Sparseness of coding in area 17 of the cat visual cortex: a comparison between pinwheel centres and orientation domains.

Optical imaging of intrinsic signals across the primary visual cortex in mammals has shown that neurons tuned to the same stimulus orientation are clustered together to form orientation domains, which converge on singularities called pinwheel centres. We used a combination of two gratings in different mutual relationships as in a plaid to study how visual cortical neurons differ in integrating these signals. Neurons in the centres of orientation domains responded to a smaller range of such composite stimuli than cells near pinwheel centres, even though orientation tuning for a single bar or grating did not differ significantly between the two locations. We believe that this difference between the two locations is related to the way local intracortical interactions generate a full complement of orientation preferences from a limited number of preferred stimulus orientations represented in the geniculate afferents to the striate cortex.