Prism-induced reversal of retinal images (student post)

I was happily absorbed in my slightly vegetative stupor on the couch when my roommate walked into the room and starting talking about physics. Ugh, physics, I thought, but I politely listened as she began talking about lenses, specifically how they are related to sight. It is common knowledge that the images we see are inverted on the retina, and then further processed. However, my roommate was discussing experiments done on humans that inverted their vision by 180 degrees and found that, though at first they could not function normally, eventually they adapted. I thought this was fascinating, and wondered what the brain had to do with this process. Unfortunately my roommate’s knowledge was pretty limited, so I decided to do some research of my own.

Research on visual distortion of the retina has been going on for quite some time. Devices have been used that invert the retinal image, so that everything is seen upside down. At first subjects wearing this device will reach for things and miss, or will bump into things as they travel about a space. Eventually, they adapt. What I wanted to know is how do they adapt? What changes take place in the brain that allow them to do so? Is it just simply learning to reach a little farther to grab something, or walk a bit differently to avoid bumping into something? What is happening at the neural level?

What I discovered is that in order to make sense of the incorrect efferent sensory information, the subject must rely on perceptual and proprioceptive feedback (proprioceptive refers to the position sense, which is what allows us to perceive the location of various parts of the body). However, while the subject can adapt to this altered state of vision, it is not accompanied by a return to upright vision. Researchers found that the contralateral posterior parietal cortex is activated when subjects were trying to reach objects while their vision was distorted, and thus has an important role in visuospatial processing. Other studies indicated that there was no evidence of remapping of retinal coordinates. Further research needs to be conducted on neurons to see what (if anything) is occurring at the neural level. However, due to the rapid recovery of normal function after vision was restored, it seems unlikely that any major modifications were made. What I learned from this investigation is that changes seem to be taking place at the processing level that allow subjects to adapt. However, how this occurs still remains to be investigated.

Linden D.E.J., Kallenbach U., Heinecke A., Singer W., Goebel R. 1999. The myth of upright vision. A psychophysical and functional imaging study of adaptation to inverting spectacles. Perception 28(4) 469 – 481.

Harris, C.S. 1965. Perceptual adaptation to inverted, reversed, and displaced vision. Psychological Review 72(6) 419-444.


  1. Hank Fox says

    However, while the subject can adapt to this altered state of vision, it is not accompanied by a return to upright vision.

    Does it mean they continue to see things upside-down? But that they become good at navigating despite that?

    I’d read stuff in the past that seemed to say experimental subjects learned to flip the inverted visual image in their brains while wearing the inversion glasses, until eventually both ways of seeing looked rightside up to them.

    While I was reading your post, I was hoping you were going to say you were going to try it yourself.

    Find out a way to do it, dude! Experience it for yourself for some great firsthand experimental data. And let us know.

    Eye-related, but not on the same subject: I’ve wondered if humans can learn to operate their eyes independently. You can get some idea of what I’m talking about if you get a friend to cross his eyes, and then turn his visual field sharply to the left or right. One of the eyes remains fixed, the other moves independent of it. It looks freaky.

    Anyway, could a person learn to look ahead with one eye, look to the side with the other? Could they learn to diverge their fields of vision, so that both eyes were looking to opposite sides? Could they learn to look up and down simultaneously?

    I don’t see why not. It seems like something — like raising one eyebrow or twitching one ear — you could learn in about a week (although PERFECTING it might take much longer).

    And yet I’ve never heard of anybody doing it.

  2. Sili says

    An acquaintance once told me that primate researchers have tried the more permanent experiment of turning an ape’s eye upside down. It too adapted to it, but I don’t know any details.

    Another trick is the bike with gearing in the handlebars so that you have to turn to the wrong side to steer. I vaguely recall something about it being immensely easier to ride such a bike by wearing left-to-right swapping glasses akin to those you talk about.

  3. Nix says

    Anyway, could a person learn to look ahead with one eye, look to the side with the other? Could they learn to diverge their fields of vision, so that both eyes were looking to opposite sides?

    This is a common disorder of the visual system, amblyopia. It’s only nice if you like having little depth perception, constant double vision, and looking weird thanks to having one eye pointing off to the side all the time. (If you’ve always had amblyopia the double vision is more easily ignored unless you’re tired).

    It’s not so much `learnt’ as `always there unless you explicitly concentrate on looking at something with both eyes’. It’s not exactly useful, not least because the direction and distance of the divergence is not under conscious control.

    (I’m amblyopic.)

  4. sailor says

    When I first learnt about this experment back in college, it was implied that the subjects sight inverted after some days. Little introspective comment was asked for or reported on as I remember. I have been told later replicating sutdies did ask their subjects and bascially they still saw upside down but learnt to deal with it.

  5. says

    The original study became the source of a pervasive and persistent bit of psychology folklore, which the poster refers to obliquely by disclaiming it: “… no evidence of remapping … rapid recovery … unlikely that any major modifications were made …”

    The folklore being disclaimed here was repeated in countless dormitory bull-sessions from the late 1960’s on. It would typically go something like this:

    “So, these researchers, they got some subjects and put goggles on them that made everything look upside-down. They had to wear these goggles 24 hours a day. And at first it was really disorienting, and they got sea-sick, but after a while they got used to it and could do everything normally. But the weird part is that after they got used to it, they took the goggles off, and everything looked upside-down again, and they had to re-adapt to seeing everything the right way up, and it took just as long as it had taken to get accustomed to the goggles in the first place.”

