Abstract: A computer system is proposed including an adaptive signal processing model of a kind in which a multiplicative section, such as a VLSI integrated circuit, processes data input to the model, using hidden neurons and randomly-set variables, and an adaptive output layer processes the outputs of the multiplicative section using variable parameters. Controllable switching circuitry is proposed to control which data inputs are fed to which hidden neurons, to reduce the number of hidden neurons required and increase the effective number of data inputs. An algorithm is proposed to selectively disable unnecessary hidden neurons. Normalisation, and a winner-take all stage, may be provided at the hidden layer output.