Effect of Return Electrode Placement at Apical Cochleostomy on Current Flow With a Cochlear Implant.

OBJECTIVES: 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: 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.

Ceiling effects for speech perception tests in pediatric cochlear implant users.

OBJECTIVES: The purpose of this study was to determine the prevalence of ceiling effects for commonly used speech perception tests in a large population of children who received a cochlear implant (CI) before the age of four. A secondary goal was to determine the demographic factors that were relevant for predicting which children were more likely to reach ceiling level performance. We hypothesize that ceiling effects are highly prevalent for most tests. DESIGN: Retrospective chart review of children receiving a CI between 2002 and 2014. RESULTS: 165 children were included. Median scores were above ceiling levels (≥90% correct) for the majority of speech perception tests and all distributions of scores were highly skewed. Children who were implanted earlier, received two implants, and were oral communicators were more likely to reach ceiling-level performance. Age and years of CI listening experience at time of test were negatively correlated with performance, suggesting a non-random assignment of tests. Many children were re-tested on tests for which they had already scored at ceiling. CONCLUSIONS: Commonly used speech perception tests for children with CIs are prone to ceiling effects and may not accurately reflect how a child performs in everyday listening situations.

Acceptance and Benefit of Electroacoustic Stimulation in Children.

OBJECTIVE: Children with high-frequency severe-to-profound hearing loss and low-frequency residual hearing who do not derive significant benefit from hearing aids are now being considered for cochlear implantation. Previous research shows that hearing preservation is possible and may be desirable for the use of electroacoustic stimulation (EAS) in adults, but this topic remains underexplored in children. The goal of this study was to explore factors relating to hearing preservation, acceptance, and benefits of EAS for children. STUDY DESIGN: Retrospective review. SETTING: Tertiary academic medical center. PATIENTS: Forty children (48 ears) with preoperative low-frequency pure-tone averages of 75 dB HL or less at 250 and 500 Hz (n = 48). INTERVENTION: All patients underwent cochlear implantation with a standard-length electrode. MAIN OUTCOME MEASURE: Low-frequency audiometric thresholds, speech perception, and EAS usage were measured at initial stimulation, and 3 and 12 months postoperatively. Outcomes were compared between children with and without hearing preservation, and between EAS users and nonusers. RESULTS: Hearing was preserved at similar rates as adults but worse for children with an enlarged vestibular aqueduct. Fewer than half of children who qualified to use EAS chose to do so, citing a variety of audiologic and nonaudiologic reasons. No differences were detected in speech perception scores across the groups for words, sentences, or sentences in noise tests. CONCLUSIONS: Neither hearing preservation nor EAS use resulted in superior speech perception in children with preoperative residual hearing; rather, all children performed well after implantation.

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.

Stimulating the Cochlear Apex Without Longer Electrodes: Preliminary Results With a New Approach.

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: Three adult patients who underwent cochlear implantation using this new technique. INTERVENTIONS: 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: 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.

Evaluation of a Tool for Measuring Temporal Modulation Detection.

OBJECTIVES: 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: 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.

The Perception of Ramped Pulse Shapes in Cochlear Implant Users.

The electric stimulation provided by current cochlear implants (CI) is not power efficient. One underlying problem is the poor efficiency by which information from electric pulses is transformed into auditory nerve responses. A novel stimulation paradigm using ramped pulse shapes has recently been proposed to remedy this inefficiency. The primary motivation is a better biophysical fit to spiral ganglion neurons with ramped pulses compared to the rectangular pulses used in most contemporary CIs. Here, we tested the hypotheses that ramped pulses provide more efficient stimulation compared to rectangular pulses and that a rising ramp is more efficient than a declining ramp. Rectangular, rising ramped and declining ramped pulse shapes were compared in terms of charge efficiency and discriminability, and threshold variability in seven CI listeners. The tasks included single-channel threshold detection, loudness-balancing, discrimination of pulse shapes, and threshold measurement across the electrode array. Results showed that reduced charge, but increased peak current amplitudes, was required at threshold and most comfortable levels with ramped pulses relative to rectangular pulses. Furthermore, only one subject could reliably discriminate between equally-loud ramped and rectangular pulses, suggesting variations in neural activation patterns between pulse shapes in that participant. No significant difference was found between rising and declining ramped pulses across all tests. In summary, the present findings show some benefits of charge efficiency with ramped pulses relative to rectangular pulses, that the direction of a ramped slope is of less importance, and that most participants could not perceive a difference between pulse shapes.

