If 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