Impact of cochlear implants use on voice production and quality.

Cochlear implant users experience difficulties controlling their vocalizations compared to normal hearing peers. However, less is known about their voice quality. The primary aim of the present study was to determine if cochlear implant users' voice quality would be categorized as dysphonic by the Acoustic Voice Quality Index (AVQI) and smoothed cepstral peak prominence (CPPS). A secondary aim was to determine if vocal quality is further impacted when using bilateral implants compared to using only one implant. The final aim was to determine how residual hearing impacts voice quality. Twenty-seven cochlear implant users participated in the present study and were recorded while sustaining a vowel and while reading a standardized passage. These recordings were analyzed to calculate the AVQI and CPPS. The results indicate that CI users' voice quality was detrimentally affected by using their CI, raising to the level of a dysphonic voice. Specifically, when using their CI, mean AVQI scores were 4.0 and mean CPPS values were 11.4 dB, which indicates dysphonia. There were no significant differences in voice quality when comparing participants with bilateral implants to those with one implant. Finally, for participants with residual hearing, as hearing thresholds worsened, the likelihood of a dysphonic voice decreased.

Temporal pitch matching with bilateral cochlear implants.

Interaural pitch matching is a common task used with bilateral cochlear implant (CI) users, although studies measuring this have largely focused on place-based pitch matches. Temporal-based pitch also plays an important role in CI users' perception, but interaural temporal-based pitch matching has not been well characterized for CI users. To investigate this, bilateral CI users were asked to match amplitude modulation frequencies of stimulation across ears. Comparisons were made to previous place-based pitch matching data that were collected using similar procedures. The results indicate that temporal-based pitch matching is particularly sensitive to the choice of reference ear.

Musical Interval Perception With a Cochlear Implant Alone and With a Contralateral Normal Hearing Ear.

Music through a cochlear implant (CI) is described as out-of-tune, suggesting that musical intervals are not accurately provided by a CI. One potential reason is that pitch may be insufficiently conveyed to provide reliable intervals. Another potential reason is that the size of intervals is distorted through a CI as they would be when produced by a mistuned piano. To measure intervals through a CI, listeners selected prerecorded vowels with different fundamental frequencies to represent each note in Happy Birthday. Each listener had contralateral normal hearing (NH); repeating the experiment with their NH ear allowed for a within-subject control. Additionally, the effect of listening simultaneously to both a CI and NH ear was measured. The resulting versions of Happy Birthday were analyzed in terms of their contours, interval sizes, magnitudes, consistency, and direction. Intervals with NH ears ranged from perfect to uncorrelated with target intervals. Chosen interval size with the CI was poorer than with the NH ear for all subjects. Across listeners, chosen intervals with the CI ranged from highly correlated to uncorrelated with target intervals. That CI intervals were highly correlated with target intervals for some listeners suggests that accurate intervals can be provided through a CI. For some listeners, chosen intervals were larger than target intervals, suggesting that intervals may be perceived as too small. Overall, intervals with the combination of the NH and CI ears were similar to those with the NH ear alone, suggesting that the addition of a CI has little-to-no effect on interval perception.

The effect of simulated insertion depth differences on the vocal pitches of cochlear implant users.

Cochlear implant (CI) users often produce different vocal pitches when using their left versus right CI. One possible explanation for this is that insertion depth differs across the two CIs. The goal of this study was to investigate the role of electrode insertion depth in the production of vocal pitch. Eleven individuals with bilateral CIs used maps simulating differences in insertion depth. Participants produced a sustained vowel and sang Happy Birthday. Approximately half the participants significantly shifted the pitch of their voice in response to different simulated insertion depths. The results suggest insertion depth differences can alter produced vocal pitch.

Using unilateral stimulation to create a reference for bilateral fusion judgments.

Measuring binaural fusion can be challenging, especially with bilateral cochlear implant (CI) users. This study validated a technique of using unilateral stimulation to create a reference for measuring fusion. Seven bilateral CI users listened to stimuli randomly presented to the right, left, or both ears. Participants indicated the size, number, and location of the resulting image(s) they perceived. The participants had largely unitary, punctate percepts that were lateralized to the stimulated ear for unilateral stimuli. The image was centered but more diffuse when the stimuli were presented bilaterally. The results suggest unilateral stimuli can provide a reference for binaural fusion.

Examining the Relationship Between Speech Recognition and a Spectral-Temporal Test With a Mixed Group of Hearing Aid and Cochlear Implant Users.

