• Background
• Instructions
• Illustration
• Quiz

## Background

Stuart Anstis developed what he calls the “spoked wheel” illusion (Anstis & Rogers, 2011). When you watch the pattern below move in the illusion, you see what looks like a bicycle wheel. The spokes of the disk are thin gray lines. These lines do not move, nor do they change their brightness. The apparent movement comes from the wedges between the spokes. The movement comes from the clockwise rotation of the gray of the wedges. Once the illusion is set in motion, people see both the clockwise motion of the wedges and what looks like counterclockwise motion of the spokes. This motion is both apparent and illusory, because these lines do not move. That is, the spokes remain absolutely immobile, whereas the gray wedges shift position from one frame to the next.

In this illustration, you can try your hand at this illusion and work verious ways to try to see what makes the illusion stronger or weaker.

## Instructions

### Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

### Illustration Tab

On the Illustration tab, you can start, stop and alter the motion of squares to experience optic flow.

### Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Move: Start and stop the the animation. The principle motion in this animation is of the wedges, which I am calling the wheel.
Keep Wedges in Their Spokes: select to not move the wedges relative to the spokes they are in.
Speed of Spokes: Rotate the spokes. Positive is clockwise and negative is counter clockwise. use this to cancel the illusory motion.
Wedge Speed: how fast the wedges rotate between segements.
Size of Wheel: change the size of the wheel.
Number of Spokes: change the number of spokes in the wheel.
Spoke Intensity: change the intensity of the spokes. (default is average between the light and dark wedges)
Contrast: change the degree of contrast between the bright and dark wedges.

### Reset

Pressing this button restores the settings to their default values.