Pinna Illusion Geometric Demonstration

This applet demonstrates the famous Pinna Illusion, an optical phenomenon in which static concentric circles and radial lines appear to rotate or shimmer when the viewer moves their eyes or head. Using GeoGebra commands such as PolyLine, Distance, and Sequence, it constructs the precise geometric patterns responsible for this illusion. The construction relies on carefully arranged circles and radiating lines whose intersections create subtle luminance gradients that trick the visual system into perceiving motion where none exists. Users can adjust key parameters, including the number of concentric rings, the spacing between radial lines, and the angle of intersection, to observe how each variable influences the strength and character of the perceived rotation. By interactively modifying these settings, learners can discover which geometric configurations produce the most convincing illusion and identify the thresholds at which the effect disappears. This hands-on exploration helps students understand how the human visual system processes contrast and orientation, and why certain regular patterns are particularly effective at generating false-motion sensations. The applet bridges geometry and perception, showing that what we see is not always a faithful representation of the underlying mathematical structure. It is especially useful for classroom discussions on visual cognition, pattern recognition, and the limits of human perception, while reinforcing GeoGebra skills such as dynamic parameter control and geometric construction.