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  • Advanced Audiology encompasses a range of investigations that are objective in nature. This means that any data recorded is obtained from physiological responses to sound rather than requiring the cooperation of the subject.
    These types of investigations can be used on all age groups for varying reasons, from neonatal screening, infant, pre-school, learning difficulties and non-organic loss amongst other things. These types of audiological investigations are objective, in that no behavioural response is required, so the procedure is not affected by a patient’s attention, motivation or cognitive state.

Otoacoustic Emissions

    Otoacoustic emissions (OAE) are sounds produced by the inner ear when the normally functioning cochlea is stimulated by sound (or they can occur spontaneously (SOAE)).
    When sound stimulates the cochlea, the outer hair cells (located in the cochlear) vibrate. The outer hair cells serve as an amplifier contributing to the normal passage of sound waves to the electrophysiological signal that enters the hearing systems within the brain. The vibration produces a nearly inaudible sound that also echoes back into the middle ear, this normally in the 0-15dB range.

    A probe placed in the ear canal can produce sound waves then detect and record these vibrations. People with normal hearing produce emissions but those with hearing loss greater than 25–30 decibels (dB) do not usually produce these very soft sounds. The presence of OAE is evidence of normal cochlear function while an absence of OAE can be consistent with abnormal cochlear function or the presence of an outer/middle ear problem but can also be a normal variant.

    OAE are technically simple to perform, non-invasive and usually only requires a few minutes to complete a screening test. A soft disposable tip is inserted into the ear canal, a moderate intensity of sound is played through a miniature speaker/s and a microphone records any response.

    There are three types of OAE:

    Transient evoked OAE (TOAE or TEOAE)
    Distortion product OAE (DPOAE)
    Stimulus Frequency OAE (SFOAE)

    Transient OAE is evoked by very brief sounds usually made of tone bursts or multiple frequency clicks, they are usually presented at an intensity of 80dB SPL. The cochlear echoes that these elicit are usually in the 500-4,000Hz range.Image of OAE

    Distortion Product OAE is evoked with sets of two pure tone frequencies (f2 & f1) that are closely spaced and simultaneously presented, again at moderate intensities (such as 55 and 65dB). The cochlear echoes from DPOAE can be across a frequency range of 500 to 8,000Hz.

    Stimulus Frequency OAE applies a pure tone stimulus and records any echo. These are measured by detecting the vectorial difference between the waveform of the stimulus and the waveform that is recorded.

    The status of the middle ear can interfere with the recording of OAE, if there is a middle ear effusion (fluid) or Eustachian tube dysfunction resulting in a negative middle ear pressure then OAE may not be recorded so Tympanometry should be performed before any OAE investigation is attempted.
    It is important to remember that OAE is not a test of 'hearing' but a test of cochlear function. OAE may be absent in normally hearing subjects with middle ear disorders and conversely OAE may be present in inner hair cell disorders or retro-cochlear pathology (auditory nerve and beyond) such as auditory neuropathy. This would be diagnosed by comparing the OAE result (normal) with the Auditory Brainstem Response (usually abnormal).

Auditory Evoked Responses


Another objective investigation concerning audiology is one that assesses the central auditory system. It is known by a few different names but are essentially the same test:

Auditory Brainstem Response (ABR)
Brainstem Auditory Evoked Potential (BAEP)
Brainstem Auditory Evoked Response (BAER)


Two other investigations that are similar to ABR but have some differences are discussed later:

Evoked Response Audiometry (ERA)
Auditory Steady State Responses (ASSR)




ABRThe ABR is an electrophysiological response that is evoked by auditory stimulus produced by headphones, aural inserts or bone conductors. The stimuli can be either frequency-specific tones, click stimuli or tone pips. Surface electrodes attached to the scalp record the ABR after signal averaging has been performed on the background EEG.


The signal averaged ABR generates seven waveforms, however the ABR is only concerned with the first five waves of the auditory pathway. The first two waves represent actual action potentials; Wave I from the Auditory Nerve (Cranial Nerve VIII) and Wave II is from the Cochlear Nucleus. The remaining three waves of interest are post-synaptic activity from major brainstem auditory centres; Wave III is the Superior Olivary Complex, Wave IV from Lateral Lemniscus and Wave V from Inferior Colliculus (For interest Wave VI is the Medial Geniculate Body and Wave VII is the Auditory Radiation (Cortex)).

ABR's are usually conducted using the traditional click stimulus that evokes responses in the frequency range from 100-8000 Hz and is insufficient for estimating hearing sensitivity. However, click stimulus is useful in the examination of neural integrity by stimulating at a set intensity (loudness) above a person's threshold and then recording and measuring the Waveform's amplitude and latency, the inter-peak differences and the contra-lateral (opposite side) measurements and therefore remains a crucial tool in diagnostic audiology.




ERA is similar to the ABR but threshold information is obtainable by using specific stimuli and reducing the intensity and recording the ABR until the Waveforms are no longer seen.

Threshold information can be recorded at 500, 1000, 2000, and 4000Hz and there is a good agreement (+/- 10 - 15Hz) between frequency specific ABR and behavioural audiograms in infants and young children.




Again, ASSR is similar in principal to ABR, but is another investigation to assess objective hearing thresholds. It is able to potentially evaluate four frequencies (500, 1000, 2000 & 4000Hz) in both ears simultaneously by using an amplitude/frequency modulated stimulus presented rapidly to stimulate the auditory system in both ears simultaneously. ASSR results are dependent on the statistical analysis of the probability of a response, usually at a 95% confidence level.


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