The conditions required for the maintenance of binocularity in the kitten's visual cortex.

1. In young kittens, cortical neurones, which are usually binocularly driven, have their binocularity reduced if one eye is covered, or if the eyes are made strabismic or alternately occluded. Some of the factors causing these changes were analysed. 2. If the contrast of one retinal image is abolished with no difference in mean illumination, the input from that eye is virtually lost. 3. If one eye merely has its mean retinal illumination attenuated, that eye does not specifically lose its influence in the cortex, although there is a reduction in the proportion of binocular units. This change might partly be due to a difference in the timing of signals from the two eyes but is more likely to be caused by a difference in the strength of the discharges. 4. There is little change in binocularity if one image is dimmed but contrast is absent from both. 5. If contours of very different orientation fall simultaneously on corresponding retinal regions, binocularity breaks down, as in the case of strabismus or when different patterns are presented to the two eyes. But as long as the patterns on corresponding retinal points have similar orientation, even if the visual axes are misaligned, binocularity can be maintained. 6. If the eyes are not stimulated simultaneously, binocularity is reduced, even if the contours falling on the two retinae (at different times) are identical. 7. Roughly simultaneous stimulation, with roughly congruent patterns on the two receptive fields, are needed for the upkeep of binocular connexions on to cortical cells.