Abnormal pitch perception produced by cochlear implant stimulation

The Photon-Counting CT Enters the Field of Cochlear Implantation: Comparison to Angiography DynaCT and Conventional Multislice CT

INTRODUCTION

Cochlear duct length (CDL) measurement plays a role in the context of individualized cochlear implant (CI) surgery regarding an individualized selection and implantation of the CI electrode carrier and an efficient postoperative anatomy-based fitting process. The level of detail of the preoperative temporal bone CT scan depends on the imaging modality with major impact on CDL measurements and CI electrode contact position determination. The aim of this study was to evaluate the accuracy of perioperative CDL measurements and electrode contact determination in photon-counting CT (PCCT).

METHODS

Ten human fresh-frozen petrous bone specimens were examined with a first-generation PCCT. A clinically applicable radiation dose of 27.1 mGy was used. Scans were acquired before and after CI insertion. Postoperative measurement of the CDL was conducted using an otological planning software and 3D-curved multiplanar reconstruction. Investigation of electrode contact position was performed by two respective observers. Measurements were compared with a conventional multislice CT and to a high-resolution flat-panel volume CT with secondary reconstructions.

RESULTS

Pre- and postoperative CDL measurements in PCCT images showed no significant difference to high-resolution flat-panel volume CT. Postoperative CI electrode contact determination was also as precise as the flat-panel CT-based assessment. PCCT and flat-panel volume CT were equivalent concerning interobserver variability.

CONCLUSION

CDL measurement with PCCT was equivalent to flat-panel volume CT with secondary reconstructions. PCCT enabled highly precise postoperative CI electrode contact determination with substantial advantages over conventional multislice CT scanners.

Differences in music appreciation between bilateral and single-sided cochlear implant recipients

OBJECTIVE

To compare changes in music appreciation after cochlear implant (CI) surgery for patients with bilateral and single-sided deafness (SSD).

METHODS

A retrospective cohort study was performed on all adult CI unilateral or bilateral recipients from November 2019 to March 2023. Musical questionnaire subset data from the Cochlear Implant Quality of Life (CIQOL) - 35 Profile Instrument Score (maximum raw score of 15) was collected. Functional CI assessment was measured with CI-alone speech-in-quiet (SIQ) scores (AzBio and CNC).

RESULTS

22 adults underwent CI surgery for SSD and 21 adults for bilateral deafness (8 sequentially implanted). Every patient group had clinically significant improvements (p < 0.001) in mean SIQ scores in the most recently implanted ear (Azbio (% correct) SSD: 14.23 to 68.48, bilateral: 24.54 to 82.23, sequential: 6.25 to 82.57). SSD adults on average had higher music QOL scores at baseline (SSD: 11.05; bilateral: 7.86, p < 0.001). No group had significant increases in raw score at the first post-operative visit (SSD: 11.45, p = 0.86; bilateral: 8.15, p = 0.15). By the most recent post-implantation evaluation (median 12.8 months for SSD, 12.3 months for bilateral), SSD adults had a significant increase in raw score from baseline (11.05 to 12.45, p = 0.03), whereas bilaterally deafened (7.86 to 9.38, p = 0.12) adults had nonsignificant increases.

CONCLUSIONS

SSD patients demonstrate higher baseline music appreciation than bilaterally deafened individuals regardless of unilateral or bilateral implantation and are more likely to demonstrate continued improvement in subjective music appreciation at last follow-up even when speech perception outcomes are similar.

Development of a feline model for preclinical research of a new translabyrinthine auditory nerve implant

Cochlear implants are among the most successful neural prosthetic devices to date but exhibit poor frequency selectivity and the inability to consistently activate apical (low frequency) spiral ganglion neurons. These issues can limit hearing performance in many cochlear implant patients, especially for understanding speech in noisy environments and in perceiving or appreciating more complex inputs such as music and multiple talkers. For cochlear implants, electrical current must pass through the bony wall of the cochlea, leading to widespread activation of auditory nerve fibers. Cochlear implants also cannot be implanted in some individuals with an obstruction or severe malformations of the cochlea. Alternatively, intraneural stimulation delivered via an auditory nerve implant could provide direct contact with neural fibers and thus reduce unwanted current spread. More confined current during stimulation can increase selectivity of frequency fiber activation. Furthermore, devices such as the Utah Slanted Electrode Array can provide access to the full cross section of the auditory nerve, including low frequency fibers that are difficult to reach using a cochlear implant. However, further scientific and preclinical research of these Utah Slanted Electrode Array devices is limited by the lack of a chronic large animal model for the auditory nerve implant, especially one that leverages an appropriate surgical approach relevant for human translation. This paper presents a newly developed transbullar translabyrinthine surgical approach for implanting the auditory nerve implant into the cat auditory nerve. In our first of a series of studies, we demonstrate a surgical approach in non-recovery experiments that enables implantation of the auditory nerve implant into the auditory nerve, without damaging the device and enabling effective activation of the auditory nerve fibers, as measured by electrode impedances and electrically evoked auditory brainstem responses. These positive results motivate performing future chronic cat studies to assess the long-term stability and function of these auditory nerve implant devices, as well as development of novel stimulation strategies that can be translated to human patients.

Anodic Polarity Minimizes Facial Nerve Stimulation as a Side Effect of Cochlear Implantation

One severe side effect of the use of cochlear implants (CI) is coincidental facial nerve stimulation (FNS). Clinical methods to alleviate FNS range from the reprogramming of processor settings to revision surgery. We systematically assessed different changes in CI stimulation modes that have been discussed in the literature as "rescue factors" from FNS: electrode configuration (broad to focused), pulse shape (symmetric biphasic to pseudo-monophasic), and pulse polarity (cathodic to anodic). An FNS was assessed, based on electrophysiological thresholds, in 204 electrically evoked compound action potential (eCAP) input/output functions recorded from 33 ears of 26 guinea pigs. The stimulation level difference between auditory nerve eCAP threshold and FNS threshold was expressed as the eCAP-to-FNS offset. Coincidental FNS occurred in all animals and in 45% of all recordings. A change from monopolar to focused (bipolar, tripolar) configurations minimized FNS. The Euclidean distance between the CI contacts and the facial nerve explained no more than 33% of the variance in FNS thresholds. For both the FNS threshold and the eCAP-to-FNS offset, the change from cathodic to anodic pulse polarity significantly reduced FNS and permitted a gain of 14-71% of the dynamic range of the eCAP response. This "anodic rescue effect" was stronger for pseudo-monophasic pulses as compared to the symmetric biphasic pulse shape. These results provide possible mechanisms underlying recent clinical interventions to alleviate FNS. The "anodic-rescue effect" may offer a non-invasive therapeutic option for FNS in human CI users that should be tested clinically, preferably in combination with current-focusing methods.

Computer-based musical interval training program for Cochlear implant users and listeners with no known hearing loss

A musical interval is the difference in pitch between two sounds. The way that musical intervals are used in melodies relative to the tonal center of a key can strongly affect the emotion conveyed by the melody. The present study examines musical interval identification in people with no known hearing loss and in cochlear implant users. Pitch resolution varies widely among cochlear implant users with average resolution an order of magnitude worse than in normal hearing. The present study considers the effect of training on musical interval identification and tests for correlations between low-level psychophysics and higher-level musical abilities. The overarching hypothesis is that cochlear implant users are limited in their ability to identify musical intervals both by low-level access to frequency cues for pitch as well as higher-level mapping of the novel encoding of pitch that implants provide. Participants completed a 2-week, online interval identification training. The benchmark tests considered before and after interval identification training were pure tone detection thresholds, pure tone frequency discrimination, fundamental frequency discrimination, tonal and rhythm comparisons, and interval identification. The results indicate strong correlations between measures of pitch resolution with interval identification; however, only a small effect of training on interval identification was observed for the cochlear implant users. Discussion focuses on improving access to pitch cues for cochlear implant users and on improving auditory training for musical intervals.

