We didn’t see this until very recently – after we had spent some time working out what we thought was a groovy paradigm to see if one can induce illusory ownership over a rubber hand by making it seem to be under voluntary control – a motor-visual congruence type illusion.
It seems that Mel Slater et al have done it and have done it in a more posh way than we were going to. We were going to use a rubber hand that moved in line with one’s own hand – Mel et al have used a virtual reality set-up. Very nice. This study is an important step because it shows that we don’t need the tactile bit to induce the illusion. Therefore, motor networks must be able to integrate with visual networks to manipulate representations relating to ownership of one’s body, or body parts in general. They went on to induce the illusion via a brain-computer interface, whereby brain activity signals are used to perform commands. They trained individuals and then got them to open and close a virtual hand (just by intending to!) and noted that when the virtual table underneath the virtual hand dropped away, the muscles of the real arm were activated as though it had dropped. Check it out, the full article is available online - some nice pictures included.
Inducing illusory ownership of a virtual body
Mel Slater[1,2], Daniel Pérez Marcos, Henrik Ehrsson and Maria V. Sanchez-Vives[2,4]
1 Experimental Virtual Environments for Neuroscience and Technology (EVENT Lab), Departament de Personalitat, Avaluació i Tractament Psicològic , Facultat de Psicologia, Universitat de Barcelona, Spain
2 Institució Catalana de Recerca i Estudis Avançats, Spain
3 Department of Neuroscience, Division of Cognitive Neuroscience, Karolinska Institutet , Sweden
4 Systems Neuroscience, Institut d’Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Spain
We discuss three experiments that investigate how virtual limbs and bodies can come to feel like real limbs and bodies.
The first experiment shows that an illusion of ownership of a virtual arm appearing to project out of a person’s shoulder can be produced by tactile stimulation on a person’s hidden real hand and synchronous stimulation on the seen virtual hand.
The second shows that the illusion can be produced by synchronous movement of the person’s hidden real hand and a virtual hand.
The third shows that a weaker form of the illusion can be produced when a brain-computer interface is employed to move the virtual hand by means of motor imagery without any tactile stimulation. We discuss related studies that indicate that the ownership illusion may be generated for an entire body. This has important implications for the scientific understanding of body ownership and several practical applications.