Two Dimensional Eyes, Three Dimensional World

Having taken a break from perception to discuss some of the latest political idiocy, I want to conclude my posting this week with a little more discussion of perception. My comments here are taken from the excellent, interactive website on the brain published by McGill University. They have an excellent section on perception which discusses vision from the molecular level all the way to the social.

One facet of the site that really caught my attention was the discussion one of the major sources of visual ambiguity, which is the fact that our visual system, specifically our retina, is only capable of taking in information about a two-dimensional world, yet our brain is able to create the visual impression of living in a three-dimensional world. Let me quote the explanation from the website:

One important source of ambiguity for the visual system is that the world is three-dimensional, but the images that it projects onto your retina are two-dimensional. Hence differing objects, depending on their distance and orientation, may occupy the same amount of surface area on your retina. Your brain therefore becomes confused, and tries to use other indicators to clarify the situation. Two such indicators are your own past experience with the object in question and the experience of the human species, which is encoded in your genes.

 They even include a helpful picture which shows how three different objects could produce the same image on our retinas:

This ties in nicely with the waterfall illusion I discussed earlier. The key there was that the impression of an impossible object was created through perspective. The artist was able to create what appeared to be an impossible object in the real world by exploiting the fact that our retinas can only receive information two-dimensionally. Thus, when we observe these different objects from the correct perspective, they appear to be one unified, impossible object.

A further illustration can be found on this interactive webpage.