Receptive field organization of complex cells in cat striate cortex

Summary The receptive field organization of complex cells was studied by analyzing interaction effects between two stationary flashing light stimuli. One was placed in the most responsive part of the receptive field to produce activity against which effects of the other in different visual field positions could be determined.The receptive field was spatially organized into antagonistic center and flanks just like the fields of simple cells. However, both center and flanks were found within the receptive field area where a single slit evoked discharge. Center and flanks were elongated along the optimal stimulus orientation. The flanks were displaced from the center normal to optimal stimulus orientation.In the center, ON- and OFF-responses were usually about equal in strength and the maximum ON- and OFF-responses occurred in about the same position. This shows that complex cells are activated by input from both ON- and OFF-center cells in the lateral geniculate nucleus (LGN) where the receptive field centers of the LGN cells overlap closely. This explains most of the specific features of complex cells, e.g., the spatially overlapping ON- and OFF-zones, the large response field, the repetitive firing when a slit moves over the receptive field, and the marked non-linear spatial summation.Strong flank suppression occurred with both ON and OFF. The effects were usually stronger on one side of the center. Maximal suppression occurred on the same side with both ON and OFF. This is consistent with the interpretation that complex cells are inhibited by input from both LGN ON- and OFF-center cells with overlapping receptive field centers.A model presuming that complex cells have overlapping but acentric excitatory and inhibitory fields was tested by computer simulation and shown to fit the experimental data. This is the same model as presented for simple cells in the preceding paper (Heggelund 1980), except that the excitatory and inhibitory fields of simple cells have input from either ON- or OFF-center LGN cells, whereas in complex cells they have input from both types.The project was financially supported by the Norwegian Research Council for Science and Humanities