Celebrating the one millionth cochlear implant

Cochlear implants have been the most successful neural prosthesis, with one million users globally. Researchers used the source-filter model and speech vocoder to design the modern multi-channel implants, allowing implantees to achieve 70%-80% correct sentence recognition in quiet, on average. Researchers also used the cochlear implant to help understand basic mechanisms underlying loudness, pitch, and cortical plasticity. While front-end processing advances improved speech recognition in noise, the unilateral implant speech recognition in quiet has plateaued since the early 1990s. This lack of progress calls for action on re-designing the cochlear stimulating interface and collaboration with the general neurotechnology community.

Human discrimination and modeling of high-frequency complex tones shed light on the neural codes for pitch

Accurate pitch perception of harmonic complex tones is widely believed to rely on temporal fine structure information conveyed by the precise phase-locked responses of auditory-nerve fibers. However, accurate pitch perception remains possible even when spectrally resolved harmonics are presented at frequencies beyond the putative limits of neural phase locking, and it is unclear whether residual temporal information, or a coarser rate-place code, underlies this ability. We addressed this question by measuring human pitch discrimination at low and high frequencies for harmonic complex tones, presented either in isolation or in the presence of concurrent complex-tone maskers. We found that concurrent complex-tone maskers impaired performance at both low and high frequencies, although the impairment introduced by adding maskers at high frequencies relative to low frequencies differed between the tested masker types. We then combined simulated auditory-nerve responses to our stimuli with ideal-observer analysis to quantify the extent to which performance was limited by peripheral factors. We found that the worsening of both frequency discrimination and F0 discrimination at high frequencies could be well accounted for (in relative terms) by optimal decoding of all available information at the level of the auditory nerve. A Python package is provided to reproduce these results, and to simulate responses to acoustic stimuli from the three previously published models of the human auditory nerve used in our analyses.

Language development in infants with hearing loss: Benefits of infant-directed speech

The majority of infants with permanent congenital hearing loss fall significantly behind their normal hearing peers in the development of receptive and expressive oral communication skills. Independent of any prosthetic intervention ("hardware") for infants with hearing loss, the social and linguistic environment ("software") can still be optimal or sub-optimal and so can exert significant positive or negative effects on speech and language acquisition, with far-reaching beneficial or adverse effects, respectively. This review focusses on the nature of the social and linguistic environment of infants with hearing loss, in particular others' speech to infants. The nature of this "infant-directed speech" and its effects on language development has been studied extensively in hearing infants but far less comprehensively in infants with hearing loss. Here, literature on the nature of infant-directed speech and its impact on the speech perception and language acquisition in infants with hearing loss is reviewed. The review brings together evidence on the little-studied effects of infant-directed speech on speech and language development in infants with hearing loss, and provides suggestions, over and above early screening and external treatment, for a natural intervention at the level of the carer-infant microcosm that may well optimize the early linguistic experiences and mitigate later adverse effects for infants born with hearing loss.

Estimating the reduced benefit of infant-directed speech in cochlear implant-related speech processing

Caregivers modify their speech when talking to infants, a specific type of speech known as infant-directed speech (IDS). This speaking style facilitates language learning compared to adult-directed speech (ADS) in infants with normal hearing (NH). While infants with NH and those with cochlear implants (CIs) prefer listening to IDS over ADS, it is yet unknown how CI processing may affect the acoustic distinctiveness between ADS and IDS, as well as the degree of intelligibility of these. This study analyzed speech of seven female adult talkers to model the effects of simulated CI processing on (1) acoustic distinctiveness between ADS and IDS, (2) estimates of intelligibility of caregivers' speech in ADS and IDS, and (3) individual differences in caregivers' ADS-to-IDS modification and estimated speech intelligibility. Results suggest that CI processing is substantially detrimental to the acoustic distinctiveness between ADS and IDS, as well as to the intelligibility benefit derived from ADS-to-IDS modifications. Moreover, the observed variability across individual talkers in acoustic implementation of ADS-to-IDS modification and the estimated speech intelligibility was significantly reduced due to CI processing. The findings are discussed in the context of the link between IDS and language learning in infants with CIs.

Benefits of Cochlear Implantation in Childhood Unilateral Hearing Loss (CUHL Trial)

Objectives/Hypotheses

Children with unilateral sensory hearing loss (UHL) struggle to understand speech in noise and locate the origin of sound and have reduced quality of hearing. This clinical trial will determine the benefits of cochlear implantation in children with UHL.

Study Design

Prospective clinical trial.

Methods

Twenty children with at least moderate to profound sensory hearing loss and poor speech perception (word score <30%) in one ear and normal hearing in the contralateral ear participated in a Food and Drug Administration‐approved clinical trial. Subjects were evaluated for speech perception in quiet, speech perception in noise, sound localization, and subjective benefits after implantation.

Results

CNC word score perception in quiet significantly improved (1% to 50%, P < .0001) by 12 months after activation. Speech perception in noise by BKB‐SIN significantly improved in all three noise configurations; there was a 3.6 dB advantage in head shadow (P < .0001), a 1.6 dB advantage in summation (P = .003), and a 2.5 dB advantage in squelch (P = .0001). Localization improved by 26° at 9 months (P < .0001). Speech, Spatial, and Qualities (SSQ) demonstrated significant improvements in speech (5.2 to 7.4, P = .0012), qualities of hearing (5.9 to 7.5, P = .0056), and spatial hearing (2.7 to 6.6, P < .0001). SSQ subscales associated with binaural hearing were significantly improved, as was listening effort (P = .0082). Subjects demonstrated a non‐significant improvement in fatigue.

Conclusions

This study demonstrates that children with UHL significantly benefit from cochlear implantation.

Level of Evidence

Level 3 Laryngoscope, 132:S1–S18, 2022

Can Haptic Stimulation Enhance Music Perception in Hearing-Impaired Listeners?

Cochlear implants (CIs) have been remarkably successful at restoring hearing in severely-to-profoundly hearing-impaired individuals. However, users often struggle to deconstruct complex auditory scenes with multiple simultaneous sounds, which can result in reduced music enjoyment and impaired speech understanding in background noise. Hearing aid users often have similar issues, though these are typically less acute. Several recent studies have shown that haptic stimulation can enhance CI listening by giving access to sound features that are poorly transmitted through the electrical CI signal. This “electro-haptic stimulation” improves melody recognition and pitch discrimination, as well as speech-in-noise performance and sound localization. The success of this approach suggests it could also enhance auditory perception in hearing-aid users and other hearing-impaired listeners. This review focuses on the use of haptic stimulation to enhance music perception in hearing-impaired listeners. Music is prevalent throughout everyday life, being critical to media such as film and video games, and often being central to events such as weddings and funerals. It represents the biggest challenge for signal processing, as it is typically an extremely complex acoustic signal, containing multiple simultaneous harmonic and inharmonic sounds. Signal-processing approaches developed for enhancing music perception could therefore have significant utility for other key issues faced by hearing-impaired listeners, such as understanding speech in noisy environments. This review first discusses the limits of music perception in hearing-impaired listeners and the limits of the tactile system. It then discusses the evidence around integration of audio and haptic stimulation in the brain. Next, the features, suitability, and success of current haptic devices for enhancing music perception are reviewed, as well as the signal-processing approaches that could be deployed in future haptic devices. Finally, the cutting-edge technologies that could be exploited for enhancing music perception with haptics are discussed. These include the latest micro motor and driver technology, low-power wireless technology, machine learning, big data, and cloud computing. New approaches for enhancing music perception in hearing-impaired listeners could substantially improve quality of life. Furthermore, effective haptic techniques for providing complex sound information could offer a non-invasive, affordable means for enhancing listening more broadly in hearing-impaired individuals.

An Approach for Individualized Cochlear Frequency Mapping Determined from 3D Synchrotron Radiation Phase-Contrast Imaging

OBJECTIVE

Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation.

METHODS

Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea.

RESULTS

The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach.

CONCLUSION AND SIGNIFICANCE

This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.