Listening to speech with a guinea pig-to-human brain-to-brain interface.

Nicolelis wrote in his 2003 review on brain-machine interfaces (BMIs) that the design of a successful BMI relies on general physiological principles describing how neuronal signals are encoded. Our study explored whether neural information exchanged between brains of different species is possible, similar to the information exchange between computers. We show for the first time that single words processed by the guinea pig auditory system are intelligible to humans who receive the processed information via a cochlear implant. We recorded the neural response patterns to single-spoken words with multi-channel electrodes from the guinea inferior colliculus. The recordings served as a blueprint for trains of biphasic, charge-balanced electrical pulses, which a cochlear implant delivered to the cochlear implant user's ear. Study participants completed a four-word forced-choice test and identified the correct word in 34.8% of trials. The participants' recognition, defined by the ability to choose the same word twice, whether right or wrong, was 53.6%. For all sessions, the participants received no training and no feedback. The results show that lexical information can be transmitted from an animal to a human auditory system. In the discussion, we will contemplate how learning from the animals might help developing novel coding strategies.

Place-Pitch Interval Perception With a Cochlear Implant.

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.

Assessing the Quality of Low-Frequency Acoustic Hearing: Implications for Combined Electroacoustic Stimulation With Cochlear Implants.

OBJECTIVES: There are many potential advantages to combined electric and acoustic stimulation (EAS) with a cochlear implant (CI), including benefits for hearing in noise, localization, frequency selectivity, and music enjoyment. However, performance on these outcome measures is variable, and the residual acoustic hearing may not be beneficial for all patients. As such, we propose a measure of spectral resolution that might be more predictive of the usefulness of the residual hearing than the audiogram alone. In the following experiments, we measured performance on spectral resolution and speech perception tasks in individuals with normal hearing (NH) using low-pass filters to simulate steeply sloping audiograms of typical EAS candidates and compared it with performance on these tasks for individuals with sensorineural hearing loss with similar audiometric configurations. Because listeners with NH had similar levels of audibility and bandwidth to listeners with hearing loss, differences between the groups could be attributed to distortions due to hearing loss. DESIGN: Listeners with NH (n = 12) and those with hearing loss (n = 23) with steeply sloping audiograms participated in this study. The group with hearing loss consisted of 7 EAS users, 14 hearing aid users, and 3 who did not use amplification in the test ear. Spectral resolution was measured with the spectral-temporal modulated ripple test (SMRT), and speech perception was measured with AzBio sentences in quiet and noise. Listeners with NH listened to stimuli through low-pass filters and at two levels (40 and 60 dBA) to simulate low and high audibility. Listeners with hearing loss listened to SMRT stimuli unaided at their most comfortable listening level and speech stimuli at 60 dBA. RESULTS: Results suggest that performance with SMRT is significantly worse for listeners with hearing loss than for listeners with NH and is not related to audibility. Performance on the speech perception task declined with decreasing frequency information for both listeners with NH and hearing loss. Significant correlations were observed between speech perception, SMRT scores, and mid-frequency audiometric thresholds for listeners with hearing loss. CONCLUSIONS: NH simulations describe a "best case scenario" for hearing loss where audibility is the only deficit. For listeners with hearing loss, the likely broadening of auditory filters, loss of cochlear nonlinearities, and possible cochlear dead regions may have contributed to distorted spectral resolution and thus deviations from the NH simulations. Measures of spectral resolution may capture an aspect of hearing loss not evident from the audiogram and be a useful tool for assessing the contributions of residual hearing post-cochlear implantation.

