Saturday, September 10, 2011

The Third Hand

Last week at the airport I read the July/August issue of Scientific American Mind, which has an interesting article "Reflections on the Mind" by two Ramachandrans from the Center for Brain and Cognition at UCSD. It is a brief walk through some recent experiments testing how our brain constructs and interprets our own body and how that interpretation can be twisted.

One experiment you have probably heard of is that letting amputees "see" a lost arm or leg with a mirror that doubles the remaining one allows them to scratch or move it. That is, scratching the reflection they see in place of the lost body part does register in the brain, even though there is no direct sensory input. Some months back, we also learned about the "body swap" illusion that makes use of somewhat more sophisticated technology to create the illusion that one is moving a different body, with the aim to test how readily the brain accepts it as one's own. The SciAm Mind article suggests some low tech experiments you can try at home. For example, using a mirror to produce an image of your hand in place of the actual hand and then stroking the image produces a conflict in the brain because the visual input doesn't match the expectation. As a result your hidden arm might feel numb, though there's nothing wrong with it.

This reminded me of a trick we used to play on the mind as children: Lock hands with a friend, with the index fingers straight (see image below). With the free hand, rub up and down your and your friend's index fingers (2nd image). We used to call it "rubber finger." Everybody I know who tried found it to feel weird. I don't know why, but it seems that the brain expects some signal from the friend's finger. It doesn't make a lot of sense to me since you'd need three hands for that. If you have a good interpretation, let me know.


  1. This reminded me of the Aristotele's illusion.

    Do you know it?

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  4. Hi Bee,

    That was an interesting piece from Scientific American, which has me wanting to subscribe again. This mind body-image is certainly a fascinating subject particularly in respect to how it seems to coincide with our consciousness as a whole in respect to our depth of self awareness. That thing about putting a paint splotch on a chimps face while asleep to find it will attempt to rub if off if shown its face a mirror after it wakes, which on the other hand a monkey will ignore in the same situation I find as particularly interesting. This has me now wondering what the lost of our tails might have to do with our increase in self awareness.

    As for that mind trick of yours it seems to be related to the same as the out of body experience set up with the mirror and another person’s body matched onto your legs when you walk towards it. This has me interested yet it will have to wait for an opportunity to hold hands with someone. It also has me think of a simpler mind confusion trick which one can do all by themselves. This entails just crossing your fingers on one hand as if one is doing it for luck (the more crossed the better), then placing a pen between their ends and sliding them along it. It should feel like one finger trapped between two pens or a pen with a gap in between; you can use the edge of a table in place of a pen. This is of course has to do having reversed the sides that your fingers pick up the signal yet your brain still thinking they are positioned relative to each other as they normally should be. So this business in respect to mind-body image thing turns out to be a powerful thing.



  5. Hi Goitis,

    Just noticed that after posting my comment you had already mentioned the same example; perhaps mind-body images get entangled at times over distance as well:-)



    P.S. I find a pen however lending a more powerful effect than a pea. Then of course Aristotle didn't have one; well at least not a ball point

  6. Hi Bee,

    And for those interested a little more regarding Aristotle's Illusion and related things.

    “Reality is merely an illusion, albeit a very persistent one.”

    -Albert Einstein



  7. Yes, I remember your previous blog posting in regards to this subject.

    In creating virtual images can we illicit emotive responses from programmer algorithmic functions devised by human hands?

    Yes we can.

    How much more "by extension" the the third hand, but by recognizing the robotic arm in space as to putting satellites in the cargo bay and by unloading the shuttle contents?

    Just some thoughts floating around my head as I look at your bog posting.

    Bee:My interest in these studies lies in the question of extension.

    What did you mean Bee by "extension."


  8. If, when I was growing up, my room had been adorned with only a single mirror, my childhood daydreams might have been very different. But it had two. And each morning when I opened the closet to get my clothes, the one built into its door aligned with the one on the wall, creating a seemingly endless series of reflections of anything situated between them. It was mesmerizing. All the reflections seemed to move in unison—but that, I knew, was a mere limitation of human perception; at a young age I had learned of light’s finite speed.Our Universe May Be a Giant Hologram

    If you were to diagnose whether this belongs too some "tactile experience located in the brain" according to the information provided based on what you now know about mirrors, what would you say of Brian Greene's experience as a youth?

    Today, however, we do have the opportunity not only to observe phenomena in four and higher dimensions, but we can also interact with them. The medium for such interaction is computer graphics. Computer graphic devices produce images on two-dimensional screens. Each point on the screen has two real numbers as coordinates, and the computer stores the locations of points and lists of pairs of points which are to be connected by line segments or more complicated curves. In this way a diagram of great complexity can be developed on the screen and saved for later viewing or further manipulationFrom Flatland to Hypergraphics: Interacting with Higher Dimensions

    The understanding that our computer screens becomes a much more developed world then what has been isolated to a 2d dimensional reference increases our capacity for a "5d world?"


  9. Hi Giotis,

    This reminded me of the Aristotele's illusion.

    I know this illusion - it was mentioned in some book with all kinds of experiments I did read as a kid - but I wasn't aware of that famous name!

    Cheers, Stefan

  10. Hi Bee,

    with people who suffered an half sides apoplectic stroke there's a therapy with a mirror, which is put in the middle between the two sides of the body. The healthy part is moved, and the patient watches that part. After a while the other side starts to move again. I've watched that report on TV but I don't remember how good the rate of success is.

    Best, Kay

  11. While speaking of the illusion, it is also proper to speak of "tactfulness" in other ways? Not just of what one may say of reality in relation too, as an illusion.

    At its simplest, the system works when activity in a sensory neuron is triggered by a specific stimulus such as heat; this signal eventually passes to an area in the brain uniquely attributed to that area on the body—this allows the processed stimulus to be felt at the correct location. The point-to-point mapping of the body surfaces in the brain is called a homunculus and is essential in the creation of a body image. This brain-surface ("cortical") map is not immutable, however. Dramatic shifts can occur in response to stroke or injury.(Bold added for emphasis by myself in quote)


  12. As if to share our questions on life as we know it, how is the question of what one can provide as an informational posting say that the success to life is to see life in new ways?

    Stand inside the cave and move with the mathematical experience?:)Remember, mapping in correlation too?


  13. Plato,
    Regarding the linked excerpt from Brian Greene’s, “The Hidden Reality”:

    “Our familiar three-dimensional reality, these bold thinkers suggest, would then be likened to a holographic projection of those distant two-dimensional 
physical processes.”

    Is there something requiring this surface should be “distant”? Why not something more intimate and flame-like, our reality emerging along a rolling interface?

    Anyway, it would be a major change of paradigm; I still have to remind myself that sun is not moving across the sky.



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