Parallel Retinocortical Channels: X and Y and P and M

This chapter discusses parallel retinocortical channels. The retina contains many visual systems within it. In the cat, the X and Y and the many W classes project from the retina to diverse targets within the brain. The different spatially filtered versions of the world presented by these different neurons are obviously used for different visual functions. In the monkey, because of the extraordinary importance of color vision, the segregation of function between different retinocortical channels is even more obvious than in the cat. The P pathway, from P ganglion cells through the Parvocellular layers of the LGN to primary visual cortex V1. carries signals about color and location. The M pathway carries signals about contrast and motion. These two pathways are kept separated up to visual cortex, but there are important interactions between the pathways in cortex that remain to be explored.