Adult Cochlear Implant Listeners Research Articles

Spectral sparsification of speech signals and its interaction with top-down mechanisms in adult cochlear implant users

The ability to understand speech varies significantly among cochlear implant (CI) listeners as it depends on a variety of individual and environmental factors. Especially in adverse listening situations, good cognitive and linguistic (“top-down”) skills and the use of signal pre-processing algorithms are considered beneficial. However, not much is known about the interactions between these top-down and perceptive bottom-up processes in CI listeners. To shed light on the relation between the spectral representation of speech sounds and the ability of CI listeners to decode these signals, two methods for the simplification of speech signals through spectral sparsification were developed and evaluated in listening tests with postlingually deaf adult CI listeners. Speech signals were separated into transient and harmonic parts. After sparsification of the harmonic spectrum by principal component analysis (PCA) or by an individualized spectral peak picking approach, the transient and the sparsened harmonic parts were remixed. Furthermore, cognitive parameters of the subjects were assessed via a neurocognitive test battery (ALAcog) and their correlation with recognition scores evaluated. The PCA-based sparsification method showed a significant benefit in speech recognition relative to the unprocessed signal. Furthermore, subjects with better performance in working memory and mental flexibility showed larger improvements.

Single-Channel Focused Thresholds Relate to Vowel Identification in Pediatric and Adult Cochlear Implant Listeners.

Speech recognition outcomes are highly variable among pediatric and adult cochlear implant (CI) listeners. Although there is some evidence that the quality of the electrode-neuron interface (ENI) contributes to this large variability in auditory perception, its relationship with speech outcomes is not well understood. Single-channel auditory detection thresholds measured in response to focused electrical fields (i.e., focused thresholds) are sensitive to properties of ENI quality, including electrode-neuron distance, intracochlear resistance, and neural health. In the present study, focused thresholds and speech perception abilities were assessed in 15 children and 21 adult CI listeners. Focused thresholds were measured for all active electrodes using a fast sweep procedure. Speech perception performance was evaluated by assessing listeners’ ability to identify vowels presented in /h-vowel-d/ context. Consistent with prior literature, focused thresholds were lower for children than for adults, but vowel identification did not differ significantly across age groups. Higher across-array average focused thresholds, which may indicate a relatively poor ENI quality, were associated with poorer vowel identification scores in both children and adults. Adult CI listeners with longer durations of deafness had higher focused thresholds. Findings from this study demonstrate that poor-quality ENIs may contribute to reduced speech outcomes for pediatric and adult CI listeners. Estimates of ENI quality (e.g., focused thresholds) may assist in developing customized programming interventions that serve to improve the transmission of spectral cues that are important in vowel identification.

Novel Web-Based Music Re-Engineering Software for Enhancement of Music Enjoyment Among Cochlear Implantees.

Cochlear implant (CI) listeners experience diminished music perception and enjoyment from a variety of patient-related and implant-related factors. We investigate the hypothesis that patient-directed music re-engineering may enhance music enjoyment with CI. Prospective cohort study. Academic cochlear implant center. A multidisciplinary team of neurotologists, audiologists, and a sound/audio engineer collaborated with a web developer to create a music re-engineering application. Experienced adult CI listeners rated original excerpts from five major genres of music on enjoyment using a visual analog scale (VAS). Subjects were then allowed to re-engineer the original by adjusting treble frequencies, bass frequencies, percussion emphasis, and reverberation and again rated on enjoyment. Total of 46 subjects, with a mean age of 57.6 years (SD = 16; range, 18-90) participated in the study. User-mixed audio was rated higher across all measures of enjoyment than original recordings (mean difference +0.92; p < 0.05, CI [0.22, 1.62]), an effect that was seen across all genres except for country music. Subjects preferred louder bass frequencies (mean difference +7.1 dB; p < 0.01, CI [2.15, 24.3]) and more reverberation (mean difference +6.6 ms; p < 0.01, CI [2.85, 10.7]). Re-engineered music increased enjoyment in 57%, and 79% reported an interest in being able to mix music of their own choosing. User-directed music re-engineering increases music enjoyment for CI listeners. The cochlear implantee preferred heightened bass, reverberation, and treble across musical genres. These findings support the implementation of patient-directed music re-engineering to enhance music enjoyment with technology that is readily available today.

The Benefit of Remote and On-Ear Directional Microphone Technology Persists in the Presence of Visual Information.

Both the Roger remote microphone and on-ear, adaptive beamforming technologies (e.g., Phonak UltraZoom) have been shown to improve speech understanding in noise for cochlear implant (CI) listeners when tested in audio-only (A-only) test environments. Our aim was to determine if adult and pediatric CI recipients benefited from these technologies in a more common environment-one in which both audio and visual cues were available and when overall performance was high. Ten adult CI listeners (Experiment 1) and seven pediatric CI listeners (Experiment 2) were tested. Adults were tested in quiet and in two levels of noise (level 1 and level 2) in A-only and audio-visual (AV) environments. There were four device conditions: (1) an ear canal-level, omnidirectional microphone (T-mic) in quiet, (2) the T-mic in noise, (3) an adaptive directional mic (UltraZoom) in noise, and (4) a wireless, remote mic (Roger Pen) in noise. Pediatric listeners were tested in quiet and in level 1 noise in A-only and AV environments. The test conditions were: (1) a behind-the-ear level omnidirectional mic (processor mic) in quiet, (2) the processor mic in noise, (3) the T-mic in noise, and (4) the Roger Pen in noise. In each test condition, sentence understanding was assessed (percent correct) and ease of listening ratings were obtained. The sentence understanding data were entered into repeated-measures analyses of variance. For both adult and pediatric listeners in the AV test conditions in level 1 noise, performance with the Roger Pen was significantly higher than with the T-mic. For both populations, performance in level 1 noise with the Roger Pen approached the level of baseline performance in quiet. Ease of listening in noise was rated higher in the Roger Pen conditions than in the T-mic or processor mic conditions in both A-only and AV test conditions. The Roger remote mic and on-ear directional mic technologies benefit both speech understanding and ease of listening in a realistic laboratory test environment and are likely do the same in real-world listening environments.

Corrigendum to “Polarity Sensitivity in Pediatric and Adult Cochlear Implant Listeners”

Corrigendum to “Polarity Sensitivity in Pediatric and Adult Cochlear Implant Listeners”

Polarity Sensitivity in Pediatric and Adult Cochlear Implant Listeners.

Modeling data suggest that sensitivity to the polarity of an electrical stimulus may reflect the integrity of the peripheral processes of the spiral ganglion neurons. Specifically, better sensitivity to anodic (positive) current than to cathodic (negative) current could indicate peripheral process degeneration or demyelination. The goal of this study was to characterize polarity sensitivity in pediatric and adult cochlear implant listeners (41 ears). Relationships between polarity sensitivity at threshold and (a) polarity sensitivity at suprathreshold levels, (b) age-group, (c) preimplantation duration of deafness, and (d) phoneme perception were determined. Polarity sensitivity at threshold was defined as the difference in single-channel behavioral thresholds measured in response to each of two triphasic pulses, where the central high-amplitude phase was either cathodic or anodic. Lower thresholds in response to anodic than to cathodic pulses may suggest peripheral process degeneration. On the majority of electrodes tested, threshold and suprathreshold sensitivity was lower for anodic than for cathodic stimulation; however, dynamic range was often larger for cathodic than for anodic stimulation. Polarity sensitivity did not differ between child- and adult-implanted listeners. Adults with long preimplantation durations of deafness tended to have better sensitivity to anodic pulses on channels that were estimated to interface poorly with the auditory nerve; this was not observed in the child-implanted group. Across subjects, duration of deafness predicted phoneme perception performance. The results of this study suggest that subject- and electrode-dependent differences in polarity sensitivity may assist in developing customized cochlear implant programming interventions for child- and adult-implanted listeners.

The Effects of Auditory Experience on Psychophysical Tuning Curves in Pediatric and Adult Cochlear Implant Listeners

The Effects of Auditory Experience on Psychophysical Tuning Curves in Pediatric and Adult Cochlear Implant Listeners

Modulation detection interference in cochlear implant listeners under forward masking conditions.

Little is known about cochlear implant (CI) users' ability to process amplitude modulation (AM) under conditions of forward masking (forward-modulation detection/discrimination interference, or F-MDI). In this study, F-MDI was investigated in adult CI listeners using direct electrical stimulation via research interface. The target was sinusoidally amplitude modulated at 50 Hz, and presented to a fixed electrode in the middle of the array. The forward masker was either amplitude modulated at the same rate (AM) or unmodulated and presented at the peak amplitude of its AM counterpart (steady-state peak, SSP). Results showed that the AM masker produced higher modulation thresholds in the target than the SSP masker. The difference (F-MDI) was estimated to be 4.6 dB on average, and did not change with masker-target delays up to 100 ms or with masker-target spatial electrode distances up to eight electrodes. Results with a coherent remote cue presented with the masker showed that confusion effects did not play a role in the observed F-MDI. Traditional recovery from forward masking using the same maskers and a 20-ms probe, measured in four of the subjects, confirmed the expected result: higher thresholds with the SSP masker than the AM masker. Collectively, the results indicate that significant F-MDI occurs in CI users.

Neural Correlates of Phonetic Learning in Postlingually Deafened Cochlear Implant Listeners.

The present training study aimed to examine the fine-scale behavioral and neural correlates of phonetic learning in adult postlingually deafened cochlear implant (CI) listeners. The study investigated whether high variability identification training improved phonetic categorization of the /ba/-/da/ and /wa/-/ja/ speech contrasts and whether any training-related improvements in phonetic perception were correlated with neural markers associated with phonetic learning. It was hypothesized that training would sharpen phonetic boundaries for the speech contrasts and that changes in behavioral sensitivity would be associated with enhanced mismatch negativity (MMN) responses to stimuli that cross a phonetic boundary relative to MMN responses evoked using stimuli from the same phonetic category. A computer-based training program was developed that featured multitalker variability and adaptive listening. The program was designed to help CI listeners attend to the important second formant transition cue that categorizes the /ba/-/da/ and /wa/-/ja/ contrasts. Nine adult CI listeners completed the training and 4 additional CI listeners that did not undergo training were included to assess effects of procedural learning. Behavioral pre-post tests consisted of identification and discrimination of the synthetic /ba/-/da/ and /wa/-/ja/ speech continua. The electrophysiologic MMN response elicited by an across phoneme category pair and a within phoneme category pair that differed by an acoustically equivalent amount was derived at pre-post test intervals for each speech contrast as well. Training significantly enhanced behavioral sensitivity across the phonetic boundary and significantly altered labeling of the stimuli along the /ba/-/da/ continuum. While training only slightly altered identification and discrimination of the /wa/-/ja/ continuum, trained CI listeners categorized the /wa/-/ja/ contrast more efficiently than the /ba/-/da/ contrast across pre-post test sessions. Consistent with behavioral results, pre-post EEG measures showed the MMN amplitude to the across phoneme category pair significantly increased with training for both the /ba/-/da/ and /wa/-/ja/ contrasts, but the MMN was unchanged with training for the corresponding within phoneme category pairs. Significant brain-behavior correlations were observed between changes in the MMN amplitude evoked by across category phoneme stimuli and changes in the slope of identification functions for the trained listeners for both speech contrasts. The brain and behavior data of the present study provide evidence that substantial neural plasticity for phonetic learning in adult postlingually deafened CI listeners can be induced by high variability identification training. These findings have potential clinical implications related to the aural rehabilitation process following receipt of a CI device.

Prior exposure to a reverberant listening environment improves speech intelligibility in adult cochlear implant listeners

Objectives: The goal of this study is to investigate whether prior exposure to reverberant listening environment improves speech intelligibility of adult cochlear implant (CI) users.Methods: Six adult CI users participated in this study. Speech intelligibility was measured in five different simulated reverberant listening environments with two different speech corpuses. Within each listening environment, prior exposure was varied by either having the same environment across all trials (blocked presentation) or having different environment from trial to trial (unblocked).Results: Speech intelligibility decreased as reverberation time increased. Although substantial individual variability was observed, all CI listeners showed an increase in the blocked presentation condition as compared to the unblocked presentation condition for both speech corpuses.Conclusion: Prior listening exposure to a reverberant listening environment improves speech intelligibility in adult CI listeners. Further research is required to understand the underlying mechanism of adaptation to listening environment.

Reducing Channel Interaction Through Cochlear Implant Programming May Improve Speech Perception: Current Focusing and Channel Deactivation.

Speech perception among cochlear implant (CI) listeners is highly variable. High degrees of channel interaction are associated with poorer speech understanding. Two methods for reducing channel interaction, focusing electrical fields, and deactivating subsets of channels were assessed by the change in vowel and consonant identification scores with different program settings. The main hypotheses were that (a) focused stimulation will improve phoneme recognition and (b) speech perception will improve when channels with high thresholds are deactivated. To select high-threshold channels for deactivation, subjects’ threshold profiles were processed to enhance the peaks and troughs, and then an exclusion or inclusion criterion based on the mean and standard deviation was used. Low-threshold channels were selected manually and matched in number and apex-to-base distribution. Nine ears in eight adult CI listeners with Advanced Bionics HiRes90k devices were tested with six experimental programs. Two, all-channel programs, (a) 14-channel partial tripolar (pTP) and (b) 14-channel monopolar (MP), and four variable-channel programs, derived from these two base programs, (c) pTP with high- and (d) low-threshold channels deactivated, and (e) MP with high- and (f) low-threshold channels deactivated, were created. Across subjects, performance was similar with pTP and MP programs. However, poorer performing subjects (scoring < 62% correct on vowel identification) tended to perform better with the all-channel pTP than with the MP program (1 > 2). These same subjects showed slightly more benefit with the reduced channel MP programs (5 and 6). Subjective ratings were consistent with performance. These finding suggest that reducing channel interaction may benefit poorer performing CI listeners.

Computer-based auditory phoneme discrimination training improves speech recognition in noise in experienced adult cochlear implant listeners

Objective: Specific computer-based auditory training may be a useful completion in the rehabilitation process for cochlear implant (CI) listeners to achieve sufficient speech intelligibility. This study evaluated the effectiveness of a computerized, phoneme-discrimination training programme. Design: The study employed a pretest-post-test design; participants were randomly assigned to the training or control group. Over a period of three weeks, the training group was instructed to train in phoneme discrimination via computer, twice a week. Sentence recognition in different noise conditions (moderate to difficult) was tested pre- and post-training, and six months after the training was completed. The control group was tested and retested within one month. Study sample: Twenty-seven adult CI listeners who had been using cochlear implants for more than two years participated in the programme; 15 adults in the training group, 12 adults in the control group. Results: Besides significant improvements for the trained phoneme-identification task, a generalized training effect was noted via significantly improved sentence recognition in moderate noise. No significant changes were noted in the difficult noise conditions. Improved performance was maintained over an extended period. Conclusions: Phoneme-discrimination training improves experienced CI listeners’ speech perception in noise. Additional research is needed to optimize auditory training for individual benefit.

Acoustic cue integration in speech intonation recognition with cochlear implants.

The present article reports on the perceptual weighting of prosodic cues in question-statement identification by adult cochlear implant (CI) listeners. Acoustic analyses of normal-hearing (NH) listeners' production of sentences spoken as questions or statements confirmed that in English the last bisyllabic word in a sentence carries the dominant cues (F0, duration, and intensity patterns) for the contrast. Furthermore, these analyses showed that the F0 contour is the primary cue for the question-statement contrast, with intensity and duration changes conveying important but less reliable information. On the basis of these acoustic findings, the authors examined adult CI listeners' performance in two question-statement identification tasks. In Task 1, 13 CI listeners' question-statement identification accuracy was measured using naturally uttered sentences matched for their syntactic structures. In Task 2, the same listeners' perceptual cue weighting in question-statement identification was assessed using resynthesized single-word stimuli, within which fundamental frequency (F0), intensity, and duration properties were systematically manipulated. Both tasks were also conducted with four NH listeners with full-spectrum and noise-band-vocoded stimuli. Perceptual cue weighting was assessed by comparing the estimated coefficients in logistic models fitted to the data. Of the 13 CI listeners, 7 achieved high performance levels in Task 1. The results of Task 2 indicated that multiple sources of acoustic cues for question-statement identification were utilized to different extents depending on the listening conditions (e.g., full spectrum vs. spectrally degraded) or the listeners' hearing and amplification status (e.g., CI vs. NH).

Acoustic Change Complexes Recorded in Adult Cochlear Implant Listeners

The objectives of this study were to determine: 1) whether the acoustic change complex (ACC) could be reliably recorded in cochlear implant listeners and, 2) whether different speech sounds evoke distinct ACC patterns. Eight adults wearing the Nucleus-24 cochlear implant (CI) were tested using naturally produced speech tokens /si/ and /i/. Stimuli were tokens from the standardized UCLA version of the Nonsense Syllable Test. Using a repeated-measures design, participants were tested and retested within a 3-wk period. Intraclass correlation coefficients for grand mean and individual-response waveforms recorded from the syllables /si/ and /i/ ranged from 0.63 to 0.89 from test to retest. Also, ACC latencies signaling the onset of a vowel in /i/ were significantly earlier than those evoked by /si/. The ACC can be reliably recorded in individuals wearing CI. Furthermore, the naturally produced speech syllables /si/ and /i/ evoke distinct ACC patterns. Because of its good stability and the ease with which it can be recorded in individual CI listeners, the ACC can be evoked using complex signals (such as naturally produced speech syllables) when studying central auditory function in CI listeners.