njtt, as stated above, I agree with you. I hope we’re not just getting caught up on semantics. I understand there’s no little projector screen in our brains, but there is some correlation to a stochastic array of sensors on our retina, and our visual cortex creates a pretty accurate “picture” from this flux of nerve impulses (albeit, not so much as it seems we do) in a way that relates almost 1:1 to our exterior world.
If our sense of balance and proprioception were not factors in how our brains form our vision (in context of orientation), then why would our visual cortex ultimately flip our perception when wearing reversing goggles?
Without our vestibular senses, we’d have no sense of up and down, nor velocity. Without proprioception, hand/eye coordination would seem very difficult.
Sigh.
Yes, by using complex and sophisticated techniques, and expensive equipment, it is possible for a scientist to see a (highly distorted) “image” in the visual cortex of the brain that reflects the pattern of stimulation of the retina. However, this “image” does not in any way function as an image for the visual system. To nearly all intents and purposes, its existence is merely an artefact of the way the retina is hooked up to the brain by multiple ‘cables’ running in parallel. It would not affect how vision works if this “image” in the brain was flipped upside down or sideways, or stretched out or squashed more together, or even if it were broken up into 10,000 little pieces which were then scattered in a random pattern around the neocortex. All that matters, so far as visual processing is concerned, is that the relevant neurons at the relevant stage of visual processing are hooked up in the right way to each other, and to all the other relevant neurons involved in other stages of visual processing. The principal reason that this apparent “image” exists (I should really say “images,” because actually there are several of them in several different visual processing areas of the brain, but the same considerations apply to them all) is simply that wiring things up this way allows for most of the ‘wires’ to be kept relatively short, which thus helps to minimize the overall bulk of the brain (and helps to keep processing time down a bit).
Yes, my point is, in a sense, a ‘merely’ semantic one, but it is a very important semantic point. Calling the momentary pattern of activation of retinotopically organized visual cortex “an image” is something that can and, more often than not, really does lead people (even, sometimes, experts who should know better) into radical misunderstandings about how visual perception works. It is all too easy to fall from this sort of “inner image” talk (with a smug, implicit or parenthetical acknowledgment that of course one is not silly enough to imagine that there is anyone in there who gets to see this image) into an account of perception that implicitly actually does require there to be a little man in there to experience and interpret . . . well, perhaps not that image, but perhaps another, hypothetical, more “processed” one somewhere down the line, or an inner “description” of the image, or whatever. This way of thinking about vision is extremely tempting for most people, and it permeates popular and even many not-so-popular accounts of how the visual system works. I think that, in large part, this is because of the unfortunate prevalence of the “inner image” metaphor.
And here is a beautiful example of how this “image” talk misleads people’s thinking about visual perception. As I have repeated explained already in this thread, nothing gets “flipped” when people adapt to reversing goggles. It has been shown that the momentary activation patterns in the retinotopically organized visual cortex (what you insist on calling the “image”) do not flip over when the person adapts to the goggles (although they do get flipped over when the goggles are initially put on), and, indeed, careful questioning reveals that it does not even seem subjectively to the people involved as if things “flip” when they adapt* (although some might sometimes use that metaphor when speaking casually about what has happened to them: they are just as likely as anyone else to frame their talk and thinking about visual perception in terms of the misleading “inner image” metaphor). Note that the process of adaptation is gradual. What would a part-way “flipped” visual experience be like? Would everything look as though it were turned sideways? The “flipped” metaphor only seems appropriate when people implicitly assume that what we experience is an inner image that can be presented to the inner homunculus either one way up or the other.
I already explained at some length, in post #9, why and (in outline) how people adapt to reversing goggles. It is about their need to move about and otherwise act in a world about which their goggles are (initially, before they get the hang of them) feeding them systematically misleading information. I did not find it necessary to refer to proprioception or vestibular sense in the course of that explanation. What matters are the attempts to act in the world and the discovery that these attempts do not bring about the results that their (initial) visual experience would lead them to expect, and the way that they gradually learn to deal with that situation. I confidently predict that if someone were to sit stock still in a chair for the duration of the experiment, after donning the goggles, and they kept staring straight ahead, and did not attempt to reach and touch or take hold of anything, then their visio-motor system would not adapt, and everything would continue to look upside-down** even though their proprioceptive and vestibular senses would still be fully operative
I suppose that you are probably right that, in practice, proprioception and vestibular sense do play a (secondary) role in adaptation to the goggles, as the subjects attempt to move around in the world and these senses provide them with feedback about what is happening,*** but I still fail to see why you think that it is a significant point to raise in the context of this discussion. Smell and hearing might play minor roles too, as we do get some information about the spatial layout of our environment from those senses, but so what?
*Linden, David E.J., Ulrich Kallenbach, Armin Heinecke, Wolf Singer, and Rainer Goebel (1999), “[The myth of upright vision. A psychophysical and functional imaging study of adaptation to inverting spectacles](wexler.free.fr/library/files/linden%20(1999)%20the%20myth%20of%20upright%20vision.%20a%20psychophysical%20and%20functional%20imaging%20study%20of%20adaptation%20to%20inverting%20spectacles.pdf)”, *Perception 28:* 469-81.
**I am oversimplifying somewhat here, because, if their gaze were fully fixed, and the scene in front of them were static, they would soon cease to see anything at all. On the other hand, if their eyes were allowed to move (a form of action in the world), they would probably eventually adapt to the goggles.
***Essentially, these senses will be telling them, “You really did move in the direction that you intended to, even though your senses of touch and vision are telling you (quite correctly) that you have not arrived at the place where your visual sense led you to believe you would arrive.”
Yep, we’re saying the same thing. Sorry, I just skimmed you’re previous post before (#9).
But I would like to stress there’s a strong role our proprioception and vestibular sense plays in the way we perceive the world around us, and interact within it when doing things that require vision. That’s what the visuo-motor system is.
It sure as hell does not look like it to me.:mad: You keep talking about images in the brain, and “flipping”, and I keep saying there is no such thing as either.
That, we can agree on. But
[QUOTE=cmyk;14379032That’s what the visuo-motor system is.[/QUOTE]
Well, that is not what I meant when I mentioned the visuo-motor system (and not what I think most other people would understand by it). I was referring to the interaction of the visual system and the motor system that produces actual actions, movements of the body. Of course you are right that vestibular sense and proprioception play a large role in the coordination of action too, and that they interact with vision (and other senses). I don’t think we disagree in any substantive way about that, but I think we do disagree about images and flipping (unless you are now disavowing your original use of those terms).
The paper I linked to in post #22, incidentally, is particularly adamant (and provides excellent evidence) that nothing resembling ‘flipping’ takes place, even subjectively, when people adapt to inverting goggles.