Binocular Cues
Modified: 2024-06-11 2:45 PM CDST
Retinal Disparity
or Stereoscopic Vision
- One of the major perceptual tasks is judging depth in a visual
stimulus, or, being able to tell which objects are closer to you from
those that are further away.
- This task is accomplished many ways.
- One
way is via binocular cues for depth perception, or cues that require
the use of both eyes.
- The binocular cues are more powerful than the
monocular cues.
- You can prove this to yourself by trying to perform a
task that requires depth perception, for example, shooting a
basketball.
- You should be more accurate in the long run if you shoot
with both eyes open.
- In the lab, special tests demonstrate the
superiority of binocular cues.
- Retinal disparity is the major binocular cue.
- Each eye sees a
slightly different image.
- You can demonstrate that by holding a
pencil at arm's length in front of you.
- Then pick a target some
distance away from you that is in line with your eye and the pencil.
- Now, look at the pencil; you should see two targets.
- Then, look at the
target you should see two pencils.
- The brain takes those two slightly
different images, and extracts distance information from them.
- Below, there is only one flag.
- Look at your thumb and you will see two flags (each eye's image)
- Look at the flag, and you will see two thumbs (each eye's image))

- Interestingly, range finders on some old cameras work the same way. Video
- You
focus those by bringing the view of two lenses together.
- Range finders of
this type (with two lenses) are also made for deer hunters and golfers so they
can aim their shots more accurately.
- Even battleships used retinal
disparity to determine range, but the lenses involved were widely
separated, and the ranges were measured in miles or kilometers. Video
Binocular Convergence
Take your pen or pencil and hold it about 2 feet away from your
face. Then, bring it slowly toward your face. At about 7-9 inches
away you should feel your eye muscles straining and they will lose
focus. Move the pencil or pen within that short range. The muscle
strain was caused by your eyes rotating inward to their limit.
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