Abstract
Asymmetric bilateral directional fitting (ABDF) has been reported by Bentler et al8) in 2004, in which the hearing aid in one side was on directional microphone mode while the contralateral side was on omnidirectional mode. The authors reported that there was no significant difference in speech recognition thresholds (SRT) using HINT or word recognition scores between the conditions of asymmetric fitting and symmetric fitting. On the other hand, Hornsby et al.9) reported that there was a significant difference between the two conditions and concluded that symmetric bilateral directional fitting (SBDF) was better. In this study, the SRTs in 28 normal hearing and 13 hearing impaired participants were measured to find the directional benefit of ABDF. As predicted, SRTs in noise and directional benefit were the best in SBDF, ABDF, and bilateral omnidirectional in that order. SBDF had a 1-1.5 dB directional advantage on average compared to ABDF. However, ABDF was still approximately 3dB better than bilateral omnidirectional fitting. There was no significant difference between asymmetric and symmetric directional in terms of directional benefit in the hearing impaired group only. The findings suggested that asymmetric fitting would still be beneficial in the order of 3 dB compared to bilateral omnidirectional, and certainly it can be considered as an option for those who want to receive the advantage of directional microphone mode yet do not want to miss hearing sounds in their environment from all directions.
