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Pure tone audiometry (PTA) is the key hearing test used to identify hearing threshold levels of an individual. It helps us in determining the degree, type and configuration of a hearing loss. Patient is asked to respond for the pure tone stimuli presented at different frequencies & hence PTA is a subjective, behavioural measurement of hearing threshold. Therefore, PTA is used on adults and children old enough to cooperate with the test procedure. PTA is performed in sound treated rooms with calibrated audiometers by a professional Audiologist. Both Air conduction & bone conduction thresholds are found in this test.
Immitance audiometry is a test in which ones middle ear is analysed. It is a very quick, simple, reliable, and relatively objective method of determining middle-ear function hence finding out presence of middle ear fluid presence, ear drum perforation etc. Acoustic-immitance measurements obtain sophisticated data that give us valuable information about the middle ear mechanism as a whole.
Speech Audiometry coupled with PTA testing provides a more credible result to determining the patients hearing and communication status as it helps to ascertain the patients ability to understand speech.
Using Speech Audiometry, we determine the threshold of speech which is the lowest level at which speech is audible or intelligible. The lowest level at which the speech signal can be heard 50 percent of the time is the speech /detection threshold (SDT) or Speech Awareness Threshold (SAT).
Another undermining factor is the SRT or the speech recognition threshold which is the lowest level at which a speech signal is intelligible enough to be recognized 50 percent of the time. The SRT is usually obtained by asking the patient to repeat the spondee words (Bi syllabic words with equal emphasis on both the syllables).
Otoacoustic emission test helps us to assess the functioning of the hair cells in cochlea. OAE tests are simple, quick, non-invasive test for hearing defects in newborn babies and in children who are too young to cooperate in conventional hearing tests. It is considered as the test for the universal new born hearing screening programme. Periodic early childhood hearing screenings program are also done utilizing OAE technology.
The brainstem evoked response audiometry (BERA) is an objective neurophysiological method for the evaluation of the hearing threshold and diagnosing retrocochlear lesions.
In a BERA test, brain stem potentials (as wave forms) are elicited in response to audiological click stimuli. These waves are recorded by electrodes placed over the scalp.
BERA test is an effective tool for finding hearing thresholds of difficult to test population like new borns, children, bed ridden patients, mentally challenged, patients with behavioural problems etc.