Applicability of white-noise nonlinear system analysis to the peripheral auditory system

A functional series is capable of describing the input-output relationship of a general class of systems, linear or nonlinear. Wiener and his associates demonstrated methods by which these functionals could be measured from the response of the system to white noise. This paper is a critique of the application of this functional series approach to the measurement of the input-output relationship of the peripheral auditory system. The Wiener functionals are shown to be dependent on the parameters of the white noise used to measure them. The approximation of the output of a system by a truncated Wiener series is shown to have unpredictable error properties when inputs other than white Gaussian noise are used. Estimates of the Wiener functionals using the white-noise approach do not converge when the system has a point process output (e.g., spike train output).