Neurophilosophy

DO you think that you perceive your body and the world around you as they really are? If your answer to that question is “yes”, then think again. Our perceptions are little more than the brain’s best guess of the nature of reality, constructed from fragments of information it receives through the senses. This is demonstrated by visual illusions, which produce discrepancies between physical reality and what we see of it, and by illusions of bodily awareness, which distort the way we perceive our bodies.

Psychologists and neuroscientists have long used illusions to investigate the mechanisms underlying perception. This is usually done in a laboratory setting, using specially designed equipment and, in the case of visual illusions, sensory stimuli. Some illusions of bodily awareness can, however, be easily induced without an elaborate experimental set-up or complex images. You too can dazzle your friends by perturbing their bodily awareness, using nothing more than the items that are commonly found in pubs and bars. Continue reading to see how…





The first illusion that I have adapted for the pub is the rubber hand illusion. As shown in the video above, this involves seating a subject at a table, with one hand placed in front of them on the table surface and the other placed out of sight on their thigh. A fake hand is then placed onto the table, where the hidden hand might realistically be positioned. The experimenter then uses two pens or paintbrushes to synchronously stroke the subject’s hidden hand and the fake hand. The subject therefore feels their real hand being stroked and sees the fake hand being stroked in the same way and at the same time.

Simply manipulating the sensory information about the hand in this way causes the subject to perceive the felt sensations as originating in the fake hand and not their real one. It occurs because the brain has been tricked into incorporating the fake hand into its representation of the body, effectively treating it as if it were a part of the body. (In other words, the brain takes ownership of the rubber hand.) How do we know that this happens? If the experimenter lunges at the rubber hand with a knife, the subject reacts as if it were their real hand being attacked, and various physiological reactions – such as sweating and increased heart rate – can be measured. Lorimer Moseley and his colleagues found that the temperature of the real hand drops, showing that the brain neglects – or disowns - it during the illusion. I also predict that the real hand becomes insensitive to pain, and this is now being tested. 

hand swap illusion.jpgPhoto: Sophia Collins

I have been practising the rubber hand illusion, and so far have induced it with varying degrees of success in about half a dozen willing participants, using a Star Nail Practice Hand purchased from Amazon, which is designed for trainee beauticians to practice their manicure skills. Recently I described the illusion to a group of people in a pub, and wanted to demonstrate it to them, but of course I didn’t have my rubber hand with me. Then it occurred to me that I could probably induce it without a rubber hand, by using my own hand instead.

The photograph above shows it was done. In it, you can see my experimental subject’s right hand on the left and my left hand on the right. Out of view to the right was my assistant, who used two knives to synchronously stroke my experimental subject’s left hand and mine. My  subject reported that the illusion worked, or at least that she felt confused about where the sensations she felt were coming from. I could have verified this by asking Jo to stab my hand, but for obvious reasons I did not. Nevertheless, my attempt to induce what might hereafter be referred to as the “hand-swap illusion” – basically, a scaled-down version of the body swap illusion – was apparently successful.

crossed feet illusion.jpg

I have also “discovered” a novel variation of Aristotle’s illusion, also known as the crossed fingers illusion. As its name suggests, this involves first crossing your fingers, then touching the fingertips simultaneously with a small spherical object such as a pea. This induces the sensation that you are touching two objects. It can also be done by touching the tip of your nose with the crossed fingers and, I have found, using the tip of a pen. My pub variation involves standing with your legs crossed and placing a pool cue so that it touches both feet simultaneously (as shown in the photo above). This should induce the illusion that your feet are being touched by two objects and not one.

Like the rubber hand illusion, this one arises because crossing your fingers alters the sensory information entering the brain. Specifically, it is thought to occur because two regions of the skin, which are usually further apart and would not normally be touched simultaneously by the same object, are brought closer together. Conversely, touching two areas of the skin surface that are ordinarily close together with two objects gives the impression of touching one object. Try it for yourself – cross your fingers, then lightly squeeze their outer sides with the thumb and forefinger of the other hand. This will feel like you are holding a single object between your crossed fingers.

