Corresponding points refers to a situation in which a point on the left retina and a point on the right retina would coincide if the two retinae were superimposed. In contrast, noncorresponding points refers to a situation in which a point on the left retina and a point on the right retina would not coincide if the two retinae were superimposed. For example, when looking at your thumb with your hand held out at arm’s length, the image of your thumb falls on corresponding points on your left and right retinae. The lamp beyond it does not. This is why you have the illusion of seeing two lamps (see Figure 7.18). Now imagine a semicircle in front of you, with all the points at the same distance from your eyes as your thumb. This imaginary line is the horopter. Thus, if you stretch out your other arm alongside the one you are fixated on, your other thumb is not your fixation point, but lies along the horopter. Technically, the horopter is the region in space where the two images from an object fall on corresponding locations on the two retinae. If you switch your focus from your thumb to the lamp, you now have established a new horopter.
Use this activity to explore the horopter and how it realates to our vergence.
To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.
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.
Pressing this button restores the settings to their default values.