The effects of early visual experience on the cat's visual cortex and their possible explanation by Hebb synapses.

1. Kittens were dark-reared until 4-6 weeks old, and then for another 4-7 weeks with various combinations of cylindrical lenses, monocular occlusion, and normal vision. 2. Single unit recordings from 816 neurones of the visual cortex (area 17) were obtained after the end of exposure. Clear-cut effects on the distributions of the neurones' ocular dominance and orientation preference were found yielding close correlations with the rearing conditions. 3. It was confirmed that most cortical neurones prefer vertical stimulus orientations when experience is restricted to vertical contours in both eyes. It was further confirmed that, if the experienced orientations are different in the two eyes, each eye dominates over those neurones whose orientation preference corresponds to the orientation this eye has experienced. 4. When one eye is covered while the other sees only contours of one orientation, the ocular dominance distribution of cortical neurones shows a bias towards the open eye. Neurones dominated by this eye prefer orientations corresponding to the experienced range. Neurones preferring other orientations are shared between both eyes. 5. When vision is unimpaired in one eye and restricted to vertical contours in the other, binocularity is common among neurones preferring vertical orientations. Neurones with orientation preferences off the vertical are mainly monocular and dominated by the eye with unrestricted vision. 6. When normal monocular vision of one eye precedes restricted monocular vision of the other eye, only a few binocular units are encountered. Reversal of the initial effects of monocular experience is found only in neurones preferring the orientation that has been experienced by the newly opened eye. The other neurones remain dominated by the originally open eye. Thus, complementary distributions of orientation preferences are found for the two eyes. 7. A good correlation was found between the amount of orientational experience as determined by the number of orientations exposed and the number of normally tuned neurones. Conversely, the number of neurones responding to all orientations decreases with increasing amount of experience.