Initial development of a spatially separated speech-in-noise and localization training program.

OBJECTIVE: This article describes the initial development of a novel approach for training hearing-impaired listeners to improve their ability to understand speech in the presence of background noise and to also improve their ability to localize sounds. DESIGN: Most people with hearing loss, even those well fit with hearing devices, still experience significant problems understanding speech in noise. Prior research suggests that at least some subjects can experience improved speech understanding with training. However, all training systems that we are aware of have one basic, critical limitation. They do not provide spatial separation of the speech and noise, therefore ignoring the potential benefits of training binaural hearing. In this paper we describe our initial experience with a home-based training system that includes spatially separated speech-in-noise and localization training. RESULTS: Throughout the development of this system patient input, training and preliminary pilot data from individuals with bilateral cochlear implants were utilized. Positive feedback from subjective reports indicated that some individuals were engaged in the treatment, and formal testing showed benefit. Feedback and practical issues resulted from the reduction of an eight-loudspeaker to a two-loudspeaker system. CONCLUSIONS: These preliminary findings suggest we have successfully developed a viable spatial hearing training system that can improve binaural hearing in noise and localization. Applications include, but are not limited to, hearing with hearing aids and cochlear implants.

The effect of reducing the number of electrodes on spatial hearing tasks for bilateral cochlear implant recipients.

BACKGROUND: Many studies have documented the effect of reducing spectral information for speech perception in listeners with normal hearing and hearing impairment. While it is understood that more spectral bands are needed for unilateral cochlear implant listeners to perform well on more challenging listening tasks such as speech perception in noise, it is unclear how reducing the number of spectral bands or electrodes in cochlear implants influences the ability to localize sound or understand speech with spatially separate noise sources. PURPOSE: The purpose of this study was to measure the effect of reducing the number of electrodes for patients with bilateral cochlear implants on spatial hearing tasks. RESEARCH DESIGN: Performance on spatial hearing tasks was examined as the number of bilateral electrodes in the speech processor was deactivated equally across ears and the full frequency spectrum was reallocated to a reduced number of active electrodes. Program parameters (i.e., pulse width, stimulation rate) were held constant among the programs and set identically between the right and left cochlear implants so that only the number of electrodes varied. STUDY SAMPLE: Nine subjects had used bilateral Nucleus or Advanced Bionics cochlear implants for at least 12 mo prior to beginning the study. Only those subjects with full insertion of the electrode arrays with all electrodes active in both ears were eligible to participate. DATA COLLECTION AND ANALYSIS: Two test measures were utilized to evaluate the effect of reducing the number of electrodes, including a speech-perception-in-noise test with spatially separated sources and a sound source localization test. RESULTS: Reducing the number of electrodes had different effects across individuals. Three patterns emerged: (1) no effect on localization (two of nine subjects), (2) at least two to four bilateral electrodes were required for maximal performance (five of nine subjects), and (3) performance gradually decreased across conditions as electrode number was reduced (two of nine subjects). For the test of speech perception in spatially separated noise, performance was affected as the number of electrodes was reduced for all subjects. Two categories of performance were found: (1) at least three or four bilateral electrodes were needed for maximum performance (five of seven subjects) and (2) as the number of electrodes were reduced, performance gradually decreased across conditions (two of seven subjects). CONCLUSION: Large individual differences exist in determining maximum performance using bilateral electrodes for localization and speech perception in noise. For some bilateral cochlear implant users, as few as three to four electrodes can be used to obtain maximal performance on localization and speech-in-noise tests. However, other listeners show a gradual decrement in performance on both tasks when the number of electrodes is reduced.

Performance over time on adults with simultaneous bilateral cochlear implants.

