Three tactile illusions to trick your brain

We’ve blogged before about The Rubber Hand Illusion - a simple experiment where psychologists found that they could convince people that a rubber hand was their own by putting it on a table in front of them, hiding their real hand, and then stroking it in the same way as their real hand.

Source: KCL

Source: KCL

By mixing up the signals from two different senses – sight and touch - we can trick our minds to believe that the fake hand is our own.

The illusion is so compelling partly because of the priority our brains give to our sense of sight. In fact, most of the back of our brain is devoted to visual processing and around half of the cortex is involved with sight. Even in situations where the brain processes ‘multisensory information’ - for example, when you hear the screech of tyres as you see a car stop - vision tends to dominate.

But The Rubber Hand Illusion is just one trick. Here are three more you can try at home!

1. The Aristotle Illusion

One of the oldest tactile illusions is the Aristotle illusion - it’s also one of the most simple.

First, cross your forefinger and index finger. Next, touch a small spherical object such as a rolled up piece of blu-tac. 

It will feel like you are touching two balls of Blu Tack and not one. You can also achieve the same effect if you touch your nose!

In this illusion the brain has failed to process the fact that you have crossed your fingers. Because the ball or Blu Tack touches the outside of both fingers at the same time – something that very rarely happens – your brain interprets it as two separate objects.

2. Tricks for your fingertips

Our fingertips are exceptionally sensitive. As such, it’s relatively easy to trick them.

This illusion directly from New Scientist shows you one way you can fool them!

“Take an ordinary comb and pencil and lay your index finger along the top of the comb, then run the pencil back and forth along the side of the teeth. Even though the teeth are moving from side to side in a wave-like motion, your finger will feel as if a raised dot is travelling up and down the comb.

“According to Hayward, this works because the unfamiliar motion of the teeth causes similar skin deformation to the more usual action of running your finger over a raised bump, so your brain interprets it that way.”

3. Hot and cold coins

Take two coins and put them in the freezer until they are thoroughly chilled. When this is done, take them out of the freezer and place them on a table - one on either side of a coin that’s been kept at room temperature.

Touch the two cold coins with the tips of your index finger and ring finger, leaving the middle finger to touch the middle coin.

Amazingly, the middle finger will feel equally cold. 

Interestingly, your middle finger will not feel cold unless it is in contact with a neutral coin; if there are no tactile sensations, the brain is reluctant to “fill in the gap” and ascribe cold to it.

Have you tried any of these? Tell us what happened!