How is vision possible?

 

OPTICS

-- the study of the behavior of light; it is a branch of physics

RETINAL IMAGE

-- the pattern of light that is projected on the back of the eyeball onto a patch of tissue called the RETINA
-- light reflects off of objects in the world, it passes through the LENS at the front of the eye and it is focused at the back of the eye.
-- the LENS also flips the image upside down in the process of focussing it to a small point

 

Consider this RETINA IMAGE

It could be caused by FIVE very different objects.

(A), is a small stick held at an angle a few inches from the eye
(B) is a chopstick standing straight up-and-down a foot away
(C) is a round curtain rod
(D) a piece of wood dowling
(E) is a polevault

How does our visual system take the information that it receives from the world -- the two-dimensional, upside-down image in B -- and produce in us an experience of the rich three dimensional world?

-- Textures & gradients
-- Stereoscopic vision (information from 2 eyes)

MAIN POINT -- Your brain is doing a TREMENDOUS AMOUNT OF PROCESSING


How many objects do you see?

For one object to be occluded by another is for it to be partially obscured or hidden behind it.

We see the circle as occluded by the triangle, the square occluded by the triangle, and so on.

THERE WAS A MISTAKE IN THE ONLINE DESCRIPTION!!! -- DID YOU CATCH IT????

But why do we "see" the image in that way? There is nothing in the image itself that points to a three-dimensional space.



The picture is ambiguous because it can be interpreted in more than one way.

Every time that you look at the world, the image projected on your retina has only two-dimensions and also can be interpreted as indicating the existence of more than one three-dimensional situation in the world.

So our visual system must overcome the inverse problem.

The Inverse Problem in Vision: The problem of retreiving all of the visual information about the 3D environment using only the more limited information contained in the 2D image projected on the retina of the eye.

How can we learn WHAT the BRAIN is doing and HOW it is doing it?

 

Proceed to NEXT LESSON.