Article

Adaptive Directional Benefit in the Near Field: Competing Sound Angle and Level Effects

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Abstract

Two experiments were performed that examined adaptive directional benefit and directional benefit as a function of competing noise level. Fourteen bilaterally fitted adult listeners with sloping, sensorineural hearing loss participated in both experiments. The results of the first experiment provide additional support for an adaptive advantage in environments with a discrete competing noise source placed near the listener. This advantage occurs even if the noise source is moving and only is present when the angle of the noise source relative to the listener does not correspond to an angle for which the fixed directional mode is optimized. Speech transmission index (STI) calculations do not generally support adaptive directional benefit in the presence of multiple competing noise sources. Specifically, an adaptive advantage was measured using the STI only when the intensity level of one of the competing noise sources in a group was at least 12 to 15 dB greater than all other sources combined. The results of the second experiment revealed more directional benefit for poorer signal-to-noise ratios (SNRs). However, if the SNR was held constant, the absolute noise level did not affect the magnitude of directional benefit.

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... here are two sound ports in ixed directional microphones, signals entering at the back port are acoustically delayed and then are subtracted from those which enters from the front of microphone 30 . Many researchers have shown advantages of it but its performance reduces when there is a uniform noise of moderate level 31 . he next advancement in directional microphone technology is Multi-channel automatic adaptive directional microphone. ...
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Background/Objectives: To shed light on the history of development of hearing aid, along with the various pros and cons of each developed technological solution. Methods/Statistical Analysis: A historical survey has been conducted, which highlights some of the more renowned and widely deployed hearing aids within the market. The different types of hearing losses and the varying degree of assistance provided by the different technological solutions have been discussed. Over the years, the overall accuracy as well as practicality of the hearing aids have improved, ranging from cumbersome and heavy hearing aids in the early 1960-1970s to the portable and wearable ones available in the market at present. Findings: Technological innovation is spearheading massive improvement within the hearing aids. Some of the key features causing these changes include wireless technology, frequency lowering, directional microphones and digital noise reduction algorithms. Although DSP has provided significant changes in the hearing technology, limitations still exist, which require re-search contributions from different fields like clinical audiology, psychoacoustics and signal processing. Application/Improvements: Most of the portable and reliable hearing aid devices are very expensive. Therefore, there is a need to develop affordable pieces of equipment that is able to cater to basic hearing functionalities.
... That is, this difference would be eliminated if the same physical design and timing parameters implemented by the adaptive mode in a diffuse field were applied in the fixed mode (e.g. Ricketts, Hornsby and Johnson 2005). In the case of the test instrument however, the fixed directional mode was optimized for attenuation of competing noises located directly behind the listener (Ricketts and Henry 2002). ...
... Ricketts and Hornsby (2003) reported a directional benefit in rooms with low and moderate reverberation except when the speech source was moved to a distal field of 4.8 m. Furthermore, Ricketts, Hornsby, and Johnson (2005) later found that the advantage of using the automatic adaptive directional microphone was greatly reduced when there was a moderate level of uniform noise present. ...
