Training in ABR

ABR Masking Case

10 mins
02 January 2017


How much masking should we use in this ABR case example?

We tested a 7-month old baby with a bilateral conductive hearing loss. We wanted to check whether we need to mask or not. The not-masked hearing thresholds by BC were 15 dB nHL and the AC thresholds bilaterally were 40 dB nHL. We want to know what the BC threshold is on the other side?

Answer: This is potentially very complicated because, just like in conventional audiometry, a bilateral conductive loss raises the prospect of cross masking (and therefore masking dilemma) because of the need to increase the masking level in the non-test ear to overcome the attenuation from the conductive component.

The amount of masking noise depends on what you estimate the conductive loss to be in the non-test ear (ref: the BC threshold). Depending on the estimated size of the air-bone gap, the maximum masking level possible (for the Eclipse) might be reached.

Although the patient is 7 months old, it could be worth checking back to any earlier records for ABR data in the neonatal period to help answer the question. At earlier ages the BC values are more ear specific as the plates of the cranium are not fused. This could mean the BC thresholds give ear specific information even without applying masking.

Related course: Beyond the basics: Threshold ABR


Michael Maslin
After working for several years as an audiologist in the UK, Michael completed his Ph.D. in 2010 at The University of Manchester. The topic was plasticity of the human binaural auditory system. He then completed a 3-year post-doctoral research program that built directly on the underpinning work carried out during his Ph.D. In 2015, Michael joined the Interacoustics Academy, offering training and education in audiological and vestibular diagnostics worldwide. Michael now works for the University of Canterbury in Christchurch, New Zealand, exploring his research interests which include electrophysiological measurement of the central auditory system, and the development of clinical protocols and clinical techniques applied in areas such as paediatric audiology and vestibular assessment and management.

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