The effect of frequency-dependent microphone directionality on horizontal localization performance in hearing-aid users.

Frequency-dependent microphone directionality alters the spectral shape of sound as a function of arrival azimuth. The influence of this on horizontal-plane localization performance was investigated. Using a 360 degrees loudspeaker array and five stimuli with different spectral characteristics, localization performance was measured on 21 hearing-impaired listeners when wearing no hearing aids and aided with no directionality, partial (from 1 and 2 kHz) directionality, and full directionality. The test schemes were also evaluated in everyday life. Without hearing aids, localization accuracy was significantly poorer than normative data. Due to inaudibility of high-frequency energy, front/back reversals were prominent. Front/back reversals remained prominent when aided with omnidirectional microphones. For stimuli with low-frequency emphasis, directionality had no further effect on localization. For stimuli with sufficient mid- and high-frequency information, full directionality had a small positive effect on front/back localization but a negative effect on left/right localization. Partial directionality further improved front/back localization and had no significant effect on left/right localization. The field test revealed no significant effects. The alternative spectral cues provided by frequency-dependent directionality improve front/back localization in hearing-aid users.

Directional effects on infants and young children in real life: implications for amplification.

PURPOSE: This study examined the head orientation of young children in naturalistic settings and the acoustics of their everyday environments for quantifying the potential effects of directionality. METHOD: Twenty-seven children (11 with normal hearing, 16 with impaired hearing) between 11 and 78 months of age were video recorded in naturalistic settings for analyses of head orientation. Reports on daily activities were obtained from caregivers. The effect of directionality in different environments was quantified by measuring the Speech Transmission Index (STI; H. J. M. Steeneken & T. Houtgast, 1980). RESULTS: Averaged across 4 scenarios, children looked in the direction of a talker for 40% of the time when speech was present. Head orientation was not affected by age or hearing status. The STI measurements revealed a directional advantage of 3 dB when a child looked at a talker but a deficit of 2.8 dB when the talker was sideways or behind the child. The overall directional effect in real life was between -0.4 and 0.2 dB. CONCLUSIONS: The findings suggest that directional microphones in personal hearing devices for young children are not detrimental and have much potential for benefits in real life. The benefits may be enhanced by fitting directionality early and by counseling caregivers on ways to maximize benefits in everyday situations.