Second Biennial Hearing Aid Research and Development Conference

September 22-24, 1997
National Institutes of Health
Bethesda, Maryland

Field Trial Evaluation of Switched Directional/Omnidirectional ITE Hearing Instrument

This study evaluated the effect of a switched first-order gradient directional/omnidirectional microphone on speech recognition in noise and the ability of hearing-impaired persons to function in daily listening environments. Hearing instruments used were Micro-Tech Persona Choice full-shell ITE directional instruments with class D AGC-O compression limiting amplifiers. Each had a 2-position toggle switch for user-selectable microphone mode. Ten adults who had never worn hearing instruments were fitted binaurally. Audiometric thresholds ranged from 0 to 50 dB HL at 250 and 500 Hz, and from 40 to 75 dB HL at 2 and 4 kHz. The instruments were adjusted to NAL-r in omnidirectional mode via REIG measures. REIR measures from 0- to 180-degrees for the directional microphone mode were compared to directivity indexes obtained on KEMAR in an anechoic chamber.

Subjects wore the hearing instruments for 3-5 weeks, completing an APHAB questionnaire for each microphone mode. Following the home trial, the Hearing-In-Noise Test (HINT) was given under each microphone mode with uncorrelated speech-spectrum noise at 120- and 240-degrees fixed at 65 dB SPL, and the speech level varied to determine SNR for 50%-correct sentence recognition. Paired comparison testing of microphone modes was also completed for evaluation of perceived sound clarity, quality, and background noise annoyance, in quiet with speech at 65 dB SPL, and in babble noise at +8 dB SNR. The directional mode of the ITEs was found to produce a substantial reduction in gain at rear azimuths relative to omnidirectional. Results suggest benefit of the directional mode for at least some subjects.

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