Some ECMR properties in relation to other signals from the auditory periphery

Some basic characteristics of monkey and human acoustic emissions are reviewed and some new data presented. These characteristics are discussed in relation to the sensorineural output of the cochlea. Input--output functions and the frequency dispersal in the waveform of acoustic emissions (AE) from monkeys are described. New findings include changes in the human AE during trains of clicks and sustained suppression of the AE after short bursts of noise of moderate intensity. The similarly of click-evoked AE latencies and whole-nerve action potential (AP) latencies for low stimulus level toneburst stimuli, and the apparent discrepancy between these latencies and those of single cochlear nerve-fibre action potentials and derived impulse responses is discussed. It is argued that at low stimulus levels AE are generated either coincident with the primary cochlear impulse or very soon afterwards. It is proposed that the AE generator is peripheral to the afferent synapse of the inner hair cells because of the lack of adaptation effects in AE. However, attention is drawn to changes in the waveform of the click-evoked AE with increasing stimulus intensity and with diuretic intoxication, that qualitatively parallel known changes in single nerve-fibre firing properties. These observations are consistent with the concept that AE are a product of a sharply tuned and vulnerable cochlear filter mechanism.