Extended high-frequency audiometry in research and clinical practice.

Audiometric testing in research and in clinical settings rarely considers frequencies above 8 kHz. However, the sensitivity of young healthy ears extends to 20 kHz, and there is increasing evidence that testing in the extended high-frequency (EHF) region, above 8 kHz, might provide valuable additional information. Basal (EHF) cochlear regions are especially sensitive to the effects of aging, disease, ototoxic drugs, and possibly noise exposure. Hence, EHF loss may be an early warning of damage, useful for diagnosis and for monitoring hearing health. In certain environments, speech perception may rely on EHF information, and there is evidence for an association between EHF loss and speech perception difficulties, although this may not be causal: EHF loss may instead be a marker for sub-clinical damage at lower frequencies. If there is a causal relation, then amplification in the EHF range may be beneficial if the technical difficulties can be overcome. EHF audiometry in the clinic presents with no particular difficulty, the biggest obstacle being lack of specialist equipment. Currently, EHF audiometry has limited but increasing clinical application. With the development of international guidelines and standards, it is likely that EHF testing will become widespread in future.