Trends in Amplification

Publications in this journal

• Article: The Master Hearing Aid.

  James R Curran, Jason A Galster
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  ABSTRACT: As early as the 1930s the term Master Hearing Aid (MHA) described a device used in the fitting of hearing aids. In their original form, the MHA was a desktop system that allowed for simulated or actual adjustment of hearing aid components that resulted in a changed hearing aid response. Over the years the MHA saw many embodiments and contributed to a number of rationales for the fitting of hearing aids. During these same years, the MHA was viewed by many as an inappropriate means of demonstrating hearing aids; the audio quality of the desktop systems was often superior to the hearing aids themselves. These opinions and the evolution of the MHA have molded the modern perception of hearing aids and the techniques used in the fitting of hearing aids. This article reports on a history of the MHA and its influence on the fitting of hearing aids.
  Trends in Amplification 05/2013;
• Article: Psychoacoustic and Phoneme Identification Measures in Cochlear-Implant and Normal-Hearing Listeners.

  Ray L Goldsworthy, Lorraine A Delhorne, Louis D Braida, Charlotte M Reed
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  ABSTRACT: The purpose of this study is to identify precise and repeatable measures for assessing cochlear-implant (CI) hearing. The study presents psychoacoustic and phoneme identification measures in CI and normal-hearing (NH) listeners, with correlations between measures examined. Psychoacoustic measures included pitch discrimination tasks using pure tones, harmonic complexes, and tone pips; intensity perception tasks included intensity discrimination for tones and modulation detection; spectral-temporal masking tasks included gap detection, forward and backward masking, tone-on-tone masking, synthetic formant-on-formant masking, and tone in noise detection. Phoneme perception measures included vowel and consonant identification in quiet and stationary and temporally gated speech-shaped noise. Results on psychoacoustic measures illustrate the effects of broader filtering in CI hearing contributing to reduced pitch perception and increased spectral masking. Results on consonant and vowel identification measures illustrate a wide range in performance across CI listeners. They also provide further evidence that CI listeners obtain little to no release of masking in temporally gated noise compared to stationary noise. The forward and backward-masking measures had the highest correlation with the phoneme identification measures for CI listeners. No significant correlations between speech reception and psychoacoustic measures were observed for NH listeners. The superior NH performance on measures of phoneme identification, especially in the presence of background noise, is a key difference between groups.
  Trends in Amplification 02/2013;
• Article: Nonlinear frequency compression: effects on sound quality ratings of speech and music.

  Vijay Parsa, Susan Scollie, Danielle Glista, Andreas Seelisch
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  ABSTRACT: Frequency lowering technologies offer an alternative amplification solution for severe to profound high frequency hearing losses. While frequency lowering technologies may improve audibility of high frequency sounds, the very nature of this processing can affect the perceived sound quality. This article reports the results from two studies that investigated the impact of a nonlinear frequency compression (NFC) algorithm on perceived sound quality. In the first study, the cutoff frequency and compression ratio parameters of the NFC algorithm were varied, and their effect on the speech quality was measured subjectively with 12 normal hearing adults, 12 normal hearing children, 13 hearing impaired adults, and 9 hearing impaired children. In the second study, 12 normal hearing and 8 hearing impaired adult listeners rated the quality of speech in quiet, speech in noise, and music after processing with a different set of NFC parameters. Results showed that the cutoff frequency parameter had more impact on sound quality ratings than the compression ratio, and that the hearing impaired adults were more tolerant to increased frequency compression than normal hearing adults. No statistically significant differences were found in the sound quality ratings of speech-in-noise and music stimuli processed through various NFC settings by hearing impaired listeners. These findings suggest that there may be an acceptable range of NFC settings for hearing impaired individuals where sound quality is not adversely affected. These results may assist an Audiologist in clinical NFC hearing aid fittings for achieving a balance between high frequency audibility and sound quality.
  Trends in Amplification 01/2013; 17(1):54-68.
• Article: Perception of pure tones and iterated rippled noise for normal hearing and cochlear implant users.