Music Perception and Speech-in-Noise Skills of Typical Hearing and Cochlear Implant Listeners

Purpose Adult cochlear implant (CI) users rate music as one of the most important auditory stimuli, second to speech perception. However, few studies simultaneously examine music perception and speech-in-noise perception in adult CI recipients. This study explores the effect of auditory status on music perception and speech-in-noise perception recognition in noise as well as the relationship among music engagement, music perception, and speech-in-noise perception. Method Participants include 10 adults with typical hearing (TH) and 10 adults with long-term CI use. All participants completed the Music-Related Quality of Life Questionnaire, which assesses subjective music experiences and their importance; the Pitch Direction Discrimination, Familiar Melody Recognition, and Timbre Recognition subtests of the Clinical Assessment of Music Perception for Cochlear Implants; the Unfamiliar Melody Recognition subtest of the Profile of Music Perception Skills; and the Bamford-Kowal-Bench Speech-in-Noise Test. Results The TH group significantly outperformed the CI group for speech-in-noise perception and on all four music perception tasks. The CI group exhibited not only significantly poorer mean scores but also greater variability in performance compared to the TH group. Only Familiar Melody Recognition and Unfamiliar Melody Recognition subtests significantly correlated with speech-in-noise scores. Conclusions Patients and professionals should not assume speech perception and music perception in adult CI users derive from the same auditory or cognitive foundations. The lack of significant relationships among music engagement, music perception, and speech-in-noise perception scores in adult CI users suggests this population enjoys music despite poor and variable performance in discrete music tasks.

Acoustic features of infant-directed speech to infants with hearing loss

This study investigated the effects of hearing loss and hearing experience on the acoustic features of infant-directed speech (IDS) to infants with hearing loss (HL) compared to controls with normal hearing (NH) matched by either chronological or hearing age (experiment 1) and across development in infants with hearing loss as well as the relation between IDS features and infants' developing lexical abilities (experiment 2). Both experiments included detailed acoustic analyses of mothers' productions of the three corner vowels /a, i, u/ and utterance-level pitch in IDS and in adult-directed speech. Experiment 1 demonstrated that IDS to infants with HL was acoustically more variable than IDS to hearing-age matched infants with NH. Experiment 2 yielded no changes in IDS features over development; however, the results did show a positive relationship between formant distances in mothers' speech and infants' concurrent receptive vocabulary size, as well as between vowel hyperarticulation and infants' expressive vocabulary. These findings suggest that despite infants' HL and thus diminished access to speech input, infants with HL are exposed to IDS with generally similar acoustic qualities as are infants with NH. However, some differences persist, indicating that infants with HL might receive less intelligible speech.

Cortical processing of location and frequency changes of sounds in normal hearing listeners

Sounds we hear in our daily life contain changes in the acoustic features (e.g., frequency, intensity, and duration or "what" information) and/or changes in location ("where" information). The purpose of this study was to examine the cortical auditory evoked potentials (CAEPs) to the change within a stimulus, the acoustic change complex (ACC), in frequency (F) and location (L) of the sound in normal hearing listeners. Fifteen right-handed young normal hearing listeners participated in the electroencephalographic (EEG) recordings. The acoustic stimuli were pure tones (base frequency at 250 Hz) of 1 s, with a perceivable change either in location (L, 180°), frequency (F, 5% and 50%), or both location and frequency (L+F) in the middle of the tone. Additionally, the 250 Hz tone of 1 sec without any change was used as a reference. The participants were asked to listen passively to the stimuli and not to move their heads during the testing. Compared to the reference tone, by which only the onset-CAEP was elicited, the tones containing changes (L, F, or L+F) elicited both onset-CAEP and the ACC. The waveform analysis of ACCs from the vertex electrode (electrode Cz) showed that, larger sound changes evoked larger peak amplitudes [e.g., (L+50%F)- > L-change; (L+50%F)- > 5%F-change] and shorter the peak latencies ([(L+5%F)- < 5%F-change; 50%F- < 5%F-change; (L+50%F)- < 5%F-change] . The current density patterns for the ACC N1' peak displayed some differences between L-change vs. F-change, supporting different cortical processing for "where" and "what" information of the sound; regardless of the nature of the sound change, larger changes evoked a stronger activation than smaller changes [e.g., L- > 5%F-change; (L+5%F)- > 5%F-change; 50%F- > 5%F-change] in frontal lobe regions including the cingulate gyrus, medial frontal gyrus (MFG), superior frontal gyrus (SFG), the limbic lobe cingulate gyrus, and the parietal lobe postcentral gyrus. The results suggested that sound change-detection involves memory-based acoustic comparison (the neural encoding for the sound change vs. neural encoding for the pre-change stimulus stored in memory) and involuntary attention switch.

Individual Differences in Mothers' Spontaneous Infant-Directed Speech Predict Language Attainment in Children With Cochlear Implants

Purpose Differences across language environments of prelingually deaf children who receive cochlear implants (CIs) may affect language acquisition; yet, whether mothers show individual differences in how they modify infant-directed (ID) compared with adult-directed (AD) speech has seldom been studied. This study assessed individual differences in how mothers realized speech modifications in ID register and whether these predicted differences in language outcomes for children with CIs. Method Participants were 36 dyads of mothers and their children aged 0;8-2;5 (years;months) at the time of CI implantation. Mothers' spontaneous speech was recorded in a lab setting in ID or AD conditions before ~15 months postimplantation. Mothers' speech samples were characterized for acoustic-phonetic and lexical properties established as canonical indices of ID speech to typically hearing infants, such as vowel space area differences, fundamental frequency variability, and speech rate. Children with CIs completed longitudinal administrations of one or more standardized language assessment instruments at variable intervals from 6 months to 9.5 years postimplantation. Standardized scores on assessments administered longitudinally were used to calculate linear regressions, which gave rise to predicted language scores for children at 2 years postimplantation and language growth over 2-year intervals. Results Mothers showed individual differences in how they modified speech in ID versus AD registers. Crucially, these individual differences significantly predicted differences in estimated language outcomes at 2 years postimplantation in children with CIs. Maternal speech variation in lexical quantity and vowel space area differences across ID and AD registers most frequently predicted estimates of language attainment in children with CIs, whereas prosodic differences played a minor role. Conclusion Results support that caregiver language behaviors play a substantial role in explaining variability in language attainment in children receiving CIs. Supplemental Material https://doi.org/10.23641/asha.12560147.

Enhanced Pitch Discrimination for Cochlear Implant Users with a New Haptic Neuroprosthetic

The cochlear implant (CI) is the most widely used neuroprosthesis, recovering hearing for more than half a million severely-to-profoundly hearing-impaired people. However, CIs still have significant limitations, with users having severely impaired pitch perception. Pitch is critical to speech understanding (particularly in noise), to separating different sounds in complex acoustic environments, and to music enjoyment. In recent decades, researchers have attempted to overcome shortcomings in CIs by improving implant technology and surgical techniques, but with limited success. In the current study, we take a new approach of providing missing pitch information through haptic stimulation on the forearm, using our new mosaicOne_B device. The mosaicOne_B extracts pitch information in real-time and presents it via 12 motors that are arranged in ascending pitch along the forearm, with each motor representing a different pitch. In normal-hearing subjects listening to CI simulated audio, we showed that participants were able to discriminate pitch differences at a similar performance level to that achieved by normal-hearing listeners. Furthermore, the device was shown to be highly robust to background noise. This enhanced pitch discrimination has the potential to significantly improve music perception, speech recognition, and speech prosody perception in CI users.

Device profile of the MED-EL cochlear implant system for hearing loss: overview of its safety and efficacy

INTRODUCTION

Patients suffering from severe to profound hearing loss or even deafness can achieve a hearing improvement with a cochlear implant (CI) treatment that is significantly higher than the results achieved with conventional hearing aids. The CI system consists of an implantable stimulator, which is inserted retro-auricularly into the mastoid, and an externally worn processor unit, which provides the pickup of sound and processing of acoustic information as well as the power supply for the stimulator and internal current sources. The stimulator has an electrode array that is inserted into the cochlea.

