Extended high frequency hearing and speech perception implications in adults and children.

Extended high frequencies (EHF), above 8 kHz, represent a region of the human hearing spectrum that is generally ignored by clinicians and researchers alike. This article is a compilation of contributions that, together, make the case for an essential role of EHF in both normal hearing and auditory dysfunction. We start with the fundamentals of biological and acoustic determinism - humans have EHF hearing for a purpose, for example, the detection of prey, predators, and mates. EHF hearing may also provide a boost to speech perception in challenging conditions and its loss, conversely, might help explain difficulty with the same task. However, it could be that EHF are a marker for damage in the conventional frequency region that is more related to speech perception difficulties. Measurement of EHF hearing in concert with otoacoustic emissions could provide an early warning of age-related hearing loss. In early life, when EHF hearing sensitivity is optimal, we can use it for enhanced phonetic identification during language learning, but we are also susceptible to diseases that can prematurely damage it. EHF audiometry techniques and standardization are reviewed, providing evidence that they are reliable to measure and provide important information for early detection, monitoring and possible prevention of hearing loss in populations at-risk. To better understand the full contribution of EHF to human hearing, clinicians and researchers can contribute by including its measurement, along with measures of speech in noise and self-report of hearing difficulties and tinnitus in clinical evaluations and studies.

Acoustic method for calibration of audiometric bone vibrators.

The standard method for the calibration of audiometric bone vibrators requires the use of an artificial mastoid, a device that converts vibratory energy to an electrical analog. The mechanical input impedance of the device is designed to represent the average mechanical impedance of the human head. For calibration purposes, it is not necessary that the coupling device represent the impedance of the head. It is only necessary that it provides a repeatable measurement of the output of the vibrator that can be related to the normal threshold of hearing at each test frequency. In addition to the mechanical output that serves as the stimulus for the hearing test, bone vibrators produce an acoustic signal that is proportional to the mechanical force delivered to the head. By determining the transfer function relating the acoustic sound pressure to the mechanical force, the acoustic signal can serve as a proxy for the vibratory stimulus. This article describes the design and validation of an acoustic coupler for the calibration of audiometric bone vibrators.