Effects of in-the-ear microphone directionality on sound direction identification

Abstract

As advanced signal processing algorithms have been proposed to enhance hearing protective device (HPD) performance, it is important to determine how directional microphones might affect the localization ability of users and whether they might cause safety hazards. The effect of in-the-ear microphone directivity was assessed by measuring sound source identification of speech in the horizontal plane. Recordings of speech in quiet and in noise were made with Knowles Electronic Manikin for Acoustic Research wearing bilateral in-the-ear hearing aids with microphones having adjustable directivity (omnidirectional, cardioid, hypercardioid, supercardioid). Signals were generated from 16 locations in a circular array. Sound direction identification performance of eight normal hearing listeners and eight hearing-impaired listeners revealed that directional microphones did not degrade localization performance and actually reduced the front-back and lateral localization errors made when listening through omnidirectional microphones. The summed rms speech level for the signals entering the two ears appear to serve as a cue for making front-back discriminations when using directional microphones in the experimental setting. The results of this study show that the use of matched directional microphones when worn bilaterally do not have a negative effect on the ability to localize speech in the horizontal plane and may thus be useful in HPD design.

Evaluation of a Localization Training Program for Hearing Impaired Listeners

“…The ability to localize can also provide a more natural listening experience (Byrne & Noble 1998). Unfortunately, hearing loss results in a reduction of localization ability (Byrne & Noble 1998), especially for sounds that originate from the back (Köbler & Rosenhall 2002;Chung et al 2008;Keidser et al 2009;Best et al 2010). Hearing aid features that restore the cues for localization are slowly emerging in recent years.…”

“…Likewise, one should also expect a directional microphone to improve front/back localization. Chung et al (2008) examined localization performance of eight normal-hearing and eight hearing-impaired listeners. For both groups, the localization performance with a directional microphone was better than with an omnidirectional microphone.…”

Effect of Occlusion, Directionality and Age on Horizontal Localization

“…Previous research has failed to control for age and has compared the performance of older hearing impaired listeners to young normal hearing adult listeners (Noble et al, 1994;Van den Bogaert et al, 2006;Chung et al, 2008). Prior work examining neurophysiological responses have suggested that overall responsiveness of the central auditory system and age are correlated (Polich, 2004;Harkrider et al, 2005); consequently, it was reasonable to hypothesize that age may affect localization acuity as part of the aging process in adults.…”

“…Impaired hearing degrades an individual's ability to localize sounds (Hausler, Colburn, & Marr, 1983) and hearing aids often erode performance further. The effects of bilateral hearing aid use have been examined in two main capacities; degree of occlusion and hearing aid technology Noble et al, 1998;Drennan et al, 2005;Keidser et al, 2006;Van den Bogaert et al, 2006;Chung et al, 2008). Extensive research has been done on sound source localization within these areas.…”

“…Further, adaptive directionality significantly degraded horizontal localization performance. Chung et al (2008) evaluated the effects of in-the-ear (ITE) microphone directionality on localization. Two groups of adult participants were included; experienced hearing aid wearers and normal hearing listeners.…”