• Background
  • Instructions
  • Illustration
  • Quiz


The correspondence problem is how the visual system determines which object’s image in one eye matches the same object’s image in the other eye. Here we explain how stereograms can be used to study the correspondence problem and potentially derive some solutions. How the visual system is able to solve the correspondence problem is quite complex computationally. The specifics of this computation were the subject of a debate that took place about the nature of stereopsis. On one side was the view that the visual system must bring to bear knowledge of objects and use that knowledge to match images. The other view was that the visual system matches the left and right images before bringing knowledge to bear on the situation.

In order to distinguish these hypotheses, Hungarian American vision researcher Béla Julesz invented randomdot stereograms (Julesz, 1971). Random-dot stereograms are stereograms in which the images consist of a randomly arranged set of black and white dots. The lefteye and right-eye image are arranged identically, except that a portion of the dots is moved to the left or the right in one of the images to create either a crossed or an uncrossed disparity. This creates the experience that part of the image is either in front of or behind the rest of the dots.

In this activity, you can experience random dot stereogram, manipuate the disparity of a small square and the backgroun, make the square move, and even have the dots change constantly.


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 of Anaglyph: Controls the way the anaglyph is being created. You can choose from Red-Cyan, Red-Blue, and Red-Green. The first word is the color for the left eye. The default is Red-Cyan which are the type of anaglyphs used in the book.
Square Disparity: The disparity of the dots in the square in number of pixels on the screen. Positive values refer to crossed disparity.
Background Disparity: The disparity of the background dots in number of pixels on the screen. Negative values refer to uncrossed disparity.
Size of Dots: Make the dots bigger and larger.
Update Stereogram: Static refers to the dots do not change. Dyanimc refers to the dots constantly changing with new random patters always being presented. You get a faster update with larger dots.
Move: Have the square move randomly over the background.
Center: Redraw the small square in the center of the screen.
Speed of Square: How fast the square moves when moving.


Pressing this button restores the settings to their default values.