Purpose Audiology clinics have a need for a nonlinguistic test for assessing speech scores for patients using hearing aids or cochlear implants. One such test, the Spectral-Temporally Modulated Ripple Test Lite for computeRless Measurement (SLRM), has been developed for use in clinics, but it, as well as the related Spectral-Temporally Modulated Ripple Test, has primarily been assessed with cochlear implant users. The main goal of this study was to examine the relationship between SLRM and the Arizona Biomedical Institute Sentence Test (AzBio) for a mixed group of hearing aid and cochlear implant users. Method Adult hearing aid users and cochlear implant users were tested with SLRM, AzBio in quiet, and AzBio in multitalker babble with a +8 dB signal-to-noise ratio. Results SLRM scores correlated with both AzBio recognition scores in quiet and in noise. Conclusions The results indicated that there is a significant relationship between SLRM and AzBio scores when testing a mixed group of cochlear implant and hearing aid users. This suggests that SLRM may be a useful nonlinguistic test for use with individuals with a variety of hearing devices.

Comparing Methods for Pairing Electrodes Across Ears With Cochlear Implants.

OBJECTIVES: Currently, bilateral cochlear implants (CIs) are independently programmed in clinics using frequency allocations based on the relative location of a given electrode from the end of each electrode array. By pairing electrodes based on this method, bilateral CI recipients may have decreased sensitivity to interaural time differences (ITD) and/or interaural level differences (ILD), two cues critical for binaural tasks. There are multiple different binaural measures that can potentially be used to determine the optimal way to pair electrodes across the ears. Previous studies suggest that the optimal electrode pairing between the left and right ears may vary depending on the binaural task used. These studies, however, have only used one reference location or a single bilateral CI user. In both instances, it is difficult to determine if the results that were obtained reflect a measurement error or a systematic difference across binaural tasks. It is also difficult to determine from these studies if the differences between the three cues vary across electrode regions, which could result from differences in the availability of binaural cues across frequency regions. The purpose of this study was to determine if, after experience-dependent adaptation, there are systematic differences in the optimal pairing of electrodes at different points along the array for the optimal perception of ITD, ILD, and pitch. DESIGN: Data from seven bilateral Nucleus users was collected and analyzed. Participants were tested with ITD, ILD, and pitch-matching tasks using five different reference electrodes in one ear, spaced across the array. Comparisons were conducted to determine if the optimal bilateral electrode pairs systematically differed in different regions depending on whether they were measured based on ITD sensitivity, ILD sensitivity, or pitch matching, and how those pairs differed from the pairing in the participants' clinical programs. RESULTS: Results indicate that there was a significant difference in the optimal pairing depending on the cue measured, but only at the basal end of the array. CONCLUSION: The results suggest that optimal electrode pairings differ depending on the cue measured to determine optimal pairing, at least for the basal end of the array. This also suggests that the improvements seen when using optimally paired electrodes may be tied to the particular percept being measured both to determine electrode pairing and to assess performance, at least for the basal end of the array.

Influence of bilateral cochlear implants on vocal control.

Receiving a cochlear implant (CI) can improve fundamental frequency (F0) control for deaf individuals, resulting in increased vocal pitch control. However, it is unclear whether using bilateral CIs, which often result in mismatched pitch perception between ears, will counter this benefit. To investigate this, 23 bilateral CI users were asked to produce a sustained vocalization using one CI, the other CI, both CIs, or neither. Additionally, a set of eight normal hearing participants completed the sustained vocalization task as a control group. The results indicated that F0 control is worse with both CIs compared to using the ear that yields the lowest vocal variability. The results also indicated that there was a large range of F0 variability even for the relatively stable portion of the vocalization, spanning from 6 to 46 cents. These results suggest that bilateral CIs can detrimentally affect vocal control.

Cochlear Implant Users' Vocal Control CorrelatesAcross Tasks.

Cochlear implants (CIs) provide access to auditory information that can affect vocal control. For example, previous research shows that, when producing a sustained vowel, CI users will alter the pitch of their voice when the feedback of their own voice is perceived to shift. Although these results can be informative as to how perception and production are linked for CI users, the artificial nature of the task raises questions as to the applicability of the results to real-world vocal productions. To examine how vocal control, when producing sustained vowels, relates to vocal control for more ecologically valid tasks, 10 CI users' vocal control was measured across two tasks: (1) sustained vowel production, and (2) singing. The results found that vocal control, as measured by the variability of the participants' fundamental frequency, was significantly correlated when producing sustained vowels and when singing, although variability was significantly greater when singing. This suggests that, despite the artificial nature of sustained vowel production, vocal control on such tasks is related to vocal control for more ecologically valid tasks. However, the results also suggest that vocal control may be overestimated with sustained vowel production tasks.

Pitch Matching Adapts Even for Bilateral Cochlear Implant Users with Relatively Small Initial Pitch Differences Across the Ears.

