![]() From 1 to 2 years, the conditioned orientation reflex (COR) towards the sound source allows the use of the child's attention by rewarding him visually for correct answers.Around 6 months, the child has better motor control, and tests based on orientaion reflexes can be used: the child's reaction to noisy toys is observed, for example.The latter tests are less common in the clinic as interpretation is subjective and can require loud sounds. Muscle and eye-movements in response to acoustic stimuli are measured. Before 3 months, objective measures are used, such as otoacoustic emissions and auditory evoked potentials (AEPs).In children under the age of 5 years, tests are adapted depending on the child's attention and comprehension abilities. We won't go into masking techniques here, but masking is important to avoid diagnotic errors. Contralateral masking stops the sound from being perceived by the ear contralateral to the test ear. Frequencies above 8192 Hz are tested by high-frequency audiometry. The examiner varies the intensity and the frequency of the acoustic stimulus in order to determine the minimum intensity perceived by the subject for given frequencies from 125 to 8192 Hz. The subject is asked to indicate as soon as they perceive a continuous or pulsed sound (even if it is very quiet). In adult listeners, this test is generally easy to carry out, but can require efficient masking. The audiogram is typically presented in decibel hearing loss (dB HL - see the chapter on the decibel scale). The audiogram represents the hearing thresholds of a subject for each tested frequency compared to average values determined from a large number of young adults considered to have normal hearing. It is carried out in a sound attenuated booth, which must satisfy particular criteria. Similar to conduction testing, tonal audiometry tests air conduction (via headphones) and bone conduction (via a vibrator placed on the mastoid bone). This device plays various types of sound (pure tones, broadband noise, white noise, etc) at different frequencies and intensities to determine a subject's hearing range. In the case of conductive hearing loss, the sound is perceived by the affected ear (2): the sound cannot 'leak' via the ossicular chain, which results in a false sense of amplification compared to the healthy contralateral ear.Īuditory acuity can be measured using an audiometer. The cochlea with increased thresholds does not provide auditory sensation. The dominant cochlea (with the lowest auditory threshold) causes the sound to be perceived as localised to that side. ![]() As the stimulus is presented to the centre of the skull, it arrives simultaneously at both cochleae. In the case of sensorineural hearing loss, sound is perceived by the ear with better hearing (1). ![]() It is particularly informative in the case of unilateral hearing loss. The Weber test gives an indication of bone conduction (the probe is placed on the vertex). This stimulation avoids the middle ear and stimulates the cochlea directly. Bone conduction travels by the vibration of the bone itself when the foot of the tuning fork is placed on the vertex (the top of the skull), or the forehead. The sound wave travels along the ear canal and through the tympano-ossicular chain towards the cochlea. To study air conduction, the tuning fork is struck to cause it to resonate and it is a brought to the ear. Using a tuning fork, a hearing loss can be determined as either conductive or perceptual by comparing air and bone conduction. In practice, air and bone conduction testing is often carried out before tonal audiometry. Tonal audiometry uses pure tones to determine auditory thresholds, and supra-threshold pure tones can be used to determine the frequency and temporal selectivity of the ear. Tonal audiometry is a behavioural test used to quickly evaluate auditory acuity.
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