Article
Digital signal processing (DSP) has provided significant advances and improvements in hearing aid technology. These advances, and the increased process-ing speed that DSP offers, have resulted in improved and expanded features in current hearing aid technology. These advances have also served to expand the fitting range of amplification for patients who previously could not benefit from amplification. This article reviews the advances and supporting research in specific hearing aid features, devices, and assistive technology developments that allow a greater number of patients access to amplification. These features and devices include directional microphones, Bluetooth and other wireless technology, digital noise reduction, devices for patients with single-sided deafness, frequency transposition, self-learning and adaptation managers, and integrated real ear measures. Despite the changes in hearing aids created by DSP, limitations still exist. Additionally, peer-reviewed research is not yet available to support the reported benefits of some of these advances. earing aids have undergone significant improvements since the days when ear trumpets and animal horns were used to transmit sounds to the ear. As digital technology came to the forefront in the field of telecommunications, its application expanded to the field of amplification. In 1996, digital signal processing (DSP) was introduced into hearing aid processing algorithms (Edwards, 2007). Since then, advances in digital technology and the processing speed of the DSP chip have opened the door to expand and improve the available features in modern hearing aids. Even with these advances, however, hearing aid users continue to complain of difficulty hearing speech in noise and performance with telephones. According to the MarkeTrak V data, 25.3% of hearing aid users reported that they have a hard time listening when there is a lot of background noise present, and approximately 1% of users reported difficulty using the telephone (Kochkin, 2000). Recent developments in directional microphone technol-ogy and improvements in access to and use of wireless technology are improving speech recognition in noise, or the signal-to-noise ratio (SNR). Access to newer forms of wireless transmission and improvements in coupling this technology to hearing aids not only enhances patients' abilities to use telephones, but also allows patients to directly connect to a multitude of external devices. Noise reduction algorithms have also advanced to help improve hearing aid users' comfort and ease of listening in noise, and several algorithms have attempted to improve speech recognition in noise. In addition, several devices and features are now being used to assist individuals with hearing impairment who have not previously experienced benefit with hearing aids. There are also devices and/or features that make the fitting process easier for the audiologist and the patient. These newer devices include hearing aids for single-sided deafness (SSD), frequency transposition for patients exhibiting severe high-frequency hearing loss, self-learning features on hearing aids, and hearing aids that allow for integrated real ear measures.
... By focusing on these common features, it is expected that study findings are salient to the highest number of hearing aid dispensing audiologists. In addition, numerous research studies have demonstrated benefits of dispensing three of these features (e.g., directional processing, Cord, Surr, Walden, & Dyrlund, 2004;Killion, 2004;Kochkin, 2003;Ricketts & Henry, 2002;Ricketts, Henry, & Gnewikow, 2003;Ricketts & Hornsby, 2003;Ricketts, Hornsby, and Johnson, 2005;Walden, Surr, Cord, & Dyrland, 2004; digital feedback suppression processing, Chung, 2004;Freed & Soli, 2006;Greenberg, Zurek, & Brantley, 2000;E. E. Johnson, Ricketts, & Hornsby, 2007;Kates, 1999;Kiessling, Brenner, Jespersen, Groth, & Jensen, 2005; and the telecoil, Pettersson, 1987;Stoker, French, & Lyons, 1986). ...
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The purpose of the study was to develop and examine a list of potential variables that may account for variability in the dispensing rates of four common hearing aid features. A total of 29 potential variables were identified and placed into the following categories: (1) characteristics of the audiologist, (2) characteristics of the hearing aids dispensed by the audiologist, (3) characteristics of the audiologist's patient population, and (4) evidence-based practice grades of recommendation for each feature. The potentially associative variables then were examined using regression analyses from the responses of 257 audiologists to a dispensing practice survey. There was a direct relation between price and level of hearing aid technology with the frequency of dispensing product features. There was also a direct relation between the belief by the audiologist that a feature might benefit patients and the frequency of dispensing that feature. In general, the results suggested that personal differences among audiologists and the hearing aids audiologists choose to dispense are related more strongly to dispensing rates of product features than to differences in characteristics of the patient population served by audiologists. An additional finding indicated that evidence-based practice recommendations were inversely related to dispensing rates of product features. This finding, however, may not be the result of dispensing trends as much as hearing aid manufacturing trends.
... In addition, the level of the "higher-level" loudspeaker was always 10 dB greater than the level of each of the individual "lowerlevel" loudspeakers. These competing noise conditions were chosen specifically for evaluation of adaptive directional processing (see Ricketts et al, 2005, for further details). ...
Article
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Article
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This study aimed to document improvements in speech recognition when listening through fixed or adaptive directional microphone arrays relative to listening through omnidirectional micro-phone arrays in a variety of near-field noise conditions. Twelve participants with mild to severe hearing loss were recruited. Data were analyzed in a manner to facilitate discussion of both group and individual performance. The activation of directional microphones significantly improved speech recognition in all listening conditions when compared to omnidirectional listening conditions. Significant differences in speech recognition performance were not observed between fixed and adaptive directional microphone conditions. Analysis of individual outcomes shows a wide range of both absolute speech recognition scores and directional benefit across treatment conditions.
