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Medical Adopting a Rubber Hand, and a New Twist on the Phantom Limb Phenomenon

  1. Apr 7, 2009 #1
    This indicates that sense of body position is arrived at by input from sight, touch, and proprioception, and that, when the stimuli are inconsistent, sight and touch are "believed" by the brain over proprioception:

    http://www.sciencedaily.com/releases/2004/07/040702093052.htm
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    This completely different article talks about a kind of phantom limb I've never heard about before, extra limbs experienced by stroke patients who haven't actually lost any limbs. Here which sense is believed is reversed, it seems, such that proprioception and touch cause the patients to "see" limbs that aren't there:

    http://www.sciencedaily.com/releases/2009/03/090325162626.htm
     
  2. jcsd
  3. Apr 11, 2009 #2

    Q_Goest

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    Hi zoobyshoe,
    This seems to challenge fundamental notions of how our mind produces subjective experiences. The brain of course, produces these subjective experiences, meaning that subjective experiences are supervenient on the brain and not on the actual neurons in the hand that might be “stroked with a paintbrush”.

    Correct me if I’m wrong, but I believe the paradigm we’ve lived with over the years is that the nervous system has a structure which is in some way, fundamental and intrinsic to the brain. By that I mean that the brain has inputs from the eyes, skin, nose, ears, etc… and those inputs produce the subjective experience in the brain because signals coming from those parts of the body come in to the brain in a preprogrammed way. I guess this still isn’t disproven, there are interesting articles I’ve read recently which seem to maintain this paradigm (I’m thinking of the naked mole rats that don’t experience pain in a conventional sense*). However, the experiments you’ve provided seem to challenge this basic conception. These experiments seem to suggest, at the very least, that it isn’t JUST this ‘preprogrammed’ wiring set up by the brain which creates subjective experiences, it is also other inputs including visual cues.

    I seem to remember some experiments done in which people were subjected to a virtual world by having visual and physical stimulation provided by a computer simulation. But rather than being human, these subjects were immersed in a simulation which had them as other animals, lobsters for example. The results seemed to indicate that subjects’ brains could reprogram subjective experiences of the body such that the subjects actually felt as if they had claws, extra legs, and the back fin of a lobster for example. I’ve not seen this study but heard about it somewhere online a few years back. I wonder if you’ve seen anything like that.

    * Ref: http://www.nature.com/news/2008/080128/full/news.2008.535.html
     
  4. Apr 11, 2009 #3
    I think the rubber hand adoption explains that in many cases the brain takes input from different senses about the same external phenomena and coordinates them for greater depth of understanding. Most visual things also make sounds, for example, but sound and vision get to the brain by completely different routes from completely different receptors. Some areas of the brain are dedicated to coordinating these completely different kinds of stimuli produced by the same phenomenon such that we recognize they are two aspects of the same thing, and we don't experience them as two completely separate, unrelated, coincidentally co-occuring things. Gnosias are created. Knowings.

    Full gnosia of the hand, it seems, from this experiment, to be created from three sources, as mentioned before. I think what is happening is that the pattern of gnosia held in the brain tries to sustain itself when the agreement of the inputs is disrupted. The agreeing two of the previous three inputs are "believed" over the one dissenting one, and the 'improper' input is ignored and replaced with one jury-rigged to agree with the two thirds majority.

    A simple and often encountered version of the same thing is that moment of startle you feel when you're at a red light and the car next to you creeps forward a bit making you suddenly think you're rolling backward. Vision is suddenly believed over inner ear.

    I want to link you to this very entertaining and readable article which leads up to a mention of the fact that there is debate and disagreement about how qualia are formed. The article springs off from a discussion of Migraine to the larger issues of how and how much "filling in" the brain does, a sort of cache vs refresh, which helps explain why the brain can adopt a rubber hand so relatively quickly: it is always "filling in" quite a bit already: every detail of every sensory input isn't constantly updated, it seems. Expectation of sameness in the external environment causes "filling in" without checking too often for change.

    http://migraine.blogs.nytimes.com/2008/02/17/lifting-lights-and-little-people/

    As for the phenomenon of gnosias the title story in The Man Who Mistook His Wife For A Hat is the easiest and most comprehensive introduction. The patient's eyes are working perfectly well, but some part of his brain is compromised such that he can no longer form a knowing of what he is looking at. He has a kind of global visual agnosia that Sacks had never encountered before.

    So, the signals may come in in a preprogrammed way, but there's a huge amount of processing that goes on between that and coherent conscious experience.
     
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