when I walk around without my glasses. I have nearly normal sight in my right eye, but I’m severely short sighted in my left eye. When I take my glasses off I can feel my left eye not working, and it also feels kind of like it’s shrinking back into my head.
    Oh, and for the eyepatch thing – British soldiers are still taught to cover their shooting eye when flares go up so they don’t lose their night vision.

  7. #7 rfguy
    May 15, 2008

    Oddly enough, I’ve experienced a similar illusion while caving – after turning off all light sources, the cave was completely dark, and I felt like my eyes were closed. I had to repeatedly close and open my eyes to make the illusion go away. This didn’t depend on differential light adaptation in my eyes, but seems to be the brain interpreting the absolute lack of visual input as ‘eyes closed’.

    I’ll have to try the experiment described in your post later, to see how the illusion compares.


  8. #8 Robyn
    May 15, 2008

    I remember doing this when I was a child. I was intrigued by the light through the bathroom window in our rented Victorian house. I played with the shade and then noticed that when it was down all the way, it took time for me to see my hands in front of my face in the darkness; I had to put them up to where I could feel my eyelashes on the insides of my fingers to know my eyes were open. Then I had some fun switching hands to see if there was any difference. I only quit when my mother asked what the heck I was doing in there! I’d forgotten all about it until this post. Thanks.

  9. #9 Greg
    May 15, 2008

    This happened to me by accident, and for a moment I actually panicked. I was lying in bed on my side such that I had to close one eye. My girlfriend entered the room and turned on the lights for a moment, and then turned them out again. I rolled over and looked around, and immediately got the sense that I had gone blind in one eye, or that it was closed and I couldn’t open it, having completely forgotten that the other had been covered. I started looking at light sources and shifting my head around, trying to confirm that I could (or could not) see out of one eye. Then my girlfriend asked me what was wrong, and I realized that it was just the sensory difference. I felt silly that I had become anxious about it, but it was an… interesting experience, nonetheless. I don’t advise doing this experiment when drowsy or otherwise impaired of mental faculty. 🙂

  10. #10 Felstatsu
    May 15, 2008

    Just tried it out, it definitely felt like my one eye was drooping or closed until it got readjusted to the dark, and the feeling went away when I could feel my hand covering my eye. Rather funny feeling, but entertaining enough to try again and see what else can be done to mess around with the effects.

  11. #11 Freiddie
    May 16, 2008

    Here’s what I felt when I did this experiment just now: one eye (the dark-adapted one) feels normal, while the other eye (the light-adapted one) feels as if there’s a black patch covering the entire eye. Is this expected?

  12. #12 Bjørnar Tuftin
    May 16, 2008

    That was really neat. Especially covering the “blind” eye, feeling it was actually open, uncovering it again and experiencing the “blind” feeling returning!

  13. #13 Hank Roberts
    May 16, 2008

    I have experienced this for years. I’m also naturally very nearsighted in one eye, and — after a cataract replacement — a bit farsighted in the other.

    When I’m up late at night I read with the nearsighted eye, keeping the farsighted eye closed; when I then walk through the darkened house, the eye I’ve been reading with has no dark adaptation and feels just as described.

    Nice to see science has discovered this!

  14. #14 Peter Zelchenko
    May 16, 2008

    I hate to do this, but there’s a real problem with the experiment’s methodology. It wasn’t double-blind.

  15. #15 DIRT
    May 16, 2008

    I often get the same effect as Jefrir but with a twist since I don’t have glasses. I am significantly shortsighted in my right eye it often feels “droopy” or half closed when I am viewing anything further away than my focus distance in that eye. Annoying as hell at Uni since lecturers seem to be in love with the powerpoint on the screen allaway “over there” I frequently have to physically close my bad eye (sometimes with my fingers sadly) to focus on the presentation. Also leads to some very weird sensations when in half light dusk\dawn, partially lit rooms. It adds a “unreality” feeling when viewing completely normal things, hard to describe really. It seems half my attention is clear but the other half is “mystical” (yeah mystical = unfocused so bite me).

  16. #16 Sammy
    May 16, 2008

    Nice one, Peter!

