Derived evoked potentials for continuous tones using a hybrid electrical-acoustical stimulation

Averaged VIIIth nerve and brainstem potentials are recorded in normal guinea pigs in response to electrical stimulation of the ear presented once without and once with a simultaneous masking continuous pure tone. The waveform difference yields a well synchronized 'derived signal' which is the response to the electrical stimulation of only the group of fibers masked by the pure tone. Study of very low frequency activation is a new possibility brought by this method which is efficient whatever the sound frequency. Pure tone thresholds obtained are similar to previous measurements. Response amplitudes are likely a measure of the number of fibers stimulated by the sounds.