Serious problems with interpreting rubber hand illusion experiments
The rubber hand illusion (RHI), in which participants report experiences of ownership over a fake hand, appears to demonstrate that subjective ownership over one’s body can be easily disrupted. In RHI, ownership is typically quantified through ratings of agreement with statements putatively about body ownership. It was recently shown that propensity to agree with these statements is correlated with trait phenomenological control (the ability to generate experience to meet expectancies arising from direct or indirect suggestion) and that existing methods of controlling for suggestion effects in RHI are invalid. Here, we present the results of simulated experiments that mimic standard practice in RHI studies, using real participant data. In each experiment the sample was biased in selection for trait phenomenological control. Using samples comprised of participants higher in trait phenomenological control almost guarantees that an experiment provides evidence for RHI. By contrast, samples comprised of only participants lower in trait phenomenological control find evidence for RHI only around half the time (and “ownership” experience just 4% of the time). It is therefore likely that existing RHI experiments have studied phenomenological control by proxy. Previous RHI studies cannot be used to make inferences about the sense of ownership in humans generally.