In this figure A & B are the receptive fields from the Lateral Geniculate Nucleus (LGN). These are “simple cells” and the particular receptive field will be one specific area of the retina. They are still similar to the receptive fields of ganglion cells. These receptive fields may be either “centre on” or “centre off”.
In C & D, these are still “simple cells”, but now in the V1- cortex, it can only detect a very simple pattern. Now moving to E & F: we have “complex cells” of the cortex which receive input from various “simple cells”. This means that a particular V1 complex cell may be “tuned” to detect a particular shape, colour or movement from anywhere in the visual field.
This model for the visual processing in the primary visual cortex (V1) comes from Hubel & Wiesel 1962.