  Richard T Penninger, Wade W Chien, Patpong Jiradejvong, Emily Boeke, Courtney L Carver, Charles J Limb
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  ABSTRACT: Cochlear Implant (CI) users typically perform poorly on musical tasks, especially those based on pitch ranking and melody recognition. It was hypothesized that CI users would demonstrate deterioration in performance for a pitch ranking and a melody recognition task presented with iterated rippled noise (IRN) in comparison to pure tones (PT). In Addition, it was hypothesized that normal hearing (NH) listeners would show fewer differences in performance between IRN and PT for these two tasks. In this study, the ability of CI users and NH subjects to rank pitches and to identify melodies created with IRN and PT was assessed in free field in a sound-isolated room. CI subjects scored significantly above chance level with PT stimuli in both tasks. With IRN stimuli their performance was around chance level. NH subjects scored significantly above chance level in both tasks and with all stimuli. NH subjects performed significantly better than CI subjects in both tasks. These results illustrate the difficulties of CI subjects to rank pitches and to identify melodies.
  Trends in Amplification 01/2013; 17(1):45-53.
• Article: A systematic review of electric-acoustic stimulation: device fitting ranges, outcomes, and clinical fitting practices.

  Paola V Incerti, Teresa Y C Ching, Robert Cowan
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  ABSTRACT: Cochlear implant systems that combine electric and acoustic stimulation in the same ear are now commercially available and the number of patients using these devices is steadily increasing. In particular, electric-acoustic stimulation is an option for patients with severe, high frequency sensorineural hearing impairment. There have been a range of approaches to combining electric stimulation and acoustic hearing in the same ear. To develop a better understanding of fitting practices for devices that combine electric and acoustic stimulation, we conducted a systematic review addressing three clinical questions: what is the range of acoustic hearing in the implanted ear that can be effectively preserved for an electric-acoustic fitting?; what benefits are provided by combining acoustic stimulation with electric stimulation?; and what clinical fitting practices have been developed for devices that combine electric and acoustic stimulation? A search of the literature was conducted and 27 articles that met the strict evaluation criteria adopted for the review were identified for detailed analysis. The range of auditory thresholds in the implanted ear that can be successfully used for an electric-acoustic application is quite broad. The effectiveness of combined electric and acoustic stimulation as compared with electric stimulation alone was consistently demonstrated, highlighting the potential value of preservation and utilization of low frequency hearing in the implanted ear. However, clinical procedures for best fitting of electric-acoustic devices were varied. This clearly identified a need for further investigation of fitting procedures aimed at maximizing outcomes for recipients of electric-acoustic devices.
  Trends in Amplification 01/2013; 17(1):3-26.
• Article: NAL-NL2 Empirical Adjustments.

  Gitte Keidser, Harvey Dillon, Lyndal Carter, Anna O'Brien
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  ABSTRACT: NAL-NL1, the first procedure from the National Acoustic Laboratories (NAL) for prescribing nonlinear gain, was a purely theoretically derived formula aimed at maximizing speech intelligibility for any input level of speech while keeping the overall loudness of speech at or below normal loudness. The formula was obtained through an optimization process in which speech intelligibility and loudness were predicted from selected models. Using updated models and applying some revisions to the derivation process, a theoretically derived NAL-NL2 formula was obtained in a similar way. Further adjustments, directed by empirical data collected in studies using NAL-NL1 as the baseline response, have been made to the theoretically derived formula. Specifically, empirical data have demonstrated that (a) female hearing aid users prefer lower overall gain than male users; (b) new hearing aid users with more than a mild hearing loss prefer increasingly less gain with increasing degree of hearing loss than experienced hearing aid users, and require up to 2 years to adapt to gain levels selected by experienced hearing aid users; (c) unilaterally and bilaterally fitted hearing aid users prefer overall gain levels that vary less than estimated by the bilateral correction factor; (d) adults prefer lower overall gain than children; and (e) people with severe/profound hearing loss prefer lower compression ratios than predicted when fitted with fast-acting compression. The literature and data leading to these conclusions are summarized and discussed in this article, and the procedure for implementing the adjustments to the theoretically derived NAL-NL2 formula is described.
  Trends in Amplification 11/2012;
• Article: Observations From a Musician With Hearing Loss.

