Here’s a cool visual illusion to share with your kids. It’s got lots of names: the disappearing dots illusion, the lilac chaser, the Pac-Man illusion. Curious? It’s quick and easy.
Instructions for the lilac chaser
The image is below. Make sure you master each step before moving to next.
1. Follow the movement of the rotating pink dot with your eyes. What color do you see?
- You should only see one color: pink.
2. Now stare directly at the black + in the center. What happens to the moving dot?
- The moving dot should turn to green.
3. Now concentrate on the black + in the center. Stay very focused on the +. Does something happen to the dots?
- The pink dots should start to disappear. You may only see a single green dot rotating.
4. Finally, move your face close to the screen as you stare carefully at the +. Wait until the pink dots disappear, and you only see the green dot like in step 3. Now, slowly move your face away from the screen. What happens?
- You should see a green light show explode out from the pink dots.
Optical illusion science: What’s happening here?
This optical illusion reveals how our eyes and brain perceive colors (negative afterimage) and motion (Troxler’s fading).
1. When your eyes follow the rotating pink dot, your brain is actively engaged in tracking the motion and perceiving the pink color, so you register the continual appearance and disappearance of pink.
- But get this: there is no circular motion occurring in this image at all. It’s just the rapid appearance and disappearance of pink dots in consistent order. Nothing is moving, only flashing! This illusion of apparent motion is called the phi phenomenon.
2. When you stare at the black +, you’re not actively tracking, and the pink dots appear in your peripheral vision. Your peripheral vision detects the appearance of pink, and when the pink disappears, you experience the afterimage effect: the appearance of the opposite (or complimentary) color, green.
- It happens because the cells that carry signals from the retina in your eye to the visual system in your brain get used to the color it sees (lilac). This is called neural adaptation: basically, when we get used to things, we stop noticing them. When the lilac disappears, your brain interprets the change as an increase in the complimentary color (green), rather than a disappearance of the existing lilac.
3. The complete disappearance of the pink dots is also because of neural adaptation. Again, our sensory systems prefer novel stimulation, and familiar stimuli quickly fade from consciousness.
- This particular phenomenon is called the Troxler’s fading, after the Swiss physician Ignaz Paul Vital Troxler, who first noticed it in 1804.
4. The green light show that appears when you move your eyes away from the cross spreads the afterimage effect across a wider areas.
Pretty cool, right?
Optical illusions like these give us a glimpse into how our visual system processes colors and motion. It’s also a reminder that our perception of reality is easily manipulated.
Do you trust everything you see?
Source: if you want to further dive into these phenomena, Wikipedia is a good place to start.
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