 
Summary: Discussion
Discreteness and Relevance: A Reply to Roman
Poznanski
CHRIS ELIASMITH
First, a clarification. Poznanski says that I conclude that: "encoding and decoding
spike trains must be discrete at some level." There are two possible interpretations
to his characterization: (1) the process of encoding and decoding must be discrete;
and (2) our characterization of the process must be discrete. I hope it is evident
that I don't claim that the process in neural systems is discrete, but rather that
a complete characterization of the process can be discrete; these of course are
significantly different claims. Only the second is endorsed by my paper and it is
deducible from the claim Poznanski labels `ii)', i.e., that the: "continuous nature of
neurons is not relevant to the information they process". So, I will take this to be
the claim that Poznanski finds problematic.
Now, as surprising as my contention may initially seem, in some ways it
shouldn't be surprising at all. We know for a fact that such claims are true of
some physical systems. Consider a typical digital computer. The processes in such
machines are indeed continuous (to a similar extent that processes in neural systems
are). That is, transistors that make up integrated circuits are, in fact, continuous
physical devices. Their transfer function traces out a (nonlinear, continuous) S
