1. An apparatus comprising: means for receiving an incoming excitation signal having a signal spectrum to which a body part would be responsive if the body part was functioning normally; a signal analyser configured to perform dimension reduction or factorisation of the excitation signal in the time domain or in the frequency domain followed by a sparse transform, the analyser producing a clean output signal for input to an inverse transformation step to create the sparsified signal; means for providing electrical pulses to neurons of a deficient signal-responsive body part based on the sparsified signal, whereby the signal analyser converts the excitation signal into a sparsified signal for electrically stimulating the neurons, thereby reducing the redundancy of the stimuli applied to the neurons by the electrical pulse means.