Yu-Hsiang Wu

Digital noise reduction: Outcomes from laboratory and field studies

The purpose of this study was to determine the impact of a digital noise reduction (DNR) scheme implemented in a current commercial hearing aid. In a double-blinded design, three conditions of onset time (4, 8, 16 seconds) were randomly assigned to the 25 subjects, plus one condition wherein the noise-reduction feature was disengaged. Subsequently, a fifth trial/condition, wherein the subject had access to three memories in which the different onsets were programmed, was carried out. For each of the five conditions, the subjects had an at-home trial, prior to obtaining self-report measures. Laboratory measures of speech perception showed no effect of the DNR, with or without the provision of visual cues. Laboratory-based ratings of ease of listening showed DNR-on (all onset times) to be rated significantly better than DNR-off; for ratings of listening comfort, the 4-second onset time was rated significantly lower (poorer) than the 8-second onset or the DNR-off condition; for ratings of sound quality, DNR-on or -off had no differential effect. Self-report measures indicated significantly higher aversiveness in the DNR-off condition compared to the pre-test scores

Measuring listening effort: driving simulator versus simple dual-task paradigm

Objectives: The dual-task paradigm has been widely used to measure listening effort. The primary objectives of the study were to (1) investigate the effect of hearing aid amplification and a hearing aid directional technology on listening effort measured by a complicated, more real world dual-task paradigm and (2) compare the results obtained with this paradigm to a simpler laboratory-style dual-task paradigm. Design: The listening effort of adults with hearing impairment was measured using two dual-task paradigms, wherein participants performed a speech recognition task simultaneously with either a driving task in a simulator or a visual reaction-time task in a sound-treated booth. The speech materials and road noises for the speech recognition task were recorded in a van traveling on the highway in three hearing aid conditions: unaided, aided with omnidirectional processing (OMNI), and aided with directional processing (DIR). The change in the driving task or the visual reaction-time task performance across the conditions quantified the change in listening effort. Results: Compared to the driving-only condition, driving performance declined significantly with the addition of the speech recognition task. Although the speech recognition score was higher in the OMNI and DIR conditions than in the unaided condition, driving performance was similar across these three conditions, suggesting that listening effort was not affected by amplification and directional processing. Results from the simple dual-task paradigm showed a similar trend: hearing aid technologies improved speech recognition performance, but did not affect performance in the visual reaction-time task (i.e., reduce listening effort). The correlation between listening effort measured using the driving paradigm and the visual reaction-time task paradigm was significant. The finding showing that our older (56 to 85 years old) participants’ better speech recognition performance did not result in reduced listening effort was not consistent with literature that evaluated younger (approximately 20 years old), normal hearing adults. Because of this, a follow-up study was conducted. In the follow-up study, the visual reaction-time dual-task experiment using the same speech materials and road noises was repeated on younger adults with normal hearing. Contrary to findings with older participants, the results indicated that the directional technology significantly improved performance in both speech recognition and visual reaction-time tasks. Conclusions: Adding a speech listening task to driving undermined driving performance. Hearing aid technologies significantly improved speech recognition while driving, but did not significantly reduce listening effort. Listening effort measured by dual-task experiments using a simulated real-world driving task and a conventional laboratory-style task was generally consistent. For a given listening environment, the benefit of hearing aid technologies on listening effort measured from younger adults with normal hearing may not be fully translated to older listeners with hearing impairment.

Impact of Visual Cues on Directional Benefit and Preference: Part I-Laboratory Tests