There is often a mismatch for bilateral cochlear implant (CI) users between the electrodes in the two ears that receive the same frequency allocation and the electrodes that, when stimulated, yield the same pitch. Studies with CI users who have extreme mismatches between the two ears show that adaptation occurs in terms of pitch matching, reducing the difference between which electrodes receive the same frequency allocation and which ones produce the same pitch. The considerable adaptation that occurs for these extreme cases suggests that adaptation should be sufficient to overcome the relatively minor mismatches seen with typical bilateral CI users. However, even those with many years of bilateral CI use continue to demonstrate a mismatch. This may indicate that adaptation only occurs when there are large mismatches. Alternatively, it may indicate that adaptation occurs regardless of the magnitude of the mismatch, but that adaptation is proportional to the magnitude of the mismatch, and thus never fully counters the original mismatch. To investigate this, six bilateral CI users with initial pitch-matching mismatches of less than 3 mm completed a pitch-matching task near the time of activation, 6 months after activation, and 1 year after activation. Despite relatively small initial mismatches, the results indicated that adaptation still occurred.

Spectral-temporally modulated ripple test Lite for computeRless Measurement (SLRM): A Nonlinguistic Test for Audiology Clinics.

OBJECTIVES: Many clinics are faced with the difficulty of evaluating performance in patients who speak a language for which there are no validated tests. It would be desirable to have a nonlinguistic method of evaluating these patients. Spectral ripple tests are nonlinguistic and highly correlated with speech identification performance. However, they are generally not amenable to clinical environments as they typically require the use of computers which are often not found in clinic sound booths. In this study, we evaluate the Spectral-temporally Modulated Ripple Test (SMRT) Lite for computeRless Measurement (SLRM), which is a new variant of the adaptive SMRT that can be implemented via a CD player. DESIGN: SMRT and SLRM were measured for 10 normal hearing and 10 cochlear implant participants. RESULTS: Performance on the two tests was highly correlated (r = 0.97). CONCLUSIONS: The results suggest that SLRM can be used interchangeably with SMRT but can be implemented without a computer.

When singing with cochlear implants, are two ears worse than one for perilingually/postlingually deaf individuals?

Many individuals with bilateral cochlear implants hear different pitches when listening with their left versus their right cochlear implant. This conflicting information could potentially increase the difficulty of singing with cochlear implants. To determine if bilateral cochlear implants are detrimental for singing abilities, ten perilingually/postlingually deaf bilateral adult cochlear implant users were asked to sing "Happy Birthday" when using their left, right, both, or neither cochlear implant. The results indicated that bilateral cochlear implant users have more difficulty singing the appropriate pitch contour when using both cochlear implants as opposed to the better ear alone.

Changing stimulation patterns can change the broadness of contralateral masking functions for bilateral cochlear implant users.

Past studies have found that contralateral masking functions are sharper than ipsilateral masking functions for cochlear implant (CI) users. This could suggest that contralateral masking effects are only sensitive to the peak of the masker stimulation for this population. To determine if that is the case, this study investigated whether using broader stimulation patterns affects the broadness of the contralateral masking function. Contralateral masking functions were measured for six bilateral CI users using both a broad and narrow masker. Findings from this study revealed that the broad masker resulted in a broader contralateral masking function. This would suggest that stimulation outside of the peak of the masker affects contralateral masking functions for CI users.

Localization performance correlates with binaural fusion for interaurally mismatched vocoded speech.

Bilateral cochlear implant users often have difficulty fusing sounds from the two ears into a single percept. However, measuring fusion can be difficult, particularly with cochlear implant users who may have no reference for a fully fused percept. As a first step to address this, this study examined how localization performance of normal hearing subjects relates to binaural fusion. The stimuli were vocoded speech tokens with various interaural mismatches. The results reveal that the percentage of stimuli perceived as fused was correlated with localization performance, suggesting that changes in localization performance can serve as an indicator for binaural fusion changes.

Comparison of the Spectral-Temporally Modulated Ripple Test With the Arizona Biomedical Institute Sentence Test in Cochlear Implant Users.

