Changes in synthetic and natural vowel perception after specific training for congenitally deafened patients using a multichannel cochlear implant

Effects of training length on adaptation to noise-vocoded speech

Listeners show rapid perceptual learning of acoustically degraded speech, though the amount of exposure required to maximize speech adaptation is unspecified. The current work used a single-session design to examine the length of auditory training on perceptual learning for normal hearing listeners exposed to eight-channel noise-vocoded speech. Participants completed short, medium, or long training using a two-alternative forced choice sentence identification task with feedback. To assess learning and generalization, a 40-trial pre-test and post-test transcription task was administered using trained and novel sentences. Training results showed all groups performed near ceiling with no reliable differences. For test data, we evaluated changes in transcription accuracy using separate linear mixed models for trained or novel sentences. In both models, we observed a significant improvement in transcription at post-test relative to pre-test. Critically, the three training groups did not differ in the magnitude of improvement following training. Subsequent Bayes factors analysis evaluating the test by group interaction provided strong evidence in support of the null hypothesis. For these stimuli and procedure, results suggest increased training does not necessarily maximize learning outcomes; both passive and trained experience likely supported adaptation. Findings may contribute to rehabilitation recommendations for listeners adapting to degraded speech signals.

Many tasks, same outcome: Role of training task on learning and maintenance of noise-vocoded speech

Listeners who use cochlear implants show variability in speech recognition. Research suggests that structured auditory training can improve speech recognition outcomes in cochlear implant users, and a central goal in the rehabilitation literature is to identify factors that maximize training. Here, we examined factors that may influence perceptual learning for noise-vocoded speech in normal hearing listeners as a foundational step towards clinical recommendations. Three groups of listeners were exposed to anomalous noise-vocoded sentences and completed one of three training tasks: transcription with feedback, transcription without feedback, or talker identification. Listeners completed a word transcription test at three time points: immediately before training, immediately after training, and one week following training. Accuracy at test was indexed by keyword accuracy at the sentence-initial and sentence-final position for high and low predictability noise-vocoded sentences. Following training, listeners showed improved transcription for both sentence-initial and sentence-final items, and for both low and high predictability sentences. The training groups showed robust and equivalent learning of noise-vocoded sentences immediately after training. Critically, gains were largely maintained equivalently among training groups one week later. These results converge with evidence pointing towards the utility of non-traditional training tasks to maximize perceptual learning of noise-vocoded speech.

A Randomized Controlled Crossover Study of the Impact of Online Music Training on Pitch and Timbre Perception in Cochlear Implant Users

Cochlear implant (CI) biomechanical constraints result in impoverished spectral cues and poor frequency resolution, making it difficult for users to perceive pitch and timbre. There is emerging evidence that music training may improve CI-mediated music perception; however, much of the existing studies involve time-intensive and less readily accessible in-person music training paradigms, without rigorous experimental control paradigms. Online resources for auditory rehabilitation remain an untapped potential resource for CI users. Furthermore, establishing immediate value from an acute music training program may encourage CI users to adhere to post-implantation rehabilitation exercises. In this study, we evaluated the impact of an acute online music training program on pitch discrimination and timbre identification. Via a randomized controlled crossover study design, 20 CI users and 21 normal hearing (NH) adults were assigned to one of two arms. Arm-A underwent 1 month of online self-paced music training (intervention) followed by 1 month of audiobook listening (control). Arm-B underwent 1 month of audiobook listening followed by 1 month of music training. Pitch and timbre sensitivity scores were taken across three visits: (1) baseline, (2) after 1 month of intervention, and (3) after 1 month of control. We found that performance improved in pitch discrimination among CI users and NH listeners, with both online music training and audiobook listening. Music training, however, provided slightly greater benefit for instrument identification than audiobook listening. For both tasks, this improvement appears to be related to both fast stimulus learning as well as procedural learning. In conclusion, auditory training (with either acute participation in an online music training program or audiobook listening) may improve performance on untrained tasks of pitch discrimination and timbre identification. These findings demonstrate a potential role for music training in perceptual auditory appraisal of complex stimuli. Furthermore, this study highlights the importance and the need for more tightly controlled training studies in order to accurately evaluate the impact of rehabilitation training protocols on auditory processing.

