Speech and music have different requirements for spectral resolution

Loudness Balancing Optimization for Better Speech Intelligibility, Music Perception, and Spectral Temporal Resolution in Cochlear Implant Users

HYPOTHESIS

The behaviorally based programming with loudness balancing (LB) would result in better speech understanding, spectral-temporal resolution, and music perception scores, and there would be a relationship between these scores.

BACKGROUND

Loudness imbalances at upper stimulation levels may cause sounds to be perceived as irregular, gravelly, or overly echoed and may negatively affect the listening performance of the cochlear implant (CI) user. LB should be performed after fitting to overcome these problems.

METHODS

The study included 26 unilateral Med-EL CI users. Two different CI programs based on the objective electrically evoked stapedial reflex threshold (P1) and the behaviorally program with LB (P2) were recorded for each participant. The Turkish Matrix Sentence Test (TMS) was applied to evaluate speech perception; the Random Gap Detection Test (RGDT) and Spectral-Temporally Modulated Ripple Test (SMRT) were applied to evaluate spectral temporal resolution skills; the Mini Profile of Music Perception Skills (mini-PROMS) and Melodic Contour Identification (MCI) tests were applied to evaluate music perception, and the results were compared.

RESULTS

Significantly better scores were obtained with P2 in TMS tests performed in noise and quiet. SMRT scores were significantly correlated with TMS in quiet and noise, and mini-PROMS sound perception results. Although better scores were obtained with P2 in the mini-PROMS total score and MCI, a significant difference was found only for MCI.

CONCLUSION

The data from the current study showed that equalization of loudness across CI electrodes leads to better perceptual acuity. It also revealed the relationship between speech perception, spectral-temporal resolution, and music perception.

The Impact of Vocal Boost Manipulations on Musical Sound Quality for Cochlear Implant Users

OBJECTIVE

To evaluate the impact of vocal boost manipulations on cochlear implant (CI) musical sound quality appraisals.

METHODS

An anonymous, online study was distributed to 33 CI users. Participants listened to auditory tokens and assessed the musical quality of acoustic stimuli with vocal boosting and attenuation using a validated sound quality rating scale. Four versions of real-world musical stimuli were created: a version with +9 dB vocal boost, a version with -9 dB vocal attenuation, a composite stimulus containing a 1,000 Hz low-pass filter and white noise ("anchor"), and an unaltered version ("hidden reference"). Subjects listened to all four versions and provided ratings based on a 100-point scale that reflected the perceived sound quality difference of the music clip relative to the reference excerpt.

RESULTS

Vocal boost increased musical sound quality ratings relative to the reference clip (11.7; 95% CI, 1.62-21.8, p = 0.016) and vocal attenuation decreased musical sound quality ratings relative to the reference clip (28.5; 95% CI, 18.64-38.44, p < 0.001). When comparing the non-musical training group and musical training group, there was a significant difference in musical sound quality rating scores for the vocal boost condition (21.2; 95% CI: 1.76-40.7, p = 0.028).

CONCLUSIONS

CI-mediated musical sound quality appraisals are impacted by vocal boost and attenuation. Musically trained CI users to report greater musical sound quality enhancement with a vocal boost with respect to CI users with no musical training background. Implementation of front-end vocal boost manipulations in music may improve sound quality and music appreciation among CI users.

LEVEL OF EVIDENCE

2 (Individual cohort study) Laryngoscope, 133:938-947, 2023.

Speech phoneme and spectral smearing based non-invasive COVID-19 detection

COVID-19 is a deadly viral infection that mainly affects the nasopharyngeal and oropharyngeal cavities before the lung in the human body. Early detection followed by immediate treatment can potentially reduce lung invasion and decrease fatality. Recently, several COVID-19 detections methods have been proposed using cough and breath sounds. However, very little study has been done on the use of phoneme analysis and the smearing of the audio signal in COVID-19 detection. In this paper, this problem has been addressed and the classification of speech samples has been carried out in COVID-19-positive and healthy audio samples. Additionally, the grouping of the phonemes based on reference classification accuracies have been proposed for effectiveness and faster detection of the disease at a primary stage. The Mel and Gammatone Cepstral coefficients and their derivatives are used as the features for five standard machine learning-based classifiers. It is observed that the generalized additive model provides the highest accuracy of 97.22% for the phoneme grouping "/t//r//n//g//l/." This smearing-based phoneme classification technique can also be used in the future to classify other speech-related disease detections.

