Vision

Light reflected off of objects enters the eye through the cornea and pupil and is focused by the lens onto the retina, a sheet of neural tissue at the back of the eye.

Here, light is absorbed by rod and cone photoreceptors which respond by changing their rate of neurotransmitter release. Basic characteristics such as wavelength, perceived as color, are encoded by the activity of these cells.

Photoreceptors send this information to other cells in the retina which integrate information from multiple photoreceptors, allowing simple visual features, such as edges to be detected. Retinal ganglion cells then send this information through the optic nerve, which partially crosses, so that each side of the brain gets input from both eyes.

Most optic nerve fibers synapse in the thalamus of the brain where different characteristics, such as color and motion, are processed in different regions. Then the information travels to the primary visual cortex for higher level processing. For instance, identifying the direction of movement.

Inputs to the primary visual cortex are organized topographically so that there's an accurate map of visual space. From here, information is sent to other areas of the cerebral cortex for even more complex analysis, such as object recognition.