Objectives: The purpose of the laboratory tests of the current investigation was to examine how visual cues impact directional (DIR) benefit and preference for the DIR microphone hearing aid (re: the omnidirectional [OMNI] microphone). Specifically, three hypotheses were examined: (1) the presence of visual cues would improve OMNI-aided performance to ceiling levels and therefore reduce DIR benefit and preference, (2) DIR benefit measured in the audiovisual (AV) condition could not be predicted by that measured using auditory-only (AO) testing, and (3) with visual cues, listeners with greater lipreading skills would perceive less DIR benefit than did listeners with lesser lipreading skills. Design: Twenty-four adults with sensorineural hearing loss were recruited. Their speech recognition performances were measured in two hearing aid microphone modes (DIR and OMNI), at various signal-to-noise ratios (SNR, −10 to +10 dB in 4-dB steps) and under two presentation conditions (AV and AO) by using the AV version of the Connected Speech Test. Microphone preference (DIR versus OMNI) was also assessed with and without visual cues at each of the SNRs by using the same Connected Speech Test sentences. Lipreading skills were measured using the Utley test. Results: The speech recognition data revealed that the participants obtained significantly less DIR benefit in the AV condition because their AV performances were at the ceiling level. Consistent with this, the likelihood of preferring DIR processing was significantly reduced when visual cues were available to the listeners. Further, DIR benefit measured in the AV condition was not correlated with that measured in the AO condition while being significantly and negatively correlated with lipreading skill. Conclusions: These results suggest that AO laboratory testing overestimates the DIR benefit and preference for DIR processing that hearing aid users may have in most face-to-face conversations in typical SNR, real-world environments. Additionally, because the DIR benefit measured in the AV condition cannot be predicted by the benefit score obtained from traditional AO laboratory testing, the effect of visual cues should be considered in establishing a valid laboratory/clinical environment and protocol for DIR microphone hearing aid testing. In light of these findings, consultations should be provided for hearing aid users with superior lipreading skills to help them adjust their expectations regarding the possibly small perceivable benefit gained from DIR microphone hearing aids.

The equivalence of acceptable noise level (ANL) with English, Mandarin, and non-semantic speech: A study across the U.S. and Taiwan

Abstract Objective: Acceptable noise level (ANL) determines the maximum noise level that a listener is willing to accept while listening to speech. The objective of this study was to determine the equivalence of ANL measured using different speech stimuli for native speakers who lived in the U.S. and Taiwan. Design: ANLs were measured using English, Mandarin, and the international speech test signal (ISTS) at each site. The same babble noise was used across speech stimuli. The ANLs were considered equivalent if the difference was unlikely to be greater than 3 dB. Study sample: Thirty adults with normal hearing were recruited at each site. Results: For each site, the equivalence test suggested that the native-language and foreign-language ANLs were equivalent. Between the two sites, ANLs measured using the listener’s native language were also equivalent. Although the ISTS ANL obtained within each site was equivalent to, and highly correlated to, the native-language ANL, the data were unable to confirm the equivalence of the ISTS ANLs obtained from the two sites. Conclusions: The results suggested the possibility of directly comparing ANL measures carried out in different countries using different languages. However, it remains unclear if the ISTS can serve as an international ANL stimulus.

Psychometric Functions of Dual-Task Paradigms for Measuring Listening Effort.

Objectives: The purpose of the study was to characterize the psychometric functions that describe task performance in dual-task listening effort measures as a function of signal to noise ratio (SNR). Design: Younger adults with normal hearing (YNH, n = 24; experiment 1) and older adults with hearing impairment (n = 24; experiment 2) were recruited. Dual-task paradigms wherein the participants performed a primary speech recognition task simultaneously with a secondary task were conducted at a wide range of SNRs. Two different secondary tasks were used: an easy task (i.e., a simple visual reaction-time task) and a hard task (i.e., the incongruent Stroop test). The reaction time (RT) quantified the performance of the secondary task. Results: For both participant groups and for both easy and hard secondary tasks, the curves that described the RT as a function of SNR were peak shaped. The RT increased as SNR changed from favorable to intermediate SNRs, and then decreased as SNRs moved from intermediate to unfavorable SNRs. The RT reached its peak (longest time) at the SNRs at which the participants could understand 30 to 50% of the speech. In experiments 1 and 2, the dual-task trials that had the same SNR were conducted in one block. To determine if the peak shape of the RT curves was specific to the blocked SNR presentation order used in these experiments, YNH participants were recruited (n = 25; experiment 3) and dual-task measures, wherein the SNR was varied from trial to trial (i.e., nonblocked), were conducted. The results indicated that, similar to the first two experiments, the RT curves had a peak shape. Conclusions: Secondary task performance was poorer at the intermediate SNRs than at the favorable and unfavorable SNRs. This pattern was observed for both YNH and older adults with hearing impairment participants and was not affected by either task type (easy or hard secondary task) or SNR presentation order (blocked or nonblocked). The shorter RT at the unfavorable SNRs (speech intelligibility < 30%) possibly reflects that the participants experienced cognitive overload and/or disengaged themselves from the listening task. The implication of using the dual-task paradigm as a listening effort measure is discussed.

