Virtual out-of-body experiences

In 2005, Olaf, his PhD student Bigna Lenggenhager, and I embarked on a series of virtual-reality experiments. Our first goal was to turn the OBE into a fully replicable phenomenon in healthy subjects. Proper research required that we be able to investigate and repeat out-of-body experiences in the lab. The guiding question was whether there could be an integrated kind of bodily self-consciousness that is a phenomenal confabulation. In short, could one experience a hallucinated and a bodily self at the same time, a full-body analog of the rubber-hand illusion?

Here is an example of one of our early experimental protocols using the paraphernalia of virtual reality: a head-mounted display (HMD) consisting of goggles that showed two separate images to each eye, creating the three-dimensional illusion of being in a virtual room. Subjects were able to see their own backs, which were filmed from a distance of 2 meters and projected into the threedimensional space in front of them with the help of a 3D-encoder. When I acted as the subject of the experiment, I felt as if I had been transposed into a 3D-version of René Magritte’s painting La reproduction interdite. Suddenly I saw myself from the back, standing in front of me.

While I was looking at my own back as seen in the head-mounted display, Bigna Lenggenhager was stroking my back, while the camera was recording this action. As I watched my own back being stroked, I immediately had an awkward feeling: I felt subtly drawn toward my virtual body in front of me, and I tried to “slip into” it. This was as far as things went.

Figure 11: Magritte’s La Reproduction Interdite (1937)

Figure 12: Creating a whole-body analog of the rubber-hand illusion. (A) Participant (darker trousers) sees through a HMD his own virtual body (lighter-colored trousers) in 3D, standing 2 m in front of him and being stroked synchronously or asynchronously at the participant’s back. In other conditions, the participant sees either (B) a virtual fake body (lighter trousers) or (C) a virtual noncorporeal object (light gray) being stroked synchronously or asynchronously at the back. Dark colors indicate the actual location of the physical body or object, whereas light colors represent the virtual body or object seen on the HMD. Illustration by M. Boyer.

Our studies became more systematic. All of our subjects would be shown their own backs being stroked (this was the “own-body condition”) and in a subsequent test would be shown either the back of a mannequin (the “fake-body condition”) or a large rectangular slab (which didn’t look like a body at all, the “object condition”) being stroked. An additional condition was the degree of synchronicity between the seen and the felt stroking, which could be varied by projecting the camera image into cyberspace with a certain time lag.

Afterwards, an independent measure for the strength of the illusion was introduced. They were blindfolded, moved around and disoriented, as in a game of blindman’s buff, and then asked to return to their initial position.

At the end of the experiment, the subjects were asked to fill out a questionnaire about their experiences. Results showed that for the synchronous conditions in which they were observing either their own body or a mannequin, they often felt as though the virtual figure was their own body, actually identifying with and “jumping into” it. This impression was less likely to occur in the case of the wooden slab, as well as in all of the asynchronous conditions. The synchronous experiments also showed a significantly larger shift by the subjects toward the projected real or fake body than did the asynchronous control conditions. In other control conditions, subjects observed a screen without a body in it and were then displaced (visual scene), or were simply displaced only. These data suggest that locating the “self” in the case of conflicting visual and somatosensory input is as prone to error as was reported for a body part in the rubber-hand illusion.

Here is what I call the “embedding principle”: The bodily self is phenomenally represented as inhabiting a volume in space, whereas the seeing self is an extensionless point — namely, the center of projection for our visuospatial perspective, the geometrical origin of our perspectival visual model of reality. Normally this point of origin (behind the eyes, as if a little person were looking out of them as one looks out a window) is within the volume defined by the felt bodily self. Yet, as our experiments demonstrated, seeing and bodily self can be separated, and the fundamental sense of selfhood is found at the location of the visual body representation.

Дата добавления: 2015-10-31