1. A system for selecting a signal processing program to be executed by a signal processor in a hearing aid and comprising: a single layer of neurons each having one or more neighbors and being arranged in a memory device, and each neuron including a neuron vector referring to a specific acoustic situation and a neuron label referring to signal processing program associated with said specific acoustic situation, and a sensor that detects an external acoustic situation and defines a sensor vector associated with said external acoustic situation and includes a detector that detects a speech to noise ratio and provides a parameter for said sensor vector; and a processor that calculates a vector difference between said sensor vector and each of said neuron vectors, identifies that neuron providing the smallest vector difference, and selects a signal processing program referred to by a neuron label of that neuron.