Do you feel a Phantom Hand?

A cream and pink exhibit table and back board that has a vertical mirror on the table and the words 'do you feel a phantom hand?' on the backboard.

Mismatching touch and sight sensory signals can create the strange sensation of a unconnected hand.

How it works

This exhibit requires two people. One person will place their hands on either side of a mirror and keep watching their hand's reflection in the mirror. The second person will brush or stroke the other person’s palms in a particular pattern, so the other person feels their hand being touched, but not see anything touch their hand!

Things to try or ask around the exhibit

  • Try this experiment back home using a standing mirror and different people.
  • Does it feel strange to feel your hidden hand being touched?
  • Do you start to perceive the reflection of your hand in the mirror to be your other hand hidden behind the mirror?

Background

Our brains process matching sensory signals every day, such as simultaneously seeing and feeling something touch our hand but this exhibit provides your brain with conflicting feedback from touch and visual channels. When using this exhibit, some people start to assume that their hand’s reflection in the mirror is actually their left hand and not simply a reflection of their right hand. So when they see nothing touching their perceived ‘left’ hand, but they feel something touching their perceived ‘left’ hand, it can feel unsettling.

Your brain can adapt and remap what it accepts as belonging to your body, what is alien and how your body is positioned in space. This is known as body schema and in this exhibit, your body schema gets confused and your brain finds it difficult to calculate where your (hidden) arm is located. Body schema maps of your limbs are malleable and changeable (which is called neural plasticity). An area of your brain called the somatosensory cortex is like a strip that runs over the top of your head a bit like a head band. This area handles tactile sensations from your arms and legs as well as your face.

Finding the science in your world

Body schema can create some unusual perceptual effects for people. Some sportspeople start to perceive their sporting equipment (such as a tennis racquet) as being an extension of their own body.

People who feel pain where their amputated limb was once positioned are said to suffer from phantom limb syndrome. Similarly, some people who have intact arms or legs feel such a strong rejection of a limb that they need to have it surgically removed.

Phantom limb sufferers can see that their limb is missing, but they feel that they can move their ‘phantom’ except it feels ‘paralysed’ in a cramped and painful position. Phantom limb paralysis develops because every time the patient attempts to move the ‘paralysed limb’, the patient receives sensory feedback (through vision and body position awareness or proprioception), that the limb did not move, which is translated and reinforced as ‘paralysis’.