When masking is not used is that one may incorrectly conclude that there is better hearing in a "bad" ear, than is really the case, because without masking, some of the sound is actually appreciated by the good ear. This situation occurs when there is a conductive type hearing loss in both ears, which is moderate to severe. The dilemma is that an adequate intensity to mask the non-test ear crosses over to the testing ear and invalidates the thresholds.
Enough masking is too much masking. There are several "work arounds" to this. When one is masking air conduction, if one can i. Other methods include using bone-ABR testing, ABR is unaffected by the central effect of masking but the sound still stimulates both ears and also one is limited by one's bone stimulator. Another method is the SAL sensorineural acuity level technique. Even though the interaural attenuation is very individual and varies with frequency, it can on average be estimated to be a minimum of 40 dB for supra-aural headphones and 50 dB for inserts.
In bone conduction, the interaural attenuation is a minimum of 0 dB, which means that the stimulus may cross over, and this is what one should assume. In patients with normal hearing on one ear, but a moderate to severe hearing loss on the other, there is a potential risk of the good ear hearing the tone when trying to test the damaged ear. That is, the sound vibration may travel through the head and be heard by the opposite good ear when the vibrations of the signal are large enough.
This could be the case in Figure 1, where the right ear better ear should be masked while reassessing the left ear poorer ear. Masking is also needed to differentiate between sensorineural, conductive, and mixed hearing losses. The origin will be revealed by obtaining the bone conduction threshold for the left ear while occupying the right ear with masking. The procedure is outline below in several steps, some of which are specific to Interacoustics equipment.
Select which ear to mask and choose the appropriate masking transducer headphones or insert phones. If we refer to Figure 1, channel 2 should be set to the right ear non-test ear using the preferred masking stimulus usually NB.
The masking frequency will automatically change along with the tone frequency when masking is turned on. While trying to establish the true threshold of the left ear, the right ear is now distracted with noise. You separate them by covering one then testing the other to determine if it is normal or impaired.
In audiology noise is used as the masker. Instead, noise is introduced to one ear while the other ear is tested with a tone or speech signal. To indicate that the hearing thresholds were obtained using masking, masked threshold symbols are used on the audiogram. Most speech pathologists never have to worry about performing masking, but they do have to be able to interpret audiograms and understand why the masked symbols were used.
Current research and teaching interests include aural rehabilitation management of deaf and hard of hearing children, auditory processing performance of young adults, voice science, and literacy acquisition, particularly, by racial and ethnic minority children.
Jones' current research and teaching interests include aural rehabilitation management of deaf and hard of hearing children, auditory processing performance of young adults, voice science, and literacy acquisition, particularly, by racial and ethnic minority children.
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Free course Hearing. Figure 38 The procedure for a masking experiment. Each arrow indicates a frequency where the threshold is measured. Figure 39 Results of a masking experiment. The red line indicates the amount that the threshold is raised in the presence of a masking noise centred at Hz.
So for a Hz tone, the threshold is raised by about 60 dB above absolute threshold. Figure 40 Vibration patterns on the basilar membrane caused by , and Hz tones.
Figure 41 The procedure for measuring a psychophysical tuning curve.
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