  Richard Einhorn
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  ABSTRACT: Extensive personal experience with professional recording and audio signal processing technology has enabled the author to continue his music career after experiencing sudden sensorineural hearing loss. The iPhone(™) is one such device that has been found useful for many music and general listening situations that would otherwise be intractable. Additional techniques and technologies are described that the author has found useful for specific situations, including music composition, rehearsal, and enjoyment.
  Trends in Amplification 11/2012;
• Article: Effects of Bandwidth, Compression Speed, and Gain at High Frequencies on Preferences for Amplified Music.

  Brian C J Moore
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  ABSTRACT: This article reviews a series of studies on the factors influencing sound quality preferences, mostly for jazz and classical music stimuli. The data were obtained using ratings of individual stimuli or using the method of paired comparisons. For normal-hearing participants, the highest ratings of sound quality were obtained when the reproduction bandwidth was wide (55 to 16000 Hz) and ripples in the frequency response were small (less than ± 5 dB). For hearing-impaired participants listening via a simulated five-channel compression hearing aid with gains set using the CAM2 fitting method, preferences for upper cutoff frequency varied across participants: Some preferred a 7.5- or 10-kHz upper cutoff frequency over a 5-kHz cutoff frequency, and some showed the opposite preference. Preferences for a higher upper cutoff frequency were associated with a shallow high-frequency slope of the audiogram. A subsequent study comparing the CAM2 and NAL-NL2 fitting methods, with gains slightly reduced for participants who were not experienced hearing aid users, showed a consistent preference for CAM2. Since the two methods differ mainly in the gain applied for frequencies above 4 kHz (CAM2 recommending higher gain than NAL-NL2), these results suggest that extending the upper cutoff frequency is beneficial. A system for reducing "overshoot" effects produced by compression gave small but significant benefits for sound quality of a percussion instrument (xylophone). For a high-input level (80 dB SPL), slow compression was preferred over fast compression.
  Trends in Amplification 11/2012;
• Article: Musical Sound Quality Impairments in Cochlear Implant (CI) Users as a Function of Limited High-Frequency Perception.

  Alexis T Roy, Patpong Jiradejvong, Courtney Carver, Charles J Limb
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  ABSTRACT: The purpose of this study was to (a) apply the musical sound quality assessment method, Cochlear Implant-MUltiple Stimulus with Hidden Reference and Anchor (CI-MUSHRA), to quantify musical sound quality deficits in CI (cochlear implant) users with respect to high-frequency loss, and (b) assess possible correlations between CI-MUSHRA performance and self-reported musical sound quality, as assessed by more traditional rating scales. Five versions of real-world musical stimuli were created: 8-,4-, and 2-kHz low-pass-filtered (LPF) versions with increasing high-frequency removal, a composite stimulus containing a 1-kHz LPF-filtered version and white noise ("anchor"), and an unaltered version ("hidden reference"). Using the CI-MUSHRA methodology, these versions were simultaneously presented to participants in addition to a labeled reference. Participants listened to all versions and provided ratings based on a 100-point scale that reflected perceived sound quality difference among the versions. A total of 25 musical stimuli were tested. As comparison measures, participants completed four Visual Analogue Scales (VAS) to assess musical sound quality. Overall, compared to normal hearing (NH) listeners, CI users demonstrated an impaired ability to discriminate between unaltered and altered musical stimuli with variable amounts of high-frequency information removed. Performance using CI-MUSHRA to evaluate this parameter did not correlate to measurements of musical sound quality, as assessed by VAS. This study identified high-frequency loss as one acoustic parameter contributing to overall CI-mediated musical sound quality limitations. CI-MUSHRA provided a quantitative assessment of musical sound quality. This method offers the potential to quantify CI impairments of many different acoustic parameters related to musical sound quality in the future.
  Trends in Amplification 11/2012;
• Article: Single and multiple microphone noise reduction strategies in cochlear implants.