Efficacy of Multiple-Talker Phonetic Identification Training in Postlingually Deafened Cochlear Implant Listeners

PURPOSE

This study implemented a pretest-intervention-posttest design to examine whether multiple-talker identification training enhanced phonetic perception of the /ba/-/da/ and /wa/-/ja/ contrasts in adult listeners who were deafened postlingually and have cochlear implants (CIs).

METHOD

Nine CI recipients completed 8 hours of identification training using a custom-designed training package. Perception of speech produced by familiar talkers (talkers used during training) and unfamiliar talkers (talkers not used during training) was measured before and after training. Five additional untrained CI recipients completed identical pre- and posttests over the same time course as the trainees to control for procedural learning effects.

RESULTS

Perception of the speech contrasts produced by the familiar talkers significantly improved for the trained CI listeners, and effects of perceptual learning transferred to unfamiliar talkers. Such training-induced significant changes were not observed in the control group.

CONCLUSION

The data provide initial evidence of the efficacy of the multiple-talker identification training paradigm for CI users who were deafened postlingually. This pattern of results is consistent with enhanced phonemic categorization of the trained speech sounds.

Environmental sound training in cochlear implant users

PURPOSE

The study investigated the effect of a short computer-based environmental sound training regimen on the perception of environmental sounds and speech in experienced cochlear implant (CI) patients.

METHOD

Fourteen CI patients with the average of 5 years of CI experience participated. The protocol consisted of 2 pretests, 1 week apart, followed by 4 environmental sound training sessions conducted on separate days in 1 week, and concluded with 2 posttest sessions, separated by another week without training. Each testing session included an environmental sound test, which consisted of 40 familiar everyday sounds, each represented by 4 different tokens, as well as the Consonant Nucleus Consonant (CNC) word test, and Revised Speech Perception in Noise (SPIN-R) sentence test.

RESULTS

Environmental sounds scores were lower than for either of the speech tests. Following training, there was a significant average improvement of 15.8 points in environmental sound perception, which persisted 1 week later after training was discontinued. No significant improvements were observed for either speech test.

CONCLUSIONS

The findings demonstrate that environmental sound perception, which remains problematic even for experienced CI patients, can be improved with a home-based computer training regimen. Such computer-based training may thus provide an effective low-cost approach to rehabilitation for CI users, and potentially, other hearing impaired populations.

Categories of auditory performance and speech intelligibility ratings of early-implanted children without speech training

OBJECTIVE

To assess whether speech therapy can lead to better results for early cochlear implantation (CI) children.

PATIENTS

A cohort of thirty-four congenitally profoundly deaf children who underwent CI before the age of 18 months at the Sixth Hospital affiliated with Shanghai Jiaotong University from January 2005 to July 2008 were included. Nineteen children received speech therapy in rehabilitation centers (ST), whereas the remaining fifteen cases did not (NST), but were exposed to the real world, as are normal hearing children.

METHODS

All children were assessed before surgery and at 6, 12, and 24 months after surgery with the Categories of Auditory Performance test (CAP) and the Speech Intelligibility Rating (SIR). Each assessment was given by the same therapist who was blind to the situation of the child at each observation interval. CAP and SIR scores of the groups were compared at each time point.

RESULTS

Our study showed that the auditory performance and speech intelligibility of trained children were almost the same as to those of untrained children with early implantation. The CAP and SIR scores of both groups increased with increased time of implant use during the follow-up period, and at each time point, the median scores of the two groups were about equal.

CONCLUSIONS

These results indicate that great communication benefits are achieved by early implantation (<18 months) without routine speech therapy. The results exemplify the importance of enhanced social environments provided by everyday life experience for human brain development and reassure parents considering cochlear implants where speech training is unavailable.

Cochlear implant outcomes in adults and adolescents with early-onset hearing loss

OBJECTIVES

The aims of the study were to investigate (1) speech perception outcomes in people with an early-onset hearing loss (HL) who received a cochlear implant as an adolescent or adult, (2) prognostic factors associated with positive speech perception outcomes, and (3) self-report outcomes in these participants.

