Dead or Alive? A look into the “Dead Finger” sensory illusion

Posted on May 2nd, 2022 by

Written by Samantha Dorgan, Emma Barrett, Mariah Chalamila, and Trina Toeben

 

Playing with reality

Sensory illusions are being used more widely today for more reasons than just party tricks. Some clinical settings use sensory illusions, such as the disappearing hand trick, to allow for those undergoing paralysis therapy to experience body sensations (Stone, K. D., et al., 2018). For more information on the disappearing hand trick navigate to this article by Roger Newport and Helen Gilpin. This post is specifically looking at the dead finger trick, an illusion that, if done correctly, can give individuals the perception of being dissociated from their own fingers. The dead finger trick can be used to promote awareness to those experiencing body-limb dissociation and hopefully generate more public conversations regarding such mental processes.

 

Why do people experience the illusion?

Our skin is the biggest organ of the human body and touch receptors are embedded within it (Wolfe, et al., 2017). When the brain is taking in sensory information, it sometimes fails to take all factors into account (as this illusionary trick demonstrates). The sensation we think we feel is therefore incomplete and known as a perceptual disjunction. For example, in the activity below, our brains “forget” that there is another object (your partner’s finger) blocking us from feeling both sides of our index finger. The sensory illusion is essentially tricking your brain into believing that there is no feeling in your finger (“Do the Dead Finger Trick”, 2015).  

When you stroke just that one side of your finger “it results in the feeling that the finger has gone numb” (“Numb Fingers” 2020). If this task is done correctly, it should give you the sensation of touching what is called a dead finger, meaning that the finger feels like it does not have any nerve endings in it. And that’s not all, there are many tricks out there that can teach us more about sensory illusions, you just have to keep your fingers alive to feel them. So, if you want to experience this phantom sensation, follow the steps below. 

 

Steps: Adapted from “Do the Dead Finger Trick,” 2015.

  1. Find a friend who is interested in experiencing this sensory illusion with you.
  2. Remove any accessories from both your hands and the hands of your friend.
  3. Face each other, and place your hands together (as if you were high-fiving). You can choose to be seated or stand.
  4. Slowly pull your hand away from your partner, except for the tips of your index fingers, which should remain in contact.
  5. In order to perform the rest of this illusion, you must rub up and down along the length of the index fingers (which are still touching) with your thumb and index finger of your free hand. Your thumb should run the length of one of the touching fingers, and your index finger should run the length of the other touching finger (illustration available here). 
  6. Experience the dead finger sensation!

*Disclaimer: Not all who partake in this activity may feel this sensation! There could be many reasons ranging from personal focus, attention-spans, errors in how they completed the task, expectations, etc. There is not enough information to fully understand why some people may not experience illusions, but it’s likely due to simple mistakes in interpretation. Another explanation for why an individual may not experience the intended sensation is because the brain does not function uniformly in every person. Since everyone’s brain will process sensory information differently, there will be a wide spectrum of sensations felt during this illusion ranging from not feeling the sensation at all, to experiencing the sensation of a “dead finger”.

 

References

“Do the Dead Finger Trick” (2015). Kipkis. https://kipkis.com/Do_the_Dead_Finger_Trick

“Numb Fingers” (2020). Science World. https://www.scienceworld.ca/resource/numb-fingers/ 

Stone, K. D., Bullock, F., Keizer, A., & Dijkerman, H. C. (2018). The disappearing limb trick and the role of sensory suggestibility in illusion experience. Neuropsychologia, 117, 418–427. https://doi.org/10.1016/j.neuropsychologia.2018.07.012 

Wolfe, J. M., et al. (2017). Sensation & perception (6th ed.). New York, NY: Oxford University Press.

 

Comments are closed.