AREAS COVERED

This is a descriptive overview of MED-EL's multichannel CI system (MED-EL, Innsbruck, Austria), which was introduced to the European market in 1994. The continuing development of the implant as well as the external components is outlined and various other aspects (stimulation strategy, adaptation, results, reliability) are discussed.

EXPERT COMMENTARY

The strength of the company is the continuous pursuit of innovative ideas. This is evidenced by numerous innovations. The reliability of the implants has been continuously improved. The current SYNCHRONY models of the manufacturer show no indication of technically caused failures over an observation period of 5 years.

Music and psychoacoustic perception abilities in cochlear implant users with auditory neuropathy spectrum disorder

OBJECTIVE

Auditory neuropathy spectrum disorder (ANSD) is a condition wherein the pre-neural or cochlear outer hair cell activity is intact, but the neural activity in the auditory nerve is disrupted. Cochlear implant (CI) can be beneficial for subjects with ANSD; however, little is known about the music perception and psychoacoustic abilities of CI users with ANSD. Music perception in CI users is a multidimensional and complex ability requiring the contribution of both auditory and nonauditory abilities. Even though auditory abilities lay the foundation, the contribution of patient-related variables such as ANSD may affect the music perception. This study aimed to evaluate the psychoacoustic and music perception abilities of CI recipients with ANSD.

STUDY DESIGN

Twelve CI users with ANSD and twelve age- and gendermatched CI users with sensorineural hearing loss (SNHL) were evaluated. Music perception abilities were measured using the Turkish version of the Clinical Assessment of Music Perception (T-CAMP) test. Psychoacoustic abilities were measured using the spectral ripple discrimination (SRD) and temporal modulation transfer function (TMTF) tests. In addition, the age of diagnosis and implantation was recorded.

RESULTS

Pitch direction discrimination (PDD), timbre recognition, SRD, and TMTF performance of CI users with ANSD were concordant with those reported in previous studies, and differences between ANSD and SNHL groups were not statistically significant. However, the ANSD group performed poorly compared with SNHL group in melody recognition subtest of T-CAMP, and the difference was statistically significant.

CONCLUSION

CI can prove beneficial for patients with ANSD with respect to their music and psychoacoustic abilities, similar to patients with SNHL, except for melody recognition. Recognition of melodies requires both auditory and non-auditory abilities, and ANSD may have an extensive but subtle effect in the life of CI users.

The Perception of Multiple Simultaneous Pitches as a Function of Number of Spectral Channels and Spectral Spread in a Noise-Excited Envelope Vocoder

Cochlear implant (CI) listeners typically perform poorly on tasks involving the pitch of complex tones. This limitation in performance is thought to be mainly due to the restricted number of active channels and the broad current spread that leads to channel interactions and subsequent loss of precise spectral information, with temporal information limited primarily to temporal-envelope cues. Little is known about the degree of spectral resolution required to perceive combinations of multiple pitches, or a single pitch in the presence of other interfering tones in the same spectral region. This study used noise-excited envelope vocoders that simulate the limited resolution of CIs to explore the perception of multiple pitches presented simultaneously. The results show that the resolution required for perceiving multiple complex pitches is comparable to that found in a previous study using single complex tones. Although relatively high performance can be achieved with 48 channels, performance remained near chance when even limited spectral spread (with filter slopes as steep as 144 dB/octave) was introduced to the simulations. Overall, these tight constraints suggest that current CI technology will not be able to convey the pitches of combinations of spectrally overlapping complex tones.

The CI MuMuFe - A New MMN Paradigm for Measuring Music Discrimination in Electric Hearing

Cochlear implants (CIs) allow good perception of speech while music listening is unsatisfactory, leading to reduced music enjoyment. Hence, a number of ongoing efforts aim to improve music perception with a CI. Regardless of the nature of these efforts, effect measurements must be valid and reliable. While auditory skills are typically examined by behavioral methods, recording of the mismatch negativity (MMN) response, using electroencephalography (EEG), has recently been applied successfully as a supplementary objective measure. Eleven adult CI users and 14 normally hearing (NH) controls took part in the present study. To measure their detailed discrimination of fundamental features of music we applied a new multifeature MMN-paradigm which presented four music deviants at four levels of magnitude, incorporating a novel "no-standard" approach to be tested with CI users for the first time. A supplementary test measured behavioral discrimination of the same deviants and levels. The MMN-paradigm elicited significant MMN responses to all levels of deviants in both groups. Furthermore, the CI-users' MMN amplitudes and latencies were not significantly different from those of NH controls. Both groups showed MMN strength that was in overall alignment with the deviation magnitude. In CI users, however, discrimination of pitch levels remained undifferentiated. On average, CI users' behavioral performance was significantly below that of the NH group, mainly due to poor pitch discrimination. Although no significant effects were found, CI users' behavioral results tended to be in accordance with deviation magnitude, most prominently manifested in discrimination of the rhythm deviant. In summary, the study indicates that CI users may be able to discriminate subtle changes in basic musical features both in terms of automatic neural responses and of attended behavioral detection. Despite high complexity, the new CI MuMuFe paradigm and the "no-standard" approach provided reliable results, suggesting that it may serve as a relevant tool in future CI research. For clinical use, future studies should investigate the possibility of applying the paradigm with the purpose of assessing discrimination skills not only at the group level but also at the individual level.

Approximations to the Voice of a Cochlear Implant: Explorations With Single-Sided Deaf Listeners

Fourteen single-sided deaf listeners fit with an MED-EL cochlear implant (CI) judged the similarity of clean signals presented to their CI and modified signals presented to their normal-hearing ear. The signals to the normal-hearing ear were created by (a) filtering, (b) spectral smearing, (c) changing overall fundamental frequency (F0), (d) F0 contour flattening, (e) changing formant frequencies, (f) altering resonances and ring times to create a metallic sound quality, (g) using a noise vocoder, or (h) using a sine vocoder. The operations could be used singly or in any combination. On a scale of 1 to 10 where 10 was a complete match to the sound of the CI, the mean match score was 8.8. Over half of the matches were 9.0 or higher. The most common alterations to a clean signal were band-pass or low-pass filtering, spectral peak smearing, and F0 contour flattening. On average, 3.4 operations were used to create a match. Upshifts in formant frequencies were implemented most often for electrode insertion angles less than approximately 500°. A relatively small set of operations can produce signals that approximate the sound of the MED-EL CI. There are large individual differences in the combination of operations needed. The sound files in Supplemental Material approximate the sound of the MED-EL CI for patients fit with 28-mm electrode arrays.

Development and Clinical Introduction of the Nurotron Cochlear Implant Electrode Array

As the only medical device used in the treatment for deafness, the cochlear implant has benefited to more than half a million individuals worldwide. However, the device has limited penetration due to its high cost, especially in low- and middle-income countries. China alone has 27.8 million deaf people, but less than 100,000 of them have received a cochlear implant. The Nurotron Venus device was developed to address the need for an affordable yet safe and effective cochlear implant. The present study describes the design, development, and evaluation of the Nurotron intracochlear electrode array. The standard array is 22 mm in length from the round window marker to the apical tip of the carrier and has 24 electrodes, with a surface area of 0.32 mm2 and center-to-center spacing of 0.85 mm. The Nurotron array has been tested to meet the mechanical, chemical, and electrical requirements specified by the ISO Standard 14708-07. Human temporal bone and clinical trial results showed that the Nurotron array is easy to insert (7.8/10 rating with 10 indicating the highest ease of use) and has a low complication rate (12.5%) of severe insertion trauma while achieving high device stability and reliability (6 array failures in 43,000 patient years of experience). As a critical component, the Nurotron array has contributed to the high level of Nurotron implant speech performance, equivalent to that produced by other existing devices. The Nurotron device has benefited 10,000 deaf people and helped reduce the unit cost from US$25,000 in 2011 to US$4,620 in 2017 through the Chinese Government Tender Program. New, slim, and micromachined electrodes are being developed to further improve performance and accessibility.

