Roger Newport gave a talk on his research at the Body Up conference last week. [See work with the MIRAGE box here Augmented Hands]  Speaking to him afterwards, he asked if I had ever experienced the 6 finger Illusion? He reached into his bag and revealed a mirror which he placed on the table. Placing my hand one side of the mirror, he skilfully performed the illusion. Looking into the mirror I watched as each finger was stroked predictably in series, moving from thumb to the little finger, but then continuing to apparently stroke an invisible 6th finger. This worked perfectly for me. What is really interesting is that apparently a very small amount of people have reported seeing this 6th finger! 

“Six-Finger Illusion: better understanding our perception of our body and our avatar.”

This VR experimental platform is designed to explore ways in which we can adapt to structural changes in our body. In this experiment, a 6th finger is added to the hand. A virtual brush is used to stroke the hand.

The Shrunken Finger Illusion.

Placing a half  Ping-Pong ball- or as the researcher say an “amodally completed hemisphere” onto the end of a finger and looking down, gives the illusion of having a shrunken. Looking down at the sphere, the brain competes for the shape, mistaking this for a complete ball, leading to the conclusion that the finger has shrunken. The researchers in this paper suggest that rather than a simple ‘cognitive failure’ there is, in fact, a specific a perceptual process taking place completing the hidden backsides objects. https://jov.arvojournals.org/article.aspx?articleid=2434234