Mel Slater's Presence Blog

Thoughts about research and radical new applications of virtual reality - a place to write freely without the constraints of academic publishing,and have some fun.

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I still find immersive virtual reality as thrilling now as when I first tried it 20 years ago.

03 August, 2008

Virtual Pain in Dubrovnik

I attended the Second PEACH Summer School in Dubrovnik, Croatia 9-11th July, 2008.

The title of the school was ‘Presence: Technologies and Applications’. There were many interesting talks during the week, and I hope that eventually some will be put on the web site, and they are well-worth watching.

The courses were supposed to be more ‘hands on’ this year, with practical applications, exercises and so on. Originally I was going to do an experiment with the students utilising Second Life, in real-time. However, this turned out not to be possible, since there were not appropriate or a sufficient number of computers available.

Nevertheless, in my talk, I wanted to illustrate some ideas in a practical way, rather than just by talking about them.

A central feature of an experience in virtual reality is that you respond to events even though you know that they are not ‘true’ (i.e., the virtual character that you feel compelled to smile back at is not really there, and you know this to be the case). In fact I would take it as part of the definition of ‘presence’ that you know that the illusion is not ‘true’ (but nevertheless finding yourself responding as if it is true). If you didn’t know that it wasn’t true, i.e., if you fully believed that what appeared to be happening was really happening, and that you really were in the place that you appeared to be, then it is no longer ‘virtual reality’ but simply ‘reality’ (for you).

How could I give a demonstration of this, without any actual virtual reality system? The aspect of ‘presence’ that I wanted to concentrate on was not the illusion of being in a place, but rather that what was happening was ‘true’. I am going to label this phenomenon ‘psi’ (if I give it any actual word, then just like the word ‘presence’ there will be endless debates about the ‘true meaning’ of the word, so here I just use a label). By ‘psi’ I mean the illusion that the events and situation that appears to be happening are what they seem to be, even though the person involved (the ‘participant’) knows for sure that they are not really happening. In other words the participant knows that what is happening is fake, but nevertheless gets drawn in, and finds themselves behaving as if it were true. A very powerful illustration of this can be found in is role playing, but of course it happens to some extent also in theatre and movies. It especially happens in children’s games.

So I wanted to set up a situation where no one could really believe that what they were seeing was ‘true’, but would nevertheless find themselves responding as if it were.

I combined two different scenarios – the Stanley Milgram Obedience experiments (of which I have written before) and the rubber hand illusion.

At the beginning of my talk I asked for two volunteers. One man and one woman were selected from the audience and they came out to the front. Let’s call the man the ‘learner’ (L). I gave him some sheets of paper on which were printed some quiz questions and answers, and I asked him to sit down and learn as many of these as possible. He said “There are quite a lot!”, I told him to remember as many as he could. Meanwhile I was explaining a bit more to the audience. I said that I had only done this experiment “once before”, while he was learning the answers to the quiz questions.


After a few minutes I asked L to sit by a table that had been prepared at the front, on which was a small grey screen and a rubber arm. I positioned his real right arm behind the screen so that it was out of the view of L, and placed the rubber arm where his real right arm would be. I covered with my jacket the space between his shoulder and the rubber arm, so that it looked like his arm was sticking out from underneath the jacket. Then as is the case with the rubber hand illusion, I synchronously touched and stroked the visible rubber hand and the non-visible real hand. In other words L saw the rubber hand being touched, and simultaneously felt his own hand being touched in the same location, but only saw the rubber hand. After a few minutes of this stimulation I asked him if he felt any thing, and he said “That’s my hand!” indicating the rubber hand. In other words it seemed to him as though the rubber hand were his real hand. Then I stopped tapping, and asked him what he felt – he reported that he still felt that the rubber hand was his hand. Meanwhile the audience had crowded round so that they could see more closely what was happening.
The second volunteer I will call ‘the Teacher’ (T). Her instructions were to read out the quiz questions one by one. Whenever L got a correct answer she was to just move on to another question. Whenever he got the wrong answer she was to say ‘Incorrect’, stick a pin in the rubber hand, and then give the correct answer. Each time the answer was wrong she was to leave the pin sticking in the rubber hand for longer. I emphasised that she was only to stick the pin in the rubber hand and not in the L’s real hand! L also emphasised this point.

Then the procedure started. I was standing by L, occasionally reinforcing the rubber hand illusion with some more synchronous stroking and tapping.

After the first wrong answer, T stuck the pin in the rubber hand, and L just shrugged as if to say ‘nothing happened’.

After the second wrong answer T stuck the pin in the hand, waited a short time, and at first there was no response from L, but then suddenly he said “Ouch!” this time he felt something. I reinforced the rubber hand illusion a bit more at that time.

After the third wrong answer (of course he was giving some right answers too) she stuck the pin in longer, again there was a pause, and then he screamed quite loudly. The fourth time he really yelled very loudly, exhibiting many signs of pain.
T said to me that maybe she shouldn’t continue, because L was obviously in distress. I said “Although the procedure involves some discomfort, there is no permanent damage, and that for the sake of the experiment we should continue.” L himself was very reluctant to do one more, and said that I would owe him a pint if he continued. So we agreed to continue. Meanwhile the jacket had fallen off and the rubber hand was simply laying there on the table with no connection whatsoever to L’s body!

The next time after an error L let out one almighty yell. T had tears in her eyes saying that she didn’t want to continue. I was saying that although there is discomfort there is no permanent damage etc.. By now the audience was shouting that we should stop.

At this point I asked everyone to thank the ‘volunteers’ and started clapping and there was a great applause. I explained that they were both actors who had been playing a role that we had planned together earlier. In fact L was Rod McCall, a research scientist at Fraunhofer FIT, Germany, a member of the PEACH committee who I’d recruited the day before, and who had previous acting experience. T was played by Anna Bellido, from the Event-Lab in Barcelona. Both did a very excellent performance.

The reaction of the audience was interesting. No one could have rationally believed that Rod was experiencing pain from sticking a pin in the rubber hand. But I am sure that many had doubts! Afterwards many people told me that they had found the experience unnerving. One person explained that he felt bad about what had happened, because he really wanted to come down to the front and stop what was happening, but didn’t have the courage to do so.


This illusion is an excellent illustration of ‘psi’. Everything conspired together, the serious way that I had announced it and treated it, the fact that I said “I have only done this once before”, the quality of the acting, the fact that people may have not been sure whether the rubber hand illusion extended to pain. Even I, who knew that the whole thing was fake, nevertheless started experiencing anxiety with increased heart beat, at Rod’s screams! This was one reason why I cut the event to a time shorter than I had originally planned.

My contention is that ‘psi’ occurs in mediated experiences – that of course even though everyone knows that the events that are apparently happening are fake, they still respond to some extent as if they were true. Virtual reality is especially powerful, because not only can psi occur (these events are what they appear to be) but there is also the illusion that you are in the same place where they are happening. This is not only happening, but it is happening to you, here directly in your vicinity. So the response is likely to be all the more powerful than if you are simply watching remote events, e.g., on tv.


I see that ‘presence’ has these two components at least – the transformation of the sense of the space that you are in, and secondly, psi, that what is happening in that space is true. But both are illusions and the participant knows that they are illusions. This knowledge dampens down responses compared to reality, but still there can be very strong responses.

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