Computational Capacity of an Odorant Discriminator: the Linear Separability of Curves

We introduce and study an artificial neural network, inspired by the probabilistic Receptor Affinity Distribution model of olfaction. Our system consists on N sensory neurons whose outputs converge on a single processing linear threshold element. The system's aim is to model discrimination of a single target odorant from a large number p of background odorants, within a range of odorant concentrations. We show that this is possible provided p does not exceed a critical value p_c, and calculate the critical capacity \alpha_c = p_c/N. The critical capacity depends on the range of concentrations in which the discrimination is to be accomplished. If the olfactory bulb may be thought of as a collection of such processing elements, each responsible for the discrimination of a single odorant, our study provides a quantitative analysis of the potential computational properties of the olfactory bulb. The mathematical formulation of the problem we consider is one of determining the capacity for linear separability of continuous curves, embedded in a large dimensional space. This is accomplished here by a numerical study, using a method that signals whether the discrimination task is realizable or not, together with a finite size scaling analysis.