Head-related transfer function for the measurements of otoacoustic emissions evoked by localized sound sources

Abstract

Abstract Not one but two ears enable us to identify the location of a sound source by comparing the amplitudes and phases of acoustic signals. In this study, we explore the response of the inner ears to localized sounds by measuring otoacoustic emissions (OAEs) which refers to sounds produced by the inner ear in response to external sounds, thus governed by the activities of the acoustic receptors. OAEs were recorded simultaneously from both ears by fitting a small microphone-speaker probe into each ear canal. The binaural sounds used to evoke OAEs were designed to correspond to a localized sound source by using Head-related transfer functions (HRTFs) measured from a head-and-torso simulator. OAEs were elicited by bursts of pure tones originating from two virtual sound sources, one in front of the participants, and the other to their left ears. Our results demonstrated that, for tone bursts at 0.5 kHz, 1.0 kHz, and 2.0 kHz, the intensity and time differences of bilateral OAEs were enhanced by 3.57 dB – 6.70 dB when the virtual sound moved from 0 to 90 degrees. This was consistent with the amplitude and time differences of the stimuli. For tone bursts at 4.0 kHz, however, the average OAE amplitude difference was 20.11 dB, exceeding that of the stimuli at 7.78 dB. Our results demonstrate that bilateral OAEs directly reflect the amplitude and phase differences of the incoming signals and that the developed technique could be used for the investigations of OAEs during sound localization.