Figure 9. Schematic of the differences in activity evoked in the SC by visual and auditory targets.

When a target is visual, a "hill" of activity will be evoked at a location in the SC that corresponds to the visual response field of the neurons. Visual stimuli at different locations would evoke activity at different sites in the SC (A, B, C left panels). In contrast, auditory stimuli at different locations will evoke activity across the SC but with different discharge rates (A, B, C right panels). We note that this schematic does not address the code for the vertical dimension, nor does it consider the possibility that the inflection points of auditory response functions might vary with location in the SC. If the latter is true, then the auditory code would show some topography, with the edge of a broad hill varying with target location.