• Background
  • Instructions
  • Illustration
  • Quiz


Size constancy is the perception of an object as having a fixed size, despite the change in the size of the visual angle that accompanies changes in distance. That is, we have a tendency to see an object as the same size regardless of the size of its image on our retinae. As we have seen, there are limits to size constancy. Cars look like small toys as we get high enough during take off so tall when we see him from far away. However, at the range of normal viewing, size constancy allows us to see objects as the “right” size even as they move away from or toward us. For example, consider talking to a friend. You see her as the same size if she is standing 6 feet away from you or if she is standing 3 feet away from you. If she is standing 6 feet away and suddenly takes a step closer to you, you do not see her grow, even though her visual angle is now twice as large on your retina. Thus, size constancy usually allows us to see objects as not changing in size.

In this activity, you will manipulate a couple of pictorial depth cues to see how they impact the perception of size. Since there is no real depth in this illustration, size constancy will be illustrated by creating an illusion.


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 adjust these parameters:

Adjust Sizes: selecting this check box allows you to adjust the sizes of the circles.
Size: adjust the relative sizes of the different circles making the right hand circle smaller and the other circles porportionally smaller keeping the left hand circle unchanged.
Texture Gradient: selecting this adds a texture gradient to the screen.
Depth of Gradient: adjusts how much depth is represented by the texture gradient.
Adjust Height: allows you to adjust the relative height of the different circles, moving the right hand circle to the highest point, the middle circles intermediate heights, and leaving the left hand circle unchanged.
Height: controls the amount of relative height depicted.


Pressing this button restores the settings to their default values and allows you to adjust speed and relative size. It also resets the counter before you can indicate if you have the objects arriving at the same time.