If depth perception works because the brain checks the difference in the position of the object between the two eyes and concludes how far away it is, how can we still see depth when one eye is closed?

Question

If depth perception works because the brain checks the difference in the position of the object between the two eyes and concludes how far away it is, how can we still see depth when one eye is closed?

In: 3602

Answer 1

What you’re referring to, inferring depth from the disparity between images in the two eyes, is called *stereopsis*. It is only one of many cues that your brain uses to infer depth – albeit a powerful one. [This wikipedia article](https://en.wikipedia.org/wiki/Depth_perception) has a nice overview. Notice all the things listed under “Monocular cues”. *Monocular* as in “requiring only one (*mono*) eye (*oculus*)”. These cues all remain when one eye is closed or disabled. They are also the cues that allow you to interpret 2-D images in three dimensions. Even though you need stereopsis to have the full experience of depth, you can still watch a 2-D movie (or image) without it just looking like a bunch of flat shapes.

For the same reason, it is possible to get a stronger experience of depth from a 2-D video, by closing one eye and sitting close to the screen (to remove conflicting depth cues from your environment). It doesn’t always work because there are often some subtler conflicts in depth information too (e.g. your eye can tell that it is focused a certain distance away on the flat plane of the screen), but especially in scenes with a lot of (camera) motion, the pictorial depth cues can be strong enough to override the conflicts and really make you experience depth.