Before revision:  A system of interest, when exposed to a stimulus S, adopts a deterministic response R of which a  noisy measurement M is made. Given a large number of measurements and corresponding stimuli , we wish to identify the correct " response function " relating R to S . However the "noise function" relating M to R is unknown a priori.
After revision:  A system of interest, when exposed to a stimulus S, adopts a deterministic response R of which a noisy measurement M . From a large number of measurements and corresponding stimuli , we wish to identify the correct " response function " relating R to S . However the "noise function" relating M to R is unknown a priori.