Frequency change detection and speech perception in cochlear implant users

Dynamic frequency changes in sound provide critical cues for speech perception. Most previous studies examining frequency discrimination in cochlear implant (CI) users have employed behavioral tasks in which target and reference tones (differing in frequency) are presented statically in separate time intervals. Participants are required to identify the target frequency by comparing stimuli across these time intervals. However, perceiving dynamic frequency changes in speech requires detection of within-interval frequency change. This study explored the relationship between detection of within-interval frequency changes and speech perception performance of CI users. Frequency change detection thresholds (FCDTs) were measured in 20 adult CI users using a 3-alternative forced-choice (3AFC) procedure. Stimuli were 1-sec pure tones (base frequencies at 0.25, 1, 4 kHz) with frequency changes occurring 0.5 s after the tone onset. Speech tests were 1) Consonant-Nucleus-Consonant (CNC) monosyllabic word recognition, 2) Arizona Biomedical Sentence Recognition (AzBio) in Quiet, 3) AzBio in Noise (AzBio-N, +10 dB signal-to-noise/SNR ratio), and 4) Digits-in-noise (DIN). Participants' subjective satisfaction with the CI was obtained. Results showed that correlations between FCDTs and speech perception were all statistically significant. The satisfaction level of CI use was not related to FCDTs, after controlling for major demographic factors. DIN speech reception thresholds were significantly correlated to AzBio-N scores. The current findings suggest that the ability to detect within-interval frequency changes may play an important role in speech perception performance of CI users. FCDT and DIN can serve as simple and rapid tests that require no or minimal linguistic background for the prediction of CI speech outcomes.

A Cross-Sectional Questionnaire Study of Tinnitus Awareness and Impact in a Population of Adult Cochlear Implant Users

Supplemental Digital Content is available in the text.

Objectives:

The primary aim was to identify the proportion of individuals within the adult cochlear implant population who are aware of tinnitus and those who report a negative impact from this perception, using a bespoke questionnaire designed to limit bias. A secondary aim was to use qualitative analysis of open-text responses to identify themes linked to tinnitus perception in this population.

Design:

A cross-sectional questionnaire study of a large clinical population who received an implant from Cambridge University Hospitals, United Kingdom.

Results:

Seventy-five percent of respondents reported tinnitus awareness. When impact scores for six areas of difficulty were ranked, 13% of individuals ranked tinnitus their primary concern and nearly a third ranked tinnitus in the top two positions. Tinnitus impact was not found to reduce with duration since implantation. The most common open-text responses were linked to a general improvement postimplantation and acute tinnitus alleviation specific to times when the device was in use.

Conclusions:

Tinnitus is a problem for a significant proportion of individuals with a cochlear implant. Clinicians, scientists, and cochlear implant manufacturers should be aware that management of tinnitus may be a greater priority for an implantee than difficulties linked to speech perception. Where a positive effect of implantation was reported, there was greater evidence for masking of tinnitus via the implant rather than reversal of maladaptive plasticity.

Interaural Time-Difference Discrimination as a Measure of Place of Stimulation for Cochlear-Implant Users With Single-Sided Deafness

Current clinical practice in programming a cochlear implant (CI) for individuals with single-sided deafness (SSD) is to maximize the transmission of speech information via the implant, with the implicit assumption that this will also result in improved spatial-hearing abilities. However, binaural sensitivity is reduced by interaural place-of-stimulation mismatch, a likely occurrence with a standard CI frequency-to-electrode allocation table (FAT). As a step toward reducing interaural mismatch, this study investigated whether a test of interaural-time-difference (ITD) discrimination could be used to estimate the acoustic frequency yielding the best place match for a given CI electrode. ITD-discrimination performance was measured by presenting 300-ms bursts of 100-pulses-per-second electrical pulse trains to a single CI electrode and band-limited pulse trains with variable carrier frequencies to the acoustic ear. Listeners discriminated between two reference intervals (four bursts each with constant ITD) and a moving target interval (four bursts with variable ITD). For 17 out of the 26 electrodes tested across eight listeners, the function describing the relationship between ITD-discrimination performance and carrier frequency had a discernable peak where listeners achieved 70% to 100% performance. On average, this peak occurred 1.15 octaves above the CI manufacturer’s default FAT. ITD discrimination shows promise as a method of estimating the cochlear place of stimulation for a given electrode, thereby providing information to optimize the FAT for SSD-CI listeners.

Cortical Processing of Frequency Changes Reflected by the Acoustic Change Complex in Adult Cochlear Implant Users

The purpose of this study was to examine neural substrates of frequency change detection in cochlear implant (CI) recipients using the acoustic change complex (ACC), a type of cortical auditory evoked potential elicited by acoustic changes in an ongoing stimulus. A psychoacoustic test and electroencephalographic recording were administered in 12 postlingually deafened adult CI users. The stimuli were pure tones containing different magnitudes of upward frequency changes. Results showed that the frequency change detection threshold (FCDT) was 3.79% in the CI users, with a large variability. The ACC N1' latency was significantly correlated with the FCDT and the clinically collected speech perception score. The results suggested that the ACC evoked by frequency changes can serve as a useful objective tool in assessing frequency change detection capability and predicting speech perception performance in CI users.

A Follow-Up Study on Music and Lexical Tone Perception in Adult Mandarin-Speaking Cochlear Implant Users

OBJECTIVE

The aim was to evaluate the development of music and lexical tone perception in Mandarin-speaking adult cochlear implant (CI) users over a period of 1 year.

STUDY DESIGN

Prospective patient series.

SETTING

Tertiary hospital and research institute.

PATIENTS

Twenty five adult CI users, with ages ranging from 19 to 75 years old, participated in a year-long follow-up evaluation. There were also 40 normal hearing adult subjects who participated as a control group to provide the normal value range.

INTERVENTIONS

Musical sounds in cochlear implants (Mu.S.I.C.) test battery was undertaken to evaluate music perception ability. Mandarin Tone Identification in Noise Test (M-TINT) was used to assess lexical tone recognition. The tests for CI users were completed at 1, 3, 6, and 12 months after the CI switch-on.

MAIN OUTCOMES MEASURES

Quantitative and statistical analysis of their results from music and tone perception tests.

RESULTS

The performance of music perception and tone recognition both demonstrated an overall improvement in outcomes during the entire 1-year follow-up process. The increasing trends were obvious in the early period especially in the first 6 months after switch-on. There was a significant improvement in the melody discrimination (p < 0.01), timbre identification (p < 0.001), tone recognition in quiet (p < 0.0001), and in noise (p < 0.0001).

CONCLUSIONS

Adult Mandarin-speaking CI users show an increasingly improved performance on music and tone perception during the 1-year follow-up. The improvement was the most prominent in the first 6 months of CI use. It is essential to strengthen the rehabilitation training within the first 6 months.

Establishing a mental lexicon with cochlear implants: an ERP study with young children

In the present study we explore the implications of acquiring language when relying mainly or exclusively on input from a cochlear implant (CI), a device providing auditory input to otherwise deaf individuals. We focus on the time course of semantic learning in children within the second year of implant use; a period that equals the auditory age of normal hearing children during which vocabulary emerges and extends dramatically. 32 young bilaterally implanted children saw pictures paired with either matching or non-matching auditory words. Their electroencephalographic responses were recorded after 12, 18 and 24 months of implant use, revealing a large dichotomy: Some children failed to show semantic processing throughout their second year of CI use, which fell in line with their poor language outcomes. The majority of children, though, demonstrated semantic processing in form of the so-called N400 effect already after 12 months of implant use, even when their language experience relied exclusively on the implant. This is slightly earlier than observed for normal hearing children of the same auditory age, suggesting that more mature cognitive faculties at the beginning of language acquisition lead to faster semantic learning.