Acceptance and Benefits of Electro-Acoustic Stimulation for Conventional-Length Electrode Arrays.

BACKGROUND: Prior studies have shown an advantage for electro-acoustic stimulation (EAS) in cochlear implant (CI) patients with residual hearing, but the degree of benefit can vary. The objective was to explore which factors relate to performance with and acceptance of EAS for CI users with conventional-length electrodes. METHODS: A retrospective chart review was conducted for adults with an average threshold of 75 dB hearing loss or better across 250 and 500 Hz preoperatively (n = 83). All patients underwent cochlear implantation with a conventional-length electrode. Low-frequency audiometric thresholds were measured at initial activation as well as 3 and 12 months postoperatively to determine who met the criteria for EAS. Speech perception for CNC words and AzBio sentences in quiet and +10 dB SNR noise was evaluated 3 and 12 months after activation. RESULTS: Speech perception in quiet and noise was similar regardless of whether or not the patient was eligible for EAS. Less than half of the patients who met the EAS criteria chose to use it, citing reasons such as physical discomfort or lack of perceived benefit. EAS users performed better on CNC words but not sentence recognition than EAS nonusers. CONCLUSIONS: EAS use is dependent on audiologic and nonaudiologic issues. Hearing preservation is possible with conventional electrodes, but hearing preservation alone does not guarantee superior speech perception.

Melodic interval perception with acoustic and electric hearing in bimodal and single-sided deaf cochlear implant listeners.

Two notes sounded sequentially elicit melodic intervals and contours that form the basis of melody. Many previous studies have characterized pitch perception in cochlear implant (CI) users to be poor which may be due to the limited spectro-temporal resolution and/or spectral warping with electric hearing compared to acoustic hearing (AH). Poor pitch perception in CIs has been shown to distort melodic interval perception. To characterize this interval distortion, we recruited CI users with either normal (single sided deafness, SSD) or limited (bimodal) AH in the non-implanted ear. The contralateral AH allowed for a stable reference with which to compare melodic interval perception in the CI ear, within the same listener. Melodic interval perception was compared across acoustic and electric hearing in 9 CI listeners (4 bimodal and 5 SSD). Participants were asked to rank the size of a probe interval presented to the CI ear to a reference interval presented to the contralateral AH ear using a method of constant stimuli. Ipsilateral interval ranking was also measured within the AH ear to ensure that listeners understood the task and that interval ranking was stable and accurate within AH. Stimuli were delivered to the AH ear via headphones and to the CI ear via direct audio input (DAI) to participants' clinical processors. During testing, a reference and probe interval was presented and participants indicated which was larger. Ten comparisons for each reference-probe combination were presented. Psychometric functions were fit to the data to determine the probe interval size that matched the reference interval. Across all AH reference intervals, the mean matched CI interval was 1.74 times larger than the AH reference. However, there was great inter-subject variability. For some participants, CI interval distortion varied across different reference AH intervals; for others, CI interval distortion was constant. Within the AH ear, ipsilateral interval ranking was accurate, ensuring that participants understood the task. No significant differences in the patterns of results were observed between bimodal and SSD CI users. The present data show that much larger intervals were needed with the CI to match contralateral AH reference intervals. As such, input melodic patterns are likely to be perceived as frequency compressed and/or warped with electric hearing, with less variation among notes in the pattern. The high inter-subject variability in CI interval distortion suggests that CI signal processing should be optimized for individual CI users.

Music Is More Enjoyable With Two Ears, Even If One of Them Receives a Degraded Signal Provided By a Cochlear Implant.

OBJECTIVES: 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: 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.

Pleasantness Ratings for Harmonic Intervals With Acoustic and Electric Hearing in Unilaterally Deaf Cochlear Implant Patients.

