Auditory Cortical Images of Cochlear-Implant Stimuli: Coding of Stimulus Channel and Current Level

This study quantified the accuracy with which populations of neurons in the auditory cortex can represent aspects of electrical cochlear stimuli presented through a cochlear implant. We tested the accuracy of coding of the place of stimulation (i.e., identification of the active stimulation channel) and of the stimulus current level. Physiological data came from the companion study, which recorded spike activity of neurons simultaneously from 16 sites along the tonotopic axis of the guinea pig's auditory cortex. In that study, cochlear electrical stimuli were presented to acutely deafened animals through a 6-electrode animal version of the 22-electrode Nucleus banded electrode array (Cochlear). Cochlear electrode configurations consisted of monopolar (MP), bipolar (BP + N) with N inactive electrodes between the active and return electrodes (0 ≤ N ≤ 3), tripolar (TP) with one active electrode and two flanking return electrodes, and common ground (CG) with one active electrode and as many as five return electrodes. In the present analysis, an artificial neural network was trained to recognize spatiotemporal patterns of cortical activity in response to single presentations of particular stimuli and, thereby, to identify those stimuli. The accuracy of pair-wise discrimination of stimulation channels or of current levels was represented by the discrimination index, d′, where d′ = 1 was taken as threshold. In many cases, the threshold for discrimination of place of cochlear stimulation was <0.75 mm, and the threshold for discrimination of current levels was <1 dB. Cochlear electrode configurations varied in the accuracy with which they signaled to the auditory cortex the place of cochlear stimulation. The BP + N and TP configurations provided considerably greater sensitivity to place of stimulation than did the MP configuration. The TP configuration maintained accurate signaling of place of stimulation up to the highest current levels, whereas sensitivity was degraded at high current levels in BP + N configurations. Electrode configurations also varied in the dynamic range over which they signaled stimulus current level. Dynamic ranges were widest for the BP + 0 configuration and narrowest for the TP configuration. That is, the configuration that showed the most accurate signaling of cochlear place of stimulation (TP) showed the most restricted dynamic range for signaling of current level. These results suggest that the choice of the optimal electrode configuration for use by human cochlear-prosthesis users would depend on the particular demands of the speech-processing strategy that is to be employed.

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Auditory Cortical Images of Cochlear-Implant Stimuli: Dependence on Electrode Configuration

Journal of Neurophysiology ◽

10.1152/jn.00212.2001 ◽

2002 ◽

Vol 87 (1) ◽

pp. 478-492 ◽

Cited By ~ 124

Author(s):

Julie Arenberg Bierer ◽

John C. Middlebrooks

Keyword(s):

Cochlear Implant ◽

Guinea Pigs ◽

Common Ground ◽

Dynamic Range ◽

Primary Auditory Cortex ◽

Stimulus Level ◽

Electrode Configuration ◽

Spatiotemporal Pattern ◽

Active Electrode ◽

Sensitive Site

This study examines patterns of auditory cortical activity elicited by single-pulse cochlear implant stimuli that vary in electrode configuration, cochlear place of stimulation, and stimulus level. Recordings were made from the primary auditory cortex (area A1) of ketamine-anesthetized guinea pigs. The spatiotemporal pattern of neural spike activity was measured simultaneously across 16 cortical locations spanning approximately 2–3 octaves of the tonotopic axis. Such a pattern, averaged over 40 presentations of any particular stimulus, was defined as the “cortical image” of that stimulus. Acutely deafened guinea pigs were implanted with a 6-electrode animal version of the 22-electrode Nucleus banded electrode array (Cochlear). Cochlear electrode configurations consisted of monopolar (MP), bipolar (BP + N) with N inactive electrodes between the active and return electrodes (0 ≤ N ≤ 4), tripolar (TP) with one active electrode and two flanking return electrodes, and common ground (CG) with one active electrode and as many as five return electrodes. Cortical images typically showed a focus of maximum spike probability and minimum latency. Spike probabilities tended to decrease, and latencies tended to increase, with increasing cortical distance from that focus. Cortical images of TP stimuli were the most spatially compact, followed by BP + N images, and then MP images, which were the broadest. Images of CG stimuli were rather variable across animals and stimulus channels. The locations of cortical images shifted systematically from caudal to rostral as the cochlear place of stimulation changed from basal to apical. At the most sensitive cortical site for each condition, the dynamic ranges over which spike rates increased with increased current level were restricted to about 1–2 dB, regardless of configuration. Dynamic ranges tended to increase with increasing cortical distance from the most sensitive site. Electrode configurations that produced compact cortical images (e.g., TP and BP + 0) showed the greatest range of thresholds within each cortical image and the largest dynamic range at cortical sites removed from the most sensitive site.

