Distribution of VIII nerve excitation by pure tones, derived by electrical stimulation and acoustic masking.

VIII nerve compound action potentials evoked by electrical stimulation are decomposed in series of pure-tone derived potentials using masking. These potentials are in turn decomposed in a series of contributions from various frequency bands by adding high-pass masking noises. The amplitudes of the derived signals are thought to be proportional to the number of fibres activated by the masking acoustical stimulations. Thus the density of nerve fibres stimulated along the basilar membrane by pure tones as a function of frequency and intensity can be estimated.

Investigation of cochlear mechanisms using combined acoustical and electrical stimulations.

Electrically-evoked VIIIth nerve CAP responses evoked by electrical stimulation and derived by masking with sounds are recorded in the guinea pig, using different masking paradigms (pure tones and high-pass filtered white noise). CAP frequency threshold curves correlate with threshold curves determined by other means, in normal as well as in pathological guinea pigs. Amplitudes of the responses as a function of pure tones frequency and intensity are also measured. Such measurements provide an estimate of the number of fibers activated by the pure tones. These responses can be further analysed using masking with high-pass filtered white noise.