Perception of timbre in adult Cochlear implant users: Comparison of Iranian and Western musical instruments

OBJECTIVES

Cochlear implants (CI) have dramatically improved speech perception for patients with sensorineural hearing impairment. However, listening to music is a great challenge for them. This study examined the perception and appraisal of Iranian musical instruments comparing with similar Western instruments.

METHODS

Eleven adult CI users and 25 normal hearing (NH) individuals participated in this study. Musical stimuli of three commonly heard instrument pairs were prepared. Participants were asked to identify the instruments and rate their appraisal on a ten-point Likert scale (0 = dislike very much, 10 = like very much).

RESULTS

The instrument recognition rate was 40.6% among the CI users, and the mean appraisal score was 5.2 ± 2.7. NH listeners had none significant higher scores on both tasks with a recognition rate of 50.0% and the mean appraisal score of 6.9 ± 1.5. Iranian instruments were more recognized in both groups. Regarding their appraisal, the mean score for both types was almost equal in the NH group, while CI users more appraised Iranian instruments.

CONCLUSION

In addition to better recognition of Iranian instruments, they were particularly better appraised in the CI group. Iranian instruments provide suitable musical pieces for CI recipients that can be considered in rehabilitation programs.

Neural synchronization is strongest to the spectral flux of slow music and depends on familiarity and beat salience

Neural activity in the auditory system synchronizes to sound rhythms, and brain–environment synchronization is thought to be fundamental to successful auditory perception. Sound rhythms are often operationalized in terms of the sound’s amplitude envelope. We hypothesized that – especially for music – the envelope might not best capture the complex spectro-temporal fluctuations that give rise to beat perception and synchronized neural activity. This study investigated (1) neural synchronization to different musical features, (2) tempo-dependence of neural synchronization, and (3) dependence of synchronization on familiarity, enjoyment, and ease of beat perception. In this electroencephalography study, 37 human participants listened to tempo-modulated music (1–4 Hz). Independent of whether the analysis approach was based on temporal response functions (TRFs) or reliable components analysis (RCA), the spectral flux of music – as opposed to the amplitude envelope – evoked strongest neural synchronization. Moreover, music with slower beat rates, high familiarity, and easy-to-perceive beats elicited the strongest neural response. Our results demonstrate the importance of spectro-temporal fluctuations in music for driving neural synchronization, and highlight its sensitivity to musical tempo, familiarity, and beat salience.

When we listen to a melody, the activity of our neurons synchronizes to the music: in fact, it is likely that the closer the match, the better we can perceive the piece. However, it remains unclear exactly which musical features our brain cells synchronize to. Previous studies, which have often used ‘simplified’ music, have highlighted that the amplitude envelope (how the intensity of the sounds changes over time) could be involved in this phenomenon, alongside factors such as musical training, attention, familiarity with the piece or even enjoyment. Whether differences in neural synchronization could explain why musical tastes vary between people is also still a matter of debate.

In their study, Weineck et al. aim to better understand what drives neuronal synchronization to music. A technique known as electroencephalography was used to record brain activity in 37 volunteers listening to instrumental music whose tempo ranged from 60 to 240 beats per minute. The tunes varied across an array of features such as familiarity, enjoyment and how easy the beat was to perceive. Two different approaches were then used to calculate neural synchronization, which yielded converging results.

The analyses revealed that three types of factors were associated with a strong neural synchronization. First, amongst the various cadences, a tempo of 60-120 beats per minute elicited the strongest match with neuronal activity. Interestingly, this beat is commonly found in Western pop music, is usually preferred by listeners, and often matches spontaneous body rhythms such as walking pace. Second, synchronization was linked to variations in pitch and sound quality (known as ‘spectral flux’) rather than in the amplitude envelope. And finally, familiarity and perceived beat saliency – but not enjoyment or musical expertise – were connected to stronger synchronization.

