The Touch of the Phantom: When left is right and right is left

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ResearchBlogging.orgIf you watch a fake hand standing in for your right hand, and it is touched with a brush while at the same time your left hand, hidden from view, is similarly touched, you feel your right hand being touched. This spooky finding is called “phantom touch” and was reported in a recent issue of PLoS ONE.


…we report a perceptual illusion where people experience “phantom touches” on a right rubber hand when they see it brushed simultaneously with brushes applied to their left hand. Such illusory duplication and transfer of touch from the left to the right hand was only elicited when a homologous (i.e., left and right) pair of hands was brushed in synchrony for an extended period of time. This stimulation caused the majority of our participants to perceive the right rubber hand as their own and to sense two distinct touches – one located on the right rubber hand and the other on their left (stimulated) hand. … Our findings suggest that visual information augments subthreshold somatosensory responses in the [brain], thus producing a tactile experience from the non-stimulated body part. This finding is important because it reveals a new bilateral multisensory mechanism for tactile perception and limb ownership.

This is not entirely new but it includes a very new and interesting twist. The “rubber hand illusion” experiment has been around for a while (Bovinick andCohen 1998). In that now classic experiment, the same-side rubber hand located in a parallel position to the subject’s actual hand is touched (while the subject’s same-side hand is identically touched), so the only thing that is different (other than it not actually being your hand) is the angle of the elbow. This new experiment shows that the same effect can be created with the contralateral hand.

Most importantly, the researchers seem to have demonstrated that this is not simply a “rubber hand illusion” but with a contralateral hand. There are features of the rubber hand illusion, such as the distance at which the fake hand can be from the real hand before the effect stops working, that are different in this experiment. The researchers suggest that a different mechanism is involved in the phenomenon reported here. They also claim that the process revealed by this experiment is different from that revealed by the “three arm illusion.”

What causes this effect? Well, it is known that in the primate brain there are neurons connected to the tactile (touch) system that receive information from both sides of the body. These would be stimulated during the experiment, and eventually, that stimulation would be amplified by the tactile/perception system. During this experiment, the sense of touch experienced by the subjects took a while to start up. The idea here is that these cross-lateral input neurons in the brain start off with a signal too ‘quiet’ to be noticed, but over time, with the visual information of seeing the touch being involved, are amplified. Maybe.

Perhaps you have a better idea. Perhaps you have question about this research. Feel free to put your ideas or questions in the comments below, but also, please note that since this research is published in an OpenAccess journal, anybody can read the original! Just click here to go to the original article.

Petkova, V., & Ehrsson, H. (2009). When Right Feels Left: Referral of Touch and Ownership between the Hands PLoS ONE, 4 (9) DOI: 10.1371/journal.pone.0006933

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

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0 thoughts on “The Touch of the Phantom: When left is right and right is left

  1. Andrew (#2): It may not seem very practical at this stage, but this line of research is absolutely fundamental to the development of my race of Atomic Super-men.

  2. This study reminds me of the stories Dr. Oliver Sacks presents in his book, “The Man Who Mistook His Wife For a Hat”. There are several stories of people who have amputated limbs but have phantom pain or similar experiences. I wonder if the research in this study can help shed light on how to help individuals with phantom pain.

  3. I wasn’t aware of that defect. Hmm … now I feel the urge to try it out on people. I’ve heard a number of Vietnam vets telling me about their ghost pains in their amputated limbs and always wondered why the brain does that.

  4. This is going to be an oversimplification but… first of all, the rubber hand pain and the phantom limb are probably not the same thing. The phantom limb is probably from a sense of proprioception.

    Put one finger on a table top, and put your other arm under the table. Try to touch your first (on top of the table) finger with the finger of your other arm. Do it in such a way so you can’t really see your other arm.

    Those fingrs will get pretty close to being tip to tip.

    One part of that ability is knowing exactly where each of your arms/hands/fingers are because of neruons that are keeping track of your movements and sending feedback to your brain, but a lot of that is going on in your brain and not your limbs.

    It’s like when we are at the cabin and my mother in law is knwon to be driving up as well, and my wife calls her.

    “So where are you?”


    Then later MIL calls “Did you want me to stop at the Best Buy and get that thing?”

    “NO, that’s OK”

    Then 15 minutes later I say “So, where are they?” and my wife says “Just north of Baxter, I’d guess”

    Most of that calculation is in my wife’s brain; The information from “the field” (Mother in law, the arm, whatever) is vague. The Best Buy is in Baxter, so that call was made on the approach to Baxter. There are other best buys, but given the aount of time since “We’re in Rogers” and “Do you want me to stop at Best Buy” one guesses that it was Baxter.

    In other words, proprioception is a complicated and subtle information system where much of the “inference” is happening inside the brain. The limb might be there or not be there, the inferences are still going to happen with only a little, or even no, input. Eventually phantom limb sensation wears away for most people.

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