Qualities of Single Electrode Stimulation as a Function of Rate and Place of Stimulation with a Cochlear Implant

OBJECTIVES

Although it has been shown previously that changes in temporal coding produce changes in pitch in all cochlear regions, research has suggested that temporal coding might be best encoded in relatively apical locations. The authors hypothesized that although temporal coding may provide useable information at any cochlear location, low rates of stimulation might provide better sound quality in apical regions that are more likely to encode temporal information in the normal ear. In the present study, sound qualities of single electrode pulse trains were scaled to provide insight into the combined effects of cochlear location and stimulation rate on sound quality.

DESIGN

Ten long-term users of MED-EL cochlear implants with 31-mm electrode arrays (Standard or FLEX) were asked to scale the sound quality of single electrode pulse trains in terms of how "Clean," "Noisy," "High," and "Annoying" they sounded. Pulse trains were presented on most electrodes between 1 and 12 representing the entire range of the long electrode array at stimulation rates of 100, 150, 200, 400, or 1500 pulses per second.

RESULTS

Although high rates of stimulation are scaled as having a Clean sound quality across the entire array, only the most apical electrodes (typically 1 through 3) were considered Clean at low rates. Low rates on electrodes 6 through 12 were not rated as Clean, whereas the low-rate quality of electrodes 4 and 5 were typically in between. Scaling of Noisy responses provided an approximately inverse pattern as Clean responses. High responses show the trade-off between rate and place of stimulation on pitch. Because High responses did not correlate with Clean responses, subjects were not rating sound quality based on pitch.

CONCLUSIONS

If explicit temporal coding is to be provided in a cochlear implant, it is likely to sound better when provided apically. In addition, the finding that low rates sound clean only at apical places of stimulation is consistent with previous findings that a change in rate of stimulation corresponds to an equivalent change in perceived pitch at apical locations. Collectively, the data strongly suggest that temporal coding with a cochlear implant is optimally provided by electrodes placed well into the second cochlear turn.

Electro-tactile stimulation (ETS) enhances cochlear-implant Mandarin tone recognition

Objective

Electro-acoustic stimulation (EAS) is an effective method to enhance cochlear-implant performance in individuals who have residual low-frequency acoustic hearing. To help the majority of cochlear implant users who do not have any functional residual acoustic hearing, electro-tactile stimulation (ETS) may be used because tactile sensation has a frequency range and perceptual capabilities similar to that produced by acoustic stimulation in the EAS users.

Methods

Following up the first ETS study showing enhanced English sentence recognition in noise,¹ the present study evaluated the effect of ETS on Mandarin tone recognition in noise in two groups of adult Mandarin-speaking individuals. The first group included 11 normal-hearing individuals who listened to a 4-channel, noise-vocoded, cochlear-implant simulation. The second group included 1 unilateral cochlear-implant user and 2 bilateral users with each of their devices being tested independently. Both groups participated in a 4-alternative, forced-choice task, in which they had to identify a tone that was presented in noise at a 0-dB signal-to-noise ratio via electric stimulation (actual or simulated cochlear implants), tactile stimulation or the combined ETS.

Results

While electric or tactile stimulation alone produced similar tone recognition (∼40% correct), the ETS enhanced the cochlear-implant tone recognition by 17–18 percentage points. The size of the present ETS enhancement effect was similar to that of the previously reported EAS effect on Mandarin tone recognition. Psychophysical analysis on tactile sensation showed an important role of frequency discrimination in the ETS enhancement.

Conclusion

Tactile stimulation can potentially enhance Mandarin tone recognition in cochlear-implant users who do not have usable residual acoustic hearing. To optimize this potential, high fundamental frequencies need to be transposed to a 100–200 Hz range.

Vocoder Simulations Explain Complex Pitch Perception Limitations Experienced by Cochlear Implant Users

Pitch plays a crucial role in speech and music, but is highly degraded for people with cochlear implants, leading to severe communication challenges in noisy environments. Pitch is determined primarily by the first few spectrally resolved harmonics of a tone. In implants, access to this pitch is limited by poor spectral resolution, due to the limited number of channels and interactions between adjacent channels. Here we used noise-vocoder simulations to explore how many channels, and how little channel interaction, are required to elicit pitch. Results suggest that two to four times the number of channels are needed, along with interactions reduced by an order of magnitude, than available in current devices. These new constraints not only provide insights into the basic mechanisms of pitch coding in normal hearing but also suggest that spectrally based complex pitch is unlikely to be generated in implant users without significant changes in the method or site of stimulation.

Cantonese Tone Perception for Children Who Use a Hearing Aid and a Cochlear Implant in Opposite Ears

OBJECTIVES

The ability to recognize tones is vital for speech perception in tonal languages. Cantonese has six tones, which are differentiated almost exclusively by pitch cues (tones 1 to 6). The differences in pitch contours among the tones are subtle, making Cantonese a challenging language for cochlear implant users. The addition of a hearing aid has been shown to improve speech perception in nontonal languages and in Mandarin Chinese. This study (1) investigates the Cantonese tone perception ability of children who use a cochlear implant and a hearing aid in opposite ears; (2) evaluates the effect of varying pitch height and pitch contour cues on Cantonese tone perception for these children; and (3) compares the Cantonese tone perception ability for using a hearing aid and a cochlear implant together versus an implant alone.

DESIGN

Eight native Cantonese speaking children using a cochlear implant and a hearing aid in opposite ears were assessed for tone perception and word identification. The tone perception test involved discriminating and ranking tone pairs from natural and artificially manipulated Cantonese tones with various pitch heights and/or pitch contours. The word identification test involved identifying Cantonese words in a four-alternative forced-choice task. All tests were performed in two device conditions: (1) cochlear implant and hearing aid together and (2) implant alone.

RESULTS

Seven of the 8 subjects performed significantly above chance in both tests using the cochlear implant alone. Results showed that both pitch height and/or pitch direction were important perceptual cues for implant users. Perception for some tones was improved by increasing the pitch height differences between the tones. The ability to discriminate and rank the tone 2/tone 5 contrast and the tone 4/tone 6 contrast was poor, as the tones in these contrasts are similar in pitch contours and onset frequencies. No significant improvement was observed after artificially increasing the pitch offset differences between the tones in the tone 2/tone 5 and the tone 4/tone 6 contrasts. Tone perception results were significantly better with the addition of the hearing aid in the nonimplanted ear compared with using the implant alone; however, word identification results were not significantly different between using the implant alone and using both the hearing aid and the implant together. None of the subjects performed worse in tone perception or in word identification when the hearing aid was added.

CONCLUSIONS

Reduced ability to perceive pitch contour cues, even when artificially exaggerated, may explain some of the difficulties in Cantonese word recognition for implant users. The addition of a contralateral hearing aid could be beneficial for Cantonese tone perception for some individuals with a unilateral implant. The results encouraged Cantonese speakers to trial a hearing aid in the nonimplanted ear when using a cochlear implant.

Challenges in Improving Cochlear Implant Performance and Accessibility

Here I identify two gaps in cochlear implants that have been limiting their performance and acceptance. First, cochlear implant performance has remained largely unchanged, despite the number of publications tripling per decade in the last 30 years. Little has been done so far to address a fundamental limitation in the electrode-to-neuron interface, with the electrode size being a thousand times larger than the neuron diameter while the number of electrodes being a thousand times less. Both the small number and the large size of electrodes produce broad spatial activation and poor frequency resolution that limit current cochlear implant performance. Second, a similarly rapid growth in cochlear implant volume has not produced an expected decrease in unit price in the same period. The high cost contributes to low market penetration rate, which is about 20% in developed countries and less than 1% in developing countries. I will discuss changes needed in both research strategy and business practice to close the gap between prosthetic and normal hearing as well as that between haves and have-nots.

