Stereo Vision

STEREO VISION illustrates one of the rules the brain follows for perceiving depth. Two vertical rods stand against a plain background. Seen with both eyes, it is clear that one rod is farther away than the other. Seen with one eye alone, the two rods appear to be side by side. However the distance between them depends on which eye one uses. The "stereo rule" uses this difference in distance to determine which rod is farther away. If the space between the rods appears greater using the right eye than it does when using the left eye, the rod on the right is farther away.