However ironic it may seem for the new year to begin in the dead of winter, January is the time when we focus on renewal, improvement, and starting fresh. Ads are packed with gizmos and offers to help you clean up, get organized, get fit, eat right and break any bad habits you didn’t manage to break last year. But sometimes a fresh start doesn’t need to be all that much work. It can be as simple as letting go of an old convention and seeing what happens – no gym membership required! In hearing instrument fitting, clinicians have had it drummed into their heads for two decades that their clients must be fit with directionality for improved hearing in noise. During that same time, the profession has successfully worked to promote bilateral use of hearing instruments. To top it off, the vast majority of devices today offer users multiple programs that provide them with directional and omnidirectional responses to best suit particular listening environments. So if Mr. Jones is being fit with two hearing aids, conventional wisdom tells us he will get the most benefit if the settings are the same on both ears. Then he can either decide when to listen with directionality, or the hearing instruments’ “artificial intelligence” can decide for him.
ReSound was the first and remains the only manufacturer to buck tradition with an asymmetric fitting approach. A ReSound Natural Directionality fitting provides directionality on a focus ear, and an omnidirectional response on a monitor ear. This approach takes advantage of the central auditory system’s superior ability to fuse different inputs from the two ears to a unified auditory image and to take advantage of the side which has the best signal-to-noise ratio at any given time. Hearing instrument wearers don’t have to guess when they should be switching programs, and hearing instrument decision-making algorithms don’t have to guess at what the wearer actually wants to hear.
The research which inspired this approach has already demonstrated that an asymmetrical directional fitting provides equivalent directional benefit to bilateral directionality and that ease of listening is improved compared to symmetric directional or omnidirectional fittings. But as the Natural Directionality rationale continue to gain acceptance, researchers also continue to document its advantages. A new study supports the asymmetric directional fitting strategy as providing directional benefit while also increasing acceptance of background noise. Kim & Bryan (2011) fit 15 hearing aid users binaurally with BTEs in four directional microphone settings: bilateral omnidirectional, right asymmetric (right ear directional, left ear mnidirectional), left symmetric (left ear directional, right ear omnidirectional) and bilateral directional. Subjects were evaluated through the Hearing in Noise Test (HINT) and the Acceptable Noise Level (ANL) procedure. HINT results showed that speech understanding in noise was improved for the asymmetric directional fittings compared to the binaural omnidirectional microphone fittings, and that speech understanding was not significantly worse for asymmetric fittings when compared to bilateral directional fittings. ANL results indicated the hearing aid users accepted more background noise for the asymmetric fittings than for the bilateral omnidirectional fittings.
The results of this study support previous claims that asymmetric fittings can provide better speech understanding in noise than omnidirectional fittings with no significant difference from bilateral directional fittings, and that people fitted with asymmetric directionality experience better tolerance of or comfort in background noise. It is interesting to note that this study used another manufacturer’s hearing instruments, requiring the investigators to define what the best settings for an asymmetric fitting would be. ReSound is the only manufacturer to optimize the asymmetric fitting settings for prescription of directional ear, sound quality, and preservation of localization cues. In addition, the Natural Directionality II environment program in Aventa 3 makes it a simple matter to select the most favorable settings for an asymmetric fitting with one click. How much easier could a fresh start be?
Kim J.S. & Bryan M.F. (2011). The effects of asymmetric directional microphone fittings on acceptance of background noise. International Journal of Audiology, 50, pp.290-296.