These findings help to better understand how our brains allow us to perceive and connect with music. The work conducted by Weineck et al. should help other researchers to investigate this field; in particular, it shows how important it is to consider spectral flux rather than amplitude envelope in experiments that use actual music.

Conversations in Cochlear Implantation: The Inner Ear Therapy of Today

As biomolecular approaches for hearing restoration in profound sensorineural hearing loss evolve, they will be applied in conjunction with or instead of cochlear implants. An understanding of the current state-of-the-art of this technology, including its advantages, disadvantages, and its potential for delivering and interacting with biomolecular hearing restoration approaches, is helpful for designing modern hearing-restoration strategies. Cochlear implants (CI) have evolved over the last four decades to restore hearing more effectively, in more people, with diverse indications. This evolution has been driven by advances in technology, surgery, and healthcare delivery. Here, we offer a practical treatise on the state of cochlear implantation directed towards developing the next generation of inner ear therapeutics. We aim to capture and distill conversations ongoing in CI research, development, and clinical management. In this review, we discuss successes and physiological constraints of hearing with an implant, common surgical approaches and electrode arrays, new indications and outcome measures for implantation, and barriers to CI utilization. Additionally, we compare cochlear implantation with biomolecular and pharmacological approaches, consider strategies to combine these approaches, and identify unmet medical needs with cochlear implants. The strengths and weaknesses of modern implantation highlighted here can mark opportunities for continued progress or improvement in the design and delivery of the next generation of inner ear therapeutics.

Sound quality perception of cochlear implant recipients: low-frequency information and foreign-language effect

OBJECTIVE

This study aimed to adapt a method used in sound quality measurements named CI-MUSHRA (the multiple stimuli with hidden reference and anchor for cochlear implant users) to the Turkish language. The effect of low-frequency information and non-native musical stimuli on sound quality perception was investigated.

DESIGN

Subjects completed the Turkish version of the MUSHRA test, called TR-MUSHRA, and the original CI-MUSHRA test. Participants also completed the Turkish monosyllabic word recognition test and the spectral temporal modulated ripple test (SMRT).

STUDY SAMPLE

19 cochlear implant (CI) users and 16 normal-hearing (NH) adults were included.

RESULTS

CI users demonstrated a lack of ability to detect the sound quality differences between original stimuli and stimuli with omitted low-frequency information up to 600 Hz in both tests. There was no significant main effect of the test version on sound quality ratings for the two groups. No significant correlation was found between mean sound quality scores, SMRT, and speech recognition in quiet and noise conditions.

CONCLUSIONS

Our study suggests that CI users perform poorly in discriminating high-pass filtered musical sounds regardless of the language of the musical stimuli. The TR-MUSHRA can be used as a reliable research tool to evaluate the perceived sound quality.

Translation and validation of the music-related quality of life questionnaire for adults with cochlear implant in Turkish language

PURPOSE

It is important to assess the impact of music on cochlear implant (CI) users' quality of life. The aim of this study was to adapt and validate the music-related quality of life questionnaire into the Turkish language for adult CI users.

METHODS

161 CI users and 162 normal-hearing adults were included in the study. The final Turkish version of the questionnaire was prepared and evaluated for validity and reliability. The internal consistency of the questionnaire and test-retest reliability were evaluated by Cronbach's α and ICC index. Factor analysis and 'know-group' method was used to determine the construct validity.

RESULTS

Sampling adequacy for execution of factor analysis was confirmed by the results of Kaiser-Meyer-Olkin (= 0.91) and Bartlett test (p < 0.05). 2 factors for each scale were identified from exploratory factor analysis. Confirmatory factor analysis confirmed the questionnaire met the criteria standards for adequacy of fit. The reliability coefficient was determined at least 0.80. Correlation between items indicated excellent (> .80) internal consistency.

