What is it about?
We can be tricked into feeling like we have an illusory sixth finger on our hand. But do we feel like we can move and act with a six fingered hand? Here, we investigated whether experiencing the illusion of having a sixth finger changes the perception of the hand and its action abilities. After inducing the illusion, participants estimated the smallest opening their hand could fit through and the largest object they could grasp. Participants chose larger openings and larger objects after the sixth-finger illusion, showing that the perception of an extra finger can change the perceived boundaries and action capabilities of the hand.
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Photo by Shabeeba Ameen on Unsplash
Why is it important?
Our findings show that the representation of the body can be updated very rapidly. An illusory extra finger, which was invisible and could not be moved, was enough to alter the perceived action abilities of the hand. This suggests that extra body parts can become integrated into the representation of the existing body, with potential relevance for prosthetics and technologies designed to augment the human body.
Perspectives
I find fascinating how humans have the ability to feel an illusory body part that they never had. The mind is prepared to perceive the body, but it is also very flexible into perceiving extra fingers. But how far does it go? I wanted to understand whether it changed what we perceive we can do with that extra invisible finger that we know we do not have, and yet, we vividly can feel. I was surprised to find that it indeed changed action perception, making people choose wider apertures and wider blocks to grasp, after the illusion. And even more impressive, is that this was regardless of them reporting feeling an extra finger. This can be critical for the design of supernumerary robotic limbs and the embodiment of exoskeletons and prosthetics. But at a more basic level, this can also show how our brain perceives an object or empty space as an extra part of the body, and that is quite thrilling!
Denise Cadete
Birkbeck University of London
Read the Original
This page is a summary of: Beyond five: How the experience of a supernumerary sixth finger alters action perception., Journal of Experimental Psychology Human Perception & Performance, September 2026, American Psychological Association (APA),
DOI: 10.1037/xhp0001446.
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