OBJECTIVES: Although speech perception is the gold standard for measuring cochlear implant (CI) users' performance, speech perception tests often require extensive adaptation to obtain accurate results, particularly after large changes in maps. Spectral ripple tests, which measure spectral resolution, are an alternate measure that has been shown to correlate with speech perception. A modified spectral ripple test, the spectral-temporally modulated ripple test (SMRT) has recently been developed, and the objective of this study was to compare speech perception and performance on the SMRT for a heterogeneous population of unilateral CI users, bilateral CI users, and bimodal users. DESIGN: Twenty-five CI users (eight using unilateral CIs, nine using bilateral CIs, and eight using a CI and a hearing aid) were tested on the Arizona Biomedical Institute Sentence Test (AzBio) with a +8 dB signal to noise ratio, and on the SMRT. All participants were tested with their clinical programs. RESULTS: There was a significant correlation between SMRT and AzBio performance. After a practice block, an improvement of one ripple per octave for SMRT corresponded to an improvement of 12.1% for AzBio. Additionally, there was no significant difference in slope or intercept between any of the CI populations. CONCLUSION: The results indicate that performance on the SMRT correlates with speech recognition in noise when measured across unilateral, bilateral, and bimodal CI populations. These results suggest that SMRT scores are strongly associated with speech recognition in noise ability in experienced CI users. Further studies should focus on increasing both the size and diversity of the tested participants, and on determining whether the SMRT technique can be used for early predictions of long-term speech scores, or for evaluating differences among different stimulation strategies or parameter settings.

Determining the minimum number of electrodes that need to be pitch matched to accurately estimate pitch matches across the array.

OBJECTIVE: With bilateral cochlear implant (CI) users there is typically a place mismatch between the locations stimulated by the left and right electrode arrays. This mismatch can affect performance, potentially limiting binaural benefits. One way to address this is by perceptually realigning the arrays such that a given frequency in the input stimulates perceptually matched locations in the two ears. A clinically feasible technique is needed that can determine the appropriate perceptual alignment. A pitch matching task can potentially be used for this, but only if it can be performed in a clinically feasible amount of time. The objective of this study was to determine the minimal number of electrodes that need to be pitch matched to accurately determine pitch matches across the entire array. DESIGN: A retrospective analysis of pitch matching data was conducted. Subsets of pitch matches were selected and the predicted pitch matching across the array was compared to that predicted by the full dataset. STUDY SAMPLE: 16 bilateral CI users. RESULTS: The results indicated that nine pitch matches are sufficient, which can typically be obtained in approximately 7 min. CONCLUSION: The results reveal a clinically feasible method for determining pitch matches across the array.

Clinically Paired Electrodes Are Often Not Perceived as Pitch Matched.

For bilateral cochlear implant (CI) patients, electrodes that receive the same frequency allocation often stimulate locations in the left and right ear that do not yield the same perceived pitch, resulting in a pitch mismatch. This pitch mismatch may be related to degraded binaural abilities. Pitch mismatches have been found for some bilateral CI users and the goal of this study was to determine whether pitch mismatches are prevalent in bilateral CI patients, including those with extensive experience with bilateral CIs. To investigate this possibility, pitch matching was conducted with 16 bilateral CI patients. For 14 of the 16 participants, there was a significant difference between those electrodes in the left and right ear that yielded the same pitch and those that received the same frequency allocation in the participant's clinical map. The results suggest that pitch mismatches are prevalent with bilateral CI users. The results also indicated that pitch mismatches persist even with extended bilateral CI experience. Such mismatches may reduce the benefits patients receive from bilateral CIs.

Perceptually aligning apical frequency regions leads to more binaural fusion of speech in a cochlear implant simulation.

For bilateral cochlear implant users, the left and right arrays are typically not physically aligned, resulting in a degradation of binaural fusion, which can be detrimental to binaural abilities. Perceptually aligning the two arrays can be accomplished by disabling electrodes in one ear that do not have a perceptually corresponding electrode in the other side. However, disabling electrodes at the edges of the array will cause compression of the input frequency range into a smaller cochlear extent, which may result in reduced spectral resolution. An alternative approach to overcome this mismatch would be to only align one edge of the array. By aligning either only the apical or basal end of the arrays, fewer electrodes would be disabled, potentially causing less reduction in spectral resolution. The goal of this study was to determine the relative effect of aligning either the basal or apical end of the electrode with regards to binaural fusion. A vocoder was used to simulate cochlear implant listening conditions in normal hearing listeners. Speech signals were vocoded such that the two ears were either predominantly aligned at only the basal or apical end of the simulated arrays. The experiment was then repeated with a spectrally inverted vocoder to determine whether the detrimental effects on fusion were related to the spectral-temporal characteristics of the stimuli or the location in the cochlea where the misalignment occurred. In Experiment 1, aligning the basal portion of the simulated arrays led to significantly less binaural fusion than aligning the apical portions of the simulated array. However, when the input was spectrally inverted, aligning the apical portion of the simulated array led to significantly less binaural fusion than aligning the basal portions of the simulated arrays. These results suggest that, for speech, with its predominantly low frequency spectral-temporal modulations, it is more important to perceptually align the apical portion of the array to better preserve binaural fusion. By partially aligning these arrays, cochlear implant users could potentially increase their ability to fuse speech sounds presented to the two ears while maximizing spectral resolution.