by Brian Taylor, AuD, Editor-At-Large
For decades, directional microphones (also known as beamformers) have been recognized as the go-to solution for improving speech understanding in noise. Relying on the spatial separation of speech and background noise for optimal performance, extensive research supports their effectiveness in many noisy environments. These documented benefits, however, come with some limitations. For example, to maximize benefit, wearers should remain stationary and try to keep the talker of interest in front of them as much as possible. Further, some studies suggest many wearers report improved sound quality and better localization ability when their hearing aids are in the omni-directional, rather than directional microphone, mode.
Hearing aid manufacturers, clinicians, and wearers continually try to thread the needle when it comes to the use of directional microphone technology. Considering that wearer intentions vary so much, depending on the noise level, reverberation effects, as well as several other factors, unusual types of polar patterns, automatic-switching algorithms and other assorted processing strategies have been employed to optimize hearing aid performance in noise.
Some of these approaches to noise reduction are more popular than others, while many of them have not been extensively studied by independent labs. Further, some approaches that are quite effective in noise can make listening in quiet worse. So, for clinicians and wearers alike there are many factors to balance. Luckily, research can sometimes be a guide in the oftentimes arduous hearing aid selection and counseling process.
Hearing Aid Beamforming Technology
Two recent studies, examining some of the more recent incremental innovations in beamforming technology, demonstrate that the eye of the needle is shrinking a bit. One study, published online in June by the International Journal of Audiology (IJA), compared the more traditional symmetrical beamformer arrangement (both hearing aids in either the omni or directional mode simultaneously) to what is referred to as the asymmetrical mode in which one hearing aid is in the directional mode, while the other remains in the omni-directional setting.
Although this novel asymmetrical approach to threading the needle has been around for a while, it hasn’t been studied by independent researchers much.
In this study, the Vanderbilt University researchers examined the effects of three different microphone modes – symmetrical omnidirectional, symmetrical directional and asymmetrical directional – on speech recognition, localization and microphone listening preference. Additionally, the researchers looked for a predictive relationship between several unaided pre-fitting measures, including speech recognition in noise testing and microphone preference.
Results of this study, conducted on 20 adult wearers with mild to moderately-severe bilateral hearing loss, demonstrated a few of clinically useful findings.
- Both the symmetrical and asymmetrical directional microphone modes yielded about the same speech understanding in noise benefit for the wearers.
- Localization ability was significantly better for the symmetrical directional arrangement than the asymmetrical directional arrangement when speech was coming from behind the wearer. (This is somewhat of a remarkable finding, given that many clinicians believe, based largely on some product claims, that a more omnidirectional response contributes to improved localization).
- Wearers who had a strong preference for the sound quality of the symmetrical directional setting tended to have significantly poorer unaided speech recognition in noise scores. A finding that suggests the value of conducting unaided speech recognition in noise tests prior to selecting a specific hearing aid and counseling patients about expectations.
An important bottom-line conclusion from this study is that asymmetrical beamformers are no more effective than traditional symmetrical beamformers on measures of speech understanding, localization and sound quality preference judgments. In fact, the more traditional symmetrical beamformer might have a slight overall edge.
Another challenge associated with traditional directional microphones is this: They simply are not as effective when a person is walking around, trying to converse with a walking partner and other similar situations when a person is in motion.
To address this problem a couple different hearing aid manufacturers have added motion-based beamformers to their platforms. The basic idea of motion-based beamforming being that when a wearer is walking around trying to hear sounds coming from the side or back, that wearer requires a more omni-directional pattern and when the wearer is stationary, and the talker of interest is coming from the front, the hearing aids transition into a directional pattern. Another recent study, published at IJA online in August, examined the real-world effectiveness of these motion-based beamformers on measures of self-reported speech understanding, environmental awareness, overall listening and sound quality – metrics gathered in a simulated real world listening condition.
Results of this study, comprised of 22 older adults with moderate-to-severe hearing loss, showed that most wearers had a preference for motion-based beamforming. Measures of speech understanding and localization were significantly better for the motion-based beamforming condition. Results favored motion-based beamforming across several real-world metrics, suggesting that older adult patients with moderate-to-severe hearing loss are likely to prefer and benefit from this feature.
Hearing in the presence of background noise remains a challenge for many patients – one that requires impeccably effective counseling skills to navigate successfully. Fortunately, incremental innovations in hearing technology such as motion-based beamformers help us more effectively thread the needle on the benefits and limitations of directional microphone technology.