"Layers"

[Dr Josef Skrzypek]

 A layer of "neurons" means that all units (cells) in this layer
are at the same FUNCTIONAL distance from some reference point e.g.
the input. It is rather simple and unambiguous.

There is no need to discriminate against the input units by calling them
 something else but "units". Think of them as the same type of "neurons"
which have a specialized transduction function. For example, photoreceptors
transduce photons into electrical signals while other "neurons" transduce
neurotransmitter modulated ionic fluxes into electrical signals.
Such input unit might have many modifiable weights, some from lateral
connections, others from the feedback pathways and one dedicated to the
main trasduction function. Similar argument can be used for output units
or "hidden" units (why do they hide? and from whom?).

A layer should refer to "neurons" (units) and not synapses (weights) because
it is possible to have multiple synaptic interactions between two layers
of "neurons". A layer of units, regardless of their function is rather
unambiguous.

Josef