Effectiveness of Directional Microphones and Noise Reduction Schemes in Hearing Aids: A Systematic Review of the Evidence

Department of Speech Pathology and Audiology, University of Iowa, Iowa City 52242, USA.
Journal of the American Academy of Audiology (Impact Factor: 1.58). 06/2005; 16(7):473-84. DOI: 10.3766/jaaa.16.7.7
Source: PubMed


A systematic review of the literature was undertaken to find evidence of real-world effectiveness of directional microphone and digital noise reduction features in current hearing aids. The evidence was drawn from randomized controlled trials, nonrandomized intervention studies, and descriptive studies. The quality of each study was evaluated for factors such as blinding, power of statistical analyses, and use of psychometrically strong outcome measures. Weaknesses in the identified studies included small sample size, resultant poor power to detect potentially worthwhile differences, and overlapping experimental conditions. Nine studies were identified for directional microphones, and the evidence (albeit weak) supports effectiveness. Two studies were identified for the noise reduction feature, and the evidence was equivocal. For the researcher, such a systematic review should encourage the careful consideration of appropriate methodologies for assessing feature effectiveness. For the clinician, the outcomes reported herein should encourage use of such a systematic review to drive clinical practice.

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Available from: Ruth Bentler, Feb 28, 2015
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    • "By default, Cochlear Custom Sound ® programming software creates a SCAN program as well as a non-SCAN program using standard directionality. Adjustable microphone activation and directionality improve speech detection and enhancement in the presence of background noise (Amlani, 2001; Bentler, 2005). The Freedom processor utilized two microphones that were hard wired and a voice activity detector (VAD) to distinguish speech from noise (Spriet et al., 2007). "
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    ABSTRACT: To demonstrate the performance benefit of the Automatic Scene Classifier (SCAN) algorithm available in the Nucleus® 6 (CP900 series) sound processor over the default processing algorithms of the previous generation Nucleus 5 (CP810) and Freedom® Hybrid™ sound processors.
    09/2015; DOI:10.1016/j.joto.2015.09.001
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    • "Modern hearing aids often incorporate directional microphones that can provide a substantial signal-to-noise ratio (SNR) improvement—and typically a corresponding speech-intelligibility benefit—over omnidirectional microphones (Bentler 2005). To obtain the maximal benefit, however, requires an ideal set of conditions (Valente et al. 1995): the listening environment should have no more than moderate reverberation (i.e., the level of the direct and reflected sound should be at least equal), the background noise should be at the side or the rear of the listener, and the listener should be more or less facing the signal of interest (Ricketts & Dhar 1999; Hornsby & Ricketts 2007). "
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    ABSTRACT: Objectives: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes. The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones. Design: The authors instructed hearing-impaired individuals to turn and face a female talker in simultaneous surrounding male-talker babble. Participants pressed a button when they felt they were accurately oriented in the direction of the female talker. Participants completed three blocks of trials with their hearing aids in omnidirectional mode and three blocks in directional mode, with mode order randomized. Using a Vicon motion tracking system, the authors measured head position and computed fixation error, fixation latency, trajectory complexity, and proportion of misorientations. Results: Results showed that for larger off-axis target angles, listeners using directional microphones took longer to reach their targets than they did when using omnidirectional microphones, although they were just as accurate. They also used more complex movements and frequently made initial turns in the wrong direction. For smaller off-axis target angles, this pattern was reversed, and listeners using directional microphones oriented more quickly and smoothly to the targets than when using omnidirectional microphones. Conclusions: The authors argue that an increase in movement complexity indicates a switch from a simple orienting movement to a search behavior. For the most off-axis target angles, listeners using directional microphones appear to not know which direction to turn, so they pick a direction at random and simply rotate their heads until the signal becomes more audible. The changes in fixation latency and head orientation trajectories suggest that the decrease in off-axis audibility is a primary concern in the use of directional microphones, and listeners could experience a loss of initial target speech while turning toward a new signal of interest. If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account.
    Ear and Hearing 09/2014; 35(5):e204-e212. DOI:10.1097/AUD.0000000000000053 · 2.84 Impact Factor
    • "They can be used to produce a static pattern of directionality, where the point of maximum attenuation or null is fixed, or an adaptive one, where the null dynamically follows the direction of noise incidence (Kompis and Dillier, 2001). These multiple microphone beamformers have been incorporated successfully into hearing aids since the 1990s and two systematic reviews identified weak to moderate evidence of their effectiveness in improving speech perception in noise (Bentler, 2005; McCreery et al., 2012; Ricketts and Dhar, 1999; Ricketts and Henry, 2002). However, the first adaptive beamforming algorithms integrated into CI speech processors were not commercially introduced until 2005 (Spriet et al., 2007). "
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    ABSTRACT: Objectives To compare the Naida CI UltraZoom adaptive beamformer and T-Mic settings in a real life environment. Methods Speech reception thresholds (SRTs) were measured in a moderately reverberant room, using the German Oldenburger sentence test. The speech signal was always presented from the front loudspeaker at 0° azimuth and fixed masking noise was presented either simultaneously from all eight loudspeakers around the subject at 0°, ±45°, ±90°, ±135°, and 180° azimuth or from five loudspeakers positioned at ±70°, ±135°, and 180° azimuth. In the third test setup, an additional roving noise was added to the six loudspeaker arrangement. Results There was a significant difference in mean SRTs between the Naida CI T-Mic and UltraZoom in each of the three test setups. The largest improvements were seen in the six speaker roving and fixed noise conditions. Adding ClearVoice to the Naida CI T-Mic setting significantly improved the SRT in both fixed noise conditions, but not in the roving noise condition. In each setup, the lowest SRTs were obtained with the UltraZoom plus ClearVoice setting. Discussion The degree of improvement was consistent with previous beamforming studies. In the most challenging listening situation, with noise from eight speakers and speech and noise presented coincidentally from the front, UltraZoom still provided a significant benefit. When a moving noise source was added, the improvement in SRT provided by UltraZoom was maintained. Conclusion When tested in challenging and realistic noise environments, the Naida CI UltraZoom adaptive beamformer resulted in significantly lower mean SRTs than when the T-Mic alone was used.
    Cochlear Implants International 07/2014; 16(2). DOI:10.1179/1754762814Y.0000000088
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