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(
)
(
)
+
(
)
+-
(
)
p
=-
1
p
p
1
-
p
p p
1
-
p
1
p
12
,
p p
12
3
12
3
which yields:
pp ppp
=
2
123
.
Uniform stimulation, i.e.,
p
1
=
p
2
=
p
3
=
p
o
, produces a “leakage” frequency
ppp
uni
=-,
3
o
o
which disappears for strong stimulation (see fig. 27a bold line). With either
element (1) or (3) OFF, i.e., with an “edge” in the stimulus field, we have
pp
edg
=
,
o
the difference between these frequencies D
p
is, of course, an indication of
detection sensitivity. Inspection of fig. 27a shows that this element is a poor
edge detector in the dark, but does very well in bright light.
It might be worthwhile to note that a reversed action function (1; -2; 1)
with lateral facilitation has two operational modes, one of them with con-
siderable sensitivity for low intensities (fig. 27b). A slight nystagmus with
an amplitude of one element switches between these two modes, and thus
represents an edge detector superior to the one with lateral inhibition.
FIGURE 27. Transfer function of a McCulloch formal neuron net when operated
asynchronously. (a) lateral inhibiting network. (b) lateral facilitating network.
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