Development of orientation-selective receptive fields in primary visual cortex of higher mammals can occur through activity-dependent competition between ON-center and OFF-center inputs. This competition yields orientation and spatial-frequency-selective 'simple cells' if the dark activity of ON (or OFF)-center inputs is best correlated with that of other ON (or OFF)-center inputs at small retinotopic separations and with that of OFF (ON)-center inputs at larger separations. Features of cat and monkey cortical organization emerge, including continuous and periodic arrangement of preferred orientation across the cortex. A new feature, systematic variation of receptive field spatial phase, is predicted. Experimental tests of this hypothesis are proposed.