The Rubber Hand Illusion


This week I have been working primarily on the first chapter of The Third Day, entitled ‘Chapter 1 – The Engineer’. More specifically I have been working on two systems within this chapter; the hand controller system and the audio system.

I have mentioned before that there is a profound moment that occurs in the experience of virtual reality, it is the fraction of a second after you remove the headset, when suddenly the strange new world you have to acquaint yourself with is the everyday world that you have spent your life in. The term ‘immersion’ is now a blanket term covering a range of experiences but I have been interested in these past few years to investigate the parameters of ‘immersion’. What does that term mean to a psychologist, for example?

There are a great many tricks that an artist can play to intensify the feeling of immersion, it is something we talk about a lot in my guest lecturing posts around the world, there is a lot of interest in it and even a cursory look at audience trends demonstrates that audiences are craving immersive involvement in their culture.

To me, however, what is far more interesting than simple immersion in fake worlds is just how easy it is to disrupt the sensory perception of this world, the one we are living in, as something concrete and dependable.

In 2004 psychologists Ehrsson, Spence and Passingham conducted an experiment which became known as the rubber hand illusion. You will find endless rubber hand illusion videos on youtube and, if you get the chance, I recommend you try it for yourself. A person is sat at a table with their left arm out of sight on the far side of an upright board and a fake rubber hand within sight on the near side of the board. The experimenter strokes two small paint brushes simultaneously down the index finger of both the rubber hand and the real hand and within a very short time the subject’s brain begins to adopt the rubber hand as their own. Moreover the real hand begins to lose temperature and, if the experimenter suddenly pulls out a hammer and smashes the rubber hand, then the subject feels the same rush of adrenaline and shock as if it had been their real hand being attacked.

The important finding here is that the brain builds a picture of what is real based on the synchronisation of multiple senses and that it is easily fooled. The rubber hand does not need to be realistic, so long as the physical kin-aesthetic sensations are in sync with a visual confirmation of those sensations then the illusion will occur.

In order for that profound VR moment to be maximised the artist needs to pull the same trick. The VR world does not need to look realistic at all so long as the visual and physical stimuli are in sync. On a very basic level the audience member experiences the curious effect of turning one’s head in the real world and the VR world moving precisely in sync with that physical motion. What I have noticed, however, is that the sense of embodiment in a virtual world is greatly enhanced by the accuracy of the audio responses and the physical feedback of the hand controllers. You reach out and touch a button, it clicks in response and the button sinks back precisely as a vibration hits the hand controller and a something changes in the VR world as a result. The experience of this repeated numerous times persuades the brain of the fake world’s veracity.

This week I have been creating those interactions, using a very basic hand model for now, enabling the audience member to trigger four parts of a string quartet using simple buttons within the virtual space. These interactions are not there just to give the audience member something to do in the scene, but to reinforce the sense of body immersion by repeating an action involving the synchronisation of visual and physical senses. The audio speakers which play the sound within the space, and the acoustics of the space itself are another part of the equation. The space is a hugely reverberant cooling tower and there is a complex interaction between volume and reverberation of sounds coming from each speaker depending on how near or far you are from them. When you are very close to a speaker the sound emanating from it is louder and the reverb is less present, when you are further away you hear more of the reverberation of the sound – the multiple reflections off the walls of the cooling tower back and forth – and less of the original source sound. The aim, this week, was to make all of this as accurate as possible, to maximise body immersion so that the profound moment is all the more profound; and so that the re-entry to the real world contains an element of displacement and doubt.

The music itself is a string quartet I wrote and recorded many years ago when I was 24 years old. It was always my dream to have it played in a cooling tower but I could never make it happen, until now.


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