Out of body experience

For most people, out-of-body experiences firmly belong in the twilight zone, the realm of the weird and flaky.

They are associated with paranormal phenomena, psychics, shamans, New Age nuttiness and the effects of strong hallucinogenic drugs.

Yet for one in 10 of the population, out-of-body experiences or OBEs are real. That is the proportion of people who claim to have been parted, temporarily, from their bodies - or at least felt as if they have.

In some cases, OBEs have been reported by people suffering from migraines or epilepsy.

Typically an OBE, which also goes under the name of astral projection involves the sensation of floating away from your physical self and seeing your body from a distance.

It’s not the kind of thing that would appear to have any connection with serious science.

Yet two independent teams of scientists have just published studies showing how a close approximation to an OBE can be artificially produced in a laboratory.

In both cases, "virtual reality" techniques are used to create the illusion. By mixing up sensory signals, healthy participants not under the influence of any drugs could be tricked into experiencing the disquieting feeling that they had left their bodies.

The scientists might be accused of cheating to some extent. Both teams employed video cameras or computer graphics to fool the brain, which would not have a role to play in a real OBE.

But the findings seem to suggest that disconnection between circuits in the brain, something grounded in reality and not in the least paranormal, may be responsible for these experiences.

One experiment at University College London involved fitting a volunteer with goggles linked to a pair of cameras showing a 3D view of his or her back.

A researcher standing out of sight prodded the participant's chest with a stick while at the same time moving another rod in front of the cameras, towards the apparent position of the image.

When this was done, volunteers experienced the sensation of sitting behind their physical body and looking at it from that location.

"This was a bizarre, fascinating experience for the participants - it felt absolutely real for them and was not scary," said neuroscientist Dr Henrik Ehrsson, who devised the study. "Many of them giggled and said ‘wow, this is so weird!’"

To test the illusion further, Dr Ehrsson swung a hammer in front of the cameras so that it appeared to hit the region where the volunteers perceived themselves to be.

Electrodes attached to the volunteers’ fingers recorded changes in the conductivity of the skin that normally occur when registering a threat.

The other experiment by researchers at the Swiss Federal Institute of Technology in Lausanne also employed "virtual reality" goggles.

In this case, volunteers stood in front of a camera that produced computer-enhanced 3D images of their own bodies seen from behind.

When their backs were stroked with a highlighter pen, they saw their "virtual body" being stroked at the same time.

Volunteers were made to feel as if the computer image was in fact their own body. After the camera was switched off, blindfolded subjects guided back a few steps consistently overshot when asked to return to their former position.

They walked to a spot closer to the apparent location of the virtual body they had seen earlier.

When the volunteers were shown a computer image of a human-sized block-shape instead of their own body, the spell was broken and they returned to their correct original standing position.

Professor Olaf Blanke, who led the Swiss team, said: "Full-body consciousness seems to require not just the ‘bottom up’ process of correlating sensory information but also the ‘top-down’ knowledge about human bodies."

The results of both studies, published in the journal Science, have fascinating implications.

Learning how to manipulate the physical sense of ‘self’ could in future find uses in telemedicine, helping surgeons to imagine they are in the same room as the patients they are operating on remotely.

It might also produce the nearest thing possible to a Star Trek "holodeck", making video games seem so real that you really feel transported into the virtual world.