Nonlinear phenomena in click- and tone-burst-evoked otoacoustic emissions from human ears

Otoacoustic emissions have been recorded from normally hearing subjects in response to clicks and 1-kHz tone bursts. Input-output relationships for response magnitudes and wave delays are presented. For the response magnitudes, two main effects are seen: (i) nonlinearities are maximal at moderate to high intensity levels (saturation), while deviations from linearity are minimal at the lowest levels (around the psychoacoustic threshold); (ii) the nonlinear behaviour is different at different time intervals (after stimulation): deviations from linearity are maximal for the latest parts of the response. Level- and time-dependent phenomena are also observed in the delay of identifiable response waves.