Sound Localization and Lateralization by Bilateral Bone Conduction Devices, Middle Ear Implants, and Cartilage Conduction Hearing Aids

Abstract

Sound localization in daily life is one of the important functions of binaural hearing. Bilateral bone conduction devices (BCDs), middle ear implants, and cartilage conduction hearing aids have been often applied for patients with conductive hearing loss (CHL) or mixed hearing loss, for example, resulting from bilateral microtia and aural atresia. In this review, factors affecting the accuracy of sound localization with bilateral BCDs, middle ear implants, and cartilage conduction hearing aids were classified into four categories: (1) types of device, (2) experimental conditions, (3) participants, and (4) pathways from the stimulus sound to both cochleae. Recent studies within the past 10 years on sound localization and lateralization by BCDs, middle ear implants, and cartilage conduction hearing aids were discussed. Most studies showed benefits for sound localization or lateralization with bilateral devices. However, the judgment accuracy was generally lower than that for normal hearing, and the localization errors tended to be larger than for normal hearing. Moreover, it should be noted that the degree of accuracy in sound localization by bilateral BCDs varied considerably among patients. Further research on sound localization is necessary to analyze the complicated mechanism of bone conduction, including suprathreshold air conduction with bilateral devices.

Keywords: binaural hearing; bone conduction device; cartilage conduction hearing aid; hearing loss; lateralization; localization; middle ear implant.

Figure 1

Screening process and the number of resulting hits regarding the literature about the accuracy of sound localization and lateralization using a multi-loudspeaker system (2012 to August 2021). “N=” and “n=” represent the hit number for “localization” and “lateralization”, respectively.

Figure 2

Factors affecting the accuracy of sound localization or lateralization of bone-conducted sound for a participant with (simulated) bilateral conductive hearing loss. Abbreviations: AC, air conduction; BC, bone conduction; CHL, conductive hearing loss; CL, left cochlea; CR, right cochlea; ITD, interaural time difference; ILD, interaural level difference; TA, transcranial attenuation; TD, transcranial delay.