Related:


References:

Sekinea, T. & Mogia, K. (2009). Distinct neural processes of bodily awareness in crossed fingers illusion. NeuroReport 20: 467-472 [PDF]

Botvinick, M. & Cohen, J. (1998). Rubber hands ‘feel’ touch that eyes see. Nature 391: 756 [PDF]

Comments

  1. #1 Alex
    August 20, 2010

    I have been experimenting with the rubber hand illusion a lot. First, I bought a whole manikin hand and tried it with my girlfriend – it worked very well for her, but when we tried it on me, I didn’t feel I was even close to feeling anything unusual. I thought that maybe this is because the manikin hand was female, so I decided to try with a larger rubber glove filled with buckwheat. Again this worked incredibly with my girlfriend, but left me totally unaffected. I suspect this has something to do with one’s own body map resolution – it seems that in every person it is different. For example, I immediately felt whenever there was an even slight difference between felt and seen touch, and I had clear impression of differences between the felt shape of my hand and seen shape of the rubber counterpart.

  2. #2 rijkswaanvijand
    August 20, 2010

    “This will feel like you are holding a single object between your crossed fingers.”

    No it doesn’t!
    It feels like I’m holding two crossed fingers with the thumb and forefinger of my other hand..

  3. #3 Mo
    August 20, 2010

    @Alex: The RHI only works in 2/3 people for some reason. I’ve yet to have it performed on myself.

    @rijkswaanvijand: It worked for me!

  4. #4 Dunc
    August 20, 2010

    I always perturb my bodily awareness using items (or rather, liquids) commonly found in the pub. I thought that was the whole point? ;)

    The crossed fingers thing doesn’t work for me either… But I’m a guitarist and have been from an early age, so my brain may have more power dedicated to processing signals from my fingertips that is “normal”.

  5. #5 Shatterface
    August 20, 2010

    Thanks to alcohol I’ve managed to alter my body image so that I feel like I am irresistable to women and also induce the illusion that I am an eloquent and interesting speaker on a wide range of topics from politics to sport.

    I’ve found certain video games can induce an illusion of proprioception so that when my character is running, for instance, I can ‘sense’ where my virtual feet are even when I can’t see them.

  6. #6 feralboy12
    August 20, 2010

    For some real fun, try this stuff on LSD.
    Okay, maybe not.
    Back in my psychedelic days (nearly 30 years ago) my brain, under the influence, would “take ownership” of just about everything I touched, including a “magic” orange stocking cap that would become part of my hand or head.
    Talking on the phone was a real adventure. But you probably don’t want to try this at home.

  7. #7 Nikki
    August 31, 2010

    No, the crossed fingers thing definitely doesn’t work.

  8. #8 Efrain
    September 2, 2010

    ”Our perceptions are little more than the brain’s best guess of the nature of reality, constructed from fragments of information it receives through the senses.”

    Highly questionable statement. For a blog called neurophilosophy, I don’t see much philosophy as much as speculation.

    You should read my recently completed philosophy thesis, where i discuss these exact experiments at length, in well, a philosophical context. At least do yourself a favor and read the introduction.

    http://wesscholar.wesleyan.edu/cgi/viewcontent.cgi?article=1534&context=etd_hon_theses

  9. #9 Mo
    September 3, 2010

    @Efrain: A highly questionable statement? I don’t think so. I’ll look at your thesis, but perhaps *you* should read some neuroscience. Anyone with even a basic understanding of the subject knows that we don’t perceive the world as it really is. Read about photoreceptors, for example, and you’ll learn that they’re sensitive to the tiny fragment of the electromagnetic spectrum that we call visible light. And being a philosopher, you may have heard of Maurice Merleau-Ponty – I highly recommend his book, The Phenomenology of Perception, for insight into the subjective nature of bodily awareness.