CONCLUSION

The Turkish version of the questionnaire has good validity and reliability and can be used to investigate the relationship between music and quality of life and as a diagnostic tool in identifying individuals who need music support and to guide and evaluate music rehabilitation.

Music perception and training for pediatric cochlear implant users

INTRODUCTION

Cochlear implants (CIs) are biomedical devices that restore sound perception for people with severe-to-profound sensorineural hearing loss. Most postlingually deafened CI users are able to achieve excellent speech recognition in quiet environments. However, current CI sound processors remain limited in their ability to deliver fine spectrotemporal information, making it difficult for CI users to perceive complex sounds. Limited access to complex acoustic cues such as music, environmental sounds, lexical tones, and voice emotion may have significant ramifications on quality of life, social development, and community interactions.

AREAS COVERED

The purpose of this review article is to summarize the literature on CIs and music perception, with an emphasis on music training in pediatric CI recipients. The findings have implications on our understanding of noninvasive, accessible methods for improving auditory processing and may help advance our ability to improve sound quality and performance for implantees.

EXPERT OPINION

Music training, particularly in the pediatric population, may be able to continue to enhance auditory processing even after performance plateaus. The effects of these training programs appear generalizable to non-trained musical tasks, speech prosody and, emotion perception. Future studies should employ rigorous control groups involving a non-musical acoustic intervention, standardized auditory stimuli, and the provision of feedback.

Effects of Exogenous Auditory Attention on Temporal and Spectral Resolution

Previous research in the visual domain suggests that exogenous attention in form of peripheral cueing increases spatial but lowers temporal resolution. It is unclear whether this effect transfers to other sensory modalities. Here, we tested the effects of exogenous attention on temporal and spectral resolution in the auditory domain. Eighteen young, normal-hearing adults were tested in both gap and frequency change detection tasks with exogenous cuing. Benefits of valid cuing were only present in the gap detection task while costs of invalid cuing were observed in both tasks. Our results suggest that exogenous attention in the auditory system improves temporal resolution without compromising spectral resolution.

Understanding music with cochlear implants

Direct stimulation of the auditory nerve via a Cochlear Implant (CI) enables profoundly hearing-impaired people to perceive sounds. Many CI users find language comprehension satisfactory, but music perception is generally considered difficult. However, music contains different dimensions which might be accessible in different ways. We aimed to highlight three main dimensions of music processing in CI users which rely on different processing mechanisms: (1) musical discrimination abilities, (2) access to meaning in music, and (3) subjective music appreciation. All three dimensions were investigated in two CI user groups (post- and prelingually deafened CI users, all implanted as adults) and a matched normal hearing control group. The meaning of music was studied by using event-related potentials (with the N400 component as marker) during a music-word priming task while music appreciation was gathered by a questionnaire. The results reveal a double dissociation between the three dimensions of music processing. Despite impaired discrimination abilities of both CI user groups compared to the control group, appreciation was reduced only in postlingual CI users. While musical meaning processing was restorable in postlingual CI users, as shown by a N400 effect, data of prelingual CI users lack the N400 effect and indicate previous dysfunctional concept building.

Perception of degraded speech sounds differs in chinchilla and human listeners

The behavioral responses of chinchillas to noise-vocoded versions of naturally spoken speech sounds were measured using stimulus generalization and operant conditioning. Behavioral performance for speech generalization by chinchillas is compared to recognition by a group of human listeners for the identical speech sounds. The ability of chinchillas to generalize the vocoded versions as tokens of the natural speech sounds is far less than recognition by human listeners. In many cases, responses of chinchillas to noise-vocoded speech sounds were more similar to responses to band limited noise than to the responses to natural speech sounds. Chinchillas were also tested with a middle C musical note as played on a piano. Comparison of the responses of chinchillas for the middle C condition to the responses obtained for the speech conditions suggest that chinchillas may be more influenced by fundamental frequency than by formant structure. The differences between vocoded speech perception in chinchillas and human listeners may reflect differences in their abilities to resolve the formants along the cochlea. It is argued that lengthening of the cochlea during human evolution may have provided one of the auditory mechanisms that influenced the evolution of speech-specific mechanisms.

