The effect of horizontal‐plane environment on the development of binocular receptive fields of cells in cat visual cortex

1. The different perception of vertical in the two eyes (Helmholtz, 1864) was interpreted as an adaptation of cortical binocular receptive fields to the bias distribution of orientation disparity in the visual environment resulting from the relative frequency of contours in horizontal planes below eye level (ground, table) compared to other orientations in space. 2. Kittens were reared in environments where visible contours were confined to a horizontal plane which was the floor for two kittens and the ceiling for two other kittens. The floor tended to produce negative, the ceiling positive, orientation disparities. In either case, the disparities were maximal about the vertical retinal meridians and zero at the horizontal meridian. The preferred stimulus orientations of binocular neurones in area 17 of the visual cortex were determined at 3‐4 months age in these four kittens and in seven normal cats for control. Automatic stimulus variation, quantitative analysis, and eye drift correction were used. 3. In the ‘floor cats’ neurones with near‐vertical orientations showed a mean interocular angle between the preferred orientations of ‐8.7° relative to neurones with near‐horizontal orientations; in the ‘ceiling cats’, the angle was +2.8°; in the normal cats it was ‐0.4°. 4. Since these angles are independent of the alignment of the eyes, the difference between floor cats and ceiling cats reflects different functional connexions at cortical level. This indicates that the orientations of the developing receptive fields can be modified by visual experience. 5. These observations in kittens suggest that the perceptual difference between the eyes in man is also caused by early visual experience.