A composite model of he auditory periphery has been developed to process speech sounds in a manner consistent with physiological responses recorded from the mammalian auditory nerve. The model consists of discrete stages simulating (1) the middle ear, (2) the motion of the basilar membrane, (3) the receptor potential of inner hair cells and (4) the synaptic properties of the inner-hair-cell/auditory-nerve-fiber junction. The spatio-temporal discharge pattern of the auditory nerve is displayed as the output of the model, responding in a nonlinear manner, most accurately simulates the coherent synchrony patterns of auditory-nerve fibers distributed over a broad range of characteristic frequencies evoked by speech sounds. It is further shown that such a nonlinear model is capable of preserving the basic spatio-temporal representation of speech under low signal-to-noise conditions. A cross-channel correlation technique can be used to extract formant information from the distribution of temporal discharge activity, providing a spectral representation of the signal which is relatively invariant over a wide range of signal-to-noise ratios.