BACKGROUND: Maximum performance and long-term stability of bilateral cochlear implants has become an important topic because there has been increasing numbers of recipients of bilateral cochlear implants. PURPOSE: To determine the performance over time (up to 6yr) of subjects with simultaneous bilateral cochlear implants (CI+CI) on word recognition and localization. RESEARCH DESIGN: Over-time investigation of word recognition in quiet (CNC) and sound localization in quiet (Everyday Sounds Localization Test). STUDY SAMPLE: The subjects were 48 adults who simultaneously received their cochlear implants at the University of Iowa. RESULTS: For word recognition, percent correct scores continuously improved up to 1 yr postimplantation with the most benefit occurring within the first month of implantation. In observing up to 72 mo, the averaged scores reached to the plateau of about 63% correct in CNC after 2 yr (N = 31). But, when we followed 17 subjects who have complete data set between 12 mo and 48+ months, word recognition scores were significantly different from 12 mo to 48 + months, which implies binaural advantages need more time to be developed. Localization test results suggested that the root mean square (RMS) error scores continuously improved up to 1 yr postimplantation with most benefits occurring within the first 3 mo. After 2 yr, the averaged scores reached to the plateau of about 20 degrees RMS error (N = 27). When we followed 10 subjects who have complete data set between 12 mo and 48+ months, localization scores were not improved from 12 mo to 48+ months. There were large individual differences in performance over time. CONCLUSIONS: In general, substantial benefits in both word recognition and localization were found over the first 1-12 mo postimplantation for subjects who received simultaneous bilateral cochlear implants. These benefits were maintained over time up to 6yr postimplantation.

An attempt to improve bilateral cochlear implants by increasing the distance between electrodes and providing complementary information to the two ears.

OBJECTIVES: The purpose of this investigation was to determine if adult bilateral cochlear implant recipients could benefit from using a speech processing strategy in which the input spectrum was interleaved among electrodes across the two implants. DESIGN: Two separate experiments were conducted. In both experiments, subjects were tested using a control speech processing strategy and a strategy in which the full input spectrum was filtered so that only the output of half of the filters was audible to one implant, while the output of the alternative filters was audible to the other implant. The filters were interleaved in a way that created alternate frequency "holes" between the two cochlear implants. RESULTS: In experiment one, four subjects were tested on consonant recognition. Results indicated that one of the four subjects performed better with the interleaved strategy, one subject received a binaural advantage with the interleaved strategy that they did not receive with the control strategy, and two subjects showed no decrement in performance when using the interleaved strategy. In the second experiment, 11 subjects were tested on word recognition, sentences in noise, and localization (it should be noted that not all subjects participated in all tests). Results showed that for speech perception testing one subject achieved significantly better scores with the interleaved strategy on all tests, and seven subjects showed a significant improvement with the interleaved strategy on at least one test. Only one subject showed a decrement in performance on all speech perception tests with the interleaved strategy. Out of nine subjects, one subject preferred the sound quality of the interleaved strategy. No one performed better on localization with the interleaved strategy. CONCLUSION: Data from this study indicate that some adult bilateral cochlear implant recipients can benefit from using a speech processing strategy in which the input spectrum is interleaved among electrodes across the two implants. It is possible that the subjects in this study who showed a significant improvement with the interleaved strategy did so because of less channel interaction; however, this hypothesis was not directly tested.

A daily alternating method for comparing different signal-processing strategies in hearing aids and in cochlear implants.

BACKGROUND: Although we always want to select the best signal-processing strategy for our hearing-aid and cochlear-implant patients, no efficient and valid procedure is available. Comparisons in the office are without listening experience, and short-term take-home trials are likely influenced by the order of strategies tried. PURPOSE: The purpose of this study was to evaluate a new procedure for comparing signal-processing strategies whereby patients listen with one strategy one day and another strategy the next day. They continue this daily comparison for several weeks. We determined (1) if differences existed between strategies without prior listening experience and (2) if performance differences (or lack there of) obtained at the first listening experience are consistent with performance after two to three months of alternating between strategies on a daily basis (equal listening experience). RESEARCH DESIGN: Eight subjects were tested pretrial with a vowel, sentence, and spondee recognition test, a localization task, and a quality rating test. They were required to listen to one of two different signal processing strategies alternating between strategies on a daily basis. After one to three months of listening, subjects returned for follow-up testing. Additionally, subjects were asked to make daily ratings and comments in a diary. RESULTS: Pre-trial (no previous listening experience), a clear trend favoring one strategy was observed in four subjects. Four other subjects showed no clear advantage. Post-trial (after alternating daily between strategies), of the four subjects who showed a clear advantage for one signal processing strategy, only one subject showed that same advantage. One subject ended up with an advantage for the other strategy. Post-trial, of the four subjects who showed no advantage for a particular signal processing strategy, three did show an advantage for one strategy over the other. CONCLUSION: Patients are willing to alternate between signal processing strategies on a daily basis for up to three months in an attempt to determine their optimal strategy. Although some patients showed superior performance with initial fittings (and some did not), the results of pre-trial comparison did not always persist after having equal listening experience. We recommend this daily alternating listening technique when there is interest in determining optimal performance among different signal processing strategies when fitting hearing aids or cochlear implants.

