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Quick Science: Finger Illusion

If you liked Where’s Your Blind Spot and Is There a Hole in my Hand? here’s another quick activity that demonstrates how our eyes can fool us.

A drawing of a skull with a striped background

Hold your hands in front of you at eye level.

Point your index fingers towards each other leaving a small space between the tips of your fingers.

Focus on the wall past your fingers.

Wiggle your fingers up and down slowly.

What do you see? A hovering finger is seen wiggling between your fingers. The right eye sees the end of the right finger wiggling. The left eye sees the end of the left finger wiggling. There seems to be a short finger floating in front of your eyes. What is seen by two eyes can be misleading!

Optional Extensions: Change the activity, predict results, and test predictions. What if you don’t wiggle your fingers? wiggle only one finger? move the fingers closer or farther apart? move one up while the other moves down?

Consider a class activity: Discuss how it can be important to confirm the facts when you see something happening especially at a distance so you don’t have information you can hear. For example, why does she seem to be yelling at her? Is she’s angry or excited? Why is he wildly waving his arms at him? Is he extremely frustrated or trying to encourage him? Especially from a distance body language and facial expression might not be enough information to know what’s going on in a situation.

Write an emotion on a card and ask a student to gesture that emotion while classmates guess the emotion. Ask the student: Is it easy or difficult to express an emotion without words? Ask the class: Is it easy or difficult to guess the emotion with limited information? Repeat having the student gesture an emotion from across the room. 

To save you some time, I’ve created a simple set of emotion cards you might print and cut apart for this activity.

Quick Science suggestions take minimal prep time and use common materials.