DESIGN

Outcomes for 38 implant recipients with a Nucleus device were investigated retrospectively. All participants were diagnosed with a bilateral HL at age #3 yr and were implanted at age 14 yr or older. Nineteen participants had confirmed bilateral, severe to profound HL at age #12 mo (prelingual); nine had confirmed bilateral, severe to profound HL at age.12 mo and #3 yr (perilingual); and the remaining 10 had a diagnosis of bilateral sensorineural HL at age #3 yr which progressed to severe to profound HL after 3 yrs of age (progressive). There were 24 females and 14 males, and the average age at implantation was 33 yr (range 5 14-65 yr). Closed-set and open-set speech perception tests administered pre- and postimplant were analyzed for all participants, in addition to self-report survey measures of benefit, satisfaction, and implant usage.

RESULTS

Participants were placed into one of five hierarchic categories of speech perception performance preimplantation and at 12 mo postimplantation. The categories ranged from sound detection only (category 1) to excellent open-set speech perception (category 5). To be in category 4 or 5, the participant had to score.30% words correct on a recorded version of either the Central Institute for the Deaf Everyday Sentence Lists or the City University of New York Sentences. Before implantation, two recipients (5%) were in category 4 or 5 compared with 20 (53%) at 12 mo postimplant. Consistent with previous studies, there was large intersubject variability in speech scores. Three factors accounted for 63% of the variance on open-set sentence test scores, postimplant: mode of communication in childhood (oral versus total communication/sign), stable as opposed to progressive loss, and time without a hearing aid on the implant ear. More than 80% of survey respondents used their device.8 hr a day, and 90% reported that their ability to understand speech with visual cues was "much better" with the implant. In addition, all reported being satisfied with the device.

CONCLUSION

These results indicate that a cochlear implant should be considered as an option for adults and adolescents with early-onset HL. The majority of participants gained benefit from the device and were satisfied with it. In addition, a substantial number gained good open-set speech perception ability, postimplant. Recipients who used oral communication in childhood, had a progressive loss, and wore a hearing aid on the implant ear up to the time of surgery were more likely to obtain better speech perception outcomes.

The listening cube: a three dimensional auditory training program

OBJECTIVES

Here we present the Listening Cube, an auditory training program for children and adults receiving cochlear implants, developed during the clinical practice at the KIDS Royal Institute for the Deaf in Belgium. We provide information on the content of the program as well as guidance as to how to use it.

METHODS

The Listening Cube is a three-dimensional auditory training model that takes the following into consideration: the sequence of auditory listening skills to be trained, the variety of materials to be used, and the range of listening environments to be considered. During auditory therapy, it is important to develop training protocols and materials to provide rapid improvement over a relatively short time period. Moreover, effectiveness and the general real-life applicability of these protocols to various users should be determined.

RESULTS

Because this publication is not a research article, but comes out of good daily practice, we cannot state the main results of this study. We can only say that this auditory training model is very successful. Since the first report was published in the Dutch language in 2003, more than 200 therapists in Belgium and the Netherlands followed a training course elected to implement the Listening Cube in their daily practice with children and adults with a hearing loss, especially in those wearing cochlear implants.

CONCLUSION

The Listening Cube is a tool to aid in planning therapeutic sessions created to meet individual needs, which is often challenging. The three dimensions of the cube are levels of perception, practice material, and practice conditions. These dimensions can serve as a visual reminder of the task analysis and of other considerations that play a role in structuring therapy sessions.

