On Constructing a Reality - Understanding Understanding: Essays on Cybernetics and Cognition - page 224

FIGURE 16. FIGURE 17.

FIGURE 18.

receives two excitatory signals from the receptor above, but only one
inhibitory signal from the sensor to the left. We now understand the impor-
tant function of this net, for it computes any spatial variation in the visual
field of this “eye,” independent of the intensity of the ambient light and
its temporal variations, and independent of place and extension of the
obstruction.
Although all operations involved in this computation are elementary,
the organization of these operations allows us to appreciate a principle of
considerable depth, namely, that of the computation of abstracts, here the
notion of “edge.”
I hope that this simple example is sufficient to suggest to you the pos-
sibility of generalizing this principle in the sense that “computation” can
be seen on at least two levels, namely, (1) the operations actually performed
and (2) the organization of these operations represented here by the struc-
ture of the nerve net. In computer language (1) would again be associated
with “operations,” but (2) with the “program.” As we shall see later, in “bio-
logical computers” the programs themselves may be computed on. This
leads to the concepts of “metaprograms,”“meta-metaprograms,” and so on.
This, of course, is the consequence of the inherent recursive organization of
those systems.