Computation in Neural Nets - Understanding Understanding: Essays on Cybernetics and Cognition - page 85

FIGURE 31. Response distribution elicited by a uniform stimulus confined to a
square. Contour detection is the consequence of a distributed action function
obtained by superposition of a facilitatory and inhibitory Gaussian distribution.
FIGURE 32. Geometrical relationship between layers of neurons with perpendicular
orientation of their axes.
We consider pyramidal neurons and represent them by spheres. We let
the North pole (+) coincide with basal axonal departure and the South pole
(-) with the upper branchings of apical dendrites. The perikaryon is central.
This spherical dipole assumes physiological significance if we associate with
the neuron's structural difference when seen from north or from south dif-
ferent probabilities for the establishment of facilitatory or inhibitory
synapses. For simplicity we assume that for an afferent fiber the probabil-
ity of making facilitatory or inhibitory connection is directly proportional
to the projected areas of northern southern hemisphere respectively, seen
by this fiber when approaching the neuron. Hence, a fiber approaching
along the equatorial plane has a 50-50 chance to either inhibit or facilitate.