In functional terms, retinocortical pathway can be modeled as a
computational channel from a * source*-layer and a * target*-layer.
The computation is specified as a transformation mapping
that relates stimulations on the * source*-layer to patterns of
excitation on the * target*-layer.
These layers represent respectively the visual field (**S**) and the cortical
plane , where simple cells are supposed uniformly
distributed. Assumed the homogeneity and continuity of the layers and the
linearity of simple cell responses, we can describe the behavior of the
system by using linear operator theory.
Thus, if is the visual input, the spatial distribution of
excitation on the cortical plane can be written as:

where is an integral linear operator of kernel :