cause new language learners acquire knowledge of digits relatively early, and audiologists can easily score the responses (Ramkissoon, Proctor, Lansing, and Bilger, 2002). This digit-SRT test can be administered to listeners from any language, and results appear to be valid, based on high correlations between digit-SRTs and the PTA measured for nonnative English speakers (Ramkissoon et al., 2002). A comparable test for assessing suprathreshold speech recognition in listeners with various linguistic backgrounds has not been developed.

Acoustic Immittance Measures

Acoustic immittance measures are a series of electrophysiologic tests that assess the integrity of the middle ear system and the structures comprising the acoustic reflex pathway. Acoustic immittance measures are administered routinely as part of the standard audiometric evaluation (Martin et al., 1998), using commercially available acoustic immittance systems calibrated according to ANSI standards (American National Standards Institute, 2002a). Interpretation of the acoustic immittance test results, in conjunction with the audiogram, aids in determining the site of the lesion associated with a hearing loss. The three basic subtests of the acoustic immittance battery are tympanometry, acoustic reflex thresholds, and acoustic reflex adaptation.

Tympanometry

Tympanometry is an assessment of the ease of acoustic energy transfer (acoustic admittance) through the middle ear system, as a function of air pressure. In the normal middle ear system, energy transfer of the middle ear, as measured at the plane of the tympanic membrane, is maximal at atmospheric pressure (0 dekaPascals, or daPa) and is minimal at air pressures that produce a stiffening of the middle ear system (air pressures remote from 0 daPa, such as +200 daPa or –200 daPa).

Tympanometry is performed by presenting a probe tone to the ear canal and measuring the acoustic admittance (in mmhos, an expression of the ease of energy flow that has a reciprocal relationship with impedance as measured in acoustic ohms) of this tone, as the air pressure presented to the sealed ear canal varies from positive to negative (usually in the range +200 daPa to -400 daPa). The standard probe tone frequency is 226 Hz, although many additional probe frequencies can be presented. The resulting tympanogram is a pressure-admittance function that depicts the admittance characteristics of the tympanic membrane and middle ear system of the test ear. Three parameters of the tympanogram can be quantified: peak admittance (Peak Y), tympanometric width (TW), and equiva-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement