Perceptual organization of sequential stimuli in cochlear implant listeners: A temporal processing approach.

OBJECTIVE: Cochlear Implant (CI) users often suffer difficulties in perceiving speech in noisy environments that could be attributed to reduced Auditory Stream Segregation (ASS) ability. ASS is the process used to separate a complex sound into different perceptual streams. The evidence that CI listeners routinely experience stream segregation skill is limited and equivocal. The present study was aimed to investigate the effects of temporal cues on ASS performance in postlingually deaf listeners with CI. METHODS: Nineteen (age range: 28-64 years old) monaurally cochlear implanted listener participated in this study. They were presented with 30-s sequences of alternating stimuli in a repeating A-B-A-A-B-A…sequence, where "tone A" corresponds to a stimulus applied to electrode 11, and "tone B" to a stimulus on one of the other electrode. To investigate the effect of temporal cues on ASS, four different tone repetition times (TRTs) were utilized: 50, 100, 150, and 200 ms. Speech discrimination scores in noise were also recorded for every CI recipients. RESULTS: Only 6 (32%) CI users demonstrated ASS pattern similar to the normal hearing subjects, while the majority of the users (n=13) possessed poorer ASS skills. An analysis of variance showed a significant effect of electrode separation (p<0.001) and TRT (p=0.041), but there was no significant interaction between electrode separation and TRT variables. The best ASS performance was obtained when TRT was 200 ms, and there was no significant effect for other TRT conditions. Moderate, significant correlations between streaming and speech discrimination measurement in noise was also observed (r=0.62), with better stream segregation associated with better understanding of speech in noise. CONCLUSION: ASS is a contributing factor in the ability to perceive speech in background noise. The inability of some CI recipients to perform stream segregation may therefore contribute to their difficulties in noisy backgrounds. Furthermore, stream segregation ability is related to the tone repetition time between the sounds.

The effect of envelope modulations on binaural processing.

An experiment was performed with 10 young normal-hearing listeners that attempted to determine if envelope modulations affected binaural processing in bandlimited pulse trains. Listeners detected an interaurally out-of-phase carrier pulse train in the presence of different amplitude modulations. The peaks of the pulses were constant (called "flat" or F), followed envelope modulations from an interaurally correlated 50-Hz bandwidth noise (called CM), or followed modulations from an interaurally uncorrelated noise (called UM). The pulse rate was varied from 50 to 500 pulses per second (pps) and the center frequency (CF) was 4 or 8 kHz. It was hypothesized that CM would cause no change or an increase in performance compared to F; UM would cause a decrease because of the blurring of the binaural detection cue. There was a small but significant decrease from F to CM (inconsistent with the hypothesis) and a further decrease from CM to UM (consistent with the hypothesis). Critically, there was a significant envelope by rate interaction caused by a decrease from F to CM for the 200-300 pps rates. The data can be explained by a subject-based factor, where some listeners experienced interaural envelope decorrelation when the sound was encoded by the auditory system that reduced performance when the modulations were present. Since the decrease in performance between F and CM conditions was small, it seems that most young normal-hearing listeners have very similar encoding of modulated stimuli across the ears. This type of task, when further optimized, may be able to assess if hearing-impaired populations experience interaural decorrelation from encoding modulated stimuli and therefore could help better understand the limited spatial hearing in populations like cochlear-implant users.

Lateralization of virtual sound sources with a binaural cochlear-implant sound coding strategy inspired by the medial olivocochlear reflex.

Many users of bilateral cochlear implants (BiCIs) localize sound sources less accurately than do people with normal hearing. This may be partly due to using two independently functioning CIs with fixed compression, which distorts and/or reduces interaural level differences (ILDs). Here, we investigate the potential benefits of using binaurally coupled, dynamic compression inspired by the medial olivocochlear reflex; an approach termed "the MOC strategy" (Lopez-Poveda et al., 2016, Ear Hear 37:e138-e148). Twelve BiCI users were asked to localize wideband (125-6000 Hz) noise tokens in a virtual horizontal plane. Stimuli were processed through a standard (STD) sound processing strategy (i.e., involving two independently functioning sound processors with fixed compression) and three different implementations of the MOC strategy: one with fast (MOC1) and two with slower contralateral control of compression (MOC2 and MOC3). The MOC1 and MOC2 strategies had effectively greater inhibition in the higher than in the lower frequency channels, while the MOC3 strategy had slightly greater inhibition in the lower than in the higher frequency channels. Localization was most accurate with the MOC1 strategy, presumably because it provided the largest and less ambiguous ILDs. The angle error improved slightly from 25.3° with the STD strategy to 22.7° with the MOC1 strategy. The improvement in localization ability over the STD strategy disappeared when the contralateral control of compression was made slower, presumably because stimuli were too short (200 ms) for the slower contralateral inhibition to enhance ILDs. Results suggest that some MOC implementations hold promise for improving not only speech-in-noise intelligibility, as shown elsewhere, but also sound source lateralization.

Time-compression thresholds for Mandarin sentences in normal-hearing and cochlear implant listeners.

Faster speech may facilitate more efficient communication, but if speech is too fast it becomes unintelligible. The maximum speeds at which Mandarin words were intelligible in a sentence context were quantified for normal hearing (NH) and cochlear implant (CI) listeners by measuring time-compression thresholds (TCTs) in an adaptive staircase procedure. In Experiment 1, both original and CI-vocoded time-compressed speech from the MSP (Mandarin speech perception) and MHINT (Mandarin hearing in noise test) corpora was presented to 10 NH subjects over headphones. In Experiment 2, original time-compressed speech was presented to 10 CI subjects and another 10 NH subjects through a loudspeaker in a soundproof room. Sentences were time-compressed without changing their spectral profile, and were presented up to three times within a single trial. At the end of each trial, the number of correctly identified words in the sentence was scored. A 50%-word recognition threshold was tracked in the psychophysical procedure. The observed median TCTs were very similar for MSP and MHINT speech. For NH listeners, median TCTs were around 16.7 syllables/s for normal speech, and 11.8 and 8.6 syllables/s respectively for 8 and 4 channel tone-carrier vocoded speech. For CI listeners, TCTs were only around 6.8 syllables/s. The interquartile range of the TCTs within each cohort was smaller than 3.0 syllables/s. Speech reception thresholds in noise were also measured in Experiment 2, and were found to be strongly correlated with TCTs for CI listeners. In conclusion, the Mandarin sentence TCTs were around 16.7 syllables/s for most NH subjects, but rarely faster than 10.0 syllables/s for CI listeners, which quantitatively illustrated upper limits of fast speech information processing with CIs.

Improved interaural timing of acoustic nerve stimulation affects sound localization in single-sided deaf cochlear implant users.

The main impairment associated with single-sided deafness (SSD) is the loss of binaural hearing. Currently, the most effective treatment to compensate for this deficit is to supply patients suffering from SSD with a cochlear implant (CI) in the deaf ear. With this approach binaural hearing abilities can be restored to a certain extent, which is expressed in an improvement in such patients with regard to sound source localization and speech comprehension in noise after receipt of a CI. However, binaural performance of these listeners does not reach the level of normal-hearing listeners. One of the reasons for this might be that the electrical stimulation via CI and the physiological stimulation via the intact ear are not synchronized: the CI transmits the information to the auditory nerve with different timing than does the intact inner ear. As a result, there is a timing mismatch of the information transfer between the left and the right side, which may account for the limited binaural performance. The effective mismatch in timing depends on the CI system because of different stimulation strategies implemented in devices from different manufacturers. For the particular CI device used in this study (MED-EL Mi1000/Mi1200) electrical stimulation led to faster activation of the auditory nerve than natural for a wide frequency range. In particular, electrical stimulation was about 1 to up to 2 ms ahead of time for frequencies above 1.5 kHz. Hence, it was hypothesized that information transfer between the left and the right ear can be tuned by delaying the CI signal. The goal of the present study was to investigate whether such a delay in the CI signal affects binaural performance of CI users with SSD. For this purpose, sound source localization and speech perception in noise were tested in a sample of 12 CI users with SSD (mean age 51 ±â€¯12 years). The tests were performed for four different delay times of the CI signal applied spontaneously (0.5, 1, 2 and 4 ms) and for the base line condition "no delay" in the CI signal (i.e. everyday use). It was found that delaying the signal had a significant impact on sound source localization. Speech perception in noise was affected, but less pronounced than was sound localization. Regarding sound source localization, a signal delay of 1 ms applied to this particular CI device produced the best performance in our patients. It is concluded that improving the synchronisation between the CI-transferred signal and the naturally transferred signal could increase binaural hearing performance in CI users with SSD.

Effects of the relative timing of opposite-polarity pulses on loudness for cochlear implant listeners.

The symmetric biphasic pulses used in contemporary cochlear implants (CIs) consist of both cathodic and anodic currents, which may stimulate different sites on spiral ganglion neurons and, potentially, interact with each other. The effect on the order of anodic and cathodic stimulation on loudness at short inter-pulse intervals (IPIs; 0-800 µs) is investigated. Pairs of opposite-polarity pseudomonophasic (PS) pulses were used and the amplitude of each pulse was manipulated independently. In experiment 1 the two PS pulses differed in their current level in order to elicit the same loudness when presented separately. Six users of the Advanced Bionics CI (Valencia, CA) loudness-ranked trains of the pulse pairs using a midpoint-comparison procedure. Stimuli with anodic-leading polarity were louder than those with cathodic-leading polarity for IPIs shorter than 400 µs. This effect was small-about 0.3 dB-but consistent across listeners. When the same procedure was repeated with both PS pulses having the same current level (experiment 2), anodic-leading stimuli were still louder than cathodic-leading stimuli at very short intervals. However, when using symmetric biphasic pulses (experiment 3) the effect disappeared at short intervals and reversed at long intervals. Possible peripheral sources of such polarity interactions are discussed.

Patient Acceptance of Invasive Treatments for Tinnitus.

PURPOSE: The field of neuromodulation is currently seeking to treat a wide range of disorders with various types of invasive devices. In recent years, several preclinical trials and case reports in humans have been published on their potential for chronic tinnitus. However, studies to obtain insight into patients' willingness to undergo these treatments are scarce. The aim of this survey study was to find out whether tinnitus patients are willing to undergo invasive neuromodulation when taking its risks, costs, and potential benefits into account. METHOD: A Visual Analog Scale (VAS, 0-10) was used to measure the outcome. Spearman's rank-order correlation coefficients were computed to determine the correlation between patient characteristics and acceptance rates. RESULTS: Around one fifth of the patients were reasonably willing to undergo invasive treatment (VAS 5-7), and around one fifth were fully willing to do so (VAS 8-10). Hearing aids, used as a control, were accepted most, followed by cochlear implantation, deep brain stimulation, and cortical stimulation. Acceptance rates were slightly higher when the chance of cure was higher. Patients with a history of attempted treatments were more eager than others to find a new treatment for tinnitus. CONCLUSIONS: A considerable proportion of patients with tinnitus would accept a variety of invasive treatments despite the associated risks or costs. When clinical neuromodulatory studies for tinnitus are to be performed, particular attention should be given to obtaining informed consent, including explaining the potential risks and providing a realistic outcome expectation.

Cochlear implants: clinical and societal outcomes.

Over the past 30 years, hearing care clinicians have increasingly relied on cochlear implants to restore auditory sensitivity in selected patients with advanced sensorineural hearing loss. This article examines the impact of intervention with cochlear implantation in children and adults. The authors report a range of clinic-based results and patient-based outcomes reflected in the reported literature on cochlear implants. The authors describe the basic assessment of the physiologic response to auditory nerve stimulation; measures of receptive and productive benefit; and surveys of life effects as reflected measures of quality of life, educational attainment, and economic impact.

Patient preferences and willingness to pay for tinnitus treatments.

PURPOSE: There will likely be several different tinnitus treatments necessary, and it is important to understand patient preferences and factors that might contribute to treatment acceptability. This study explores the acceptability of a wide range of different tinnitus treatments, from noninvasive wearable devices to surgically implanted devices in the brain. Understanding how tinnitus sufferers consider and rank such options and how they might be influenced by their own perception of the severity of their tinnitus could help clinicians, researchers, and companies plan future efforts for approaching new treatments. DATA COLLECTION AND ANALYSIS: 197 tinnitus self-help group attendees rated their acceptance of treatments on a scale from 0 (not acceptable) to 100 (fully acceptable). The treatments included external devices, medications, cochlear implants, an implant on the brain surface, and an implant in the brain. They were also asked how much they would pay for successful treatments. RESULTS: There was a significant correlation between loudness and annoyance (r = .78). To reduce tinnitus by half, an "acceptable" response between 91 and 100 was reported by 30% of the respondents for devices, by 52% for pills, by 25% for cochlear implants, by 13% for implants on the brain surface, and by 13% for implants in the brain. To reduce tinnitus completely, a 91-100 acceptable response was reported by 42% for devices, by 62% for pills, by 38% for cochlear implants, by 21% for implants on the brain surface, and by 19% for implants in the brain. To reduce tinnitus completely, participants most commonly selected to pay at least $5000, and 20.3% were willing to pay as much as $25,000. The ratings of tinnitus loudness and annoyance were positively correlated with the likelihood of using any treatment. Surprisingly, there was a weak relationship between annoyance and the amount they were willing to pay. CONCLUSIONS: Tinnitus patients are prepared to accept a wide variety of treatments. Medications are the most acceptable. Invasive procedures can also be acceptable to many, particularly if they provide complete relief.

Perception of Mandarin Chinese with cochlear implants using enhanced temporal pitch cues.

A cochlear implant (CI) signal processing strategy named F0 modulation (F0mod) was compared with the advanced combination encoder (ACE) strategy in a group of four post-lingually deafened Mandarin Chinese speaking CI listeners. F0 provides an enhanced temporal pitch cue by amplitude modulating the multichannel electrical stimulation pattern at the fundamental frequency (F0) of the incoming speech signal. Word and sentence recognition tests were carried out in quiet and in noise. The responses for the word-recognition test were further segmented into phoneme and tone scores. Off-line implementations of ACE and F0mod were used, and electrical stimulation patterns were directly streamed to the CI subject's implant. To focus on the feasibility of enhanced temporal cues for tonal language perception, idealized F0 information that was extracted from speech tokens in quiet was used in the F0mod processing of speech-in-noise mixtures. The results indicated significantly better lexical tone perception with the F0mod strategy than with ACE for the male voice (p<0.05). No significant differences in sentence recognition were found between F0mod and ACE.

Semi-automatic attenuation of cochlear implant artifacts for the evaluation of late auditory evoked potentials.

Electrical artifacts caused by the cochlear implant (CI) contaminate electroencephalographic (EEG) recordings from implanted individuals and corrupt auditory evoked potentials (AEPs). Independent component analysis (ICA) is efficient in attenuating the electrical CI artifact and AEPs can be successfully reconstructed. However the manual selection of CI artifact related independent components (ICs) obtained with ICA is unsatisfactory, since it contains expert-choices and is time consuming. We developed a new procedure to evaluate temporal and topographical properties of ICs and semi-automatically select those components representing electrical CI artifact. The CI Artifact Correction (CIAC) algorithm was tested on EEG data from two different studies. The first consists of published datasets from 18 CI users listening to environmental sounds. Compared to the manual IC selection performed by an expert the sensitivity of CIAC was 91.7% and the specificity 92.3%. After CIAC-based attenuation of CI artifacts, a high correlation between age and N1-P2 peak-to-peak amplitude was observed in the AEPs, replicating previously reported findings and further confirming the algorithm's validity. In the second study AEPs in response to pure tone and white noise stimuli from 12 CI users that had also participated in the other study were evaluated. CI artifacts were attenuated based on the IC selection performed semi-automatically by CIAC and manually by one expert. Again, a correlation between N1 amplitude and age was found. Moreover, a high test-retest reliability for AEP N1 amplitudes and latencies suggested that CIAC-based attenuation reliably preserves plausible individual response characteristics. We conclude that CIAC enables the objective and efficient attenuation of the CI artifact in EEG recordings, as it provided a reasonable reconstruction of individual AEPs. The systematic pattern of individual differences in N1 amplitudes and latencies observed with different stimuli at different sessions, strongly suggests that CIAC can overcome the electrical artifact problem. Thus CIAC facilitates the use of cortical AEPs as an objective measurement of auditory rehabilitation.

A method for removing cochlear implant artifact.