Effects of auditory training on adult cochlear implant patients: a preliminary report

The process of learning new electrically stimulated speech patterns can be difficult for many cochlear implant users, especially congenitally deafened patients. Some implant users receive little benefit from the device, even after long-term experience. While many factors may influence individual patient outcomes, the paucity of auditory rehabilitation resources, especially for adult users, may contribute to some implant patients' poorer performance. The present study examined whether moderate auditory training, using speech stimuli, can improve the speech-recognition performance of adult cochlear implant patients. Ten cochlear implant patients with limited speech-recognition capabilities used a recently developed computer-based auditory rehabilitation tool to train at home for a period of one month or longer. Before training began, baseline speech-recognition performance was measured for each patient; baseline performance was measured for at least two weeks, until performance asymptoted. After baseline measures were complete, subjects were instructed to train themselves at home using novel monosyllable words one hour per day, five days per week. Subjects then returned to the lab every two weeks for retesting with the baseline speech materials. Preliminary results showed that there was significant improvement in all patients' speech perception performance after moderate training. While most patients did improve, the amount and time course of improvement was highly variable. Moderate training using a computer-based auditory rehabilitation tool can be an effective approach to improve cochlear implant patients' speech recognition, especially for poorer-performing implant users.

Factors influencing neurotrophic effects of electrical stimulation in the deafened developing auditory system

Research in animal models has demonstrated that electrical stimulation from a cochlear implant (CI) may help prevent degeneration of the cochlear spiral ganglion (SG) neurons after deafness. In cats deafened early in life, effective stimulation of the auditory nerve with complex signals for several months preserves a greater density of SG neurons in the stimulated cochleae as compared to the contralateral deafened ear. However, SG survival is still far from normal even with early intervention with an implant. Thus, pharmacologic agents and neurotrophic factors that might be used in combination with an implant are of great interest. Exogenous administration of GM1 ganglioside significantly reduces SG degeneration in deafened animals studied at 7-8 weeks of age, but after several months of stimulation, GM1-treated animals show only modestly better preservation of SG density compared to age-matched non-treated animals. A significant factor influencing neurotrophic effects in animal models is insertion trauma, which results in significant regional SG degeneration. Thus, an important goal is to further improve human CI electrode designs and insertion techniques to minimize trauma. Another important issue for studies of neurotrophic effects in the developing auditory system is the potential role of critical periods. Studies examining animals deafened at 30 days of age (rather than at birth) have explored whether a brief initial period of normal auditory experience affects the vulnerability of the SG or cochlear nucleus (CN) to auditory deprivation. Interestingly, SG survival in animals deafened at 30-days was not significantly different from age-matched neonatally deafened animals, but significant differences were observed in the central auditory system. CN volume was significantly closer to normal in the animals deafened at 30 days as compared to neonatally deafened animals. However, no difference was observed between the stimulated and contralateral CN volumes in either deafened group. Measurements of AVCN spherical cell somata showed that after later onset of deafness in the 30-day deafened group, mean cell size was significantly closer to normal than in the neonatally deafened group. Further, electrical stimulation elicited a significant increase in spherical cell size in the CN ipsilateral to the implant as compared to the contralateral CN in both deafened groups. Neuronal tracer studies have examined the primary afferent projections from the SG to the CN in neonatally deafened cats. CN projections exhibit a clear cochleotopic organization despite severe auditory deprivation from birth. However, when normalized for the smaller CN size after deafness, projections were 30-50% broader than normal. After unilateral electrical stimulation there was no difference between projections from the stimulated and non-stimulated ears. These findings suggest that early normal auditory experience may be essential for the normal development (or subsequent maintenance) of the topographic precision of SG-to-CN projections. After early deafness, the CN volume is markedly smaller than normal, and the spatial precision of SG projections that underlie frequency resolution in the central auditory system is reduced. Electrical stimulation over several months did not reduce or exacerbate these degenerative changes. If similar principles pertain in the human auditory system, then findings in animal models suggest that the basic cochleotopic organization of neural projections in the central auditory system is probably intact even in congenitally deaf individuals. However, the reduced spatial resolution of the primary afferent projections in our studies suggests that there may be inherent limitations for CI stimulation in congenitally deaf subjects. Spatial (spectral) selectivity of stimulation delivered on adjacent CI channels may be poorer due to the greater overlap of SG central axons representing nearby frequencies. Such CI users may be more dependent upon temporal features of electrical stimuli, and it may be advantageous to enhance the salience of such cues, for example, by removing some electrodes from the processor "map" to reduce channel interaction.