The effect of hearing aid signal-processing schemes on acceptable noise levels: perception and prediction.

Objectives: The acceptable noise level (ANL) test determines the maximum noise level that an individual is willing to accept while listening to speech. The first objective of the present study was to systematically investigate the effect of wide dynamic range compression processing (WDRC), and its combined effect with digital noise reduction (DNR) and directional processing (DIR), on ANL. Because ANL represents the lowest signal-to-noise ratio (SNR) that a listener is willing to accept, the second objective was to examine whether the hearing aid output SNR could predict aided ANL across different combinations of hearing aid signal-processing schemes. Design: Twenty-five adults with sensorineural hearing loss participated in the study. ANL was measured monaurally in two unaided and seven aided conditions, in which the status of the hearing aid processing schemes (enabled or disabled) and the location of noise (front or rear) were manipulated. The hearing aid output SNR was measured for each listener in each condition using a phase-inversion technique. The aided ANL was predicted by unaided ANL and hearing aid output SNR, under the assumption that the lowest acceptable SNR at the listener’s eardrum is a constant across different ANL test conditions. Results: Study results revealed that, on average, WDRC increased (worsened) ANL by 1.5 dB, while DNR and DIR decreased (improved) ANL by 1.1 and 2.8 dB, respectively. Because the effects of WDRC and DNR on ANL were opposite in direction but similar in magnitude, the ANL of linear/DNR-off was not significantly different from that of WDRC/DNR-on. The results further indicated that the pattern of ANL change across different aided conditions was consistent with the pattern of hearing aid output SNR change created by processing schemes. Conclusions: Compared with linear processing, WDRC creates a noisier sound image and makes listeners less willing to accept noise. However, this negative effect on noise acceptance can be offset by DNR, regardless of microphone mode. The hearing aid output SNR derived using the phase-inversion technique can predict aided ANL across different combinations of signal-processing schemes. These results suggest a close relationship between aided ANL, signal-processing scheme, and hearing aid output SNR.

Clinical measures of hearing aid directivity: assumption, accuracy, and reliability.

Objectives: A number of clinical measures of directivity, including the front-to-back ratio (FBR) and front-to-side ratio (FSR), have been suggested to audiologists to monitor the functionality of hearing aids with directional microphones. These suggestions, however, are based on the assumption that directivity measured clinically changes monotonically when compared with changes measured using the directivity index (DI) and perceptual directional benefit. The objective of the present study was to empirically examine this assumption. In addition, the reliability of the clinical directivity measure was estimated to establish a referral threshold for defective directional microphone hearing aids. Design: The directivity of the directional microphones of two behind-the-ear hearing aids was systematically degraded by plugging the microphone ports. The directivity was measured using four clinical measures: the FBR and FSR performed in the test chamber of a hearing aid analyzer and in sound field. Each measure was repeated four times in each directivity-degraded condition. The degraded directivity was also assessed using the DI measure in an anechoic chamber. The perceptual directional benefit in each directivity-degraded condition was obtained by testing 10 hearing-impaired adults in a sound field with diffuse noise using the Hearing in Noise Test (HINT). Results: The results of the DI and HINT measures showed strong correlation between the two FSRs (test chamber and sound field), while the two FBRs showed no correlation. The directivity generated by the FBRs could remain unchanged even when the directional microphone had lost more than 50% of its directivity. The results further indicated that the measures performed in the sound field were more reliable than those performed in the test chamber. Based on the results of the reliability measures, a 30% change in directivity was suggested as the referral threshold signifying defective directional systems. Conclusions: Because the FSR predicts the DI and HINT measurements more accurately than does the FBR, it is suggested that clinicians use the FSR to monitor hearing aid directivity. By using the FSR measure and informed by the suggested referral threshold, clinicians would be able to correctly identify defective directional microphone hearing aids at an early stage, rather than at a point when the directivity has been diminished completely or even reversed.