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This paper describes the first phase in the development of the Connected Speech Test (CST). This test of intelligibility of everyday speech has been developed primarily for use as a criterion measure in investigations of hearing aid benefit. The test consists of 48 passages of conversationally produced connected speech. Each passage contains 25 key words for scoring. All passages are of equal intelligibility for the average normal hearer. Key words vary in intelligibility within a passage but span the same intelligibility range in all passages. Several passages are administered, and the results averaged, to yield a single intelligibility score. For pairs of scores, each based on mean performance across 4 randomly-chosen passages, the 95% critical difference is estimated to be about 14 rationalized arcsine units (rau). The performance-intensity function for the CST has a slope of 12 rau/dB signal-to-babble ratio. Investigations of the test are continuing with hearing-impaired listeners.
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The present article is divided into four major sections dealing with the application of acoustical indices to the prediction of speech recognition performance. In the first section, two acoustical indices, the Articulation Index (AI) and the Speech Transmission Index (STI), are described. In the next section, the effectiveness of the AI and the STI in describing the performance of normal-hearing and hearing-impaired subjects listening to spectrally distorted (filtered) and temporarily distorted (reverberant) speech is examined retrospectively. In the third section, the results of a prospective investigation that examined the recognition of nonsense syllables under conditions of babble competition, filtering and reverberation are described. Finally, in the fourth section, the ability of the acoustical indices to describe the performance of 10 hearing-impaired listeners, 5 listening in quiet and 5 in babble, is examined. It is concluded that both the AI and the STI have significant shortcomings. A hybrid index, designated mSTI, which takes the best features from each procedure, is described and demonstrated to be the best alternative presently available.
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The signal-to-noise ratio necessary for a constant performance level was determined for normally hearing and hearing-impaired subjects under three levels of reverberation (0.3, 0.6, and 1.2 s) with monaural and binaural hearing aids having directional and omnidirectional microphones. Results indicated (a) a significant binaural advantage (2-3 dB) which was independent of microphone type and reverberation time, (b) a significant directional microphone advantage (3-4 dB) which was independent of hearing aid arrangement (monaural or binaural) but dependent on level of reverberation, (c) a significant reverberation effect which was larger than either the binaural or directional microphone effect, and (d) additive binaural and directional microphone advantages. The results suggest that the signal-to-noise ratio is optimized when binaural hearing aids with directional microphones are used in rooms with short reverberation times.
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A physical method for measuring the quality of speech-transmission channels has been developed. Essentially, the method represents an extension of the Articulation Index (AI) concept, which was developed mainly to account for distortions in the frequency domain (noise, bandpass-limiting). The underlying concept of the present approach, based on the Modulation Transfer Function (MTF) of a transmission channel, has been adapted to account for nonlinear distortions (peak clipping) as well as for distortions in the time domain (reverberation, echoes, AGC). The resulting index, the Speech-Transmission Index (STI), has been correlated with subjective intelligibility scores obtained on 167 different transmission channels with a wide variety of disturbances. The relative predictive power of the STI, expressed in PB-word score, appeared to be 5%. This accuracy is comparable with results obtained from subjective measurements when about four talkers and four listeners are used. Expressed in terms of signal-to-noise ratio, the accuracy is about 1 dB. Pilot studies have been carried out to evaluate the use of the STI for testing digital-speech transmission channels.
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In the recent literature on dynamic compression in hearing aids, a controversial discussion about the benefit of multichannel compression with short time constants has been raised. In this paper, some experimental results are contributed to the discussion: For low signal-to-noise ratios, a detrimental effect of fast multichannel compression on speech intelligibility in normal hearing listeners is found. However, a distinct degradation in speech quality and virtually no decrease in speech intelligibility is observed for comparatively high signal-to-noise ratios and compression ratios of up to 3. Since the predictions of the Speech Transmission Index deviate substantially from these results, its applications as an objective measure of intelligibility may not be extended to compressed speech.
