Faculty Bibliography

OBJECTIVES/OBJECTIVE:A method for stimulating the cochlear apex using perimodiolar electrode arrays is described. This method involves implanting an electrode (ECE1) into the helioctrema in addition to standard cochlear implant placement. One objective is to verify a suitable approach for implanting ECE1 in the helicotrema. Another is to determine how placement of ECE1 reshapes electric fields. DESIGN/METHODS:Two cadaveric half-heads were implanted, and electric voltage tomography was measured with ECE1 placed in many positions. RESULTS:An approach for placing ECE1 was identified. Changes in electric fields were only observed when ECE1 was placed into the fluid in the helicotrema. When inside the helicotrema, electric voltage tomography modeling suggests an increased current flow toward the apex. CONCLUSIONS:Placement of ECE1 into the cochlear apex is clinically feasible and has the potential to reshape electric fields to stimulate regions of the cochlea more apical than those represented by the electrode array.

OBJECTIVE:To investigate a new surgical and signal processing technique that provides apical stimulation of the cochlea using a cochlear implant without extending the length of the electrode array. PATIENTS/METHODS:Three adult patients who underwent cochlear implantation using this new technique. INTERVENTIONS/METHODS:The patients received a cochlear implant. The surgery differed from the standard approach in that a ground electrode was placed in the cochlear helicotrema via an apical cochleostomy rather than in its typical location underneath the temporalis muscle. Clinical fitting was modified such that low frequencies were represented using the apically placed electrode as a ground. MAIN OUTCOME MEASURES/METHODS:Pitch scaling and speech recognition. RESULTS:All surgeries were successful with no complications. Pitch scaling demonstrated that use of the apically placed electrode as a ground lowered the perceived pitch of electric stimulation relative to monopolar stimulation. Speech understanding was improved compared with preoperative scores. CONCLUSIONS:The new surgical approach and clinical fitting are feasible. A lower pitch is perceived when using the apically placed electrode as a ground relative to stimulation using an extracochlear ground (i.e., monopolar mode), suggesting that stimulation can be provided more apically without the use of a longer electrode array. Further work is required to determine potential improvements in outcomes and optimal signal processing for the new approach.

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.

OBJECTIVES/OBJECTIVE:A software tool (EasyMDT) that measures temporal modulation detection thresholds of a broadband noise carrier is presented. EasyMDT is designed to be both easy and quick to promote the use in environments where testing time is limited, and testers may not have extensive technical expertise to use typical research software. In addition, by providing a standardized stimulus and protocol, data collected by all groups using the software can be compared directly. Details of EasyMDT, including a description of the protocol, stimuli, interface and how to obtain the software, are provided along with representative sample data from both normal-hearing listeners and cochlear implant (CI) users. Performance with the EasyMDT is compared with speech understanding metrics as well as a metric of spectral-temporal resolution. DESIGN/METHODS:A "Full Curve" of modulation detection thresholds is measured using a three-interval forced-choice adaptive task in a single block for 7 modulation frequencies (10, 50, 75, 100, 150, 200, and 300 Hz). Similarly, the modulation detection thresholds were measured for only one modulation frequency in a block (either 100 Hz or 150 Hz). Modulation detection thresholds and block duration were recorded. In addition, performance on speech recognition tasks (CNC words, consonant identification, vowel identification, and AzBio sentences in noise) and a spectral-temporal resolution task (SMRT; Aronoff and Landsberger) were measured. Modulation detection thresholds were measured for both normal-hearing listeners and CI users. Only CI users participated in the speech and spectral-temporal tests. RESULTS:Modulation detection thresholds measured with EasyMDT were consistent with those previously reported from other laboratories. Modulation detection thresholds at a single modulation frequency (100 Hz or 150 Hz) were predictive of modulation detection thresholds measured as part of the Full Curve consisting of all 7 modulation frequencies. Testing durations for CI users dropped from an average of over 18 minutes for the Full Curve to under 3 minutes for either of the single modulation frequency measures. Modulation detection thresholds at 100 Hz correlated with CNC words, consonant identification, and AzBio sentences in noise, but not vowel identification. No correlations were found between modulation detection and spectral-temporal resolution. CONCLUSIONS:The EasyMDT is designed to be an easy-to-use tool that provides a nonlinguistic measure that can predict speech understanding. The test duration is short enough that it can be incorporated into clinical practice or as part of an experimental battery. The software is available for free download at https://www.ear-lab.org/software-downloads.html. The software is designed to have a minimum barrier of entry as well as provide a standardized protocol allowing direct comparison of modulation detection thresholds across studies and groups.

