Steady-state auditory evoked potentials to amplitude-modulated tones in hearing-impaired subjects

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Abstract
Evoked potentials to sinusoidal amplitude-modulated tones have been described in normally hearing adults. Our aim was to test the use of this response to estimate pure tone threshold in adults with a sensorineural hearing loss. Patients with symmetrical pure tone audiograms with near-normal responses in the lower frequencies but with a hearing loss of greater than 65 dB HL at 8 kHz were tested. The stimulus carrier frequency was 1, 2, 4 and 8 kHz and this was modulated at a frequency of 40 kHz to a depth of 85%. The resulting EEG response is a sine wave of the same frequency as the modulation frequency. Threshold is determined when the sine wave disappears. Twenty-two patients were tested. None showed a response to the high frequencies. At the lower frequencies 18 patients showed clear responses and the threshold was 16 to 27 dB above the psychoacoustical threshold. The remaining four cases showed responses at the lower frequencies but only at higher threshold levels. These evoked potentials may provide a rapid method to assess hearing in those subjects unable to provide a reliable volitional response.