Maximizing cochlear implant patients' performance with advanced speech training procedures

Advances in implant technology and speech processing have provided great benefit to many cochlear implant patients. However, some patients receive little benefit from the latest technology, even after many years' experience with the device. Moreover, even the best cochlear implant performers have great difficulty understanding speech in background noise, and music perception and appreciation remain major challenges. Recent studies have shown that targeted auditory training can significantly improve cochlear implant patients' speech recognition performance. Such benefits are not only observed in poorly performing patients, but also in good performers under difficult listening conditions (e.g., speech noise, telephone speech, music, etc.). Targeted auditory training has also been shown to enhance performance gains provided by new implant devices and/or speech processing strategies. These studies suggest that cochlear implantation alone may not fully meet the needs of many patients, and that additional auditory rehabilitation may be needed to maximize the benefits of the implant device. Continuing research will aid in the development of efficient and effective training protocols and materials, thereby minimizing the costs (in terms of time, effort and resources) associated with auditory rehabilitation while maximizing the benefits of cochlear implantation for all recipients.

Perceptual learning and auditory training in cochlear implant recipients

Learning electrically stimulated speech patterns can be a new and difficult experience for cochlear implant (CI) recipients. Recent studies have shown that most implant recipients at least partially adapt to these new patterns via passive, daily-listening experiences. Gradually introducing a speech processor parameter (eg, the degree of spectral mismatch) may provide for more complete and less stressful adaptation. Although the implant device restores hearing sensation and the continued use of the implant provides some degree of adaptation, active auditory rehabilitation may be necessary to maximize the benefit of implantation for CI recipients. Currently, there are scant resources for auditory rehabilitation for adult, postlingually deafened CI recipients. We recently developed a computer-assisted speech-training program to provide the means to conduct auditory rehabilitation at home. The training software targets important acoustic contrasts among speech stimuli, provides auditory and visual feedback, and incorporates progressive training techniques, thereby maintaining recipients' interest during the auditory training exercises. Our recent studies demonstrate the effectiveness of targeted auditory training in improving CI recipients' speech and music perception. Provided with an inexpensive and effective auditory training program, CI recipients may find the motivation and momentum to get the most from the implant device.

Technologic advances in aural rehabilitation: applications and innovative methods of service delivery

The level of interest in aural rehabilitation has increased recently, both in clinical use and in research presentations and publications. Advances in aural rehabilitation have seen previous techniques such as speech tracking and analytic auditory training reappear in computerized forms. These new delivery methods allow for a consistent, cost-effective, and convenient training program. Several computerized aural rehabilitation programs for hearing aid wearers and cochlear implant recipients have recently been developed and were reported on at the 2006 State of the Science Conference of the Rehabilitation Engineering Research Center on Hearing Enhancement at Gallaudet University. This article reviews these programs and outlines the similarities and differences in their design. Another promising area of aural rehabilitation research is the use of pharmaceuticals in the rehabilitation process. The results from a study of the effect of d-amphetamine in conjunction with intensive aural rehabilitation with cochlear implant patients are also described.

Effect of training rate on recognition of spectrally shifted speech

OBJECTIVE

Previous studies have shown that the protocol used for auditory training may significantly affect the outcome of training. However, it is unclear how often training should be performed to maximize its benefit. The present study investigated how the frequency of training contributed to normal-hearing listeners' adaptation to spectrally shifted speech.

METHODS

Eighteen normal-hearing listeners were trained with spectrally shifted and compressed speech via an 8-channel acoustic simulation of cochlear implant speech processing. Five short training sessions (1 hr per session) were completed by each subject; subjects were trained at one of three training rates: five sessions per week, three sessions per week, or one session per week. Subjects were trained to identify medial vowels presented in a cVc format; depending on the level of difficulty, the number of response choices was increased and/or the acoustic differences between vowels were reduced. Vowel and consonant recognition was measured before and after training as well as at regular intervals during the training period. Sentence recognition was measured before and after training only.

