1. An information processing system comprising a processor and memory coupled to the processor arranged to form a feed-forward neural net including a plurality of interconnected neurons, each neuron having a plurality of inputs to receive a respective plurality of neuron input signals and calculating means for producing an output signal, that is a function of at least one of said neuron input signals and of at least one of following quantities: a rate of change of at least one of said neuron input signals; and a rate of change of the particular neuron output signal.