Sleight of Hand
Winter 2017

Have you ever built a complicated Lego sculpture and thought: I wish I had three hands? In 1998, two Pitt Med psychiatrists created an experiment that let people experience having an extra mitt. 

In the experiment, subjects hid one of their hands. The researchers stroked it, and also a rubber hand the subjects could see, with paintbrushes. After 2 minutes, the subjects reported that they felt the paintbrush touching the rubber hand! 
How is this possible?
Your sensory systems—in this case, touch and sight, as well as the system for figuring out your body position (called proprioception)—tell you what’s going on based on what’s happened to you before. If your real hand is blocked from view, your brain “fills in” information. It tells you the rubber hand that you can see is attached to you, even though you know that’s not rational. 
Pitt prof Julie Fiez says that such illusions show that “we are always trying to make sense of the world in the face of incomplete, and sometimes contradictory, information.”   
And that can get a bit freaky. The rubber hand illusion also messes with our sense of “self.”  In other words, if your brain can’t recognize a fake hand from your own, how do you know what’s you and what’s something else? And how does your body process that kind of information? Some scientists and philosophers spend a lot of time delving into these questions.
There are all kinds of tricks you can play on yourself. For instance, you could make two adjacent fingers feel like one. If you tape them together, your brain would reorganize so you couldn’t tell the difference between a touch on one finger and a touch on the other. The only problem is this illusion takes several months to pull off. So, it’s probably better not to try this at home.   
Is there a topic you’d like For Real! to explore? Are you a teacher who would like to use Pitt Med in the classroom? Drop us a line: