Multiple auditory steady-state responses.

Steady-state responses are evoked potentials that maintain a stable frequency content over time. In the frequency domain, responses to rapidly presented stimuli show a spectrum with peaks at the rate of stimulation and its harmonics. Auditory steady-state responses can be reliably evoked by tones that have been amplitude-modulated at rates between 75 and 110 Hz. These responses show great promise for objective audiometry, because they can be readily recorded in infants and are unaffected by sleep. Responses to multiple tones presented simultaneously can be independently assessed if each tone is modulated at a different modulation frequency. This ability makes it possible to estimate thresholds at several audiometric frequencies in both ears at the same time. Because amplitude-modulated tones are not significantly distorted by free-field speakers or microphones, they can also be used to evaluate the performance of hearing aids. Responses to amplitude and frequency modulation may also become helpful in assessing suprathreshold auditory processes, such as those necessary for speech perception.