Parts of the Eye

Cornea

transparent covering of the eye, responsible for about 80% of focusing but it cannot change its focus.

Pupil

an opening in the iris that regulates the amount of light let into the eye by changing in size.

Iris

the pigmented ring of muscles behind the cornea

Lens

found just behind the iris, this is a bunch of onion-like layers –it changes in shape to let the eye focus on images on the retina, responsible for the other 20% of focusing.

Fovea

located directly on the line of sight in the center of the macula on the retina – the center of the object being focused falls on the fovea.

Retina

after light passes through the vitreous humor it hits the retina, the interior lining of the back of the eye.

1. In the retina there are three layers of cells that take the information and transfer it to the brain.
2. Photoreceptors—Visual Receptors – Rods and Cones: these two visual receptors have many different properties and are dispersed differently on the retina. They also have very different structures.

Photoreceptors

Rods

function well in low light (light of shorter wavelengths), there are about 120 million on the retina. They are responsible for peripheral vision and do not respond to color. In the fovea, there or NO rods...only cones. The cones are also packed closer together here in the fovea than in the rest of the retina.

Cones

there are about 6 million in the retina. They are responsible for our daytime sight (the respond best to light of longer wavelength) and they provide us with information about small features in the environment and are the source of the highest acuity. They are responsible for color vision. While there is a concentration of cones on the fovea—the rest lie on the peripheral retina (everywhere else)

Before light reaches the receptors it must pass through layers of other cells. The Ganglion (Which connect to the optic nerve), the Amacrine, the Bipolar, and the Horizontal cells. Light passes through these cells (they are transparent so they do not interfere with the light at all) to the receptors where light sensitive. The process the information after the photoreceptors turn the light into neural impulses.

On the retina, those photocells that are hit by light from the image are activated.

Photocells that do not receive any reflected light are not activate. We can think of the image as a pixellate map of activated and nonactivated photocells on the retina.

A nerve from each photocell connects to a particular location in the visual cortex of the brain. The photocells that are activated send a nerve impulse to the brain, while the photocells that are not activated do not send any impulse to the brain.

The brain, when it receives a collection of nerve signals from the eye, interprets where each signal comes from, and reconstructs the pixellate map.--The brain then interprets the pixellate map as an image.

**ALL the information about what you see is carried in these neural signals that are processed in the brain. So then this would be a good time to go over applicable perceptual phenomenon ( the prezi below has some)—color perception , size perception and maybe even change blindness (lots of info on web for this)