    This folklore, while false, was intrinsically attractive, and was spread widely and uncritically. I speculate that it was a memetic success because it matched the dominant psychological paradigm of the time: that human neurology is completely plastic and has no intrinsic preconceptions about the structure of external reality. This tenet remains popular, even after being repeatedly disproven with examples of brain adaptations for particular kinds of perception (and slightly more controversially, cognition).

    Our host is unsympathetic to the evolutionary-psychology viewpoint, and his criticisms are valid: some evo-psych enthusiasts are indeed too aggressively adaptationist. But these enthusiasts shouldn’t make us reject the entire endeavor. Some parts of the brain are indeed adapted to some tasks; the brain is indeed remarkably plastic. Plasticity and adaptation are both important aspects of our neurology, and their boundaries are a fruitful avenue of research.

  6. says

    As a teenager (30-odd years ago) I learned to read both upside down and mirrorwise, and in both cases it was remakably easy to learn to do so.

    They are both skills that I mostly retain, in spite of doing either only rarely – to the extent that a couple of years ago, on encountering a “PUSH” sign on a glass door I was walking toward, I pushed, and to my surprise found it didn’t work. It took me some time to realize the sign was on the /outside/ of the door, and I had read it without any awareness of a problem (apart from the letters themselves, the sign was clear) – I was reading them from the wrong side, without any sense that the word was backward at all.

    Once I realized the sign was on the other side of the door, I had a perceptual shift and could suddenly “see” that it was backward.

    The reading upside down thing gets used a little more, and people are almost always surprised when they realize I’m doing it. It’s very handy when playing Scrabble (we don’t need to turn the board), but it also comes in useful when I go into somebodies office to work with them, since we can both look at the same document at the same time as we discuss it, even though I’m on the wrong side of the table. I quickly lose any sense of reading upside down at all, but then if I try to write I have to stop for a second and think about which way up it’s supposed to go.

  7. RamblinDude says

    James Bond, in one of the books, takes a course in reading upside down, to help in covert spying and such.

    I remember a guy, back in 1975, telling us that he actually did the experiment with the upside down glasses when he was in high school. His experience was exactly as ACW described above. He related how he woke up in the middle of the night after the third day and the world suddenly turned right side up, and he could function normally again. (I remember him turning his hand, like twisting a knob, to demonstrate what it felt like.) When he finally took them off, the reverse happened. So now I’m surprised to hear that this was very unlikely.

    It never occurred to me that he might be lying to us.

  8. central texas says

    Interesting to hear about this again. I first encountered it in the form of a film by the Moody Bible Institute, who used to present a lot of bits of sciency things. That was probably 45-50 years ago. What I enjoyed was the attempts to portray with the camera what the subjects (who were wearing inverting lenses) experienced. These films were one of the staples of grammar school in South Dakota; shown weekly. I do not recall that there was ever an overtly religious slant. At least there is no evidence that it worked if it was there.

    I can no longer recall the exact explanation for the degree of adaption, but as I recall it, the explanation was for an ability to remap the input such that one perceived the world as right-side-up again. Maybe they were also mistaken or worse.

  9. autumn says

    I have really bad eyesight, correctable, but bad enough that my glasses, when my prescription changed, caused noticable distortion at the edges of the lenses. It took about two days of wearing new glasses before, for instance, telephone poles and walls stopped appearing to be bending over me. When I got contact lenses, the opposite occured. Now, when I have a couple of days off, and I switch to my glasses for normal stuff, I have an uncanny ability to knock things off of walls that are near doorways as I pass. Brains are funny.

  10. Jim A. says

    What autumn said. Those of us with severe nearsightedness get used to the barreling (flat surfaces appear convex) that corrective glasses give you. The other thing noticeable about glasses versus contacts is chromatic aberation. If I look at a field of blue next to a field of red through one side of my glasses there is a black line border between the two. Through the other side, the border line is white.

    And of course when the Greeks wrote Boustrephedon* the alternating lines were mirror writing, with the letters reversed rather than gnitirw sdrawkcab. Of course RongoRongo was written with alternating lines upside-down. Even we read $4.00 as “four dollars” not “dollars four.”

    *left to right, then right to left in alternating rows of text

  11. says

    I would suggest that the orientation of vision is set during infancy. The brain does wire itself and I would imagine that it sets all that up during that time. If the same devices where used on a newborn and where worn for the first year of life, their vision would likely be inverted when you take them off, and may remain that way.

    That being said, we’ll likely never know because it would be quite… unethical to do such a thing to a human child. I’m not sure how it could be done to an animal though… since none would be able to communicate the specifics of their perception.

  12. Michael Martin says

    When I first got progressive bifocal glasses (yeah, I’m an old fart) the world was really warped. I had to hold tightly to the railing on stairs to walk down. After three days I couldn’t even duplicate the problem, my eyes/brain had adapted and it disappeared.