RESULTS

Results showed that pretraining vowel recognition scores were poor (14.0% correct, on average) for all subjects, due to the severe spectral shift. After five sessions of targeted vowel contrast training, there was a significant improvement of shifted vowel recognition for most subjects. The mean improvement was comparable (approximately 15 percentage points) across the three training rate conditions, despite significant intersubject variability in pre- and pretraining baseline performance. There was no significant difference in training outcomes among the three training rates. Spectrally shifted consonant and sentence recognition also improved by approximately 20 percentage points after training, even though consonants and sentences were not explicitly trained. Similar to vowel recognition, there was no significant difference in training outcomes among the three training rates for shifted consonant and sentence recognition.

CONCLUSIONS

The results demonstrated that the training rate had little effect on normal-hearing listeners' adaptation to spectrally shifted speech, at least for the training periods (ranging from 1 to 5 wk) used in the present study. The outcome of auditory training may depend more strongly on the amount of training (i.e., total number of training sessions) rather than the frequency of training (i.e., daily or once per week). Although more frequent training may accelerate listeners' adaptation to spectrally shifted speech, there may be significant benefits from training as little as one session per week. The results of the present study suggest that appropriate training schedules can be developed to optimize the effectiveness, efficiency, and effort associated with hearing-impaired patients' auditory rehabilitation.

Effects of computer-assisted speech training on Mandarin-speaking hearing-impaired children

The present study investigated whether moderate amounts of computer-assisted speech training can improve the speech recognition performance of hearing-impaired children. Ten Mandarin-speaking children (3 hearing aid users and 7 cochlear implant users) participated in the study. Training was conducted at home using a personal computer for half an hour per day, 5 days per week, for a period of 10 weeks. Results showed significant improvements in subjects' vowel, consonant, and tone recognition performance after training. The improved performance was largely retained for 2 months after training was completed. These results suggest that moderate amounts of auditory training, using a computer-based auditory rehabilitation tool with minimal supervision, can be effective in improving the speech performance of hearing-impaired children.

Effectiveness of computer-based auditory training in improving the perception of noise-vocoded speech

Five experiments were designed to evaluate the effectiveness of "high-variability" lexical training in improving the ability of normal-hearing subjects to perceive noise-vocoded speech that had been spectrally shifted to simulate tonotopic misalignment. Two approaches to training were implemented. One training approach required subjects to recognize isolated words, while the other training approach required subjects to recognize words in sentences. Both approaches to training improved the ability to identify words in sentences. Improvements following a single session (lasting 1-2 h) of auditory training ranged between 7 and 12 %pts and were significantly larger than improvements following a visual control task that was matched with the auditory training task in terms of the response demands. An additional three sessions of word- and sentence-based training led to further improvements, with the average overall improvement ranging from 13 to 18% pts. When a tonotopic misalignment of 3 mm rather than 6 mm was simulated, training with several talkers led to greater generalization to new talkers than training with a single talker. The results confirm that computer-based lexical training can help overcome the effects of spectral distortions in speech, and they suggest that training materials are most effective when several talkers are included.

Computer-Assisted Speech Training for Cochlear Implant Patients: Feasibility, Outcomes, and Future Directions

Learning electrically stimulated speech patterns can be a new and difficult experience for cochlear implant patients. Cochlear implantation alone may not fully meet the needs of many patients, and additional auditory rehabilitation may be necessary to maximize the benefits of the implant device. A recently developed computer-assisted speech-training program provides cochlear implant patients with the means to conduct auditory rehabilitation at home. The training software targets important acoustic contrasts between speech stimuli and provides auditory and visual feedback as well as progressive training, thereby maintaining patients' interest in the auditory training exercises. Recent scientific studies have demonstrated the effectiveness of such specialized auditory training programs in improving cochlear implant patients' speech recognition performance. Provided with an inexpensive and accessible auditory training program, cochlear implant patients may find the motivation and momentum to get the most from the implant device.

