Background

Disparity arises because our two eyes are in different locations in our head and therefore have slightly different views of the world. If you hold your finger out at arm’s length and then look at it alternately with your left eye only and then your right eye only, the image of your finger relative to the world behind it will shift somewhat. This is binocular disparity, which helps provide the basis for the determination of depth.

The explanation of how disparity allows us to extract depth information is quite complex. So work through this and the next set of activities slowlty, make sure you understand the activities, and review them until you understand these concepts well. Only after you have done that can you be sure that you understand the explanation of stereopsis.

Use this activity to explore the basics of binocular disparity and how it is related to vergence.

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

Settings

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

Disparity Object X Position: Moves the disparity object (the green dot that is not being 'looked at') closer or farther from the eyes.
Disparity Object Y Position: Moves the disparity object up and down on the screen.
You can also move the dot by clicking and dragging on the screen with a mouse or by touching the screen. Fixation Object Position: Moves the fixation object (the red dot that is being 'looked at') closer or farther from the eyes.
Eye Separation: Makes the eyes closer or farther apart. The farther the separation, the greater the vergence change and the more disparity.

Reset

Pressing this button restores the settings to their default values.

Try these settings to see how binocular disparity works

In this diagram imagine you are looking down on a person's head. The right eye is on top and the left eye is below. Both eyes are looking at the red dot, the fixation object. The lines from the dot show the direction the light goes from the object to where it falls on the foveas of both eyes. The fovea is indicated by the small dot in the middle of each retina. The green dot, the disparity object, is another object in the world that this person is not 'looking at'. It does not fall on the foveas of the two eyes.

There are two green lines in the right (top) eye. The bright green line shows where the disparity object falls in the right eye. The darker green line shows where the disparity object falls in the left eye below. Thus, you can see in one eye where the same object falls on both eyes. If there is any disparity the two green lines will not fall on top of each other. If there is 0 disparity, the two green lines will fall on top of each other.

You can move the disparity object anywhere on the screen and the fixation object closer and farther from the eyes. Move the disparity object and see how the disparity changes as a result of its position in this little world. See if you can find any places other than the location of the fixationobject where there is no disparity.

Proceed to Quiz