The ocular-dominance column 
borders in upper (2, 3) and lower 
(5, 6) layers are blurred, 
compared to the sharp 
boundaries in layer 4. The 
arrows illustrate electrode 
tracks made in layer 4 (upper 
left) and layer 2 or 3 (upper 
right). The lower diagrams plot 
ocular dominance of cells 
recorded along the tracks. In 
layer 4, we find abrupt 
alternation between group 1 
(contralateral eye only) and 
group 7 (ipsilateral eye only). In 
other layers, we find binocular 
cells, and the eye dominance 
alternates by going through the 
intermediate degrees of eye 
preference. (1, 4, and 7 refer to 
ocular dominance.)

    Viewed from the side, the 
subdivisions in layer 4 appeared 
as patches. But we wanted to 
know how the pattern would 
appear if we stood above the 
cortex and looked down.