Why are several different hearing tests used together rather than one?

Each test probes a different part of the auditory system, and combining them lets findings be cross-checked; under the cross-check principle a result from one measure is confirmed by an independent measure before it is accepted.

How can hearing be tested in a newborn who cannot respond?

Objective physiological measures, chiefly otoacoustic emissions and the auditory brainstem response, assess the cochlea and auditory nerve without requiring a behavioural response, which is what makes newborn hearing screening possible.

Audiological Assessment and Testing

Audiological assessment is the systematic measurement of hearing and auditory function used to detect, describe, and localize hearing loss across the auditory pathway. It combines behavioural tests, in which the listener responds to sounds, with objective physiological measures that do not require a voluntary response, producing a profile of the type, degree, and configuration of hearing loss.

Definition

Audiological assessment and testing is the set of behavioural and physiological procedures used to quantify hearing sensitivity, characterize the type and site of auditory dysfunction, and monitor auditory function over time.

Scope

This area orients the reader to the principal families of audiological tests: pure-tone audiometry and threshold estimation, speech audiometry, acoustic immittance and tympanometry, otoacoustic emissions, and auditory evoked potentials. It frames how these methods complement one another in a test battery and how each probes a different part of the system from the outer ear to the brainstem and cortex. It is a reference overview of methods, not a protocol for clinical decision-making.

Sub-topics

Core questions

Is hearing within normal limits, and if not, what is the degree and configuration of loss?
Is the loss conductive, sensorineural, or mixed, and where along the auditory pathway does it arise?
How do behavioural and objective measures converge to cross-check a diagnosis?
How can hearing be assessed in infants and others who cannot give reliable behavioural responses?

Key concepts

Auditory threshold
Air conduction and bone conduction
Conductive, sensorineural, and mixed hearing loss
Test battery and cross-check principle
Behavioural versus objective (physiological) measures
Site-of-lesion testing
Masking

Mechanisms

The battery is organized by what each test interrogates. Pure-tone audiometry measures the softest tones a listener can detect by air and bone conduction, separating outer- and middle-ear (conductive) involvement from cochlear and neural (sensorineural) involvement. Speech audiometry measures the ability to detect and recognize speech, adding a functional dimension. Acoustic immittance and tympanometry assess middle-ear mechanics by measuring how sound energy is admitted or reflected as ear-canal pressure is varied (Jerger 1970). Otoacoustic emissions, sounds generated by the outer hair cells of the cochlea, give an objective window onto cochlear function (Kemp 1978; Probst 1991 noted in topic entries). Auditory evoked potentials record electrical activity from the auditory nerve and brainstem in response to sound, allowing objective threshold estimation and site-of-lesion testing (Jewett & Williston 1971). The cross-check principle holds that no single result should be accepted without corroboration from an independent measure.

Clinical relevance

Audiological assessment underpins the identification and description of hearing disorders and supports decisions made elsewhere about rehabilitation, amplification, and referral. Objective measures such as otoacoustic emissions and auditory brainstem responses make it possible to evaluate hearing in newborns and other listeners who cannot respond behaviourally, which is why they form the basis of newborn hearing screening programmes (JCIH 2007). This entry describes how hearing is measured; it is not a basis for individual diagnosis or treatment.

Epidemiology

Hearing loss is among the most common chronic sensory conditions worldwide, and audiological testing is the means by which it is detected and quantified at every life stage, from universal newborn hearing screening to the assessment of age-related and noise-related loss in adults. The reach of these methods into population screening is reflected in early hearing detection and intervention programmes (JCIH 2007).

History

Clinical audiology took shape in the mid-twentieth century around the calibrated pure-tone audiometer and standardized speech tests. Impedance (immittance) audiometry entered routine clinical use in the 1960s and 1970s (Jerger 1970). The recording of the auditory brainstem response (Jewett & Williston 1971) and the discovery of evoked otoacoustic emissions (Kemp 1978) added objective physiological measures, which in turn enabled universal newborn hearing screening from the late twentieth century onward.

Key figures

David Kemp
James Jerger
Don Jewett
Hallowell Davis

Seminal works

kemp-1978
jerger-1970
jewett-williston-1971

Frequently asked questions

Why are several different hearing tests used together rather than one?: Each test probes a different part of the auditory system, and combining them lets findings be cross-checked; under the cross-check principle a result from one measure is confirmed by an independent measure before it is accepted.
How can hearing be tested in a newborn who cannot respond?: Objective physiological measures, chiefly otoacoustic emissions and the auditory brainstem response, assess the cochlea and auditory nerve without requiring a behavioural response, which is what makes newborn hearing screening possible.