Detection of hearing impairment with the acoustic stapedius reflex.

The acoustic stapedius reflex (ASR) is the sound-evoked contraction of the stapedius muscle. The ASR is mediated by a neural network, receiving its afferent input from the VIIIth cranial (auditory) nerve and sending its efferent output to the VIIth cranial (facial) nerve. Several centers in the brain stem comprise the central portion of the reflex pathway. The stapedius muscle in each ear responds to ipsilateral, contralateral, and binaural stimulation. The normal ASR threshold is 90 to 95 dB SPL for tones and 70 to 75 dB SPL for wideband noise. In ears with sensorineural hearing loss, ASR thresholds are elevated more for wideband noise than for tones. These bandwidth-related changes form the basis for detection of hearing loss from ASR data. A number of methods have been proposed which differ in the nature of the outcome. Some try to quantitatively estimate hearing loss, whereas others categorize outcomes as pass or fail. In general, methods that attempt quantitative estimation of hearing loss do so at the expense of higher error rates. With adequate recording techniques, the ASR has been shown to effectively detect hearing losses exceeding 30 dB in adult subjects. Although ASR recording in newborns requires a higher probe frequency than the commonly used 226 Hz, ASR thresholds in newborns appear to be similar to those in adults. Limited information exists on the use of the ASR for detection of hearing loss in the infant population. With adequate attention to methodological requirements of testing infants, the ASR may offer a cost-effective method for the early detection of hearing loss.