Prescribing maximum hearing aid output: Differences among manufacturers found

It seems that just about every month we read about some new advance in hearing aid technology. The practitioners dispensing these instruments must continually make decisions concerning what type of digital noise reduction, directional technology, or Bluetooth applications are best for their patients. Hearing aid fitting and verification also seem to be constantly changing. We now have new prescriptive methods for both the DSL and the NAL, and real speech has become a routine input signal for probe-microphone measurements. But one thing has pretty much stayed the same: selecting the appropriate maximum output for each patient. We still usually limit the output by adjusting the AGCo kneepoint, technology that has been available since the 1940s. And, if we don’t get it right, we often have an unhappy hearing aid user. That probably hasn’t changed in the last 60 years either.

AudioSense: Enabling real-time evaluation of hearing aid technology in-situ

AudioSense integrates mobile phones and web technology to measure hearing aid performance in real-time and in-situ. Measuring the performance of hearing aids in the real world poses significant challenges as it depends on the patients listening context. AudioSense uses Ecological Momentary Assessment methods to evaluate both the perceived hearing aid performance as well as to characterize the listening environment using electronic surveys. AudioSense further characterizes a patients listening context by recording their GPS location and sound samples. By creating a time-synchronized record of listening performance and listening contexts, AudioSense will allow researchers to understand the relationship between listening context and hearing aid performance. Performance evaluation shows that AudioSense is reliable, energy-efficient, and can estimate Signal-to-Noise Ratio (SNR) levels from captured audio samples.

A method to measure hearing aid directivity index and polar pattern in small and reverberant enclosures

Abstract Objective: The directivity index (DI) and polar pattern of directional hearing aids are typically measured in an anechoic chamber, which is expensive and not commonly found. This article proposes a quasi-anechoic technique to measure hearing aid directivity in small and reverberant enclosures using the root-mean-square amplitude of the first 3 ms of the hearing aids response to the input signal. Design: The hearing aids planar DI and polar pattern were measured using the proposed method in an audiologic booth with low reverberation, a room with moderate reverberation, and an anechoic chamber. The measurement was repeated four times for each aid in each environment. The results were compared to the directivity obtained in the anechoic chamber using two benchmark measurements. Study Sample: Eight hearing aids with a fixed directional mode were tested. Results and Conclusions: The results revealed that the error of the proposed method in DI was smaller than 0.3 dB in 94% of the measurement conditions. The standard deviation of the DI was smaller than 0.1 dB in 94% of the conditions. These results suggest that the proposed quasi-anechoic method provides an accurate and repeatable way to assess non-adaptive directional microphone hearing aids in small non-anechoic enclosures. Sumario Objetivo: Típicamente el índice de direccionalidad (DI) y el patrón polar de los auxiliares auditivos direccionales son medidos en una cámara anecoica, que generalmente es costosa y difícil de encontrar. Este artículo propone una técnica quasi anecoica para medir la direccionalidad en un recinto pequeño y reverberante, utilizando el promedio de la raíz cuadrada de la amplitud de los tres primeros mili-segundos de la respuesta de los auxiliares auditivos ante la señal de entrada. Diseño: El patrón plano DI y el polar de los auxiliares auditivos fueron medidos utilizando el método propuesto en una cabina audiológica con baja reverberación, en un cuarto con moderada reverberación y en una cámara anecoica. Se repitieron las mediciones cuatro veces para cada auxiliar en cada condición ambiental. Se compararon los resultados con la direccionalidad obtenida en la cámara anecoica utilizando dos mediciones de referencia. Muestra: Se evaluaron ocho auxiliares auditivos en el modo de direccionalidad fija. Resultados Y Conclusiones: Los resultados revelaron que el error del método propuesto en DI fue menor a 0.3 dB en el 94% de las condiciones medidas. La desviación estándar del DI fue menor a 0.3dB en 94% de las condiciones de medición. Estos resultados sugieren que el método quasi anecoico propuesto proporciona una forma certera y repetible para evaluar auxiliares auditivos con micrófonos no adaptativos en un recinto no anecoico