Assessment and improvement of sound quality in cochlear implant users

Objectives

Cochlear implants (CIs) have successfully provided speech perception to individuals with sensorineural hearing loss. Recent research has focused on more challenging acoustic stimuli such as music and voice emotion. The purpose of this review is to evaluate and describe sound quality in CI users with the purposes of summarizing novel findings and crucial information about how CI users experience complex sounds.

Data Sources

Here we review the existing literature on PubMed and Scopus to present what is known about perceptual sound quality in CI users, discuss existing measures of sound quality, explore how sound quality may be effectively studied, and examine potential strategies of improving sound quality in the CI population.

Results

Sound quality, defined here as the perceived richness of an auditory stimulus, is an attribute of implant‐mediated listening that remains poorly studied. Sound quality is distinct from appraisal, which is generally defined as the subjective likability or pleasantness of a sound. Existing studies suggest that sound quality perception in the CI population is limited by a range of factors, most notably pitch distortion and dynamic range compression. Although there are currently very few objective measures of sound quality, the CI‐MUSHRA has been used as a means of evaluating sound quality. There exist a number of promising strategies to improve sound quality perception in the CI population including apical cochlear stimulation, pitch tuning, and noise reduction processing strategies.

Conclusions

In the published literature, sound quality perception is severely limited among CI users. Future research should focus on developing systematic, objective, and quantitative sound quality metrics and designing therapies to mitigate poor sound quality perception in CI users.

Level of Evidence

NA

Relative contributions of acoustic temporal fine structure and envelope cues for lexical tone perception in noise

Previous studies have shown that lexical tone perception in quiet relies on the acoustic temporal fine structure (TFS) but not on the envelope (E) cues. The contributions of TFS to speech recognition in noise are under debate. In the present study, Mandarin tone tokens were mixed with speech-shaped noise (SSN) or two-talker babble (TTB) at five signal-to-noise ratios (SNRs; -18 to +6 dB). The TFS and E were then extracted from each of the 30 bands using Hilbert transform. Twenty-five combinations of TFS and E from the sound mixtures of the same tone tokens at various SNRs were created. Twenty normal-hearing, native-Mandarin-speaking listeners participated in the tone-recognition test. Results showed that tone-recognition performance improved as the SNRs in either TFS or E increased. The masking effects on tone perception for the TTB were weaker than those for the SSN. For both types of masker, the perceptual weights of TFS and E in tone perception in noise was nearly equivalent, with E playing a slightly greater role than TFS. Thus, the relative contributions of TFS and E cues to lexical tone perception in noise or in competing-talker maskers differ from those in quiet and those to speech perception of non-tonal languages.

Audio-visual temporal perception in children with restored hearing

It is not clear how audio-visual temporal perception develops in children with restored hearing. In this study we measured temporal discrimination thresholds with an audio-visual temporal bisection task in 9 deaf children with restored audition, and 22 typically hearing children. In typically hearing children, audition was more precise than vision, with no gain in multisensory conditions (as previously reported in Gori et al. (2012b)). However, deaf children with restored audition showed similar thresholds for audio and visual thresholds and some evidence of gain in audio-visual temporal multisensory conditions. Interestingly, we found a strong correlation between auditory weighting of multisensory signals and quality of language: patients who gave more weight to audition had better language skills. Similarly, auditory thresholds for the temporal bisection task were also a good predictor of language skills. This result supports the idea that the temporal auditory processing is associated with language development.

Voice gender and the segregation of competing talkers: Perceptual learning in cochlear implant simulations

Two experiments explored the role of differences in voice gender in the recognition of speech masked by a competing talker in cochlear implant simulations. Experiment 1 confirmed that listeners with normal hearing receive little benefit from differences in voice gender between a target and masker sentence in four- and eight-channel simulations, consistent with previous findings that cochlear implants deliver an impoverished representation of the cues for voice gender. However, gender differences led to small but significant improvements in word recognition with 16 and 32 channels. Experiment 2 assessed the benefits of perceptual training on the use of voice gender cues in an eight-channel simulation. Listeners were assigned to one of four groups: (1) word recognition training with target and masker differing in gender; (2) word recognition training with same-gender target and masker; (3) gender recognition training; or (4) control with no training. Significant improvements in word recognition were observed from pre- to post-test sessions for all three training groups compared to the control group. These improvements were maintained at the late session (one week following the last training session) for all three groups. There was an overall improvement in masked word recognition performance provided by gender mismatch following training, but the amount of benefit did not differ as a function of the type of training. The training effects observed here are consistent with a form of rapid perceptual learning that contributes to the segregation of competing voices but does not specifically enhance the benefits provided by voice gender cues.

Low-frequency fine-structure cues allow for the online use of lexical stress during spoken-word recognition in spectrally degraded speech

English listeners use suprasegmental cues to lexical stress during spoken-word recognition. Prosodic cues are, however, less salient in spectrally degraded speech, as provided by cochlear implants. The present study examined how spectral degradation with and without low-frequency fine-structure information affects normal-hearing listeners' ability to benefit from suprasegmental cues to lexical stress in online spoken-word recognition. To simulate electric hearing, an eight-channel vocoder spectrally degraded the stimuli while preserving temporal envelope information. Additional lowpass-filtered speech was presented to the opposite ear to simulate bimodal hearing. Using a visual world paradigm, listeners' eye fixations to four printed words (target, competitor, two distractors) were tracked, while hearing a word. The target and competitor overlapped segmentally in their first two syllables but mismatched suprasegmentally in their first syllables, as the initial syllable received primary stress in one word and secondary stress in the other (e.g., "'admiral," "'admi'ration"). In the vocoder-only condition, listeners were unable to use lexical stress to recognize targets before segmental information disambiguated them from competitors. With additional lowpass-filtered speech, however, listeners efficiently processed prosodic information to speed up online word recognition. Low-frequency fine-structure cues in simulated bimodal hearing allowed listeners to benefit from suprasegmental cues to lexical stress during word recognition.

Musicians Are Better than Non-musicians in Frequency Change Detection: Behavioral and Electrophysiological Evidence

Objective: The objectives of this study were: (1) to determine if musicians have a better ability to detect frequency changes under quiet and noisy conditions; (2) to use the acoustic change complex (ACC), a type of electroencephalographic (EEG) response, to understand the neural substrates of musician vs. non-musician difference in frequency change detection abilities.

Methods: Twenty-four young normal hearing listeners (12 musicians and 12 non-musicians) participated. All participants underwent psychoacoustic frequency detection tests with three types of stimuli: tones (base frequency at 160 Hz) containing frequency changes (Stim 1), tones containing frequency changes masked by low-level noise (Stim 2), and tones containing frequency changes masked by high-level noise (Stim 3). The EEG data were recorded using tones (base frequency at 160 and 1200 Hz, respectively) containing different magnitudes of frequency changes (0, 5, and 50% changes, respectively). The late-latency evoked potential evoked by the onset of the tones (onset LAEP or N1-P2 complex) and that evoked by the frequency change contained in the tone (the acoustic change complex or ACC or N1′-P2′ complex) were analyzed.

Results: Musicians significantly outperformed non-musicians in all stimulus conditions. The ACC and onset LAEP showed similarities and differences. Increasing the magnitude of frequency change resulted in increased ACC amplitudes. ACC measures were found to be significantly different between musicians (larger P2′ amplitude) and non-musicians for the base frequency of 160 Hz but not 1200 Hz. Although the peak amplitude in the onset LAEP appeared to be larger and latency shorter in musicians than in non-musicians, the difference did not reach statistical significance. The amplitude of the onset LAEP is significantly correlated with that of the ACC for the base frequency of 160 Hz.

Conclusion: The present study demonstrated that musicians do perform better than non-musicians in detecting frequency changes in quiet and noisy conditions. The ACC and onset LAEP may involve different but overlapping neural mechanisms.

Significance: This is the first study using the ACC to examine music-training effects. The ACC measures provide an objective tool for documenting musical training effects on frequency detection.

