Timothy A. Holden

Role of electrode placement as a contributor to variability in cochlear implant outcomes.

Suboptimal cochlear implant (CI) electrode array placement may reduce presentation of coded information to the central nervous system and, consequently, limit speech recognition. Background: Generally, mean speech reception scores for CI recipients are similar across different CI systems, yet large outcome variation is observed among recipients implanted with the same device. These observations suggest significant recipient-dependent factors influence speech reception performance. This study examines electrode array insertion depth and scalar placement as recipient-dependent factors affecting outcome. Methods: Scalar location and depth of insertion of intracochlear electrodes were measured in 14 patients implanted with Advanced Bionics electrode arrays and whose word recognition scores varied broadly. Electrode position was measured using computed tomographic images of the cochlea and correlated with stable monosyllabic word recognition scores. Results: Electrode placement, primarily in terms of depth of insertion and scala tympani versus scala vestibuli location, varies widely across subjects. Lower outcome scores are associated with greater insertion depth and greater number of contacts being located in scala vestibuli. Three patterns of scalar placement are observed suggesting variability in insertion dynamics arising from surgical technique. Conclusion: A significant portion of variability in word recognition scores across a broad range of performance levels of CI subjects is explained by variability in scalar location and insertion depth of the electrode array. We suggest that this variability in electrode placement can be reduced and average speech reception improved by better selection of cochleostomy sites, revised insertion approaches, and control of insertion depth during surgical placement of the array.

Factors affecting open-set word recognition in adults with cochlear implants.

Objective: A great deal of variability exists in the speech-recognition abilities of postlingually deaf adult cochlear implant (CI) recipients. A number of previous studies have shown that duration of deafness is a primary factor affecting CI outcomes; however, there is little agreement regarding other factors that may affect performance. The objective of the present study was to determine the source of variability in CI outcomes by examining three main factors, biographic/audiologic information, electrode position within the cochlea, and cognitive abilities in a group of newly implanted CI recipients. Design: Participants were 114 postlingually deaf adults with either the Cochlear or Advanced Bionics CI systems. Biographic/audiologic information, aided sentence-recognition scores, a high resolution temporal bone CT scan and cognitive measures were obtained before implantation. Monosyllabic word recognition scores were obtained during numerous test intervals from 2 weeks to 2 years after initial activation of the CI. Electrode position within the cochlea was determined by three-dimensional reconstruction of pre- and postimplant CT scans. Participants’ word scores over 2 years were fit with a logistic curve to predict word score as a function of time and to highlight 4-word recognition metrics (CNC initial score, CNC final score, rise time to 90% of CNC final score, and CNC difference score). Results: Participants were divided into six outcome groups based on the percentile ranking of their CNC final score, that is, participants in the bottom 10% were in group 1; those in the top 10% were in group 6. Across outcome groups, significant relationships from low to high performance were identified. Biographic/audiologic factors of age at implantation, duration of hearing loss, duration of hearing aid use, and duration of severe-to-profound hearing loss were significantly and inversely related to performance as were frequency modulated tone, sound-field threshold levels obtained with the CI. That is, the higher-performing outcome groups were younger in age at the time of implantation, had shorter duration of severe-to-profound hearing loss, and had lower CI sound-field threshold levels. Significant inverse relationships across outcome groups were also observed for electrode position, specifically the percentage of electrodes in scala vestibuli as opposed to scala tympani and depth of insertion of the electrode array. In addition, positioning of electrode arrays closer to the modiolar wall was positively correlated with outcome. Cognitive ability was significantly and positively related to outcome; however, age at implantation and cognition were highly correlated. After controlling for age, cognition was no longer a factor affecting outcomes. Conclusion: There are a number of factors that limit CI outcomes. They can act singularly or collectively to restrict an individual’s performance and to varying degrees. The highest performing CI recipients are those with the least number of limiting factors. Knowledge of when and how these factors affect performance can favorably influence counseling, device fitting, and rehabilitation for individual patients and can contribute to improved device design and application.

Performance of postlinguistically deaf adults with the Wearable Speech Processor (WSP III) and Mini Speech Processor (MSP) of the Nucleus Multi-Electrode Cochlear Implant.

Seven postlinguistically deaf adults implanted with the Nucleus Multi-Electrode Cochlear Implant participated in an evaluation of speech perception performance with three speech processors: the Wearable Speech Process (WSP III), a prototype of the Mini Speech Processor, and the Mini Speech Processor. The first experiment was performed with the prototype and Wearable Speech Processor both programmed using the F0F1F2 speech coding strategy. The second experiment compared performance with the Mini Speech Processor programmed with the Multi-Peak speech coding strategy and the Wearable Speech Processor programmed with the F0F1F2 speech coding strategy. Performance was evaluated in the sound-only condition using recorded speech tests presented in quiet and in noise. Questionnaires and informal reports provided information about use in everyday life. In experiment I, there was no significant difference in performance using the Wearable Speech Processor and prototype on any of the tests. Nevertheless, six out of seven subjects preferred the prototype for use in everyday life. In experiment II, performance on open-set tests in quiet and noise was significantly higher with the Mini Speech Processor (Multi-Peak speech coding strategy) than with the Wearable Speech Processor. Subjects reported an increase in their ability to communicate with other people using the Mini Speech Processor (Multi-Peak speech coding strategy) compared with the Wearable Speech Processor in everyday life.

Speech recognition with the Nucleus 24 SPEAK, ACE, and CIS speech coding strategies in newly implanted adults

Objective The objective of this study was to determine whether 1) the SPEAK, ACE or CIS speech coding strategy was associated with significantly better speech recognition for individual subjects implanted with the Nucleus CI24M internal device who used the SPrint™ speech processor, and 2) whether a subject’s preferred strategy for use in everyday life provided the best speech recognition. Design Twelve postlinguistically deaf, newly implanted adults participated. Initial preference for the three strategies was obtained with paired-comparison testing on the first day of implant stimulation with seven of eight U.S. subjects. During the first 12 wk, all subjects used each strategy alone for 4 wk to give them experience with the strategy and to identify preferred speech processor program parameters and settings that would be used in subsequent testing. For the next 6 wk, subjects used one strategy at a time for 2-wk intervals in the same order they had for the first 12 wk. At the end of each 2-wk interval, speech recognition testing was conducted with all three strategies. At the end of the 6 wk, all three strategies were placed on each subject’s processor, and subjects were asked to compare listening with these three programs in as many situations as possible for the next 2 wk. When they returned, subjects responded to a questionnaire asking about their preferred strategy and responded to two lists of medial consonants using each of the three strategies. The U.S. subjects also responded to two lists of medial vowels with the three strategies. Results Six of the 12 subjects in the present study had significantly higher CUNY sentence scores with the ACE strategy than with one or both of the other strategies; one of the 12 subjects had a significantly higher score with SPEAK than with ACE. In contrast, only two subjects had significantly higher CNC word and phoneme scores with one or two strategies than with the third strategy. One subject had a significantly higher vowel score with the SPEAK strategy than with the CIS strategy; and no subjects had significantly higher consonant scores with any strategy. Seven of 12 subjects preferred the ACE strategy, three preferred the SPEAK strategy, and two preferred the CIS strategy. Subjects’ responses on a questionnaire agreed closely with strategy preference from comparisons made in everyday life. There was a strong relation between the preferred strategy and scores on CUNY sentences but not for the other speech tests. For all subjects, except one, the preferred strategy was the one with the highest CUNY sentence score or was a strategy with a CUNY score not significantly lower than the highest score. Conclusions Despite differences in research design, there was remarkably close agreement in the pattern of group mean scores for the three strategies for CNC words and CUNY sentences in noise between the present study and the Conversion study (Arndt, Staller, Arcaroli, Hines, & Ebinger, Reference Note 1). In addition, essentially the same percentage of subjects preferred each strategy. For both studies, the strategy with which subjects had the highest score on the CUNY sentences in noise evaluation was strongly related to the preferred strategy; this relation was not strong for CNC words, CNC phonemes, vowels or consonants (Skinner, Arndt, & Staller, 2002). These results must be considered within the following context. For each strategy, programming parameters preferred for use in everyday life were determined before speech recognition was evaluated. In addition, implant recipients had experience listening with all three strategies in many situations in everyday life before choosing a preferred strategy. Finally, 11 of the 12 subjects strongly preferred one of the three strategies. Given the results and research design, it is recommended that clinicians fit each strategy sequentially starting with the ACE strategy so that the preferred programming parameters are determined for each strategy before recipients compare pairs of strategies. The goal is to provide the best opportunity for individuals to hear in everyday life within a clinically acceptable time period (e.g., 6 wk).

Optimal cochlear implant insertion vectors.

Hypothesis: An optimal insertion trajectory during cochlear implantation may be determined from the anatomic relationship between the facial nerve and round window. Background: Cochlear implantation functional outcomes improve with insertion of the implant into the scala tympani. This depends on creating a cochleostomy in the proper position and inserting the electrode along a trajectory coaxial with the centerline of the scala tympani. The anatomic landmarks for this insertion trajectory have not been described. Methods: Clinical computed tomography and micro-computed tomographic analysis of 8 cadaveric temporal bones. Results: Appropriate insertion vectors pass inferior or anteroinferior to the round window membrane. In many individuals, the facial nerve interrupts all or most of the insertion vectors coaxial to the centerline of the scala tympani. Conclusion: A cochleostomy placed inferior or anteroinferior to the round window membrane may facilitate atraumatic insertion of a cochlear implant along the centerline of the scala tympani. The lateral and anterior wall of the fallopian canal must be adequately thinned to achieve an optimal insertion trajectory. This is particularly true when inserting through cochleostomies placed away from the round window along the basal turn of the cochlea.

An investigation of input level range for the nucleus 24 cochlear implant system: speech perception performance, program preference, and loudness comfort ratings.

Objective Cochlear implant recipients often have limited access to lower level speech sounds. In this study we evaluated the effects of varying the input range characteristics of the Nucleus 24 cochlear implant system on recognition of vowels, consonants, and sentences in noise and on listening in everyday life. Design Twelve subjects participated in the study that was divided into two parts. In Part 1 subjects used speech processor (Nucleus 24 SPrint™) programs adjusted for three input sensitivity settings: a standard or default microphone sensitivity setting (MS 8), a setting that increased the input sensitivity by 10.5 dB (MS 15), and the same setting that increased input sensitivity but also incorporated the automatic sensitivity control (ASC; i.e., MS 15A) that is designed to reduce the loudness of noise. The default instantaneous input dynamic range (IIDR) of 30 dB was used in these programs (i.e., base level of 4; BL 4). Subjects were tested using each sensitivity program with vowels and consonants presented at very low to casual conversational levels of 40 dB SPL and 55 dB SPL, respectively. They were also tested with sentences presented at a raised level of 65 dB SPL in multi-talker babble at individually determined signal to noise ratios. In addition, subjects were given experience outside of the laboratory for several weeks. They were asked to complete a questionnaire where they compared the programs in different listening situations as well as the loudness of environmental sounds, and state the setting they preferred overall. In Part 2 of the study, subjects used two programs. The first program was their preferred sensitivity program from Part 1 that had an IIDR of 30 dB (BL 4). Seven subjects used MS 8 and four used MS 15, and one used the noise reduction program MS 15A. The second program used the same microphone sensitivity but had the IIDR extended by an additional 8 to 10 dB (BL 1/0). These two programs were evaluated similarly in the speech laboratory and with take-home experience as in Part 1. Results Part 1 Increasing the microphone input sensitivity by 10.5 dB (from MS 8 to MS 15) significantly improved the perception of vowels and consonants at 40 and 55 dB SPL. The group mean improvement in vowel scores was 25 percentage points at 40 dB SPL and 4 percentage points at 55 dB SPL. The group mean improvement for consonants was 23 percentage points at 40 dB SPL and 11 percentage points at 55 dB SPL. Increased input sensitivity did not significantly reduce the perception of sentences presented at 65 dB SPL in babble despite the fact that speech peaks were then within the compressed range above the SPrint processors automatic gain control (AGC) knee-point. Although there was a demonstrable advantage for perception of low-level speech with the higher input sensitivity (MS 15 and 15A), seven of the 12 subjects preferred MS 8, four preferred MS 15 or 15A, and one had no preference overall. Approximately half the subjects preferred MS 8 across the 18 listening situations, whereas an average of two subjects preferred MS 15 or 15A. The increased microphone sensitivity of MS 15 substantially increased the loudness of environmental sounds. However, use of the ASC noise reduction setting with MS 15 reduced the loudness of environmental sounds to equal or below that for MS 8. Results Part 2 The increased instantaneous input range gave some improvement (8 to 9 percentage points for the 40 dB SPL presentation level) in the perception of consonants. There was no statistically significant increase in vowel scores. Mean scores for sentences presented at 65 dB SPL in babble were significantly lower (5 percentage points) for the increased IIDR setting. Subjects had no preference for the increased IIDR over the default. The IIDR setting had no effect on the loudness of environmental sounds. Conclusions Given the fact that individuals differ in threshold (T) and comfort (C) levels for electrical stimulation, and preferred microphone sensitivity, volume control, and noise-reduction settings, it is essential for the clinician and recipient to determine what combination is best for the individual over several sessions. The results of this study clearly show the advantage of using higher microphone sensitivity settings than the default MS 8 to provide better speech recognition for low-level stimuli. However, it was also necessary to adjust other parameters such as map C levels, automatic sensitivity control and base level, to optimize loudness comfort in the diversity of listening situations an individual encounters in everyday life.

Activation lateralization in human core, belt, and parabelt auditory fields with unilateral deafness compared to normal hearing.

We studied activation magnitudes in core, belt, and parabelt auditory cortex in adults with normal hearing (NH) and unilateral hearing loss (UHL) using an interrupted, single-event design and monaural stimulation with random spectrographic sounds. NH patients had one ear blocked and received stimulation on the side matching the intact ear in UHL. The objective was to determine whether the side of deafness affected lateralization and magnitude of evoked blood oxygen level-dependent responses across different auditory cortical fields (ACFs). Regardless of ear of stimulation, NH showed larger contralateral responses in several ACFs. With right ear stimulation in UHL, ipsilateral responses were larger compared to NH in core and belt ACFs, indicating neuroplasticity in the right hemisphere. With left ear stimulation in UHL, only posterior core ACFs showed larger ipsilateral responses, suggesting that most ACFs in the left hemisphere had greater resilience against reduced crossed inputs from a deafferented right ear. Parabelt regions located posterolateral to core and belt auditory cortex showed reduced activation in UHL compared to NH irrespective of RE/LE stimulation and lateralization of inputs. Thus, the effect in UHL compared to NH differed by ACF and ear of deafness.

Verification of computed tomographic estimates of cochlear implant array position: a micro-CT and histologic analysis.

Objective: To determine the efficacy of clinical computed tomographic (CT) imaging to verify postoperative electrode array placement in cochlear implant (CI) patients. Study Design: Nine fresh cadaver heads underwent clinical CT scanning, followed by bilateral CI insertion and postoperative clinical CT scanning. Temporal bones were removed, trimmed, and scanned using micro-CT. Specimens were then dehydrated, embedded in either methyl methacrylate or LR White resin, and sectioned with a diamond wafering saw. Histology sections were examined by 3 blinded observers to determine the position of individual electrodes relative to soft tissue structures within the cochlea. Electrodes were judged to be within the scala tympani, scala vestibuli, or in an intermediate position between scalae. Results: The position of the array could be estimated accurately from clinical CT scans in all specimens using micro-CT and histology as a criterion standard. Verification using micro-CT yielded 97% agreement, and histologic analysis revealed 95% agreement with clinical CT results. Conclusion: A composite, 3-dimensional image derived from a patients preoperative and postoperative CT images using a clinical scanner accurately estimates the position of the electrode array as determined by micro-CT imaging and histologic analyses. Information obtained using the CT method provides valuable insight into numerous variables of interest to patient performance such as surgical technique, array design, and processor programming and troubleshooting.

Parameter Selection to Optimize Speech Recognition with the Nucleus Implant

Speech coding strategy, frequency boundary assignment table, and speech processor program minimum and maximum stimulation levels are parameters of the Nucleus Cochlear Implant System whose selection affects speech recognition performance in adults and children. Research studies show that speech recognition is significantly better with (1) the Spectral Peak than with the Multipeak speech coding strategy and (2) frequency boundary assignment Table 7 than with Table 9 in an individuals speech processor program (MAP). Minimum and maximum stimulation levels in this MAP are based on psychophysical measurements on each electrode but often need to be modified for optimum use in everyday life. Many children and adults have increases, decreases, or fluctuations in electrical hearing that require changes in the MAP minimum and maximum levels to maintain their ability to recognize speech and other sounds.

The effect of instantaneous input dynamic range setting on the speech perception of children with the nucleus 24 implant.

Objective: The purpose of this study was to examine the effects of a wider instantaneous input dynamic range (IIDR) setting on speech perception and comfort in quiet and noise for children wearing the Nucleus 24™ implant system and the Freedom™ speech processor. In addition, childrens ability to understand soft and conversational level speech in relation to aided sound-field thresholds was examined. Design: Thirty children (age, 7 to 17 years) with the Nucleus 24 cochlear implant system and the Freedom speech processor with two different IIDR settings (30 versus 40 dB) were tested on the Consonant Nucleus Consonant (CNC) word test at 50 and 60 dB SPL, the Bamford-Kowal-Bench Speech in Noise Test, and a loudness rating task for four-talker speech noise. Aided thresholds for frequency-modulated tones, narrowband noise, and recorded Ling sounds were obtained with the two IIDRs and examined in relation to CNC scores at 50 dB SPL. Speech Intelligibility Indices were calculated using the long-term average speech spectrum of the CNC words at 50 dB SPL measured at each test site and aided thresholds. Results: Group mean CNC scores at 50 dB SPL with the 40 IIDR were significantly higher (p < 0.001) than with the 30 IIDR. Group mean CNC scores at 60 dB SPL, loudness ratings, and the signal to noise ratios-50 for Bamford-Kowal-Bench Speech in Noise Test were not significantly different for the two IIDRs. Significantly improved aided thresholds at 250 to 6000 Hz as well as higher Speech Intelligibility Indices afforded improved audibility for speech presented at soft levels (50 dB SPL). Conclusion: These results indicate that an increased IIDR provides improved word recognition for soft levels of speech without compromising comfort of higher levels of speech sounds or sentence recognition in noise.