Stereoscopic Vision

The brain is able to form just one image even though what we see comes through two eyes. This ability to form one image even though the two fields of vision overlap is called binocular vision, or stereoscopic vision. To demonstrate the value of this, close both eyes and have someone hold up a pen or pencil about two feet away. Then extend your arm from your side with index finger pointing. Now, open one eye and in the first motion try to touch the very tip of the pen or pencil. A few tries will show the value of stereoscopic vision, or the ability to judge depth.