Can humans learn to see in more than three dimensions?
What follows is highly speculative (and therefore possibly nonsense), but bear with me. (Or, if you prefer, don’t.)
First, let’s think about how humans learn to see in more than two dimensions. Your visual cortex (at least as I understand it) is pretty much two-dimensional, but apparently your brain is pretty adept at converting two dimensions worth of information into a three-dimensional picture of the world around you.
To accomplish that feat, your brain employs (at least) two tricks. First, it can infer an object’s depth (by which I mean its distance in front of you) from the angle between it and your two pupils:
Second, your brain can infer an object’s depth from the size of the accommodation reflex (change in lens shape, pupillary contraction, etc) needed to focus on it.
Ordinarily, these two methods pretty much agree, and your brain uses that answer to construct its map of the world.
But suppose I could surgically adjust your eyes in a way that breaks that agreement. For example, the angle-method might continue to work just as it does now, but I’d disrupt the accommodation reflex so that your pupils now contract by an amount that depends not on the distance to an object but on, say, its redness, or its squareness, or even just varies randomly. Better yet, suppose I could do this at a very early age, when your brain is still learning how to process visual signals.
Would you then start seeing in four dimensions, with redder objects or squarer objects or random objects appearing farther away in the fourth dimension? It strikes me as pretty plausible that this could work, but maybe someone who actually knows something about neuroanatomy (i.e. not me) will have more to say about this.
A few years ago I had gone too long without an eye exam, and my blended lenses needed to greatly strengthened in the reading area. When I put on the new glasses, the lower half of my field of vision was so distorted that I thought the sidewalk was sloping up and everyone had very short legs. The optometrist told me it would take two weeks to adjust. I gutted it out, and suddenly everything seemed normal. Maybe if you did the operation to someone who had not learned to see yet it might work, but I suspect the brain of a lifetime sighted person will adjust.
It seems plausible that our visual processing could be harnessed to slightly different ends than the one we have naturally if we could alter the inputs.
From a physics point of view, does not the lense have to accomodate differently for red and blue light anyway? Probably not enough to make a difference if so.
I think the brain learns to process the inputs in a meaningful way as it develops. Without this learning it is difficult to make any sense of the visual inputs. Sight restored to people totally blind (no light perception) from birth is unknown, but there are a few cases of people recovering from functional blindness later in life. At least initially the individual has problems assimilating what they see, such as failure to percieve depth and perspective and to recognise objects. We are used to the idea that things get smaller as they are further away, but this has to be learned. Optical illusions are therefore often not observed or diminished by the recently sighted. The necker cube is a line digram of a cube seen from the edge that appears to fluctuate between going away from you and coming towards you. This was not seen as even having depth by one well known sight restoree.
http://www.richardgregory.org/papers/recovery_blind/3-observations_p2.htm
In an apparently common finding, this man became depressed after restoring his vision. He went from a succesful blind man, proud of his ability to overcome his problems, to a man far behind everyone else in understanding what had become his new reality.
“His story is in some ways tragic. He suffered one of the greatest handicaps, and yet he lived with energy and enthusiasm. When his handicap was apparently swept away, as by a miracle, he lost his peace and his self-respect.
We may feel disappointment at a private dream come true: S.B. found disappointment with what he took to be reality.”
However, there is evidence that given sufficient time people can learn nearly all the visual factors that those sighted from birth enjoy – with a few minor gaps and longer processing times. This case of a woman in India who was almopst blind until 12, then examined agfter 20 years of restored sight shows:
http://scienceblogs.com/cognitivedaily/2008/11/11/can-a-blind-person-whose-visio/
So our 3D perception is learned. We do not know that a necker cube is a cube unless we have fmailiarised ourselves with the visual world. We learn to interpret the responses to accomodation and paralax as distance. If we substituted response to redness say instead of distance I do not think we would precieve it as a dimension as such, but we would incorporate it into our view of reality. It might be that the information would provide little extra information about the world, and we would learn to effectively ignore it as a waste of processing power.
Some people have synesthaesia – certain words have strongly associated colours for example. In many ways these people percieve the world with extra dimensions.
1) you also infer distance by interpreting sizes of known objects, e.g. Ames room illusion
2) 3-D movies work relatively well by only playing with the differential angle trick, your focus remains stable on the screen
Don’t I already demonstrate my ability to perceive in four dimensions each time I catch a baseball?
(Ok, fine — each time I nearly catch a baseball?)
This is unrelated to seeing four dimensions in the outside world, but Charles Howard Hinton in the 1800’s developed a technique called “Hinton cubes” to visualize four dimensions in the mind’s eye. It involved 81 carefully-colored wooden cubes which if manipulated, would allow you to visualize a four-dimensional hypercube.
How would this be different from seeing, say, ghosts? How do physicists deal with that now and what is going to make them change their view?
Your analysis of how 3D vision works is rather deficient. If your
description were complete, then wide-eyed or cross-eyed convergence
of a flat picture would not work (think, for example, about “magic
eye” stereograms). There is absolutely no accommodation 3D movies
or for people with cataract-replacement lenses.
The primary mechanism is one you don’t mention: binocular disparity.
I.e.: the images on the retinas of your two eyes differ. The
mechanisms you describe can supplement binocular disparity but
are secondary and not required.
#7 When I close one eye, the world does not appear 2D. A lot of the 3D effect is from learned cues about what our vision actually detects. This is why optical illusions work.
The binocular disparity is how 3D films work and is a major input into depth perception.
Depth perception is very complex, and why I say that linking say accommodation reflex to a color would be incorporated into our view of the world. I do not think that it would be of any great benefit, since we detect color by other means. I do not think we would perceive color as another dimension, as I think we instead learn that the accommodation reflex we have means depth in the real world. Learning that our accommodation reflex meant red I do not think would lead us to see red as a dimension.