Audiologic testing comprises behavioral measures of hearing sensitivity and speech-recognition performance; objective physiologic measures of middle ear, cochlear, and retrocochlear status; and objective electrophysiologic measures of peripheral auditory function and auditory nervous system function. The fundamental behavioral audiologic measures, the results of which are usually represented on an audiogram, include pure-tone air-conduction and bone-conduction hearing thresholds, speech-recognition threshold (SRT), and suprathreshold speech-recognition scores. Objective, physiologic measures of auditory function include (a) otoacoustic emissions testing for examination of peripheral auditory status and (b) the acoustic admittance test battery, including tympanometry for assessment of middle-ear status, and acoustic-reflex threshold and decay (adaptation) testing for assessment of middle-ear, cochlear, and retrocochlear status. Objective auditory electrophysiologic measures for estimation of hearing sensitivity and identification of site of lesion along the auditory pathway include auditory evoked potentials testing, most commonly electrocochleography (ECochG), auditory brainstem response (ABR) testing; auditory middle latency response (AMLR) testing; auditory steady state response (ASSR) testing; and cortical auditory evoked potentials (CAEPs). Audiologic testing also includes vestibular assessment based on measures such as videonystagmography, but vestibular testing, which is beyond the scope of this chapter, is covered elsewhere in this text.
Audiologic testing should be performed in the context of test battery, in accordance with the cross-check principle. Diagnosis of hearing loss should not be made solely on the basis of behavioral pure-tone audiometry. A test battery should be employed that includes the use of objective audiologic measures, as well as behavioral measures, in order to verify or cross-check the findings of the behavioral tests. The cross-check principle has come to be considered as a fundamental feature of basic audiologic assessment in adult and pediatric populations. Advantages of objective physiologic and electrophysiologic measures are as follows:
Because such tests are not based on behavioral responses from patients, patients need not be instructed on how to respond.
Results are not confounded by motivational, cognitive, language, or motor status.
Valid results can be obtained within a reasonable time frame.
Often, results can be obtained in sedated or sleepy patients.
Their sensitivity to the presence of auditory abnormalities tends to be high.
Results are elicited that can shed light on auditory function at various sites along the auditory pathway, and, when taken in conjunction with the results of a battery of measures, on the site of the lesion.
The purpose of audiologic assessment is multifold: (a) to quantify the hearing sensitivity in a manner that minimizes the influence of possible confounding factors such as functional or nonorganic hearing loss or cognitive status; (b) to classify the type of hearing loss, when hearing loss is present, as conductive, sensorineural, or mixed; (c) to detect middle-ear pathology; (d) to differentiate cochlear from retrocochlear pathology; (e) to detect lesions along the auditory pathway from the auditory nerve to the auditory cortex; (f) to describe the influence of the hearing impairment on auditory function; (g) to guide in audiologic and/or medical management ...