Hearing screenings and tests are important to assess an individual’s hearing. In many countries, hearing screening programs for newborns are offered, in some countries have installed screening programs for older children.
Different terms, different use
Hearing tests can either be objective or subjective. For objective screening methods, the test person does not have to actively respond to the sound stimuli presented. They are used for very young children.
Subjective hearing assessments require the cooperation of the test person. All Newborn Hearing Screenings (NHS) use objective tests which are simple, non-invasive, painless and without any side-effects.
Objective Hearing Tests
Otoacoustic Emissions (OAE), the most widely used objective test for newborns, indicate whether the hearing organ of the inner ear (cochlea) is working. OAEs are sounds produced by the outer hair cells in the cochlea as a response to a soft sound (usually a click tone). When sound reaches the cochlea, the outer hair cells vibrate which, in turn, produces an almost inaudible sound that echoes back to the middle ear and is captured by the test device.
How is a hearing screening with OAE performed?
A soft foam tip is placed in the infant’s ear. The test device will send soft sounds which will trigger an echo from the inner ear, provided the ear is functioning normally. This response is recorded on a computer.
For a precise answer, the infant should ideally be asleep or keep very still and quiet. OAEs only take a few minutes, have a good sensitivity and can be done by any trained hospital staff, not only by audiologists.
Otoacoustic Emissions deliver a pass/fail answer but do not give any hearing thresholds. If a baby fails the OAE screening, further objective tests will be performed.
Automated Auditory Brainstem Respone (AABR) = Brain Stem Evoked Response Audiometry (BERA)
Two terms for the same objective hearing test.
If a child fails the Otoacoustic Emissions screening, an AABR, also called BERA, will be performed. This objective test measures the hearing nerve’s and brain’s response to sound. It is more precise than OAEs, as it evaluates the hearing threshold of the test person across frequencies. AABR is a very reliable screening method, though more time-consuming than OAEs. Due to automatization, it can also be done by trained hospital staff, not only by audiologists.
How is a hearing screening with AABR (BERA) performed?
Soft earphones are put into the sleeping baby’s ears and electrodes placed on his or her head, just like during an EEG examination. Now clicks or tones are played through the earphones. The electrodes on the baby’s head measure the brain’s response. Normal ABR recordings all look the same. This, in turn, means that any deviation from the normal ABR pattern or a missing ABR response indicate a hearing problem. The AABR test also shows exactly where the hearing problem occurs – whether it is in the inner ear or the brain.
AABR / BERA tests are widely used to objectively determine the degree of hearing loss in children and in adults who are difficult to test.
Tests of the middle ear
Often, younger children suffer from middle ear infections or other conditions in the middle ear that lead to hearing loss. Objective tests of the middle ear are widely used and reliable diagnostic tools to assess middle ear function.
In case of a suspected hearing loss in the middle ear an objective test called tympanometry is performed. It tests how well the eardrum moves, thereby giving a picture of the middle ear function. During a tympanometry, a tiny probe is inserted into the ear canal. A small device attached to it will send air into the ear, causing the eardrum to move with different levels of air pressure. The result of this measurement is recorded in a graph called tympanogram. Its shape allows the ear specialist to diagnose a hearing problem in the middle ear.
Acoustic reflex measurement
A tiny muscle in the middle ear, the stapedius muscle, contracts involuntarily at loud sounds. The sounds are presented via a probe in the ear canal and a device will record the reflex. The acoustic reflex helps determine the type and degree of hearing loss and is helpful when a patient cannot be tested with subjective tests. It is performed with a probe in the ear and a loud sound being presented.
Subjective Hearing Tests
Objective hearing tests are usually performed in patients who cannot tell whether they hear a sound or not. They use body functions to assess hearing. Subjective tests rely on the cooperation of the patient. During a subjective hearing test, the audiologist will play sounds and assess the patient’s reaction in response to these sounds. The results determine the degree and type of hearing loss.
Here are some of the most widely used subjective hearing tests:
Pure-tone audiometry (PTA)
During a pure-tone audiometry the test person sits in a quiet room and listens to pure tones at different pitches that are presented via headphones. As soon as the test person hears the sound, they show a reaction (raise a hand, press a button, …). The audiologist takes notes of the softest tone that was heard at each frequency (“pitch”). This way, a graph called audiogram comes into place, showing the patient’s hearing thresholds at each frequency. These thresholds illustrate how well the outer, middle and inner ear process sound. PTA with conventional headphones measure “air conduction” thresholds.
If a hearing loss is detected, the audiologist will additionally take a bone conduction test which will specify where exactly the hearing loss is situated – if it is in the outer, middle or the inner ear. This way, the type of hearing loss can be determined – and appropriate treatment options discussed.
The bone conduction pure-tone audiometry is very similar to the air conduction one. The only difference is a transmitting device that is placed on the head behind the ear rather than using headphones. Thus, sound travels straight to the inner ear, bypassing the outer and middle ear. This allows the audiologist to assess the patient’s inner ear function.
PTA can be used from age 5 years on.
Speech audiometry is a basic tool for hearing loss assessment. During speech audiometry, the test person is seated in a quiet room using headphones and is required to repeat commonly known words. These words are played at different volumes. The audiologist will define the speech reception threshold, i.e. the lowest volume the test person requires to hear the words, and take notes of how well they were able to understand the words presented.
The result of speech audiometry helps audiologists to determine how well an individual hears and understands. Furthermore, they aid in finding out the degree and type of hearing loss. Age-appropriate tests allow use from approx. age three years on.
Behavioral (observation) audiometry:
Behavioral audiometry is used for younger children (0-3 years). The audiologist observes the child’s reaction to sound (noise, music, etc). Reactions vary and include stopping an ongoing activity, calming, turning the head, looking for the sound source. Every reaction to sound is rewarded, e.g. with an age-appropriate image popping up, with the aim of keeping the child motivated. Behavioral audiometry is a complementary assessment alongside objective hearing tests.
Conditioned play audiometry
This is a type of behavioural audiometry for older children (2-5 years). It utilizes a child’s longer attention span in a playful way using headphones for the first time. Common games include dropping a ball or a toy into a bucket. Like typical pure-tone audiometry, the child hears tones at different frequencies. The results are plotted onto an audiogram, delivering a good picture of a child’s hearing abilities.