We sutured closed both eyes, 
first in a newborn cat and later 
in a newborn monkey. If the 
cortical unresponsiveness in 
the path from one eye arose 
from disuse, sewing up both 
eyes should give double the 
defect: we should find virtually 
no cells that responded to the 
left or to the right eye. To our 
great surprise, the result was 
anything but unresponsive 
cells: we found a cortex in 
which fully half the cells 
responded normally, one 
quarter responded abnormally, 
and one quarter did not respond 
at all. We had to conclude that 
you cannot predict the fate of a 
cortical cell when an eye is 
closed unless you are told 
whether the other eye has been 
closed too. Close one eye, and 
the cell is almost certain to lose 
its connections from that eye; 
close both, and the chances are 
good that the control will be 
preserved. Evidently we were 
dealing not with disuse, but 
with some kind of eye 
competition. It was as if a cell 
began by having two sets of 
synaptic inputs, one from each 
eye, and with one pathway not 
used, the other took over, 
preempting the territory of the 
first pathway, as shown in the 
drawing to the left.

We suppose a cortical cell 
receives input from two 
sources, one from each eye, and 
that covering one eye has the 
effect of weakening the 
connections from that eye and 
strengthening the connections 
from the other one.

    Such reasoning, we thought, 
could hardly apply to the 
geniculate shrinkage because 
geniculate cells are monocular, 
with no obvious opportunities 
for competition. For the time 
being we could not explain the 
cell shrinkage in the layers 
corresponding to the closed eye. 
With binocular closure, the 
shrinkage of geniculate cells 
seemed less conspicuous, but it 
was hard to be sure because we 
had no normal layers to use as a 
standard of comparison. Our 
understanding of this whole 
problem did not move ahead 
until we began to use some of 
the new methods of 
experimental anatomy.