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We have witnessed a large increase in the availability of directional microphone hearing aids over the past few years. Directional microphone technology is now available in analog, digitally controlled analog, and digital hearing aids, and has been implemented into both behind-the-ear and in-the-ear styles. This Short Course reviews basic design differences across directional microphone hearing aids. A number of different laboratory and clinical evaluation methods used for assessment of both electroacoustic and behavioral directivity are then reviewed. In addition, the potential impact of test conditions such as room reverberation and type and position of competing noise(s), on listener performance when fit with directional hearing aids are considered. Recommendations and suggestions relating to the clinical and laboratory assessment of directional hearing aids are provided.
Article
To evaluate the impact of the position of noise source(s) and reverberation on the directional benefit and performance of three commercially available directional hearing aids. Directional benefit and performance were measured for four different configurations of competing noise source(s) in two different reverberant rooms. Three pairs of hearing aids representing three commercial models were selected based on electroacoustic evaluation of directivity. Directional benefit and performance of 25 subjects with symmetrical, sloping, sensorineural hearing loss were measured in all test environments using a modified version of the Hearing in Noise Test. Both reverberation and configuration of the competing noise source(s) significantly affected directional benefit and performance. There was no significant correlation between directional benefit and directional performance. The order of benefit and performance across hearing aid brands (from best to worst) varied depending on the noise source configuration. Data revealed increasing reverberation significantly decreased directional benefit and performance. The absolute and relative (rank ordering) directional benefit and performance varied across hearing aid brand, with noise source configuration. These results suggest that data collected in traditional test environments (e.g., a single competing noise placed at 180 degrees azimuth) cannot be used to accurately predict directional benefit or performance in the majority of other test and real-world environments. The impact of reverberation and noise source configuration on directional benefit/performance can be explained fairly well by the interaction between the spatial properties of the noise source(s) and the polar directivity patterns of the hearing aids.
Article
To evaluate the impact of low-threshold compression and hearing aid style (in-the-ear [ITE] versus behind-the-ear [BTE]) on the directional benefit and performance of commercially available directional hearing aids. Forty-seven adult listeners with mild-to-moderate sensorineural hearing loss were fit bilaterally with one BTE and four different ITE hearing aids. Speech recognition performance was measured through the Connected Speech Test (CST) and Hearing in Noise Test (HINT) for a simulated noisy restaurant environment. For both the HINT and CST, speech recognition performance was significantly greater for subjects fit with directional in comparison with omnidirectional microphone hearing aids. Performance was significantly poorer for the BTE instrument in comparison with the ITE hearing aids when using omnidirectional microphones. No differences were found for directional benefit between compression and linear fitting schemes. No systematic relationship was found between the relative directional benefit and hearing aid style; however, the speech recognition performance of the subjects was somewhat predictable based on Directivity Index measures of the individual hearing aid models. The fact that compression did not interact significantly with microphone type agrees well with previously reported electroacoustic data.
Article
The purpose of this study was to identify characteristics of everyday listening situations that influence user preferences for omnidirectional versus directional hearing aid microphones. Eleven experienced hearing aid users were fitted with digital hearing aids featuring switchable omnidirectional (OMNI) and adaptive-directional (DIR) modes (programs). For 6 weeks, their task was to identify and describe at least one listening situation each day in which one program performed better than the other using a checklist daily journal format. All participants reported difficulty identifying situations in which they could perceive a difference between the two microphone modes. Although an equal number had been requested, descriptions favoring the DIR outnumbered those for the OMNI. Chi-square tests were used to compare the distributions of 60 descriptions favoring the OMNI and 155 favoring the DIR across variables associated with the primary talker to whom the hearing aid user was listening, background noise, and other environmental characteristics. The results indicated that location of the primary talker, presence or absence and type of background noise, and type of space in which the communication occurred influenced microphone choice.
Article
This study explored the use patterns and benefits of directional microphone technology in real-world situations experienced by patients who had been fitted with switchable omnidirectional/directional hearing aids. Telephone interviews and paper-and-pencil questionnaires were used to assess perceived performance with each microphone type in a variety of listening situations. Patients who used their hearing aids regularly and switched between the two microphone configurations reported using the directional mode, on average, about one-quarter of the time. From brief descriptions, patients could identify listening situations in which each microphone mode should provide superior performance. Further, they reported encountering listening situations in which an omnidirectional microphone should provide better performance more frequently than listening situations in which the directional microphones should be superior. Despite using the omnidirectional mode more often and encountering situations in which an omnidirectional microphone should provide superior performance more frequently, participants reported the same level of satisfaction with each microphone type.
