Vol.101 No.3 contentsPRACTICA OTO-RHINO-LARYNGOLOGICA
Vol. 101 No. 3 March 2008
Auditory Steady-State Response Audiometry
Masaru Aoyagi
(Yamagata University School of Medicine)
This study describes the history, stimulus tones, detection techniques, source generators and clinical applications of auditory steady-state responses (ASSR). The most important benefit of ASSR in objective audiometry is that it can provide an accurate assessment of hearing at different audiometric frequencies in a frequency specific manner, if sinusoidally amplitude-modulated tones are used as tonal stimuli. Power spectrum analysis and phase coherence using fast Fourier transform are useful for the automatic detection of threshold because of the sinusoidal response waveform configuration. Because the detectability of ASSR changes under different arousal states, 40-Hz ASSR is suitable for waking adults and 80-Hz ASSR for sleeping children in the assessment of hearing. Regarding the sources of those responses, 40-Hz ASSR is considered the steady-state version of the middle latency response and 80-Hz ASSR is considered the steady-state version of auditory brainstem response (ABR). Bone conduction stimuli are also useful in the assessment of conductive hearing loss, though the responses are not reliable at the intensity level of 60 dB or higher. The difficulty in predicting a hearing level of 500 Hz or less using the 80-Hz ASSR threshold can be explained by auditory filter. Its advantage is that the thresholds at 4 different frequencies in both ears can be predicted more rapidly than ABR using the multiple simultaneous stimulation technique. In addition, the ASSR to clicks may provide a rapid screening technique. Finally, it may be helpful in assessing suprathreshold hearing to use ASSRs to sounds that sweep their intensity (sweep technique) or actual speech sounds. In this respect, ASSRs may contribute to the objective fitting of hearing aids in young children.
Key words :auditory steady-state response, objective audiometry, sinusoidally amplitude-modulated tone, Fourier analysis, power spectrum,
phase spectrum