  Kostas Kokkinakis, Behnam Azimi, Yi Hu, David R Friedland
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  ABSTRACT: To restore hearing sensation, cochlear implants deliver electrical pulses to the auditory nerve by relying on sophisticated signal processing algorithms that convert acoustic inputs to electrical stimuli. Although individuals fitted with cochlear implants perform well in quiet, in the presence of background noise, the speech intelligibility of cochlear implant listeners is more susceptible to background noise than that of normal hearing listeners. Traditionally, to increase performance in noise, single-microphone noise reduction strategies have been used. More recently, a number of approaches have suggested that speech intelligibility in noise can be improved further by making use of two or more microphones, instead. Processing strategies based on multiple microphones can better exploit the spatial diversity of speech and noise because such strategies rely mostly on spatial information about the relative position of competing sound sources. In this article, we identify and elucidate the most significant theoretical aspects that underpin single- and multi-microphone noise reduction strategies for cochlear implants. More analytically, we focus on strategies of both types that have been shown to be promising for use in current-generation implant devices. We present data from past and more recent studies, and furthermore we outline the direction that future research in the area of noise reduction for cochlear implants could follow.
  Trends in Amplification 08/2012; 16(2):102-16.
• Article: The influence of environmental sound training on the perception of spectrally degraded speech and environmental sounds.

  Valeriy Shafiro, Stanley Sheft, Brian Gygi, Kim Thien N Ho
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  ABSTRACT: Perceptual training with spectrally degraded environmental sounds results in improved environmental sound identification, with benefits shown to extend to untrained speech perception as well. The present study extended those findings to examine longer-term training effects as well as effects of mere repeated exposure to sounds over time. Participants received two pretests (1 week apart) prior to a week-long environmental sound training regimen, which was followed by two posttest sessions, separated by another week without training. Spectrally degraded stimuli, processed with a four-channel vocoder, consisted of a 160-item environmental sound test, word and sentence tests, and a battery of basic auditory abilities and cognitive tests. Results indicated significant improvements in all speech and environmental sound scores between the initial pretest and the last posttest with performance increments following both exposure and training. For environmental sounds (the stimulus class that was trained), the magnitude of positive change that accompanied training was much greater than that due to exposure alone, with improvement for untrained sounds roughly comparable to the speech benefit from exposure. Additional tests of auditory and cognitive abilities showed that speech and environmental sound performance were differentially correlated with tests of spectral and temporal-fine-structure processing, whereas working memory and executive function were correlated with speech, but not environmental sound perception. These findings indicate generalizability of environmental sound training and provide a basis for implementing environmental sound training programs for cochlear implant (CI) patients.
  Trends in Amplification 08/2012; 16(2):83-101.
• Article: Response Pattern Based on the Amplitude of Ear Canal Recorded Cochlear Microphonic Waveforms across Acoustic Frequencies in Normal Hearing Subjects.

  Ming Zhang
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  ABSTRACT: Low-frequency otoacoustic emissions (OAEs) are often concealed by acoustic background noise such as those from a patient's breathing and from the environment during recording in clinics. When using electrocochleaography (ECochG or ECoG), such as cochlear microphonics (CMs), acoustic background noise do not contaminate the recordings. Our objective is to study the response pattern of CM waveforms (CMWs) to explore an alternative approach in assessing cochlear functions. In response to a 14-msec tone burst across several acoustic frequencies, CMWs were recorded at the ear canal from ten normal hearing subjects. A relatively long tone burst has a relatively narrow frequency band. The CMW amplitudes among different frequencies were compared. The CMW amplitudes among different frequencies were compared. Two features were observed in the response pattern of CMWs: the amplitude of CMWs decreased with an increase of stimulus frequency of the tone bursts; and such a decrease occurred at a faster rate at lower frequencies than at higher frequencies. Five factors as potential mechanisms for these features are proposed. Clinical applications such as hearing screening are discussed. Therefore, the response pattern of CMWs suggests that they may be used as an alternative to OAEs in the assessment of cochlear functions in the clinic, especially at low frequencies.
  Trends in Amplification 06/2012; 16(2):117-26.
• Article: Evidence on self-fitting hearing aids.

