Abstract
The ultimate goal of objective audiometry is to draw an audiogram in a frequency specific manner with no response from the subject. Auditory evoked brainstem response (ABR) is now most commonly used for objective audiometry. However, the frequency specificity of ABR elicited with tone pips is not enough to predict accurate hearing on a frequency-specific basis across the audiometric range. Amplitude-modulation following response (AMFR), which is an auditory steady-state response elicited with sinusoidally amplitude-modulated tone, is expected to be an ideal tool for objective audiometry, because of the frequency specificity of the stimulus tone.
When detected by phase coherence, the threshold pattern of 40-Hz AMFR, which is elicited with tone amplitude modulated at 40 Hz, resembles very closely the corresponding audiogram patterns in all types of hearing impairment in adults while awake. However, 40-Hz AMFR is not sufficiently reliable for determining the hearing threshold in young children during sleep.
On the other hand, 80-Hz AMFR is clearly detected in young children during sleep with the use of phase coherence. The threshold pattern of 80-Hz AMFR also resembles closely the corresponding audiogram pattern. An 80-Hz AMFR thus appears to be potentially useful for objective audiometry in young children during sleep.
In this paper, our present knowledge about objective audiometry and AMFR is reviewed, and techniques for detecting AMFR and sources of AMFR are discussed.