    Actually, the same thing happens to me as Jefrir My right eye is nearsighted, but I don’t normally wear glasses (except when driving, because apparently I don’t have 3-d perception even though I played baseball and softball for years). For me, however, it only happens when I’ve been wearing my glasses and then take them off. I’ve never felt it just in lecture or looking at something far away, although maybe I’m just not quite as nearsighted…

    Slightly off topic, any idea why I never had any trouble seeing those 3-D Magic Eye pictures (stereograms) despite the focus difference between my eyes?

    Also slightly off topic, has anyone noticed that sometimes colors seem a bit different when you switch between looking through each eye?

  17. #17 margaret
    May 16, 2008

    I didn’t feel the effect very strongly (perhaps because I was unconsciously opening my eyes widely in preparation, or because my bathroom isn’t very dark), but then I tried blinking. My “blind” eye felt like it was barely moving, while my normal eyes felt… normal. Strange because I knew both eyelids were going the same distance and I hadn’t felt the “droopy” effect very strongly before that.

  18. #18 mark
    May 17, 2008

    People who work in photography darkrooms have used this for years. Once your eyes get adjusted to the dark, sometimes you have to turn on the light or leave the darkroom for a while. We always would just shut one eye when leaving, and then open up when going back into the darkroom.

  19. #19 althos
    May 18, 2008

    I have experienced this phenomenon many times. Having not worked in a darkroom or on a pirate ship I thought it unusual but not that useful, now I am intrigued to find a practical use for the effect.

    I also experience the colour perception difference between the eyes. I have often wondered whether it was physiological or psychological.

  20. #20 Bernard Holcman
    May 19, 2008

    Very very good. I posted on my blog in Brazil… I hope people will like it as I did! (

  21. #21 Humor
    May 21, 2008

    Very interests.interesting experience. That was really neat

  22. #22 Wade Dorrell
    May 22, 2008

    At first I didn’t feel it (perhaps my right better eye compensating for my weaker one as it does when not wearing contacts?) but after about 10 seconds, my left eye was continuously closing, and the feeling got stronger over the next 10 seconds. At that point I had the muscular feeling that it was in fact closed, I don’t know if it was or not.

    My fiance shared the 5 minutes with me, she didn’t feel the effect at all.

  23. #23 Joe User
    May 31, 2008

    Well now, this helps explain POV porn.

  24. #24 Gautham
    July 31, 2008

    yes, i felt it definitely and only because found ths website while searching. these kind of illusionary sites and sites like stereoscopic are all a mysterious kind of knowedge that i think will get only through the help of internet. Now i am finding more and more wonderful stuff like this and feels that its not going to end.

  25. #25 k
    September 9, 2008

    I find that colours look different from either eye too. It can be very annoying sometimes

  26. #26 loqk
    September 12, 2008

    one thing to watch for in this experiment is priming.

    several experiments have now shown that up to 40% of people will come to believe a false memory (eg bugs bunny at Disneyland, or interpret new evidence in the light of suggested information (eg the distance between two dots in a dark room).

    in the case of this experiment, you have already suggested the sensation of an eye half closed. in addition to people who really do feel this sensation, many people will feel this sensation due to the suggestion.

    a negative control is needed where the participants are told they will feel like their eye is very wide open.

    when i keep one eye closed to avoid loosing my dark adapted vision, I just feel that my eye is blind, or that something is covering the eye just beyond the range of perception.

    marciepooh seems to be a good control demonstrating that the effect isn’t all suggestion as she felt the sensation before the suggestion

  27. #27 Amiya
    November 21, 2008

    I’ll fool around with my eyes (or the vice versa?) tonight and will surely let you know how I felt.

  28. #28 Amiya Sarkar
    November 21, 2008

    I felt almost exactly the same you felt. I was however aware that my eye (not the dark adapted one) was open. This is probably a case of subject bias.
    An “Eye opening” experiment it is.

  29. #29 nl
    March 13, 2009

    i can look at a dim light (or shade) in a dark room and focus on an object around or in the dim light until i have no vision or the light seems to shut off, or quickly fade away.
    i know my eyes are open, they feel open. it is very hard to hold the concentration. if you move at all (move meaning the eyes or head) it is lost instantaneously, and vision is then gained. if i try it in a bright room, my eyes involuntarily shut because they feel stressed like if i really needed to blink. in other words concentration is impossible to hold in a bright room.
    does anyone know why this is happening? can you have the same experience? or what effects might come if it is continued?

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