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Effect of Speech Processor Program Modifications on Cochlear Implant Recipients’ Threshold and Maximum Acceptable Loudness Levels

American Journal of Audiology ◽

10.1044/1059-0889(1999/015) ◽

1999 ◽

Vol 8 (2) ◽

pp. 128-136 ◽

Cited By ~ 10

Author(s):

John C. Sun ◽

Margarate W. Skinner ◽

S. Y. Liu ◽

T. S. Huang

Keyword(s):

Electrical Stimulation ◽

Cochlear Implant ◽

Everyday Life ◽

Dynamic Range ◽

Active Electrode ◽

Speech Processor ◽

Significant Change ◽

Upper Boundary

This study’s purpose was to determine whether or not modifications in speech processor electrical stimulation levels were associated with changes in five Nucleus 22 cochlear implant recipients’ thresholds or maximum acceptable loudness levels (MALs). These modifications in minimum and maximum stimulation levels were made to optimize hearing in everyday life. One threshold and one MAL were obtained on each active electrode during six, weekly test sessions, three before and three after program modification. Only one participant had a significant change in threshold after program modification; this participant and four others had significant changes in MAL. Participants’ threshold variability was the same, but MAL variability was higher than that observed in other studies. Because these participants had no experience making MAL judgments prior to this study, this result suggests that implant recipients should be given sufficient practice in making MAL judgments to provide a stable clinical estimate of the upper boundary of the electrical dynamic range.

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Experimental Basis and Design of a New Cochlear Prosthesis System

Annals of Otology Rhinology & Laryngology ◽

10.1177/00034894870960s138 ◽

1987 ◽

Vol 96 (1_suppl) ◽

pp. 76-79

Author(s):

J. Génin ◽

R. Charachon

Keyword(s):

Theoretical Model ◽

Integrated Circuits ◽

Cochlear Implant ◽

Dynamic Range ◽

Complementary Metal Oxide Semiconductor ◽

Metal Oxide Semiconductor ◽

Oxide Semiconductor ◽

Semiconductor Technology ◽

Experimental Basis ◽

Cochlear Prosthesis

In a multichannel cochlear prosthesis, electrical interactions between electrodes impose severe limitations on dynamic range and selectivity. We present a theoretical model to cope with these limitations. Building a successful cochlear implant requires full custom-integrated circuits. We present the design of such a device, implemented in complementary metal oxide semiconductor technology. The area of the chip is 9 mm2 and it can stimulate 15 cochlear electrodes with current impulses.

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Efficacy of a Cochlear Implant Simultaneous Analog Stimulation Strategy Coupled with a Monopolar Electrode Configuration

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348940511401113 ◽

2005 ◽

Vol 114 (11) ◽

pp. 886-893 ◽

Cited By ~ 8

Author(s):

Li Xu ◽

Teresa A. Zwolan ◽

Catherine S. Thompson ◽

Bryan E. Pfingst

Keyword(s):

Speech Recognition ◽

Cochlear Implant ◽

Speech Processing ◽

Dynamic Range ◽

Recognition Performance ◽

Electrode Configuration ◽

Processing Strategy ◽

Open Set ◽

Hearing In Noise ◽

Noise Test

Objectives: The present study was performed to evaluate the efficacy and clinical feasibility of using monopolar stimulation with the Clarion Simultaneous Analog Stimulation (SAS) strategy in patients with cochlear implants. Methods: Speech recognition by 10 Clarion cochlear implant users was evaluated by means of 4 different speech processing strategy/electrode configuration combinations; ie, SAS and Continuous Interleaved Sampling (CIS) strategies were each used with monopolar (MP) and bipolar (BP) electrode configurations. The test measures included consonants, vowels, consonant-nucleus-consonant words, and Hearing in Noise Test sentences with a +10 dB signal-to-noise ratio. Additionally, subjective judgments of sound quality were obtained for each strategy/configuration combination. Results: All subjects but 1 demonstrated open-set speech recognition with the SAS/MP combination. The group mean Hearing in Noise Test sentence score for the SAS/MP combination was 31.6% (range, 0% to 92%) correct, as compared to 25.0%, 46.7%, and 37.8% correct for the CIS/BP, CIS/MP, and SAS/BP combinations, respectively. Intersubject variability was high, and there were no significant differences in mean speech recognition scores or mean preference ratings among the 4 strategy/configuration combinations tested. Individually, the best speech recognition performance was with the subject's everyday strategy/configuration combination in 72% of the applicable cases. If the everyday strategy was excluded from the analysis, the subjects performed best with the SAS/MP combination in 37.5% of the remaining cases. Conclusions: The SAS processing strategy with an MP electrode configuration gave reasonable speech recognition in most subjects, even though subjects had minimal previous experience with this strategy/configuration combination. The SAS/MP combination might be particularly appropriate for patients for whom a full dynamic range of electrical hearing could not be achieved with a BP configuration.

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Previous Experience as a Confounding Factor in Comparing Cochlear-Implant Processing Schemes

Journal of Speech Language and Hearing Research ◽

10.1044/jshr.2902.282 ◽

1986 ◽

Vol 29 (2) ◽

pp. 282-287 ◽

Cited By ~ 31

Author(s):

Richard S. Tyler ◽

John P. Preece ◽

Bruce J. Gantz ◽

Steven R. Otto ◽

Charissa R. Lansing

Keyword(s):

Cochlear Implant ◽

Hearing Aids ◽

Speech Processing ◽

Dynamic Range ◽

Prior Experience ◽

Previous Experience ◽

Electrode Position ◽

Formant Frequency ◽

Processing Scheme ◽

The Subject

It is of great importance to compare the relative merits of different cochlear-implant speech-processing strategies. Some groups have compared different strategies within single subjects, but usually the subject has prior experience with one strategy, and no allowance is made for this prior experience. We show in the present study that this is inappropriate. We tested one subject using the Melbourne (Cochlear Corp.) multichannel implant with the device set to process sounds in two different ways. In the first processing scheme, the device functioned normally, extracting information about voicing frequency, amplitude and second-formant frequency. This information activated the 21-channel device, determining pulse rate, pulse amplitude and electrode position (respectively). In the second processing scheme, a single electrode (with the largest dynamic range) was activated. This electrode coded overall amplitude and voicing frequency. The subject was tested on an audiovisual test of a 14-choice consonant recognition in the form/iCi/ over a period of over 4 months. During this time the subject used the 21-channel processor outside of the laboratory. Upon initial connection, there was little difference between the results obtained with the two schemes when tested in sound alone or in sound plus vision. However, after about 4 months, scores obtained with the 21-channel processor in sound plus vigion were superior to the scores obtained with the one channel. This advantage came from a superiority in the features of voicing and nasality, but not place. Scores for sound-alone conditions between the two processing schemes remained similar for the 4-month period. Studies investigating the relative merits of speech processing systems (including tactile and conventional hearing aids) must consider previous experience as an important factor.

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Effects of Chronic Electrical Stimulation on Patients using a Cochlear Prosthesis

Otolaryngology ◽

10.1177/019459989110500605 ◽

1991 ◽

Vol 105 (6) ◽

pp. 797-801 ◽

Cited By ~ 8

Author(s):

Susan B. Waltzman ◽

Noel L. Cohen ◽

William H. Shapiro

Keyword(s):

Electrical Stimulation ◽

Speech Recognition ◽

Cochlear Implant ◽

Dynamic Range ◽

Cochlear Prosthesis ◽

Postoperative Performance ◽

Open Set ◽

Chronic Electrical Stimulation

Eighteen patients using the Nucleus multichannel cochlear prosthesis underwent annual evaluations for electrical thresholds, dynamic range, and speech recognition abilities for a period of 1 to 5 years. Results revealed no correlation between length of usage of a cochlear implant and electrical thresholds. The dynamic range was initially wider in the patients with open-set speech recognition, but narrowed in subsequent years. There was a correlation between length of deafness and postoperative performance.

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Neurophysiology of Cochlear Implant Users I: Effects of Stimulus Current Level and Electrode Site on the Electrical ABR, MLR, and N1-P2 Response

Ear and Hearing ◽

10.1097/00003446-200212000-00002 ◽

2002 ◽

Vol 23 (6) ◽

pp. 502-515 ◽

Cited By ~ 63

Author(s):

Jill B. Firszt ◽

Ron D. Chambers ◽

Nina Kraus ◽

Ruth M. Reeder

Keyword(s):

Cochlear Implant ◽

Electrode Site ◽

Current Level ◽

Stimulus Current

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The Relationship Between Impedance, Programming and Word Recognition in a Large Clinical Dataset of Cochlear Implant Recipients

Trends in Hearing ◽

10.1177/23312165211060983 ◽

2022 ◽

Vol 26 ◽

pp. 233121652110609

Author(s):

Benjamin Caswell-Midwinter ◽

Elizabeth M. Doney ◽

Meisam K. Arjmandi ◽

Kelly N. Jahn ◽

Barbara S. Herrmann ◽

...

Keyword(s):

Word Recognition ◽

Cochlear Implant ◽

Speech Processing ◽

Dynamic Range ◽

Electrode Impedance ◽

Current Steering ◽

Processing Strategy ◽

Monosyllabic Word ◽

Negatively Associated ◽

Clinical Dataset

Cochlear implant programming typically involves measuring electrode impedance, selecting a speech processing strategy and fitting the dynamic range of electrical stimulation. This study retrospectively analyzed a clinical dataset of adult cochlear implant recipients to understand how these variables relate to speech recognition. Data from 425 implanted post-lingually deafened ears with Advanced Bionics devices were analyzed. A linear mixed-effects model was used to infer how impedance, programming and patient factors were associated with monosyllabic word recognition scores measured in quiet. Additional analyses were conducted on subsets of data to examine the role of speech processing strategy on scores, and the time taken for the scores of unilaterally implanted patients to plateau. Variation in basal impedance was negatively associated with word score, suggesting importance in evaluating the profile of impedance. While there were small, negative bivariate correlations between programming level metrics and word scores, these relationships were not clearly supported by the model that accounted for other factors. Age at implantation was negatively associated with word score, and duration of implant experience was positively associated with word score, which could help to inform candidature and guide expectations. Electrode array type was also associated with word score. Word scores measured with traditional continuous interleaved sampling and current steering speech processing strategies were similar. The word scores of unilaterally implanted patients largely plateaued within 6-months of activation. However, there was individual variation which was not related to initially measured impedance and programming levels.

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