Hand cooling from illusion not linked to change in body ownership

Researchers from Utrecht University have an update on temperatures in hands that may, or may not, belong to you. Their paper, “No consistent cooling of the real hand in the rubber hand illusion,” gives an example of the importance of distinguishing body ownership:

“Consider a simple task such as walking towards another person –say, this huge big shot you noticed at a conference – and shaking hands… among this sea of moving limbs you will need to keep track of which ones are yours, so you can walk away again without making a complete fool out of yourself. To do so, your brain needs to know which parts of the world are “you” and which parts are not.”

While it may seem clear to you that you own your own hand, psychologists can use the Rubber Hand Illusion (RHI)  to convince the brain that a rubber hand is your own hand. During the RHI, the real hand is hidden from sight, while a rubber hand is in view. Researchers will touch both the real and rubber hands at the same time in the same locations. The brain will eventually gain ownership of the rubber hand, causing touches on the rubber hand to be felt, even when the real hand is no longer being touched.

But what happens to the previously owned real hand? One highly cited experiment in 2008 suggested that when the real hand is disowned in favor of a rubber hand, the temperature of the real hand drops slightly. This sort of relationship with body ownership would have interesting consequences for physiology, but it has been difficult to replicate. The Utrecht University team decided to delve into the problem, using as many owned, and not owned, hands as possible.

In total, 167 participants were convinced to trade ownership of their hands for rubber hands. After extensive temperature measurements, the researchers found that:

“…although the presence of temperature changes of the hands in RHI experiments might be determined by various factors, an overall analysis of RHI  experiments in our lab in the last 5 years, covering five replications of the traditional RHI experiment and totaling 167 participants… suggests that hand temperature changes in the RHI are not causally related to changes in body ownership.”

Full article: de Haan, A., Van Stralen, H., Smit, M., Keizer, A., Van der Stigchel, S. and Dijkerman, H. (2017). No consistent cooling of the real hand in the rubber hand illusion. Acta Psychologica, 179, pp.68-77.