Cognitive Compensation of Speech Perception With Hearing Impairment, Cochlear Implants, and Aging

External degradations in incoming speech reduce understanding, and hearing impairment further compounds the problem. While cognitive mechanisms alleviate some of the difficulties, their effectiveness may change with age. In our research, reviewed here, we investigated cognitive compensation with hearing impairment, cochlear implants, and aging, via (a) phonemic restoration as a measure of top-down filling of missing speech, (b) listening effort and response times as a measure of increased cognitive processing, and (c) visual world paradigm and eye gazing as a measure of the use of context and its time course. Our results indicate that between speech degradations and their cognitive compensation, there is a fine balance that seems to vary greatly across individuals. Hearing impairment or inadequate hearing device settings may limit compensation benefits. Cochlear implants seem to allow the effective use of sentential context, but likely at the cost of delayed processing. Linguistic and lexical knowledge, which play an important role in compensation, may be successfully employed in advanced age, as some compensatory mechanisms seem to be preserved. These findings indicate that cognitive compensation in hearing impairment can be highly complicated—not always absent, but also not easily predicted by speech intelligibility tests only.

Place dependent stimulation rates improve pitch perception in cochlear implantees with single-sided deafness

In normal hearing, the pitch of an acoustic tone can theoretically be encoded by either the place of stimulation in the cochlea or the corresponding rate of vibration. Thus spectral attributes and temporal fine structure of an acoustic signal are naturally correlated. Cochlear implants (CIs), neural prosthetic devices that restore hearing in the profoundly hearing impaired, currently disregard this mechanism; electrical stimulation is provided at fixed electrode positions with default place independent stimulation rate assignments. This does not account for individual cochlear encoding depending on electrode array placement, variations in insertion depth, and the proximity to nerve fibers. Encoding pitch in such manner delivers limited tonal information. Consequently, music appraisal in CI users is often rated cacophonic while speech perception in quiet is close to normal in top performers. We hypothesize that this limitation in electric stimulation is at least partially due to the mismatch between frequency and place encoding in CIs. In the present study, we determined individual electrode locations by analysis of cochlear radiographic images obtained after surgery and calculated place dependent stimulation rates according to models of the normal tonotopic function. Pitch matching in CI users with single-sided deafness shows that place dependent stimulation rates allow thus far unparalleled restoration of tonotopic pitch perception. Collapsed data of matched pitch frequencies as a function of calculated electrical stimulation rate were well fitted by linear regression (R(2) = 0.878). Sound processing strategies incorporating place dependent stimulation rates are expected to improve pitch perception in CI users.

Rate discrimination at low pulse rates in normal-hearing and cochlear implant listeners: Influence of intracochlear stimulation site

Temporal pitch perception in cochlear implantees remains weaker than in normal hearing listeners and is usually limited to rates below about 300 pulses per second (pps). Recent studies have suggested that stimulating the apical part of the cochlea may improve the temporal coding of pitch by cochlear implants (CIs), compared to stimulating other sites. The present study focuses on rate discrimination at low pulse rates (ranging from 20 to 104 pps). Two experiments measured and compared pulse rate difference limens (DLs) at four fundamental frequencies (ranging from 20 to 104 Hz) in both CI and normal-hearing (NH) listeners. Experiment 1 measured DLs in users of the (Med-El CI, Innsbruck, Austria) device for two electrodes (one apical and one basal). In experiment 2, DLs for NH listeners were compared for unresolved harmonic complex tones filtered in two frequency regions (lower cut-off frequencies of 1200 and 3600 Hz, respectively) and for different bandwidths. Pulse rate discrimination performance was significantly better when stimulation was provided by the apical electrode in CI users and by the lower-frequency tone complexes in NH listeners. This set of data appears consistent with better temporal coding when stimulation originates from apical regions of the cochlea.

The Perception of Stress Pattern in Young Cochlear Implanted Children: An EEG Study

Children with sensorineural hearing loss may (re)gain hearing with a cochlear implant—a device that transforms sounds into electric pulses and bypasses the dysfunctioning inner ear by stimulating the auditory nerve directly with an electrode array. Many implanted children master the acquisition of spoken language successfully, yet we still have little knowledge of the actual input they receive with the implant and specifically which language sensitive cues they hear. This would be important however, both for understanding the flexibility of the auditory system when presented with stimuli after a (life-) long phase of deprivation and for planning therapeutic intervention. In rhythmic languages the general stress pattern conveys important information about word boundaries. Infant language acquisition relies on such cues and can be severely hampered when this information is missing, as seen for dyslexic children and children with specific language impairment. Here we ask whether children with a cochlear implant perceive differences in stress patterns during their language acquisition phase and if they do, whether it is present directly following implant stimulation or if and how much time is needed for the auditory system to adapt to the new sensory modality. We performed a longitudinal ERP study, testing in bimonthly intervals the stress pattern perception of 17 young hearing impaired children (age range: 9–50 months; mean: 22 months) during their first 6 months of implant use. An additional session before the implantation served as control baseline. During a session they passively listened to an oddball paradigm featuring the disyllable “baba,” which was stressed either on the first or second syllable (trochaic vs. iambic stress pattern). A group of age-matched normal hearing children participated as controls. Our results show, that within the first 6 months of implant use the implanted children develop a negative mismatch response for iambic but not for trochaic deviants, thus showing the same result as the normal hearing controls. Even congenitally deaf children show the same developing pattern. We therefore conclude (a) that young implanted children have early access to stress pattern information and (b) that they develop ERP responses similar to those of normal hearing children.

Musical training software for children with cochlear implants

Although the voice in a free field has an excellent recruitment by a cochlear implant (CI), the situation is different for music because it is a much more complex process, where perceiving the pitch discrimination becomes important to appreciate it. The aim of this study is to determine the music perception abilities among children with Cis and to verify the benefit of a training period for specific musical frequency discrimination. Our main goals were to prepare a computer tool for pitch discrimination training and to assess musical improvements. Ten children, aged between 5 and 12 years, with optimal phoneme recognition in quiet and with no disabilities associated with deafness, were selected to join the training. Each patient received, before training period, two types of exams: a pitch discrimination test, consisting of discovering if two notes were different or not; and a music test consisting of two identification tasks (melodic and full version) of one music-item among 5 popular childhood songs. After assessment, a music training software was designed and utilised individually at home for a period of six months. The results following complete training showed significantly higher performance in the task of frequency discrimination. After a proper musical training identification, frequency discrimination performance was significantly higher (p < 0.001). The same considerations can be made in the identification of the songs presented in their melodic (p = 0.0151) and full songs version (p = 0.0071). Cases where children did not reach the most difficult level may be due to insufficient time devoted to training (ideal time estimated at 2-3 hours per week). In conclusion, this study shows that is possible to assess musical enhancement and to achieve improvements in frequency discrimination, following pitch discrimination training.

Bilateral cochlear implants with large asymmetries in electrode insertion depth: implications for the study of auditory plasticity

CONCLUSION

The human frequency-to-place map may be modified by experience, even in adult listeners. However, such plasticity has limitations. Knowledge of the extent and the limitations of human auditory plasticity can help optimize parameter settings in users of auditory prostheses.

OBJECTIVES

To what extent can adults adapt to sharply different frequency-to-place maps across ears? This question was investigated in two bilateral cochlear implant users who had a full electrode insertion in one ear, a much shallower insertion in the other ear, and standard frequency-to-electrode maps in both ears.

METHODS

Three methods were used to assess adaptation to the frequency-to-electrode maps in each ear: (1) pitch matching of electrodes in opposite ears, (2) listener-driven selection of the most intelligible frequency-to-electrode map, and (3) speech perception tests. Based on these measurements, one subject was fitted with an alternative frequency-to-electrode map, which sought to compensate for her incomplete adaptation to the standard frequency-to-electrode map.

RESULTS

Both listeners showed remarkable ability to adapt, but such adaptation remained incomplete for the ear with the shallower electrode insertion, even after extended experience. The alternative frequency-to-electrode map that was tested resulted in substantial increases in speech perception for one subject in the short insertion ear.