Primary Visual Pathway

Here is a cartoon sketch of a projection of the primary visual pathway (PVP) looking down on the head.

Light enters the eye and is focused by the lens on the part of the retina known as the fovia. There cone cells convert the light into electrical potentials. As a simple approximation, these signals pass through a number of stages in the retina: the cone cell output is passed to bipolar cells whos output is then passed to ganglion cells. The response of ganglion cells takes the form of a train of impulses and the information in the signal is encoded in the firing rate. Ganglion cells carry the signal down the optic nerve, through the LGN, and finally to the an area of the brain known as the visual cortex, or more specifically, V1.
Approximately 50% of the cells in V1 are simple cells. These cells have a linear spatial response to light and receive virtually all of the retinal information.
The response of these cells is dependent on the spatial location of the light stimulus and researchers have mapped the responses of these cells to light stimulus at various locations in the field of view. The 2D mapping of these responses for a single cortical simple cell is called the receptive field profile and it represents the response of the entire PVP.