When cortical auditory evoked potentials (CAEPs) are recorded in individuals with a cochlear implant (CI), electrical artifact can make the CAEP difficult or impossible to measure. Since increasing the interstimulus interval (ISI) increases the amplitude of physiological responses without changing the artifact, subtracting CAEPs recorded with a short ISI from those recorded with a longer ISI should show the physiological response without any artifact. In the first experiment, N1-P2 responses were recorded using a speech syllable and tone, paired with ISIs that changed randomly between 0.5 and 4s. In the second experiment, the same stimuli, at ISIs of either 500 or 3000ms, were presented in blocks that were homogeneous or random with respect to the ISI or stimulus. In the third experiment, N1-P2 responses were recorded using pulse trains with 500 and 3000ms ISIs in 4 CI listeners. The results demonstrated: (1) N1-P2 response amplitudes generally increased with increasing ISI. (2) Difference waveforms were largest for the homogeneous and random-stimulus blocks than for the random-ISI block. (3) The subtraction technique almost completely eliminated the electrical artifact in individuals with cochlear implants. Therefore, the subtraction technique is a feasible method of removing from the N1-P2 response the electrical artifact generated by the cochlear implant.

Influence of stimulation rate and loudness growth on modulation detection and intensity discrimination in cochlear implant users.

In cochlear implants (CIs), increasing the stimulation rate typically increases the electric dynamic range (DR), mostly by reducing audibility thresholds. While CI users' intensity resolution has been shown to be fairly constant across stimulation rates, high rates have been shown to weaken modulation sensitivity, especially at low listening levels. In this study, modulation detection thresholds (MDTs) were measured in five CI users for a range of stimulation rates (250-2000 pulses per second) and modulation frequencies (5-100 Hz) at 8 stimulation levels that spanned the DR (loudness-balanced across stimulation rates). Intensity difference limens (IDLs) were measured for the same stimulation rates and levels used for modulation detection. For all modulation frequencies, modulation sensitivity was generally poorer at low levels and at higher stimulation rates. CI users were sensitive to modulation frequency only at relatively high levels. Similarly, IDLs were poorer at low levels and at high stimulation rates. When compared directly in terms of relative amplitude, IDLs were generally better than MDTs at low levels. Differences in loudness growth between dynamic and steady stimuli might explain level-dependent differences between MDTs and IDLs. The slower loudness growth associated with high stimulation rates might explain the poorer MDTs and IDLs with high rates. In general, high stimulation rates provided no advantage in intensity resolution and a disadvantage in modulation sensitivity.

Users' experience of a cochlear implant combined with a hearing aid.

This study examined: (1) the prevalence of hearing-aid use in a clinical population of adults with unilateral cochlear implants, (2) the relationship between hearing-aid use, severity of hearing loss, duration of deafness and duration of cochlear implant use, and (3) the benefits of bimodal hearing from the users' perspective. Using a retrospective design, 31 adults were identified as bimodal users, and 93 adults implanted in the same period were identified as non hearing-aid users. The two groups were similar in regards to duration of deafness but differed in severity of hearing loss and time since implantation. Questionnaires examining frequency and situations of hearing-aid use were completed by 24 of 31 bimodal users. Fifteen of these 24 adults reported hearing-aid use more than 50% of the time. These findings suggest that, of the 72 adults in this study with useable hearing (pure-tone average better than 110 dB), about 30% or less regularly combined a hearing aid and cochlear implant. The questionnaire results suggest that regular bimodal users prefer bimodal hearing across a variety of listening environments such as music, noise, and reverberation.

Neural tonotopy in cochlear implants: an evaluation in unilateral cochlear implant patients with unilateral deafness and tinnitus.

In cochlear implants, the signal is filtered into different frequency bands and transmitted to electrodes along the cochlea. In this study the frequency-place function for electric hearing was investigated as a means to possibly improve speech coding by delivering information to the appropriate cochlear place. Fourteen subjects with functional hearing in the contralateral ear have been provided with a MED-EL cochlear implant in the deaf ear in order to reduce intractable tinnitus. Pitch scaling experiments were performed using single-electrode, constant-amplitude, constant-rate stimuli in the implanted ear, and acoustic sinusoids in the contralateral ear. The frequency-place function was calculated using the electrode position in the cochlea as obtained from postoperative skull radiographs. Individual frequency-place functions were compared to Greenwood's function in normal hearing. Electric stimulation elicited a low pitch in the apical region of the cochlea, and shifting the stimulating electrode towards the basal region elicited increasingly higher pitch. The frequency-place function did not show a significant shift relative to Greenwood's function. In cochlear implant patients with functional hearing in the non-implanted ear, electrical stimulation produced a frequency-place function that on average resembles Greenwood's function. These results differ from previously derived data.