BACKGROUND: Harmony is an important part of tonal music that conveys context, form and emotion. Two notes sounded simultaneously form a harmonic interval. In normal-hearing (NH) listeners, some harmonic intervals (e.g., minor 2nd, tritone, major 7th) typically sound more dissonant than others (e.g., octave, major 3rd, 4th). Because of the limited spectro-temporal resolution afforded by cochlear implants (CIs), music perception is generally poor. However, CI users may still be sensitive to relative dissonance across intervals. In this study, dissonance ratings for harmonic intervals were measured in 11 unilaterally deaf CI patients, in whom ratings from the CI could be compared to those from the normal ear. METHODS: Stimuli consisted of pairs of equal amplitude MIDI piano tones. Intervals spanned a range of two octaves relative to two root notes (F3 or C4). Dissonance was assessed in terms of subjective pleasantness ratings for intervals presented to the NH ear alone, the CI ear alone, and both ears together (NH + CI). Ratings were collected for both root notes for within- and across-octave intervals (1-12 and 13-24 semitones). Participants rated the pleasantness of each interval by clicking on a line anchored with "least pleasant" and "most pleasant." A follow-up experiment repeated the task with a smaller stimulus set. RESULTS: With NH-only listening, within-octave intervals minor 2nd, major 2nd, and major 7th were rated least pleasant; major 3rd, 5th, and octave were rated most pleasant. Across-octave counterparts were similarly rated. With CI-only listening, ratings were consistently lower and showed a reduced range. Mean ratings were highly correlated between NH-only and CI-only listening (r = 0.845, p < 0.001). Ratings were similar between NH-only and NH + CI listening, with no significant binaural enhancement/interference. The follow-up tests showed that ratings were reliable for the least and most pleasant intervals. DISCUSSION: Although pleasantness ratings were less differentiated for the CI ear than the NH ear, there were similarities between the two listening modes. Given the lack of spectro-temporal detail needed for harmonicity-based distinctions, temporal envelope interactions (within and across channels) associated with a perception of roughness may contribute to dissonance perception for harmonic intervals with CI-only listening.

Validating a Quick Spectral Modulation Detection Task.

OBJECTIVES: 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: 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.

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.

ALTIS: A new algorithm for adaptive long-term SNR estimation in multi-talker babble.

We introduce a real-time capable algorithm which estimates the long-term signal to noise ratio (SNR) of the speech in multi-talker babble noise. In real-time applications, long-term SNR is calculated over a sufficiently long moving frame of the noisy speech ending at the current time. The algorithm performs the real-time long-term SNR estimation by averaging "speech-likeness" values of multiple consecutive short-frames of the noisy speech which collectively form a long-frame with an adaptive length. The algorithm is calibrated to be insensitive to short-term fluctuations and transient changes in speech or noise level. However, it quickly responds to non-transient changes in long-term SNR by adjusting the duration of the long-frame on which the long-term SNR is measured. This ability is obtained by employing an event detector and adaptive frame duration. The event detector identifies non-transient changes of the long-term SNR and optimizes the duration of the long-frame accordingly. The algorithm was trained and tested for randomly generated speech samples corrupted with multi-talker babble. In addition to its ability to provide an adaptive long-term SNR estimation in a dynamic noisy situation, the evaluation results show that the algorithm outperforms the existing overall SNR estimation methods in multi-talker babble over a wide range of number of talkers and SNRs. The relatively low computational cost and the ability to update the estimated long-term SNR several times per second make this algorithm capable of operating in real-time speech processing applications.

Perceptual Differences Between Low-Frequency Analog and Pulsatile Stimulation as Shown by Single- and Multidimensional Scaling.

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.

The effect of polarity order and electrode-activation order on loudness in cochlear implant users.

This study examined the interaction between polarity and electrode-activation order on loudness in cochlear implant users. Pulses were presented with the polarity of the leading phase alternating or constant across channels. Electrode-activation order was either consecutive or staggered. Staggered electrode-activation orders required less current for equal loudness than consecutive orders with constant polarity. Consecutive electrode-activation orders required less current than staggered orders with alternating polarity. The results support the hypothesis that crosstalk between channels can interfere with or facilitate neuronal activation depending on polarity.