Binocular Cue: Retinal Disparity

Depth cues that depend on the use of two eyes are called binocular cues. As generally known, two eyes are better than one, making the task easier with two eyes. This is the case for binocular cues. Our eyes see unique images, though each eye only sees something slightly different.

Retinal disparity is an important binocular cue, as it perceives depth, specifically the relative distance of objects. The brain processes the images our eyes see and computes the difference. The greater the perceived difference between the two objects, the closer the object is. This makes sense because from further away, both eyes are looking at the big picture (meaning that their images are more likely to be similar). The closer we are to the object, the more miniscule details each eye can pick up on.

There is an easy example to show retinal disparity and all you need is a pencil/ pen with a clip! Hold the pen about 18 inches in front of your face, with the clip barely showing on the right side. Close your left eye, and you should be able to see the clip still. Now change which eye is open, so your right eye is closed and your left eye is open. Is it harder to see the clip now? Move the pen closer to your face, and try the same thing again. The difference between the two images should be even greater now, and with your left eye open you might not see the clip at all! The first image is from 18 inches away with your left eye closed. The second image is from the same distance with your right eye closed. The next two images are left and right closed respectively, but the pencil is closer to our eyes and the difference is more noticeable.

 

Though it may just seem like a magic trick, your eyes are not fooling you. Retinal disparity is important to understand, so that you can fully understand binocular cues as well.