Motion‑Bounce Illusion

Instructions: Toggle cues and adjust speed to explore how perception changes. The new sound imitates two rigid balls colliding.

How it Works: This interactive demonstration showcases the Motion‑Bounce Illusion. Two identical discs move towards each other, meet in the middle, and then move apart. Without any additional cues, observers typically perceive the discs as passing through each other. However, adding a brief visual flash or a sound cue at the moment the discs meet can dramatically alter this perception, making it appear as though the discs bounce off each other.

Using the Controls:

• Flash cue: Toggles a brief white flash across the track when the discs meet. Enabling this often strengthens the illusion of a bounce.
• Sound cue: Toggles a percussive sound when the discs meet. This auditory cue also tends to make the discs appear to bounce. The sound is synthesized to mimic the collision of two hard objects.
• Speed: Adjusts the duration of one full cycle of the discs' movement (from starting positions, meeting, and returning). Slower speeds might make it easier to observe the "pass-through" perception, while faster speeds can interact with the cues in interesting ways. The range is from 1000ms (1 second) to 6000ms (6 seconds) per cycle.

Experiment with different combinations of cues and speeds to see how your perception of the discs' interaction changes. This illusion highlights how our brain integrates sensory information to interpret events.

The Color Change Illusion: You might notice that when the flash or sound cue is enabled, it appears as though the discs change color after they meet in the middle. This isn't actually happening—the blue disc is always blue, and the red disc is always red. What you're experiencing is a trick of perception. When your brain interprets the interaction as a "bounce," it expects the object that came from the left to return to the left. Because the discs switch paths after the midpoint, the returning disc is a different color, creating the illusion of a color change. Your brain is essentially connecting the trajectory of "the thing that bounced" even though it's a different colored disc.