The organization and physiology of the auditory thalamus and its role in processing acoustic features important for speech perception

The auditory thalamus, or medial geniculate body (MGB), is the primary sensory input to auditory cortex. Therefore, it plays a critical role in the complex auditory processing necessary for robust speech perception. This review will describe the functional organization of the thalamus as it relates to processing acoustic features important for speech perception, focusing on thalamic nuclei that relate to auditory representations of language sounds. The MGB can be divided into three main subdivisions, the ventral, dorsal, and medial subdivisions, each with different connectivity, auditory response properties, neuronal properties, and synaptic properties. Together, the MGB subdivisions actively and dynamically shape complex auditory processing and form ongoing communication loops with auditory cortex and subcortical structures.

Lexical tone perception with HiResolution and HiResolution 120 sound-processing strategies in pediatric Mandarin-speaking cochlear implant users

OBJECTIVES

Lexical tone recognition tends to be poor in cochlear implant users. The HiResolution (HiRes) sound-processing strategy is designed to better preserve temporal fine structure, or the detailed envelope information, of an acoustic signal. The newer HiRes 120 strategy builds on HiRes by increasing the amount of potential spectral information delivered to the implant user. The purpose of this study was to examine lexical tone recognition in native Mandarin Chinese-speaking children with cochlear implants using the HiRes and HiRes 120 sound-processing strategies. Tone recognition performance was tested with HiRes at baseline and then after up to 6 mo of HiRes 120 experience in the same subjects.

DESIGN

Twenty prelingually deafened, native Mandarin-speaking children, with ages ranging from 3.5 to 16.5 yr, participated. All children completed a computerized tone contrast test on three occasions: (1) using HiRes immediately before conversion to HiRes 120 (baseline), (2) 1 mo after conversion, and (3) 3 mo after conversion. Twelve of the 20 children also were tested 6 mo after conversion. In addition, the parents of 18 children completed a questionnaire at the 3-mo follow-up visit regarding the preference of sound-processing strategies and the children's experience related to various aspects of auditory perception and speech production using HiRes 120.

RESULTS

As a group, no statistically significant differences were seen between the tone recognition scores using HiRes and HiRes 120. Individual scores showed great variability. Tone recognition performance ranged from chance (50% correct) to nearly perfect. Using the conventional HiRes strategy, 6 of the 20 children achieved high-level tone recognition performance (i.e., >or=90% correct), whereas 7 performed at a level not significantly different from chance (50-60% correct). At the final test, either 3 or 6 mo after conversion, all children achieved tone recognition performance with HiRes 120 that was equal to or better than that with HiRes, although some children's tone recognition performance was worse initially at the 1 or 3 mo follow-up intervals than at baseline. Eight of the 20 children showed statistically significant improvement in tone recognition performance with HiRes 120 on at least one of the follow-up tests. Age at implantation was correlated with tone recognition performance at all four test intervals. Parents of most of the children indicated that the children preferred HiRes 120 more than HiRes.

CONCLUSIONS

As a group, HiRes 120 did not provide significantly improved lexical tone recognition compared to HiRes, at least throughout the length of the study (up to 6 mo). There were large individual differences in lexical tone recognition among the prelingually deafened, native Mandarin-speaking children with cochlear implants using either HiRes or HiRes 120. Six of the 20 children performed at or near ceiling in the baseline HiRes condition. Of the remainder, approximately half showed significantly better tone recognition when subsequently tested with HiRes 120, although the extent to which this improvement may be attributable to factors other than the change in processing strategy (e.g., general development) is unknown. The children who benefited most from HiRes 120 tended to be those who were implanted at younger ages.

