Explore Screening/Audiological assessments in more detail :
Behavioural audiological assessments (requiring responses from the subject) should be performed by a trained professional in a sound-proofed room. Some of the techniques that may be used to assess different ages are explained below:
Behavioural Observation Audiometry (BOA)
Very young children (<6 months) will not be able to respond reliably to sounds but may show repeatable involuntary responses e.g. startling, changes in sucking pattern, eye movements. Hearing professionals trained in working with very young children are able to spot these subtle responses. However, it is difficult to determine what level of loudness is required to elicit a response from each child. BOA can be used as a guide to estimate hearing levels but does not give accurate hearing thresholds.
Visual reinforcement audiometry (VRA)
VRA can be performed on young children from approximately 6 months of age, or when they are able to sit unsupported. The child is trained to turn to a visual reward (e.g. a toy or a light) when they hear a frequency specific sound. At first, both stimuli are presented together, but once the child is responding reliably, the visual reward will only be presented once the child has turned to the sound. The test may be performed in the sound field (sound presented via a speaker) or using a bone vibrator to test both ears together or using headphones or insert phones to elicit ear-specific responses. Depending on the child’s attention, minimum response levels can be determined across a range of frequencies.
Children from the age of approx. 30 months will develop the ability to wait for a sound and respond when they hear it. During performance audiometry, frequency-specific sounds are played via a speaker, hand-held warbler or bone vibrator (i.e. to both ears at the same time). The child is trained to perform a task when they hear the sound. The task should be tailored to the ability of the child, e.g. putting a ball on a peg or man in a boat, and should offer the child enough satisfaction to want to continue to play the game. The results demonstrate the hearing thresholds from the better hearing ear. If the child responds to quieter levels when the sound is presented via the bone-vibrator than from the speaker or warbler, this suggests a conductive component to the hearing loss.
Play audiometry is very similar to performance audiometry. However, the sounds are presented via headphones or insert earphones so it tends to be performed on slightly older children who will tolerate the transducer on/in their ears. The ear-specific results are taken as hearing thresholds and can be plotted on an audiogram.
Pure tone audiometry
Frequency specific sounds from 250Hz up to 8 kHz are presented via headphones, insert earphones or a bone vibrator (500Hz – 2 kHz only). The listener is asked to press a button when they hear a sound, even if the sound is very faint. The tester follows a set procedure described by their local recommended procedure (e.g. please visit this British Society of Audiology website pdf on Pure tone air and bone conduction threshold audiometry with and without masking procedure in the UK). The results are plotted on an audiogram (see ‘Interpreting the Audiogram’) and should be explained clearly to the listener.
Speech Discrimination Testing
Speech discrimination testing aims to find out how well a listener can discriminate (hear the sounds of) words. Speech testing involves the listener listening to and then repeating lists of words or sentences. In the UK and the US ‘AB word’ lists and ‘BKB sentence’ lists are commonly used and other countries will have their own verified sets of words or sentences. The words may be presented ‘live voice’ from a speaker talking at a set level, or via a speaker.
For children, lists of familiar words e.g. toys in the McCormick Toy Test, may be used to assess their ability to discriminate speech. Instead of repeating the word, a young child may be asked to point to a toy or a picture.
Speech testing results may be presented by percentage correct, or by a decibel level required to score 50 or 71% correct. The results may be used to support audiometric results, to monitor progress or to determine how much someone can hear at a set level.
Objective audiological assessments do not require co-operation or a response to the sound by the patient, although they may require the patient to stay quiet and relaxed. Specialised equipment is used to measure a physiological response to a sound.
Tympanometry does not attempt to measure hearing levels, but instead analyses the function of the middle ear. It is performed routinely on children and adults who are having their hearing assessed.
A tympanometer is used to measure the ear canal volume, middle ear pressure and compliance of each ear drum (tympanic membrane). Usually a screen will clearly show the tympnometric shape which may be peaked (normal) or flat (abnormal). These results are used to determine if the patient has normal middle ear function, a perforation of the ear drum, Eustachian Tube Dysfunction or Otitis Media with Effusion (OME, often referred to as Glue Ear).
An abnormal tympanogram is likely to be found in conjunction with a conductive hearing loss as it demonstrates that sound is not passing normally to the inner ear.
Otoacoustic Emissions (OAEs)
OAE testing involves playing a sound in to the ear via a probe encased in a soft ear tip. The probe contains a small microphone that looks to record a tiny echo that is produced in response to the sound if the inner part of the ear – the cochlea – is working normally. In order to record the OAE, the patient and the test environment need to be very quiet – the tiny response can even be masked by heavy breathing. The test can be performed on any person who is quiet and still. As such, it is one of the tests used for newborn hearing screening. OAEs are not recordable from an ear with any more than a mild hearing loss. Additionally, they may be absent if the patient has a conductive hearing loss or abnormal tympanogram.
Evoked Response Audiometry (ERA)
The term ERA covers a wide range of tests that measure hearing levels by recording auditory evoked potentials from a chosen point along the auditory pathway. These tests include Auditory Brainstem Response (ABR), Cortical testing and Electrocochleography.
The most commonly used ERA assessment in paediatric and adult hearing assessment is the ABR. During this test, sounds (clicks, chirps or tone bursts) are presented to the ears via headphones, insert earphones or a bone vibrator. The brainstem’s response to the sound is recorded by surface electrodes that are stuck on to the patient, usually behind the ears and on the forehead.
As with OAE testing, the patient must remain very quiet and relaxed while this test is performed. It is ideal if they fall asleep and it is sometimes performed under general anaesthetic in order to get the optimal response.
The ABR response has a typical pattern and normal ranges have been determined for the size and timing of a normal response. For each individual, the responses are analysed to determine the quietest level of sound that elicits a clear response. From this level, the hearing threshold can be estimated.
An ABR response may be absent if the hearing levels of the individual are higher than the level of sound presented by the system or if the individual has Auditory Neuropathy Spectrum Disorder (ANSD).
A useful booklet for parents explaining the hearing tests is available from this National Deaf Children's Society (NDCS) website page website - please see "Understanding your child's hearing tests". Please visit KidsAudiologist website for information for young people. For adults, please visit this Hearing Link website page for more information on consultation and hearing tests.