Motion Ring / Lilac Chaser
Stare steadily at the center cross. Within 10-20 seconds, the magenta dots will vanish (Troxler's Fading) and a green dot will appear to chase around the circle.
Mechanism
👻 The Green Dot (Afterimage)▼
There is no green dot! When your retina adapts to the magenta color, it becomes fatigued. When the magenta dot disappears, the "off" signal is interpreted as the complementary color: Green.
🌫️ Troxler's Fading▼
As you fixate on the cross, your peripheral vision stops noticing the static magenta dots because they aren't changing position (only flickering). This neural adaptation is called Troxler's Fading. Eventually, all you see is the moving "gap", which looks like a green object.