  Lena L N Wong
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  ABSTRACT: The research on self-fitting hearing aids is reviewed using evidence-based principles. The evaluation begins with a definition of the research questions followed by a detailed search of the literature and then a review of the relevant studies. Four features of self-fitting hearing aids are reviewed: in-situ threshold measurement, whether an initial fitting prescribed using standard prescription formulae will approximate user preferences, outcomes with training of hearing aids for preferred responses, and assembly and use of the aids. There is at least good quality evidence suggesting that in-situ thresholds can be reliably obtained, that prescribed initial fittings approximate preferred responses, and that users are able to train the hearing aids and would prefer the trained responses. However, evidence on other outcomes and the ability of users to assemble and use such instruments is limited. Gaps in research with self-fitting hearing aids are identified.
  Trends in Amplification 04/2012; 15(4):215-25.
• Article: Stem cell therapy for the inner ear: recent advances and future directions.

  Takayuki Okano, Matthew W Kelley
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  ABSTRACT: In vertebrates, perception of sound, motion, and balance is mediated through mechanosensory hair cells located within the inner ear. In mammals, hair cells are only generated during a short period of embryonic development. As a result, loss of hair cells as a consequence of injury, disease, or genetic mutation, leads to permanent sensory deficits. At present, cochlear implantation is the only option for profound hearing loss. However, outcomes are still variable and even the best implant cannot provide the acuity of a biological ear. The recent emergence of stem cell technology has the potential to open new approaches for hair cell regeneration. The goal of this review is to summarize the current state of inner ear stem cell research from a viewpoint of its clinical application for inner ear disorders to illustrate how complementary studies have the potential to promote and refine stem cell therapies for inner ear diseases. The review initially discusses our current understanding of the genetic pathways that regulate hair cell formation from inner ear progenitors during normal development. Subsequent sections discuss the possible use of endogenous inner ear stem cells to induce repair as well as the initial studies aimed at transplanting stem cells into the ear.
  Trends in Amplification 04/2012; 16(1):4-18.
• Article: Consumer preferences for hearing aid attributes: a comparison of rating and conjoint analysis methods.

  John F P Bridges, Angela T Lataille, Christine Buttorff, Sharon White, John K Niparko
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  ABSTRACT: Low utilization of hearing aids has drawn increased attention to the study of consumer preferences using both simple ratings (e.g., Likert scale) and conjoint analyses, but these two approaches often produce inconsistent results. The study aims to directly compare Likert scales and conjoint analysis in identifying important attributes associated with hearing aids among those with hearing loss. Seven attributes of hearing aids were identified through qualitative research: performance in quiet settings, comfort, feedback, frequency of battery replacement, purchase price, water and sweat resistance, and performance in noisy settings. The preferences of 75 outpatients with hearing loss were measured with both a 5-point Likert scale and with 8 paired-comparison conjoint tasks (the latter being analyzed using OLS [ordinary least squares] and logistic regression). Results were compared by examining implied willingness-to-pay and Pearson's Rho. A total of 56 respondents (75%) provided complete responses. Two thirds of respondents were male, most had sensorineural hearing loss, and most were older than 50; 44% of respondents had never used a hearing aid. Both methods identified improved performance in noisy settings as the most valued attribute. Respondents were twice as likely to buy a hearing aid with better functionality in noisy environments (p < .001), and willingness to pay for this attribute ranged from US$2674 on the Likert to US$9000 in the conjoint analysis. The authors find a high level of concordance between the methods-a result that is in stark contrast with previous research. The authors conclude that their result stems from constraining the levels on the Likert scale.
  Trends in Amplification 04/2012; 16(1):40-8.
• Article: Cost-effective hearing rehabilitation: a role for self-fitting hearing aids?