  10. #10 Stephen Hager
    September 9, 2010

    Our worldwide statistics show that 52% of the population has Kinesthetic as their dominant sensory pathway. Your article shows that our “body smart” intelligence (Kinesthetic) can deceive us. Indeed it can in everyday life as well as in the fascinating experiment you describe.

    Our Auditory sensory pathway also has amazing potential to reach erroneous conclusions and fooling us. How often can a group of people agree on what someone said, their tone of voice and the meaning of their message? Mistakes, misunderstanding and wasted time happens because of poorly developed listening skills. Approximately 8% of the population has Auditory as their primary sensory strength.

    I believe we can do a better job exchanging information by paraphrasing what we hear, asking questions, listening to tone of voice and observing body language.

    Stephen Hager

  11. #11 Eric Thomson
    September 20, 2010

    Efrain his quote seems fine, neo-behaviorist protestations to representationalism are really unconvincing.

    I never felt the RHI personally, and tried a lot when I worked on it some in grad school.

  12. #12 Eric Thomson
    September 20, 2010

    On the other hand, the following isn’t totally compelling:
    Anyone with even a basic understanding of the subject knows that we don’t perceive the world as it really is. Read about photoreceptors, for example, and you’ll learn that they’re sensitive to the tiny fragment of the electromagnetic spectrum that we call visible light.

    We could perceive the world as it really is, within the limited range of stimuli that our receptors can sample.

    I would say that we don’t directly perceive the world (that would be magic), but perceive it via neuronal representational systems. How accurate those systems are is an empirical question, and it likely depends on the sensory modality and certain features of the stimulus (such as how quickly is it changing? If it is moving too slowly or quickly for our brain to detect, then we won’t be accurate, but if it is in the range to which our brains have been tuned to operate, things are often startlingly accurate as illustrated with hyperacuity research).

    Antirepresentationalists have a lot of trouble with things like dreams, hallucinations, phantom limbs, bistable percepts, and other visual illusions. Since they also tend to be neo-behaviorists who think that perception is “skilled interaction” they also have a lot of trouble dealing with the above, but also people paralyzed but awake undergoing tortured surgery that experience every slice (this happens, still). Then there are things like long-term memory that have a happy home in representationalism (e.g., look up birdsong learning).

    When one of these neobehaviorist dynamical systems Gibson fetishists explains these phenomena in a reasonable way, then they might have an ear in mainstream neuroscience and psychology.

  13. #13 Kent
    September 28, 2010

    I tried the crossed fingers thing 3 times…it worked once.

  14. #14 Norm
    October 20, 2010

    The rubber hand didn’t work when I tried it at a demonstration they had at University awhile back. I think i surprised them since I guess it works a majority of the time.

  15. #15 Matthew Kays, DC
    November 26, 2010

    Some of the feedback and interpretation mechanisms mentioned are an integral aspect of chiropractic’s subluxation theory.
    Namely, that if there is interference between the peripheral nerve system and the central then degree to which that is taking place is the degree to which your interpretation of physical reality is hampered.
    (there’s WAY more to it, but at least that much applies to this particular entry)

  16. #16 Josh
    November 28, 2010

    “Our perceptions are little more than the brain’s best guess of the nature of reality, constructed from fragments of information it receives through the senses.”

    You’re probably aware that this thesis is debatable. I just want to point out that you might reconsider the assumptions upon which this thesis is supported. There are, for example, illusions that do not necessarily support your thesis e.g., Zöllner’s illusion. Your thesis, what Maurice Merleau-Ponty calls the “constancy hypothesis,” contends that there is a 1:1 correspondence ratio between “fragments of information” and their reception “through the senses”. When one perceives the Zöllner illusion, one does not construct the various fragments of the illusion and then perceive it. It is instead taken as a whole which, is what gives the illusion its efficacy. It is only because one first of all perceives the gestalt that one can then break it down into its atomistic components, not the obverse.

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