Take a look out the nearest window. How does our visual system make sense of that sea of light, color, detail, and motion? For starters, light travels into your eyes and is focused by the lens onto your retinas. The retina is the layer of tissue at the back of each eye that converts the light energy that enters our eyes into neural impulses. The brain processes these neural impulses and the pattern of neural activity that results is what we mean when we say we see something. As you can see in the figure at below, the image that is cast onto your retinas is upside-down and backwards. This is because the lens and cornea of the eye gather light about the rays that travel in straight lines—the straight light rays from the top of the tree are cast onto the bottom of your retina, those from the bottom of the tree are cast onto the top of your retina, those from the left go to the right of the retina, and those from the right go to the left of the retina.
However, it is worth noting that the retina is flat, and not at all three-dimensional like the world it represents for us. So, how do we perceive depth? Let's start by thinking about a fun example of how our two eyes help us see depth.
