Whence Sparseness?

It has been shown that the receptive fields of simple cells in VI can be explained byassuming optimal encoding, provided that an extra constraint of sparseness is added. This finding suggests that there is a reason, independent ofoptimal representation, for sparseness. However this work used an ad hoc model for the noise. Here I show that, if a biologically more plausible noise model, describing neurons as Poisson processes, is used sparseness does not have to be added as a constraint. Thus I conclude thatsparseness is not a feature that evolution has striven for, but is simply the result of the evolutionary pressure towards an optimal representation. 1 Introduction Recently there has been an resurgence of interest in using optimal coding strategies to'explain' the response properties of neuron in the primary sensory areas [1].