Auditory brain stem response to complex sounds: a tutorial

This tutorial provides a comprehensive overview of the methodological approach to collecting and analyzing auditory brain stem responses to complex sounds (cABRs). cABRs provide a window into how behaviorally relevant sounds such as speech and music are processed in the brain. Because temporal and spectral characteristics of sounds are preserved in this subcortical response, cABRs can be used to assess specific impairments and enhancements in auditory processing. Notably, subcortical auditory function is neither passive nor hardwired but dynamically interacts with higher-level cognitive processes to refine how sounds are transcribed into neural code. This experience-dependent plasticity, which can occur on a number of time scales (e.g., life-long experience with speech or music, short-term auditory training, on-line auditory processing), helps shape sensory perception. Thus, by being an objective and noninvasive means for examining cognitive function and experience-dependent processes in sensory activity, cABRs have considerable utility in the study of populations where auditory function is of interest (e.g., auditory experts such as musicians, and persons with hearing loss, auditory processing, and language disorders). This tutorial is intended for clinicians and researchers seeking to integrate cABRs into their clinical or research programs.

Experience-induced malleability in neural encoding of pitch, timbre, and timing

Speech and music are highly complex signals that have many shared acoustic features. Pitch, Timbre, and Timing can be used as overarching perceptual categories for describing these shared properties. The acoustic cues contributing to these percepts also have distinct subcortical representations which can be selectively enhanced or degraded in different populations. Musically trained subjects are found to have enhanced subcortical representations of pitch, timbre, and timing. The effects of musical experience on subcortical auditory processing are pervasive and extend beyond music to the domains of language and emotion. The sensory malleability of the neural encoding of pitch, timbre, and timing can be affected by lifelong experience and short-term training. This conceptual framework and supporting data can be applied to consider sensory learning of speech and music through a hearing aid or cochlear implant.

Expression of Wnt receptors in adult spiral ganglion neurons: frizzled 9 localization at growth cones of regenerating neurites

Little is known about signaling pathways, besides those of neurotrophic factors, that are operational in adult spiral ganglion neurons. In patients with sensorineural hearing loss, such pathways could eventually be targeted to stimulate and guide neurite outgrowth from the remnants of the spiral ganglion towards a cochlear implant, thereby improving the fidelity of sound transmission. To systematically identify neuronal receptors for guidance cues in the adult cochlea, we conducted a genome-wide cDNA microarray screen with 2-month-old CBA/CaJ mice. A meta-analysis of our data and those from older mice in two other studies revealed the presence of neuronal transmembrane receptors that represent all four established guidance pathways--ephrin, netrin, semaphorin, and slit--in the mature cochlea as late as 15 months. In addition, we observed the expression of all known receptors for the "wingless-related MMTV integration site" (Wnt) morphogens, whose neuronal guidance function has only recently been recognized. In situ hybridizations located the mRNAs of the Wnt receptors frizzled 1, 4, 6, 9, and 10 specifically in adult spiral ganglion neurons. Finally, frizzled 9 protein was found in the growth cones of adult spiral ganglion neurons that were regenerating neurites in culture. We conclude from our results that adult spiral ganglion neurons are poised to respond to neurite damage, owing to the constitutive expression of a large and diverse collection of guidance receptors. Wnt signaling, in particular, emerges as a candidate pathway for guiding neurite outgrowth towards a cochlear implant after sensorineural hearing loss.

Pitch processing sites in the human auditory brain

Lateral Heschl's gyrus (HG), a subdivision of the human auditory cortex, is commonly believed to represent a general “pitch center,” responding selectively to the pitch of sounds, irrespective of their spectral characteristics. However, most neuroimaging investigations have used only one specialized pitch-evoking stimulus: iterated-ripple noise (IRN). The present study used a novel experimental design in which a range of different pitch-evoking stimuli were presented to the same listeners. Pitch sites were identified by searching for voxels that responded well to the range of pitch-evoking stimuli. The first result suggested that parts of the planum temporale are more relevant for pitch processing than lateral HG. In some listeners, pitch responses occurred elsewhere, such as the temporo-parieto-occipital junction or prefrontal cortex. The second result demonstrated a different pattern of response to the IRN and raises the possibility that features of IRN unrelated to pitch might contribute to the earlier results. In conclusion, it seems premature to assign special status to lateral HG solely on the basis of neuroactivation patterns. Further work should consider the functional roles of these multiple pitch processing sites within the proposed network.