OBJECTIVES:Pitch is poorly perceived by cochlear implant (CI) users. However, as it is not well understood how pitch is encoded with electric stimulation, improving pitch representation with a CI is challenging. Changes in place of stimulation along the cochlea have been described as changes in pitch and can be accurately ranked by CI users. However, it remains unknown if place-pitch can be used to encode musical intervals, which are a necessary attribute of pitch. The objective of these experiments is to determine if place-pitch coding can be used to represent musical intervals with a CI. DESIGN:In the first experiment, 10 CI users and 10 normal hearing (NH) controls were tested on their sensitivity to changes in the semitone spacing between each of the notes in the melody "Happy Birthday." The changes were implemented by uniformly expanding or compressing the frequency differences between each note in the melody. The participant's task was to scale how "out-of-tune" the melody was for various semitone spacing distortions. The notes were represented by pure-tones ≥440 Hz to minimize potential useful temporal information from the stimuli. A second experiment replicated the first experiment using single-sided deafened CI users allowing for a within-subject control. A third experiment verified that the CI users who participated in Experiment 1 were each able to determine pitch direction reliably. RESULTS:Unlike NH listeners, CI listeners often ranked all distortions of interval spacing similarly in both the first and second experiment, and no effect of interval spacing was detected across CI users. Some participants found distorted interval spacings to be less out-of-tune than the nominally correct interval spacings. However, these patterns were inconsistent across listeners. Although performance was better for the NH listeners, the third experiment demonstrated that the CI listeners were able to reliably identify changes in pitch direction from place-pitch coding. CONCLUSIONS:The data suggest that place-pitch intervals are not properly represented through a CI sound processor. Some limited support is found for place-pitch being useful for interval encoding as some participants demonstrated improved ratings for certain interval distortions. Presumably the interval representation for these participants could be improved by a change to the frequencies represented by each electrode. However, as these patterns vary across listeners, there is not a universal correction to frequency representation that will solve this issue. As results are similar for single-sided deafened CI users, the limitations in ratings are likely not limited by an eroded representation of the melody caused by an extended duration of deafness.

OBJECTIVES/OBJECTIVE:Cochlear implants (CIs) restore speech perception in quiet but they also eliminate or distort many acoustic cues that are important for music enjoyment. Unfortunately, quantifying music enjoyment by CI users has been difficult because comparisons must rely on their recollection of music before they lost their hearing. Here, we aimed to assess music enjoyment in CI users using a readily interpretable reference based on acoustic hearing. The comparison was done by testing "single-sided deafness" (SSD) patients who have normal hearing (NH) in one ear and a CI in the other ear. The study also aimed to assess binaural musical enjoyment, with the reference being the experience of hearing with a single NH ear. Three experiments assessed the effect of adding different kinds of input to the second ear: electrical, vocoded, or unmodified. DESIGN/METHODS:In experiment 1, music enjoyment in SSD-CI users was investigated using a modified version of the MUSHRA (MUltiple Stimuli with Hidden Reference and Anchor) method. Listeners rated their enjoyment of song segments on a scale of 0 to 200, where 100 represented the enjoyment obtained from a song segment presented to the NH ear, 0 represented a highly degraded version of the same song segment presented to the same ear, and 200 represented enjoyment subjectively rated as twice as good as the 100 reference. Stimuli consisted of acoustic only, electric only, acoustic and electric, as well as other conditions with low pass filtered acoustic stimuli. Acoustic stimulation was provided by headphone to the NH ear and electric stimulation was provided by direct audio input to the subject's speech processor. In experiment 2, the task was repeated using NH listeners who received vocoded stimuli instead of electric stimuli. Experiment 3 tested the effect of adding the same unmodified song segment to the second ear, also in NH listeners. RESULTS:Music presented through the CI only was very unpleasant, with an average rating of 20. Surprisingly, the combination of the unpleasant CI signal in one ear with acoustic stimulation in the other ear was rated more enjoyable (mean = 123) than acoustic processing alone. Presentation of the same monaural musical signal to both ears in NH listeners resulted with even greater enhancement of the experience compared with presentation to a single ear (mean = 159). Repeating the experiment using a vocoder to one ear of NH listeners resulted in interference rather than enhancement. CONCLUSIONS:Music enjoyment from electric stimulation is extremely poor relative to a readily interpretable NH baseline for CI-SSD listeners. However, the combination of this unenjoyable signal presented through a CI and an unmodified acoustic signal presented to a NH (or near-NH) contralateral ear results in enhanced music enjoyment with respect to the acoustic signal alone. Remarkably, this two-ear enhancement experienced by CI-SSD listeners represents a substantial fraction of the two-ear enhancement seen in NH listeners. This unexpected benefit of electroacoustic auditory stimulation will have to be considered in theoretical accounts of music enjoyment and may facilitate the quest to enhance music enjoyment in CI users.

