  In a previous report we have evaluated analytically the mutual information
between the firing rates of N independent units and a set of
continuous+discrete stimuli, for finite N and in the limit of large noise.
Here, we extend the analysis to the case of two interconnected populations,
where input units are linked to output ones via gaussian weights and a
threshold linear transfer function. We evaluate the information carried by M
output units about continuous +discrete correlates by means of saddle point
equations under the assumption of replica symmetry. Within this limitation, we
analyze the dependence of the information on the ratio M/N, on the selectivity
of the input units and on the level of the output noise. We show analytically,
and confirm numerically, that in the limit of a linear transfer function and of
a small ratio between output and input noise, the output information approaches
asymptotically the information carried in input. Finally, we show that the
information loss in output does not depend much on the structure of the
stimulus, but mainly on the position of the threshold nonlinearity, and on the
ratio between input and output noise.