Article
The effectiveness of an adaptive directional microphone design, as implemented in the Phonak Claro behind-the-ear hearing aid, is evaluated. Participants were fit bilaterally and tested in 2 environments, an anechoic chamber and a moderately reverberant classroom, with the microphones in the fixed (cardioid) setting and the adaptive setting. Five speakers were placed between 110 degrees and 250 degrees azimuth around the listener. Speech-weighted noise was presented from those speakers at an overall level (OAL) of 65 dB (A). Noise was increased by 8 dB from 1 speaker at a time, using 2-s modulation and random assignment, while the output from the other speakers was reduced to maintain the constant OAL. Results of 2 speech perception tasks used as outcome measures indicated that the adaptive system was not able to follow the dominant noise source in the presence of lower level noise sources. Self-report measures obtained after blinded home trials were consistent with laboratory findings that the participants did not perceive this adaptive microphone design to be more effective than the default fixed-microphone option.
Article
Seventeen hearing-impaired adults were fit with omnidirectional/directional hearing aids, which they wore during a four-week trial. For each listening situation encountered in daily living during a total of seven days, participants selected the preferred microphone mode and described the listening situation in terms of five environmental variables, using a paper and pencil form. Results indicated that hearing-impaired adults typically spend the majority of their active listening time in situations with background noise present and surrounding the listener, and the signal source located in front and relatively near. Microphone preferences were fairly evenly distributed across listening situations but differed depending on the characteristics of the listening environment. The omnidirectional mode tended to be preferred in relatively quiet listening situations or, in the presence of background noise, when the signal source was relatively far away. The directional mode tended to be preferred when background noise was present and the signal source was located in front of and relatively near the listener. Results suggest that knowing only signal location and distance and whether background noise is present or absent, omnidirectional/directional hearing aids can be set in the preferred mode in most everyday listening situations. These findings have relevance for counseling patients when to set manually switchable omnidirectional/directional hearing aids in each microphone mode, as well as for the development of automatic algorithms for selecting omnidirectional versus directional microphone processing.
Article
Understanding the potential benefits and limitations of directional hearing aids across a wide range of listening environments is important when counseling persons with hearing loss regarding realistic expectations for these devices. The purpose of this study was to examine the impact of speaker-to-listener distance on directional benefit in two reverberant environments, in which the dominate noise sources were placed close to the hearing aid wearer. In addition, speech transmission index (STI) measures made in the test environments were compared to measured sentence recognition to determine if performance was predictable across changes in distance, reverberation and microphone mode. The aided sentence recognition, in noise, for fourteen adult participants with symmetrical sensorineural hearing impairment was measured in six environmental conditions in both directional and omnidirectional modes. A single room, containing four uncorrelated noise sources served as the test environment. The room was modified to exhibit either low (RT60 = 0.3 sec) or moderate (RT60 = 0.9 sec) levels of reverberation. Sentence recognition was measured in both reverberant environments at three different speech loudspeaker-to-listener distances (1.2 m, 2.4 m, and 4.8 m). STI measures also were made in each of the 12 listening conditions (2 microphone modes x 3 distances x 2 reverberation environments). A decrease in directional benefit was measured with increasing distance in the moderate reverberation condition. Although reduced, directional benefit was still present in the moderately reverberant environment at the farthest speech speaker-to-listener distance tested in this experiment. A similar decrease with increasing speaker-to-listener distance was not measured in the low reverberation condition. The pattern of average sentence recognition results across varying distances and two different reverberation times agreed with the pattern of STI values measured under the same conditions. Although these data support increased directional benefit in noise for reduced speaker-to-listener distance, some benefit was still obtained by listeners when listening beyond "effective" critical distance under conditions of low (300 msec) to moderate (900 msec) reverberation. It is assumed that the directional benefit was due to the reduction of the direct sound energy from the noise sources near the listener. The use of aided STI values for the prediction of average word recognition across listening conditions that differ in reverberation, microphone directivity, and speaker-to-listener distance also was supported.
Real world performance of an ITE directional microphone
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