Overview
The multiple auditory steady-state evoked response (MASTER) technique provides a rapid and objective assessment of hearing. The technique is based on the statistical evaluation of the electrophysiological responses evoked by multiple auditory tones presented simultaneously. These auditory steady-state responses can be recorded from the human scalp intermixed with the other activity in the electroencephalogram (EEG). A combination of averaging and frequency-analysis can distinguish the responses from the background EEG. MASTER typically presents 8 continuous tones (4 to each ear) and each tone is sinusoidally modulated at unique frequency. The detection of the interwoven responses becomes possible after the electrophysiological data are transformed into the frequency domain.MASTER evaluates the responsiveness of the auditory system to several tonal frequencies in the same time it would take to record one response if each stimulus was presented separately.
Since MASTER measures electrophysiological responses to sounds, it allows us to objectively asses how well a participant hears. This is especially useful in patients who are unable or unwilling to give reliable behavioral responses.
Overview Continued... The Research MASTER website is an online audiology resource for introducing the MASTER technique, providing extensive information and publications about the technique, and attempts to provide a forum for answering both clinical and methodological questions.
Auditory Brainstem Responses (ABRs) may offer some advantages over OAEs when evaluating hearing loss.
Central vs Peripheral Loss:A hearing loss or other type of auditory processing disorder can be a peripheral auditory processing disorder or a central auditory processing disorder. Auditory steady state responses can help evaluate both peripheral and central processing disorders rather than only detecting peripheral auditory disorders as may occurs when relying upon OAE's in a one-stage test. Disorders such as auditory neuropathy may be missed when only relying upon OAE tests.
Level of Hearing Loss:
While OAEs can rapidly detect hearing loss and provide a Pass/Fail result, the level of loss can not be determined. In order to evaluate hearing loss so that the level of loss can be determined and, if merited, hearing aids may be prescribed, the level of the loss must be evaluated. During treatment, ASSRs can also enable the amplification of the hearing aid to be set correctly, by adjusting the amplification of the hearing aid until the threshold of a subject is surpassed and hearing occurs.
Differences between ABR tests: tone-burst vs steady-state tests:
There are several differences between tone burst and steady-state tests although both tests are considered ABR tests then the rates of presentation are fast enough (tone-bursts can also be presented relatively slowly in order to generate cortical evoked responses). While tone-burst tests have a much more solid clinical base currently, the ASSR tests have been introduced clinically and an increasing number of publications will enable these to be discussed intelligently in the next several years. ASSRs are currently being used internationally, often with positive experiences on the part of audiologists. For a detailed discussion of the pros and cons associated with the two types of tests see discussion on the HAPLAB website.
ASSRs offer several advantages over traditional tone-burst ABR tests.
- Several ASSRs can be presented simultaneously leading to a more rapid testing duration.
- ASSRs can be easily analyzed in the frequency domain in order to provide an objective statistical assessment of the evoked response.
- When evaluating severe hearing loss the steady-state response can be helpful because it can contain more energy than is possible to achieve with rapid transient stimuli such as tone bursts or clicks. Accordingly, using high intensity stimuli may enable the detection of residual hearing which would not be obtained using transient ABR tests.
A major use for Auditory steady-state response (ASSR) technology is in evaluating hearing in infants who have failed a newborn hearing screening test indicating some degree of newborn hearing loss. Often universal newborn hearing screening tests are done early on since cognitive development such as language development will be affected more greatly when treatment is delayed. The assessment of hearing impairment should be try to evaluate frequency specific loss since the evaluation for hearing impaired people must detect the actual frequency-specific loss for that individual so that appropriate amplification can be achieved.
When attempting to compensate for newborn hearing loss, a hearing aid may be used. The ASSR techniques can be used for hearing aid evaluations in which frequency specific loss is evaluated, and then during the adjustment of actual amplification settings by confirming that the ASSRs are present when the auditory aid is used.
The American Academy of Audiology has recently presented special issues on the use of ASSR in the clinical environment.
There are many resources for finding out more information about how ASSRs are being used in audiology online.
Try searching using the terms "multiple auditory steady-state response" in your favorite search engine:
http://www.yahoo.com
http://www.google.com
http://metacrawler.com
or check out PUBMED
