International Hearing Aid Research Conference (IHCON) location:Lake Tahoe, CA, USA date:Aug 25 29/08/2004
By using two ears normal hearing people are able to localize sounds correctly in the horizontal plane, and are able to understand speech better in noisy scenario’s where noise and target are spatially separated. Although a lot of studies have been done on normal hearing and hearing impaired persons, little research has been done on directional hearing in bilateral hearing aid users.
A person with bilateral hearing aids is wearing two independent digital signal processors with microphones often placed on behind the ear devices. Each device introduces a certain delay and has its own compression curve and noise reduction strategies. This could mean that the interaural cues (interaural level and timing differences) are not in agreement with the actual auditory scene. This can degrade binaural processing capabilities for hearing aid users.
This study examined binaural capabilities in the frontal horizontal hemisphere of hearing impaired, bilateral hearing aid users. Localization and speech recognition in noise were studied. Localization tests were carried out using low frequency, high frequency and broadband signals, with and without hearing aids, omnidirectional configurations as well as adaptive directional microphone configurations were used. Results show that a) hearing aid users localize worse than normal hearing persons and a much larger standard deviation is noticed in this group, b) Most hearing aid persons score better without (with a louder stimulus) then with their hearing aids, c) without hearing aids, localization was worse than the normal hearing group, d) persons wearing hearing aids subjectively preferred their own ears for localization instead of their hearing aids, e) low frequency noise bands were localized more accurately then high frequency noise bands, and broadband signals were localized best, this in agreement with normal hearing persons, f) adding jammer noise sources degraded localization, with hearing aids this degradation was worse then without.