Long-term performance of Clarion 1.0 cochlear implant users.

OBJECTIVE/HYPOTHESIS: To evaluate the long-term performance of adult Clarion 1.0 cochlear implant users. STUDY DESIGN: This was a retrospective, longitudinal study evaluating word discrimination in quiet for 31 adult cochlear implant patients with preimplantation sentence scores of less than 10%. METHODS: The length of the study was 135 months with a mean follow-up length of 93 (median, 96) months. For the duration of the study, all subjects used the Clarion 1.0 cochlear implant with speech processors programmed for the use of the continuous interleaved sampling strategy. RESULTS: There was no significant growth or decline in speech perception after 24 months postimplantation unless adverse medical events were experienced. Age at implantation was significantly and substantially negatively correlated (-11% word score per decade, r = 0.68) with most recent score, maximum score, time to maximum score, range of performance, 24- to 130-month mean score, and for any longitudinal data point tested: 3 to 6 months, 6 months, 1 year, 2 years, 5 years, and 10 years. There were no age-related declines in performance. There were no observed correlations between duration of deafness and any of the variables listed above. CONCLUSIONS: The lack of correlation between duration of deafness and performance in a cohort without residual hearing suggests the presence of a strong correlation between age and speech performance with a cochlear implant. That the cochlear implant is a safe therapy for the treatment of profound deafness is supported by the stability of scores through the 10-year study period as well as a zero rate of device failures or explantation.

Speech perception and localization with adults with bilateral sequential cochlear implants.

This investigation reports measures of binaural hearing of all of our seven adults who have received sequential bilateral cochlear implants (range of time between implantation of 6 yr/8 mo and 17 yr). All subjects used both devices in everyday life. The internal array, number of channels, rate, and signal processing strategies were usually quite different between devices. Speech recognition was tested by using words in quiet and sentences in noise with the sentence stimuli presented from the front and the noise presented from the front, the right, or the left at a 90 degrees angle. Bilateral localization was tested by using an everyday sounds test with stimuli presented from one of eight loudspeakers. Results showed that all subjects received a significant bilateral improvement on at least one speech perception test compared to either implant alone. Four of seven subjects with bilateral devices demonstrated some (root-mean-square error below 30 degrees ) localization abilities. The two subjects tested unilaterally before receiving a second implant showed a bilateral improvement on localization after implantation of the second side. We conclude that sequential implants can be beneficial even after many years of monaural use and even with very different cochlear implants.

Effects of converting bilateral cochlear implant subjects to a strategy with increased rate and number of channels.

OBJECTIVES: Three different Advanced Bionics processing strategies were evaluated: 1) 8-channel, 813 pulses per second (pps), Continuous Interleaved Sampling (CIS); 2) 16-channel, 5,100 pps, HiResolution Paired (HiRes P); and 3) 16-channel, 2,900 pps, HiResolution Sequential (HiRes S). METHODS: Seven adult bilateral Clarion CII cochlear implant recipients who had been using a CIS processing strategy for at least 18 months participated in this study. Sentence recognition in multitalker babble from the front was collected on subjects using their CIS strategy and after subjects were programmed for the first time with HiRes P and HiRes S strategies. An ABAB design was implemented for 1 month whereby subjects used each HiResolution strategy every other day. Sentence recognition testing was repeated at the 1- and 3-month post-HiResolution test intervals. RESULTS: Comparisons between the CIS and HiResolution strategies showed immediate improvements for 5 subjects in favor of the HiResolution strategies. After 1 month of alternating between the HiRes P and HiRes S strategies, remarkably, 2 subjects showed improvements of 60%, 2 subjects showed improvements of 40%, and 2 subjects showed improvements of 30% over the CIS strategy that they had previously used for at least 18 months. The results after 3 months of use were consistent with those obtained at 1 month. CONCLUSIONS: The HiRes S and HiRes P strategies resulted in dramatic improvements in speech perception in noise for a subset of subjects who had been using the CIS strategy bilaterally. This finding demonstrates that these subjects were able to tolerate a more difficult signal-to-noise ratio. Further work is needed to determine the independent effects of rate versus number of channels.

