We will study the development of neurons in the visual cortex of the cat that respond preferentially to elongated stimuli presented at a particular position and angular orientation upon the retina. Specifically, we propose to try to identify those response properties which reliably discriminate between different classes of cortical cells. We propose further to identify those attributes of cortical cells which depend upon early visual stimulation for normal development. One of the proposed experiments involves a novel approach to determining the attributes which best define homogeneous sub-classes of cortical cells. A second experiment provides a direct test of our previous suggestion that cortical cells receiving X-cell (or W-cell) afferents from the LGNd require sensory stimulation to develop binocularity, but not to develop orientation selectivity, while cortical cells receiving Y-cell afferents depend upon sensory stimulation for development of orientation selectivity, but not for development of binocularity. We hope these investigations will allow us to compare and contrast the extrinsic and the intrinsic factors controlling postnatal development of the visual system.