Hearing Tests: Sleep Study For Toddlers

Hearing tests are important for toddlers as mild hearing loss can cause problems with speech, language, learning, and social skills. There are two main types of hearing screening methods for toddlers: evoked otoacoustic emissions (EOAE) and auditory brainstem response (ABR). EOAE uses a tiny, flexible plug that is put into the toddler's ear to send and record sound. On the other hand, ABR uses electrodes attached to the scalp to measure the brain's activity in response to clicking sounds played through tiny earphones in the toddler's ears. These tests are painless, quick, and can be done while the toddler is sleeping.

Auditory Brainstem Response (ABR) Test

The Auditory Brainstem Response (ABR) test is a hearing test that can be performed on toddlers and babies while they are asleep. It is used to detect hearing loss by checking how the brain's auditory nerve and brain stem respond to sound. The test is often carried out on infants and very young children who are unable to respond to behavioural hearing tests due to their age.

During the test, the audiologist will attach small, painless electrodes to the scalp, forehead and earlobes or mastoid bone. These electrodes are sensors that measure brain activity. Soft earphones will then be placed inside the ears, and clicking sounds and tones will be played. The electrodes will record the brain's response to these sounds, and the results will be displayed on a computer. The test usually takes between 30 minutes and 2 hours.

The ABR test is painless and safe, and the child will not feel anything during the procedure. It is important to ensure that the child's head and ears are clean and free of any lotions or oils, so that the electrodes can stick properly. If the child is under 6 months old, the test can be performed while the child sleeps naturally, without the use of sedatives. For older children, sedatives may be administered to help them sleep through the test.

Otoacoustic Emissions (OAE) Test

The otoacoustic emissions (OAE) test is a hearing test that can be performed on toddlers and babies while they are sleeping. It is a painless, quick test that takes just a few minutes and does not require any active participation from the child. The OAE test checks for damage in the hair cells in the cochlea, which is the organ of hearing. During the test, the audiologist puts soft earphones with small, flexible foam tips gently into each ear canal. The earphones make high and low-pitch sounds, and the machine records the response made by the cochlea's outer hair cells.

• Soft foam or rubber-tipped probes are placed into the child's ears.
• The child will hear soft sounds, such as clicks or tones, through the probes.
• A computer will record the quiet echoes from the ear. These echoes are called otoacoustic emissions (OAEs).
• The results of the test will indicate whether OAEs are present or absent.
• Present OAEs suggest normal to near-normal hearing.
• Absent OAEs may indicate a problem, such as hearing loss, wax in the ears, fluid or infection in the middle ear, or a malformed inner ear. Further testing may be required to determine the exact cause.

The OAE test is particularly useful for infants and young children who may not be able to respond to behavioural hearing tests due to their age. It is also used as a screening method for newborns to identify any hearing abnormalities.

Visual Reinforcement Audiometry (VRA) Test

Visual Reinforcement Audiometry (VRA) is a hearing test designed for infants and toddlers aged 6 months to 2 or 3 years old. It is used to assess a child's hearing threshold levels when standard hearing tests that use headphones and feedback buttons are too complex for very young children.

VRA uses a machine called an audiometer to test a child's hearing threshold levels. Standard pure tone audiometers use headphones and a feedback button, so they are not practical for young kids. VRA replaces the headphones with earphones (usually with foam tips) or sound field speakers. Visual reinforcers such as video animations or lighted toys are placed 90 degrees to each side of the patient to "train" the child to look toward the direction of the sound.

During the test, the child sits upright on a parent or caregiver's lap in a soundproof room. The audiologist will trigger visual stimuli in conjunction with sounds to collect the data. The audiologist plays a tone or some other sound to one of the child's ears. At first, the audiologist lights up the boxes in conjunction with the sound, which "trains" the child to respond by shifting their eyes or turning their head toward the sound source. Once a child understands what to do, the audiologist can "reward" the child by briefly delaying the visual stimuli.

The audiologist then reduces the intensity of both the sound and the stimuli until the child's minimum hearing threshold is reached. Tests continue using different frequencies until the audiologist has a complete set of data about the child's hearing in both ears.

VRA involves the child looking towards a visual target such as a toy or an image on a screen in response to a sound stimulus. If a toy is used, it should be screened from the view of the child by smoked Perspex with the option to illuminate it when required to become visible.

The reinforcement element is an important aspect of VRA, as the child sees the visual target each time they look towards it. The child associates the presentation of the sound stimulus with a reward, in this case, the visual target, which they receive upon performing a head turn towards that target. This concept of conditioning is the first principle of VRA testing.

There are four main considerations for VRA testing:

• Maximizing the time available: Due to the short attention span of infants, a 20 dB down, 10 dB up testing method is common. It is important to weigh the benefits of measuring in smaller steps against time limitations and the need for testing at further frequencies or using other transducers.
• Recording responses: Use a clear, time-locked head turn as the response. Record all responses or lack of responses using ticks and crosses on a VRA tick sheet to allow for clear reviewing of the test strategy and patient responses.
• Reinforce simultaneously: Display visual reinforcers as soon as the child has produced a head turn. It is advisable to maintain the sound stimulus presentation for the same duration as you display the reinforcer to help maintain conditioning.
• Avoid presenting the stimulus and/or reinforcer for excessively long durations: This can lead to the child losing interest in the game. Long durations of reinforcement (4 seconds) have been shown to lead to faster habituation than shorter durations of 0.5 to 1.5 seconds.

Play Audiometry

The test is adapted slightly for toddlers, turning it into a game. The child is asked to interact with a toy in some way (e.g. touch or move it) every time they hear a sound. This test relies on the child's cooperation, which may not always be possible.

The process of CPA has two parts:

• Conditioning: The audiologist tells the child they are going to play a game. The audiologist presses a tone and says something like, "Wow, you get a block!" The child is then given the toy. The audiologist then tells the child to place the block in a basket every time they hear the beep. Once the child understands the game, the screening can begin.
• Screening: The audiologist places headphones (or earphones) on the child. The test begins, and the audiologist reduces the intensity of the sound until the child's minimum hearing threshold is achieved. Tests continue using different frequencies until the audiologist has a complete set of data about the child's hearing in both ears.

Pure Tone Audiometry

Pure-tone audiometry (PTA) is a hearing test used to identify an individual's hearing threshold levels. PTA is a subjective, behavioural measurement of a hearing threshold, as it relies on patient responses to pure tone stimuli. It is only used on adults and older children who are able to cooperate with the test procedure. PTA can be used to determine the degree, type and configuration of a hearing loss, providing a basis for diagnosis and management.

PTA is performed using an electrical machine that makes sounds at different volumes and pitches, which are transmitted through headphones. The patient is asked to respond in some way when they hear the tone, such as raising their hand, pushing a button, or saying that they heard the sound. PTA is considered the standard form of audiometry and can generally be performed on patients older than five, although some patients may be able to participate earlier.

PTA is a valuable tool for older children, particularly those with otitis media. It is also useful for detecting hearing loss caused by environmental factors such as ototoxic medication and noise exposure, which tend to be more detrimental to high-frequency sensitivity than mid or low frequencies. PTA can also be used to detect the auditory sensitivity changes that occur with ageing.

In the UK, The British Society of Audiology (BSA) is responsible for publishing the recommended procedure for PTA, which is based on international standards. In the US, the American Speech-Language-Hearing Association (ASHA) published Guidelines for Manual Pure-Tone Threshold Audiometry in 2005.

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