Chapter 15: Electrical Response Audiometry

Basic Concepts of Electrical Response Audiometry

Electrical response audiometry (ERA) is a description used for an assortment of procedures in which electrical potentials are recorded while being evoked by a sound stimulus. The presence of the response or the response characteristic allows us to surmise the subjects’ hearing capability or the performance of their auditory pathways. ERAs are considered an “objective” evaluation because the subject is not required to actively participate in the assessment in many of the tests, unlike various other tests. The short-latency automatic components are favored for threshold estimation, as they are modestly affected by the brain state of the subject. The long-latency components are generally used to surmise the cognitive processing capacity of the brain and are often called event-related potentials (ERPs)¹. ERA and auditory-evoked potentials (AEP) are used interchangeably.

Types of ERA

Electrical response audiology is a common testing method performed in a clinical setting and in many areas of research because of its objectivity. This chapter will emphasize the ERAs that are most widely used in clinical applications. There is a great amount of literature available for ERA and the specific response or potentials. This is not an in-depth review of all available ERA.

Below is a list of electrical response testing available. However, it must be stated that not all are widely performed or available in clinical settings and there are those that are used primarily in a research capacity.

• Electrocochleography (ECoG or ECochG)

• Auditory brain stem response (ABR), brain stem-evoked response audiometry (BERA), brain stem auditory-evoked response audiometry (BAER).

• Cortical electric response audiometry (CER or CERA), N1-P2 response

• Auditory steady-state response (ASSR), auditory steady-state evoked potential (ASSEP)

• Middle-latency response (MLR)

• Cervical vestibular-evoked myogenic potentials (cVEMP)

• Occular vestibular-evoked myogenic potientials (oVEMP)

• Somatosensory-evoked potential (SSEP)

• Electroneurography (ENoG)

• Electromyography (EMG)

• Neural response telemetry (NRT)

• P300

Classification of AEPs By Latency

Burkard et al¹ stated that the classification of AEPs are primarily based on peak response latency that distinguishes between short-latency, middle-latency response (MLR), and long-latency (auditory late responses—ALR) AEPs.

• ABR peaks are indicated by roman numerals:

  1. Waves I, II, III, IV, and V

  2. The most reliable are waves I, III, and V

• MLR:

  1. Po, Na, Pa, Nb, and Pb

• Long-latency response:

  1. P1, N1, P2, and N2.

Generators of Auditory-Evoked Responses

There is ongoing debate over the generation sites of a number of evoked responses and it is commonly accepted that there is more than one neural origin involved in creating each response². This is currently the subject of much research. However, below you will find the presently recognized generator sites of the AEPs.

Sensory Function

• ABR:

  1. Cochlea, eighth nerve, and brain stem:

     • Wave I = distal end of the eighth nerve, ...