• Background
  • Instructions
  • Illustration
  • Quiz


Induced motion means that one moving object may cause another object to look like it is moving. The classic example of induced motion is the movement of clouds at night, which may make it seem as if the moon is moving. The clouds moving in one direction induce a perception that the moon is moving in the opposite direction. Similarly, the movement of your car makes it look as if the world is rushing by you, when in fact it is you in the car who is rushing by the world, and the surroundings are relatively motionless. Induced motion is illusory because we misperceive what is moving relative to the other object. Your car is really moving relative to the surface of the road, but you perceive the road as moving relative to your stable position in the car.

In this activity, you can both examine induced motion in both the classic laboratory set up and with a grating moving over the still stimulus to simulate the moon behind the clouds.


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.


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

Type: type of stimlus used to induce the motion in the dot either:
a Frame (the standard laboratory stimulus), or a Square Grating or Sine Grating.
Move: Start and stop the motion of the inducing stimlus (the frame or the grating).
Jump Rate: how often the frame moves (only for the frame stimulus).
Jump Size or Grating Speed: how far the frame moves or how fast the grating moves.
Frame or Grating Size: the size of the frame or the size of the bars in the gratings.


Pressing this button restores the settings to their default values.