Objective audiometry using amplitude-modulation following responses elicited by compound sinusoidal amplitude-modulated tones

Abstract

The amplitude-modulation following response (AMFR) test is an ideal tool for objective audiometry because of its high frequency specificity. However, this examination is time-consuming when hearing thresholds at several frequencies must be tested, even if the thresholds are automatically detected using computer techniques like phase spectral analysis. To solve this problem, a multiple stimulation technique using a compound sinusoidal amplitude-modulated tone (compound SAM tone) was used to detect 40 Hz AMFR thresholds at several frequencies. A technique for analyzing the thresholds determined by the AMFR elicited by compound SAM tones was established using the component synchrony measure method, a type of phase spectral analysis. The usefulness of this technique was then evaluated. The difference between the thresholds for the AMFR to compound SAM tones and the AMFR to simple SAM tones was clinically negligible. No difference in the threshold of the AMFR was observed when the carrier frequency and modulation frequency combinations of the 4 SAM tones, components of the compound SAM tone, were altered. The threshold pattern of the 40 Hz AMFR detected using the multiple stimulation technique closely resembled the corresponding audiogram patterns for all types of adult hearing impairments. These findings suggest that AMFR using the multiple stimulation technique has almost the same level of frequency specificity as the AMFR elicited by simple SAM tones. The time required to test the AMFR thresholds for four frequencies was, on average, about 24 minutes per ear, which was markedly shorter than the time required using simple SAM tones. AMFR detected using the multiple stimulation technique thus appears to have a high frequency specificity and to be potentially useful for objective audiometry.