We can hardly imagine that 
nature would have gone to the 
trouble of grouping cells so 
beautifully in these two 
independently coexisting sets 
of columns if it were not of 
some advantage to the animal. 
Until we work out the exact 
wiring responsible for the 
transformations that occur in 
the cortex, we are not likely to 
understand the groupings 
completely. At this point we can 
only make logical guesses. If we 
suppose the circuits proposed in 
Chapter 4 are at all close to 
reality, then what is required 
to build complex cells from 
simple ones, or to accomplish 
end-stopping or directional 
selectivity, is in each case a 
convergence of many cells onto 
a single cell, with all the 
interconnected cells having 
the same receptive-field 
orientation and roughly the 
same positions. So far, we have 
no compelling reasons to expect 
that a cell with some particular 
receptive-field orientation 
should receive inputs from 
cells with different 
orientations. (I am exaggerating 
a bit: suggestions have been 
made that cells of different 
orientation affiliations might 
be joined by inhibitory 
connections: the evidence for 
such connections is indirect 
and as yet, to my mind, not very 
strong, but it is not easily 
dismissed.) If this is so, why not 
group together the cells that are 
to be interconnected? The 
alternative is hardly attractive: 
imagine the problem of having 
to wire together the appropriate 
cells if they were scattered 
through the cortex without 
regard to common properties. By 
far the densest 
interconnections should be 
between cells having common 
orientations; if cells were 
distributed at random, without 
regard to orientation, the 
tangle of axons necessary to 
interconnect the appropriate 
cells would be massive. As it is, 
they are, in fact, grouped 
together. The same argument 
applies to ocular-dominance 
domains.

    If the idea is to pack cells 
with like properties together, 
why have sequences of small 
orientation steps? And why the 
cycles? Why go through all 
possible orientations and then 
come back to the first, and 
cycle around again, instead of 
packing together all cells with 
30-degree orientation, all cells 
with 42-degree orientation, and 
indeed all left-eye cells and all 
right-eye cells? Given that we 
know how the cortex is 
constructed, we can suggest 
many answers. Here is one 
suggestion: perhaps cells of 
unlike orientation do indeed 
inhibit one another. We do not 
want a cell to respond to 
orientations other than its 
own, and we can easily imagine 
that inhibitory connections 
result in a sharpening of 
orientation tuning. The 
existing system is then just 
what is wanted: cells are 
physically closest to cells of 
like orientation but are not too 
far away from cells of almost 
the same orientation; the 
result is that the inhibitory 
connections do not have to be 
very long.