Benefit of wearing a hearing aid on the unimplanted ear in adult users of a cochlear implant.

The purpose of this investigation was to document performance of participants wearing a cochlear implant and hearing aid in opposite ears on speech-perception and localization tests. Twelve individuals who wore a cochlear implant and a hearing aid on contralateral ears were tested on their abilities to understand words in quiet and sentences in noise, and to localize everyday sounds. All speech stimuli were presented from the front, with the noise stimuli presented from the front, the right, or the left at a 90 degrees angle. Binaural summation in quiet and in noise, binaural squelch effects, and localization were studied to determine bilateral advantages. The magnitude of the monaural head shadow effect (the difference in unilateral performance when noise was facing the unilateral device vs. when the noise was opposite the unilateral device) also was studied. The test setup for localization was composed of an 8-speaker array spanning an arc of approximately 108 degrees in front of each participant. Group results yielded a statistically significant combined benefit of wearing a hearing aid in conjunction with a cochlear implant on opposite ears in noise conditions. Those participants who received a binaural advantage in 1 condition did not necessarily show a binaural advantage in another. Only 2 participants out of 12 were able to localize when wearing 2 devices. Further efforts are required to improve the integration of information from combined use of cochlear implant and hearing aid devices for enhancement of speech perception in noise and localization.

Trade-offs between better hearing and better cosmetics.

A case study is reported of an adult bilateral cochlear implant patient who owns both a pair of ear-level and body-worn speech processors and chooses to wear them in unique configurations, knowingly compromising his auditory performance. The aim was to determine if differences in hearing could be quantified between these devices and to examine the size of these effects that would lend themselves to trading between performance and cosmetics. The patient reported wearing bilateral ear-level speech processors (programmed with the Cochlear Corporation spectral PEAK [SPEAK] coding strategy) 75% of the time for cosmetic and convenience reasons even though he "heard the best" with bilateral body-worn speech processors (programmed with the Cochlear Corporation advanced combination encoder strategy [ACE]). Speech perception and localization tests confirmed that this patient performed significantly better on monosyllabic phonemes in quiet (a difference from 60% to 75%) and localization (a total root-mean-squared-error difference from 22 degrees to 12degrees ) with bilateral body-worn speech processors and consistently rated various speech sounds as more clear than with bilateral ear-level units. There was a 2-dB difference in sentence reception threshold in noise, which was not statistically significant. These results suggest that clinicians should consider and provide options to patients when there are trade-offs to be made regarding understanding performance and cosmetics. Some individuals may choose better speech perception over cosmetics, and the ability to choose might result in greater compliance. The observations made here are relevant to hearing aid users as well.

Update on bilateral cochlear implantation.

PURPOSE OF REVIEW: Providing a unilateral cochlear implant in a patient with a profound bilateral hearing loss has now been a standard clinical practice for more than a decade. Although results are often very good, normal hearing has not been restored. One exciting opportunity to improve hearing in this population is to provide a second implant. However, it is not obvious that bilateral electrical stimulation can be integrated by the central nervous system. This article describes binaural hearing and reviews currently published articles on binaural cochlear implants. RECENT FINDINGS: Controlled laboratory trials have focused on distinguishing different categories of potential binaural advantages. A potential summation effect occurs when the same stimulus is available at two ears. Listening in noise with two ears should be better than listening with one ear when the additional ear is away from the noise. This head shadow benefit results from acoustic effects, not physiologic ones. When the second ear is added near the noise source, a binaural squelch benefit can occur, requiring neural integration from both sides. Finally, two ears may improve sound localization. Binaural implantees generally benefit from head shadow effects. Only some benefit from summation and squelch effects. Most, but not all, show improved horizontal plane localization. SUMMARY: It is now appropriate to begin experimental studies of binaural cochlear implants. Preliminary results show promise to improve head shadow, a physical advantage, and sound localization. Some benefits have been observed for improved summation and squelch. These findings have demonstrated that the brain can integrate electrical stimulation from the two ears. Future studies will be required to maximize this binaural hearing.