• Background
  • Instructions
  • Illustration
  • Quiz


Optic flow provides information about distance and consequently can be used to aid in our own movement. As we discussed in the previous chapter, objects closer to us seem to move faster past us, whereas more distant objects appear to move slowly as we move toward them. This pattern is called the gradient of flow. In simulations, if we increase the speed at which the observer is moving, this gradient of flow accelerates. If the speed of the observer decreases, the gradient of flow lessens. The horizon or destination point is the distant point at which the gradient of flow comes to zero. This point is called the focus of expansion. As we voluntarily change directions in an optic flow pattern, this focus of expansion will shift.


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:

Move/Stop: Starts or stops demonstration.
Change Direction: Causes squares to change from moving out to moving in or vice versa.
Center: Returns the motion to centering on the animation area.
Speed : Changes the speed of animation.
Clicking or touching the animation area : The animation will move to the point you click or touch and will expand or shrink into this point.


Pressing this button restores the settings to their default values.