OBJECTIVES/OBJECTIVE:The Quick Spectral Modulation Detection (QSMD) test provides a quick and clinically implementable spectral resolution estimate for cochlear implant (CI) users. However, the original QSMD software (QSMD(MySound)) has technical and usability limitations that prevent widespread distribution and implementation. In this article, we introduce a new software package EasyQSMD, which is freely available software with the goal of both simplifying and standardizing spectral resolution measurements. DESIGN/METHODS:QSMD was measured for 20 CI users using both software packages. RESULTS:No differences between the two software packages were detected, and based on the 95% confidence interval of the difference between tests, the difference between the tests is expected to be <2% points. The average test duration was under 4 minutes. CONCLUSIONS:EasyQSMD is considered functionally equivalent to QSMD(MySound) providing a clinically feasible and quick estimate of spectral resolution for CI users.

OBJECTIVES/OBJECTIVE: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/METHODS: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.

OBJECTIVES/OBJECTIVE:The auditory experience of early deafened pediatric cochlear implant (CI) users is different from that of postlingually deafened adult CI users due to disparities in the developing auditory system. It is therefore expected that the auditory psychophysical capabilities between these two groups would differ. In this study, temporal resolving ability was investigated using a temporal modulation detection task to compare the performance outcomes between these two groups. DESIGN/METHODS:The minimum detectable modulation depth of amplitude modulated broadband noise at 100 Hz was measured for 11 early deafened children with a CI and 16 postlingually deafened adult CI users. RESULTS:Amplitude modulation detection thresholds were significantly lower (i.e., better) for the pediatric CI users than for the adult CI users. Within each group, modulation detection thresholds were not significantly associated with chronologic age, age at implantation, or years of CI experience. CONCLUSIONS:Early implanted children whose auditory systems develop in response to electric stimulation demonstrate better temporal resolving abilities than postlingually deafened adult CI users. This finding provides evidence to suggest that early implanted children might benefit from sound coding strategies emphasizing temporal information.

Cochlear-implant users who have experienced both analog and pulsatile sound coding strategies often have strong preferences for the sound quality of one over the other. This suggests that analog and pulsatile stimulation may provide different information or sound quality to an implant listener. It has been well documented that many implant listeners both prefer and perform better with multichannel analog than multichannel pulsatile strategies, although the reasons for these differences remain unknown. Here, we examine the perceptual differences between analog and pulsatile stimulation on a single electrode. A multidimensional scaling task, analyzed across two dimensions, suggested that pulsatile stimulation was perceived to be considerably different from analog stimulation. Two associated tasks using single-dimensional scaling showed that analog stimulation was perceived to be less Clean on average than pulsatile stimulation and that the perceptual differences were not related to pitch. In a follow-up experiment, it was determined that the perceptual differences between analog and pulsatile stimulation were not dependent on the interpulse gap present in pulsatile stimulation. Although the results suggest that there is a large perceptual difference between analog and pulsatile stimulation, further work is needed to determine the nature of these differences.