The discrete-continuous interface. This schematic shows the connectivity between the neuronal populations in the superior colliculus in greater detail. The transverse section through the midbrain allows us to depict the terminations in the optic tectum from the optic nerve. We also illustrate the topographical arrangement of the fixation (rostral pole) and buildup (distributed throughout) cells, and the connectivity between these implied by our formulation. Note that burst neurons are the most dorsal, with buildup neurons found more ventrally. As the schematic shows, this would be consistent with the proposed extrinsic (between regions) connectivity, as each population is oriented toward the regions it is connected to. The intrinsic (within region) connectivity between buildup and fixation neurons is shown on the right, conforming to the known retinotopy of the colliculus (Paré, Crommelinck, & Guitton, 1994; Quaia, Aizawa, Optican, & Wurtz, 1998). The angles indicate the coordinates of the visual field represented at each point in the colliculus.