Auditory training with spectrally shifted speech: implications for cochlear implant patient auditory rehabilitation

After implantation, postlingually deafened cochlear implant (CI) patients must adapt to both spectrally reduced and spectrally shifted speech, due to the limited number of electrodes and the limited length of the electrode array. This adaptation generally occurs during the first three to six months of implant use and may continue for many years. To see whether moderate speech training can accelerate this learning process, 16 naïve, normal-hearing listeners were trained with spectrally shifted speech via an eight-channel acoustic simulation of CI speech processing. Baseline vowel and consonant recognition was measured for both spectrally shifted and unshifted speech. Short daily training sessions were conducted over five consecutive days, using four different protocols. For the test-only protocol, no improvement was seen over the five-day period. Similarly, sentence training provided little benefit for vowel recognition. However, after five days of targeted phoneme training, subjects' recognition of spectrally shifted vowels significantly improved in most subjects. This improvement did not generalize to the spectrally unshifted vowel and consonant tokens, suggesting that subjects adapted to the specific spectral shift, rather than to the eight-channel processing in general. Interestingly, significant improvement was also observed for the recognition of spectrally shifted consonants. The largest improvement was observed with targeted vowel contrast training, which did not include any explicit consonant training. These results suggest that targeted phoneme training can accelerate adaptation to spectrally shifted speech. Given these results with normal-hearing listeners, auditory rehabilitation tools that provide targeted phoneme training may be effective in improving the speech recognition performance of adult CI users.

Electrode discrimination and speech perception in young children using cochlear implants

OBJECTIVE

The aim was to determine the efficacy of a child-appropriate procedure to assess electrode discrimination ability in young children using cochlear implants and to investigate the relationship of electrode discrimination ability and speech perception performance in children implanted at a young age.

DESIGN

An adaptation of the play audiometry procedure was used to assess electrode discrimination in seventeen 4- to 10-yr-old children. The children were required to respond with a game-like motor response when a repeating stimulation on a reference electrode "changed" to a different electrode. They were also assessed on a speech feature discrimination test, a closed-set word recognition test and a nonverbal intelligence task.

RESULTS

Sixty-five percent of subjects demonstrated ability to discriminate adjacent electrodes in mid and apical regions of the cochlea, whilst the remaining subjects needed electrode separations of between two and nine electrodes for successful discrimination. In a forward stepwise regression analysis electrode discrimination ability was found to be the strongest factor in accounting for variance in the speech perception scores. Subject variables such as duration of deafness, nonverbal intelligence and implant experience did not significantly account for further variance in the speech perception scores for this group of children.

CONCLUSIONS

Electrode discrimination ability was the strongest factor in predicting performance on speech perception measures in a group of children using cochlear implants.

Plasticity in central representations in the inferior colliculus induced by chronic single- vs. two-channel electrical stimulation by a cochlear implant after neonatal deafness

The goal of this research is to examine the functional consequences of patterned electrical stimulation delivered by a cochlear implant in the deafened developing auditory system. In previous electrophysiological experiments conducted in the inferior colliculus (IC), we have demonstrated that the precise cochleotopic organization of the central nucleus (ICC) develops normally in neonatally deafened unstimulated cats and is unaltered despite the lack of normal auditory input during development. However, these studies also showed that chronic electrical stimulation delivered at a single intracochlear location by one bipolar channel of a cochlear implant induces significant expansion of the central representation of the stimulated cochlear sector and degrades the cochleotopic organization of the IC. This report presents additional data from a new experimental series of neonatally deafened cats that received chronic stimulation on two adjacent bipolar intracochlear channels of a cochlear implant. Results suggest that competing inputs elicited by electrical stimulation delivered by two adjacent channels can maintain the selective representations of each activated cochlear sector within the central auditory system and prevent the expansion seen after single-channel stimulation. Alternating stimulation of two channels and use of highly controlled electrical signals may be particularly effective in maintaining or even sharpening selectivity of central representations of stimulated cochlear sectors. In contrast, simultaneous stimulation using two channels of a model analog cochlear implant processor in one experimental animal failed to maintain channel selectivity and resulted in marked expansion and fusion of the central representations of the stimulated channels. This potentially important preliminary result suggests that under some conditions the central auditory system may be unable to discriminate simultaneous, overlapping inputs from adjacent cochlear implant channels as distinct.