  Harvey Dillon, Gitte Keidser
  Trends in Amplification 04/2012; 15(4):155-6.
• Article: Threshold measurements by self-fitting hearing aids: feasibility and challenges.

  Gitte Keidser, Harvey Dillon, Dan Zhou, Lyndal Carter
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  ABSTRACT: A self-fitting, self-contained hearing aid is a device that can be managed entirely by the user, without assistance from a hearing health care professional or the need for special equipment. A key component of such a device is an automated audiometer that will enable the user to self-administer measurements of in situ thresholds, which the hearing aid will use to prescribe a baseline setting for the wearer. The success of the device therefore depends on the validity and reliability of in situ threshold measurements and automatically measured thresholds. To produce a complete and self-contained device, the self-fitting hearing aid will also enable identification of audiograms that are contraindicative of hearing aid usage. The feasibility and challenges of achieving these characteristics are explored and discussed. While the overall concept seems feasible, several challenges were identified that need thorough investigation and/or development. These include the use of instructions to self-manage hearing aid insertion and in situ threshold measurements, selection of an appropriate transducer and instant-fit tip that will allow measurements of a wide range of threshold levels, control of ambient noise during threshold measurements, and self-manageable procedures that enable identification of such audiogram characteristics as asymmetry and conductive hearing loss.
  Trends in Amplification 03/2012; 15(4):167-74.
• Article: Assembly and insertion of a self-fitting hearing aid: design of effective instruction materials.

  Andrea Caposecco, Louise Hickson, Carly Meyer
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  ABSTRACT: A self-fitting hearing aid has been proposed as a viable option to meet the need for rehabilitation in areas where audiology services are unreliable. A successful outcome with a self-fitting hearing aid pivots in part on the clarity of the instructions accompanying the device. The aims of this article are (a) to review the literature to determine features that should be incorporated into written health-care materials and factors to consider in the design process when developing written instructions for a target audience of older adults and (b) to apply this information to the development of a set of written instructions as the first step in self-fitting of a hearing aid, assembling four parts and inserting the aid into the ear. The method involved a literature review of published peer reviewed research. The literature revealed four steps in the development of written health-care materials: planning, design, assessment of suitability, and pilot testing. Best practice design principles for each step were applied in the development of instructions for how to assemble and insert a hearing aid. Separate booklets were developed for the left and right aids and the content of each consisted of simple line drawings accompanied by captions. The reading level was Grade 3.5 equivalent and the Flesch Reading Ease Score was 91.1 indicating that the materials were "very easy" to read. It is essential to follow best practice design principles when developing written health-care materials to motivate the reader, maximize comprehension, and increase the likelihood of successful application of the content.
  Trends in Amplification 03/2012; 15(4):184-95.
• Article: Maximizing the spectral and temporal benefits of two clinically used sound processing strategies for cochlear implants.

  Jong Ho Won, Kaibao Nie, Ward R Drennan, Jay T Rubinstein
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  ABSTRACT: Previous work showed that the Fidelity120 processing strategy provides better spectral sensitivity, while the HiResolution processing strategy can deliver more detailed temporal information for Advanced Bionics cochlear implant users. The goal of this study was to develop a new sound processing strategy by maximizing the spectral benefit of Fidelity120 and the temporal benefit of HiResolution to improve both aspects of hearing. Using acoustic simulations of Fidelity120 and HiResolution strategies, a dual-processing strategy was created by combining Fidelity120 in the low frequency channels and HiResolution in the high frequency channels. Compared to Fidelity120, the dual processing provided an improvement in performance for Schroeder-phase discrimination at 200 Hz and temporal modulation detection at 200 Hz with the cost of a slightly decreased performance for spectral-ripple discrimination relative to Fidelity120. Spectral-ripple discrimination was better with the dual processing than with HiResolution. However, no benefit for speech perception in noise was found for the dual-processing strategy over Fidelity 120 or HiResolution in our preliminary tests. Some other more optimal combination of Fidelity120 and HiResolution may be required to maximize the spectral and temporal benefits to yield improved speech perception.
  Trends in Amplification 01/2012; 16(4):201-10.