Sight

For information on how the eye works, see eye.

The dorsal stream (green) and ventral stream (purple) are shown.

Sight is one of the senses. Having sight means to be able to see. Seeing gives animals knowledge of the world. Some simple animals can only tell light from dark, but with vertebrates, the visual system is able to form images.

Light enters the animal's eyes, and a part of the eye called the lens sends information from the light to the back part of the eye called the retina. The retina is composed of light-sensitive cells which fire a signal down the optic nerve when light hits the cell. The optic nerve is a bundle of nerve fibres from all over the retina.

When the information from the light leaves the retina, it goes to the brain. It travels along the optic chiasma until it reaches the optic cortex at the rear of the brain. The information is then processed to find out the shapes and colours of objects. From that and from memory, it can tell of what kind the object is. For example, it can somehow tell a tree from a house. The path on which this kind of information flows is called ventral stream.

The brain can also tell where objects are. For example, it can tell how far away an object is (this is called hand-eye coordination). This is needed when catching a ball. The path on which this kind of information flows is called dorsal stream.