Besides the cones, which detect light entering the eye, the biological basis of the opponent theory involves two other types of cells: bipolar cells, and ganglion cells. Information from the cones is passed to the bipolar cells in the retina, which may be the cells in the opponent process that transform the information from cones. The information is then passed to ganglion cells, of which there are two major classes: magnocellular, or large-cell layers, and parvocellular, or small-cell layers. Parvocellular cells, or P cells, handle the majority of information about color and fall into two groups: one that processes information about differences between the firing of L and M cones, and one that processes differences between S cones and a combined signal from both L and M cones. The first subtype of cells is responsible for processing red–green differences, and the second process blue–yellow differences. P cells also transmit information about the intensity of light (how much of it there is) due to their receptive fields.