Whatever we see, hear, feel, smell or taste is perceived as a direct representation of something real, something tangible. This is not something we have been taught or intuited. It is nature’s way of reacting to external stimuli. But are all our sensory experiences real? Can we experience things that aren’t really there? Or are other forces at work?

Anyone with a basic understanding of magic will know it relies upon a number of techniques to distract, camouflage and unsettle the concentration and thought patterns of its subjects via a number of different techniques including trompe l’oeil, levitation, misdirection, equivocation and many others. You can see Sarah Sparkes using trompe l’oeil as part of her The GHost Portal currently showing at FACT. It seems as we can easily be manipulated in to seeing things that are not there, or comprehending them in a different way to they actually really are. As Aristotle said, ‘our senses can be trusted but they can be easily fooled’.

It must be noted at this adjunct that seeing is NOT believing. To accurately build a portrait of reality we need to be picking up on clues from our other senses too. What some scientists argue is that there is not one overarching reality but a heavily nuanced one that we all experience slightly differently.  Some say we do not have the sensorial hardware to absorb all of the stimuli out there. When visual neuroscientist Susana Martinez-Conde was asked if the brain could ever process all of the visual stimuli present in the world, she said ‘For that our brain would need to be bigger than a building, and still then it wouldn’t be big enough’.

Give five people the same glass of wine, and it's likely they will each report differing tastes, smells, colours and guess at differing places of origin. Reality is subjective and can be stretched and manipulated, sometimes in very simple methods that are easy to replicate.

One such way is the ghost hand experiment. The illusion requires a subject to sit at a table and place both hands on the table. The right hand is hidden from the subject’s view, either using a box or cardboard partition, and in between the boxed right and the left hand a third hand is introduced. This hand is comprised of a stuffed rubber glove and a sheet covering the wrist upwards.

The scientist then uses two brushes to stroke both hands simultaneously in the same places. After a while, the subject believes the rubber hand to be their real hand. The illusion is bought to a close when the scientist asks the subject to reach for an object with their right hand, or - in a more sinister version - picks up a hammer and hits the rubber hand, waking the subject from their reverie.

Scientists have been reinterpreting this illusion by manipulating the spaces above the hands, after discovering that we have a force field around our bodies that can detect motion - a bit like when someone is standing very close behind you. This may also go some way to explain the phenomenon of the phantom limb, where amputees report feeling itches and other aches and pains in parts of the limb that have been lost.

There are other interesting developments that the ghost hand experiment could precipitate. These include an enhanced understanding of autism - autistic people do not tend to adopt the rubber hand as their own and experience difficulty in adapting to new sensory stimuli. A group of Italian scientists also discovered via transcranial magnetic stimulation that electrical impulses to the right hand also vastly decreased after the rubber hand illusion - the body was in effect winding down to stop using this part of the body. This means that people who have suffered a stroke and incurred resultant brain damage, and those who have body identity integrity disorder, may be able to recondition their body's response to the stroke and/or brain damage.

Some scientists have even gone so far as to swap the rubber hand for a shoe or table and found people to bond to that object. Ultimately, what the illusion shows, is that body ownership, much like sensory perception, is a fluid, complex matter. 

It is quite clear from the ghost hand experiment that our eyes can deceive us, and that our other senses can too. The compelling thing about the illusion is that it offers us real glimpses into medical and technological advances; the brain can and does rewire itself to acquire a new form of reality, as documented by those who have experienced hallucinations of any sort. We are still only just scratching the surface in terms of understanding the brain, but for the time being, experiments like the rubber hand illusion provide a fascinating insight into just some of its many functions.

For our free No Such Thing As Gravity themed Do Something! Saturday workshop this weekend, you’ll have the chance to take part in the Ghost Hand Experiment, make a light up snowflake badge for Christmas, and have your face scanned, and 3D printed with Face Lab. Come join us for 12pm - 4pm in the FACT Foyer!

Image credit: Still from film 'Time You Need' by Sarah Sparkes, 2015.