Multiple routes to the perceptual learning of speech

A listener's ability to utilize indexical information in the speech signal can enhance their performance on a variety of speech perception tasks. It is unclear, however, whether such information plays a similar role for spectrally reduced speech signals, such as those experienced by individuals with cochlear implants. The present study compared the effects of training on linguistic and indexical tasks when adapting to cochlear implant simulations. Listening to sentences processed with an eight-channel sinewave vocoder, three separate groups of subjects were trained on a transcription task (transcription), a talker identification task (talker ID), or a gender identification task (gender ID). Pre- to posttest comparisons demonstrated that training produced significant improvement for all groups. Moreover, subjects from the talker ID and transcription training groups performed similarly at posttest and generalization, and significantly better than the subjects from the gender ID training group. These results suggest that training on an indexical task that requires high levels of controlled attention can provide equivalent benefits to training on a linguistic task. When listeners selectively focus their attention on the extralinguistic information in the speech signal, they still extract linguistic information, the degree to which they do so, however, appears to be task dependent.

Perceptual learning of spectrally degraded speech and environmental sounds

Adaptation to the acoustic world following cochlear implantation does not typically include formal training or extensive audiological rehabilitation. Can cochlear implant (CI) users benefit from formal training, and if so, what type of training is best? This study used a pre-/posttest design to evaluate the efficacy of training and generalization of perceptual learning in normal hearing subjects listening to CI simulations (eight-channel sinewave vocoder). Five groups of subjects were trained on words (simple/complex), sentences (meaningful/anomalous), or environmental sounds, and then were tested using an open-set identification task. Subjects were trained on only one set of materials but were tested on all stimuli. All groups showed significant improvement due to training, which successfully generalized to some, but not all stimulus materials. For easier tasks, all types of training generalized equally well. For more difficult tasks, training specificity was observed. Training on speech did not generalize to the recognition of environmental sounds; however, explicit training on environmental sounds successfully generalized to speech. These data demonstrate that the perceptual learning of degraded speech is highly context dependent and the type of training and the specific stimulus materials that a subject experiences during perceptual learning has a substantial impact on generalization to new materials.

Current Steering Creates Additional Pitch Percepts in Adult Cochlear Implant Recipients

OBJECTIVE

The number of spectral channels is the number of discriminable pitches heard as current is delivered to distinct locations along the cochlea. This study aimed to determine whether cochlear implant users could hear additional spectral channels using current "steering." Current steering involves the simultaneous delivery of current to adjacent electrodes, where stimulation can be steered to sites between the contacts by varying the proportion of current delivered to each electrode in an electrode pair. Current steering may increase the number of spectral channels beyond the number of fixed electrode contacts.

STUDY DESIGN

Prospective clinical study.

SETTING

Twelve tertiary care centers in North America.

PATIENTS

The subjects were 106 adults with postlingual onset of severe-to-profound hearing loss.

INTERVENTIONS

Subjects received the Advanced Bionics CII or HiResolution 90K device (Advanced Bionics Corporation, Valencia, CA, USA).

MAIN OUTCOME MEASURES

After loudness balancing and pitch ranking the 3 electrode pairs (2 and 3, 8 and 9, and 13 and 14), the subjects identified the electrode with the higher pitch while current was varied proportionally between the electrodes in each pair. The smallest change in proportion yielding a discriminable change in pitch was defined as the spectral resolution.

RESULTS

The data from 115 ears indicate that the number of spectral channels averaged 3.8 for the basal pair, 6.0 for the midarray pair, and 5.3 for the apical pair. Assuming that the number of channels on these 3 electrode pairs represents the entire array, the total potential number of spectral channels was calculated and ranged from 8 to 451, with an average of 63.

CONCLUSION

These results indicate that additional pitch percepts can be created using current steering.