Sense of self: Can we experience ownership of artificial bodies?

Henrik Ehrsson
Professor Henrik Ehrsson from the Karolinska Institute in Sweden

From the invention of the wheel, to the development of antibiotics, history’s big scientific breakthroughs have helped shape the world as we know it. But what will the next major discovery be? As part of National Geographic Channel’s new Breakthrough series, six visionary Hollywood directors are trying to find out.

Each episode explores some of the most cutting-edge, life-changing innovations that are happening right now, and the incredible minds behind them. In the episode ‘More Than Human‘, world famous actor Paul Giamatti explores how technology is helping us to evolve and speaks to the people who are questioning what it is that makes us human. One of these people is cognitive neuroscientist Professor Henrik Ehrsson from the Karolinska Institute in Sweden, and we caught up with him to find out about his revolutionary research into how we come to sense that we own our body, and how we can project that sense of self into artificial ones.

What does your work as a cognitive neuroscientist involve?

I am interested in how we experience ownership of our bodies. How do we know what is our body and what is an object in the external world that doesn’t belong to our body? This is a complicated task for the brain, as it has to actively generate the experience of your own body. We have studied exactly how this works and what parts of the brain are involved when the brain creates this model of our physical self.

So how does the brain create a sense of self?

We found out that when the brain is updating its model of the body, it uses all available sensory information from the different sensory modalities – visual information from our eyes, touch information from the skin, position information from muscles and joints – and it integrates all this according to certain rules. This integration takes place in the frontal and parietal association cortices of the brain, and we found that activity in these regions is very tightly linked to our subjective experience of our own body.

How have you been able to test this?

We started working on limb illusions, where you experience ownership of a limb, for example a rubber hand, which feels like your own. All of these illusions happen as a consequence of simultaneous, synchronous visual and tactile information. So for example, with the rubber hand, you stroke it and at the same time you stroke the person’s real hand, but their real hand is hidden behind a screen on the table. When you stroke them both at the same time, the brain starts to connect what you see and what you feel and update its model of the body. Suddenly you feel someone touching the rubber hand as if it is part of your own body. We then started to think, can we take this to the next level and do experiments with full body illusions, where you sense a completely different body as your own.

Our of body illusion
Using simple mind tricks, people can be made to feel that they have the body of a small doll

Do these illusions work for everyone?

Around 70 to 80 per cent of the participants will experience these illusions very vividly, but there are some individuals that do not and we are not really sure why. Perhaps the simplest explanation is that all of these illusions happen as a consequence of conflicts between the different senses – the brain has to choose which one it should trust. In most people, vision tends to dominate, so the rubber hand illusion works, but in those individuals that are resistant to it, perhaps their brains rely more on the signals from the muscles and the joints, which is actually the correct perception. We don’t know why this happens, but maybe it’s because different brains put different weight on different senses. So if you are a dancer or gymnast who is very much used to sensing the position of your limbs, maybe you would be resistant to the rubber hand illusion that depends on vision.

How to create an out-of-body experience

Our of body illusion
Professor Ehrsson generates an out-of-body experience in a test subject

To generate an out-of-body illusion, Professor Ehrsson fits the participant with a head-mounted display that has two screens, one in front of each eye. These screens show live footage from high-resolution video cameras that are placed two metres (6.6 feet) behind them, showing the participant a view of their own back. An object is then moved towards the cameras, just below the field of view, and at the same time, the participant’s chest is prodded. Their brain then interprets this visual and tactile information to determine that they are sitting behind themselves in the position of the cameras and looking at a body that is not their own. This simulates the key components of real out-of-body experiences that have been described by neurological and psychiatric patients.

What are the potential real-world applications of this research?

One important application could be the development of next-generation prosthetic limb devices for amputees. There has been a lot of interest in how to create prosthetic limbs that feel like real ones, but this has not yet produced any real clinical applications for patients because it would involve invasive techniques and neurosurgery. We think that we can use these illusions as a very simple, cheap and non-invasive way of creating artificial limbs that feel real, and have already started such experiments with hand surgeons and engineers at Lund University. The idea is to put stimulators directly on the stump of the amputee and then have sensors in the fingertips of the prosthetic hand. Every time the prosthetic hand touches an object, a signal will be sent to the stimulator on the stump. The brain will then put together what the amputee sees and feels, so instead of feeling touch on the stump, they will feel it projected on the fingers of the prosthetic hand.

Do you think your work is changing the definition of what it is to be human?

Our experience of our human bodies is something that the brain is actively creating on a moment-to-moment basis. You can, for example, experience small dolls as your own body, or virtual bodies as your own, or feel that you have very long arms and all kinds of very weird body deformations. So our physical sense of being human is much more malleable and dynamic than maybe we had thought. We don’t really know the ultimate constraints here, such as how ‘un-humanlike’ a body could be but still feel like your own body. We think that this kind of research challenges one assumption of what it is to be human.

Breakthrough continues with ‘More Than Human’ on Sunday at 10pm on National Geographic Channel. 

Watch a preview of ‘More Than Human’ below…