Loudness growth observed under partially tripolar stimulation: Model and data from cochlear implant listeners

Litvak, Leonid M.; Spahr, Anthony J.; Emadi, Gulam

doi:10.1121/1.2749414

Cited by 81 publications

(162 citation statements)

References 31 publications

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“…When α was 0 or 1, relatively high ECAP amplitudes were sometimes observed around the single return electrode (i.e., EL7 for α = 0 and EL9 for α = 1), although it was unlikely to have side-lobe effects (e.g., Litvak et al 2007) with the small σ values used for ECAP recording. Further away from the main and return electrodes, the ECAP amplitudes were instead lower on the side of the single return electrode than on the other side.…”

Section: Current Steering With Steered Ptp Stimulimentioning

confidence: 99%

“…The relative amount of intracochlear return current (defined as the compensation coefficient σ) ranges from 0 to 1. In human CI users, partial TP (pTP) stimulation with σ G 1 is often needed instead of full TP stimulation with σ =1 to achieve full loudness growth within the compliance limit while keeping relatively focused excitation patterns (e.g., Mens and Berenstein 2005;Litvak et al 2007). Compared to the traditional MPmode CI processing strategy, a pTP-mode strategy has been shown to significantly improve speech recognition in noise for CI users (Srinivasan et al 2013), when both strategies were matched in the channel number and stimulation rate.…”

Section: Introductionmentioning

confidence: 99%

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Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants

Luo

2015

JARO

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Current steering in partial tripolar (pTP) mode has been shown to improve pitch perception and spectral resolution with cochlear implants (CIs). In this mode, a fraction (σ) of the main electrode current is returned within the cochlea and steered between the basal and apical flanking electrodes (with a proportion of α and 1 − α, respectively). Pitch generally decreases when α increases from 0 to 1, although the salience of pitch change varies across CI users. This study aimed to identify the mechanism of pitch changes with pTP-mode current steering and the factors contributing to the intersubject variability in pitch-ranking sensitivity. The electrical fields were measured for steered pTP stimuli on the same main electrode with α = 0, 0.5, and 1 in five implanted ears using electrical field imaging (EFI). The related excitation patterns were also measured physiologically using evoked compound action potential (ECAP) and psychophysically using psychophysical forward masking (PFM). Consistent with the pitch-ranking results in this study, the EFI, ECAP, and PFM centroids shifted apically with increasing α. An apical shift was also observed for the PFM peak but not for the EFI or ECAP peak. The pattern width was similar with different α values within a given measure (e.g., EFI, ECAP, or PFM), but the ECAP patterns were broader than the EFI and PFM patterns, possibly because ECAP was measured with smaller σ values than EFI and PFM. The amount of pattern shift with α depended on σ (i.e., the total amount of current used for steering) but was not correlated with the pitchranking sensitivity across subjects. The results revealed that the pitch changes elicited by pTP-mode current steering were not only driven by the shifts of excitation centroid.

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Section: Current Steering With Steered Ptp Stimulimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants

Luo

2015

JARO

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“…The simplest models assume that the conductivity of cochlear tissues is uniform, and that current sources (i.e., the stimulating electrodes) are point sources within this homogeneous medium [e.g. (Litvak et al, 2007a)]. In response to stimulation from a single electrode, homogenous models predict isopotential contours that are spherical in shape (Fig.…”

Section: Modeling Methodsmentioning

confidence: 99%

Current focusing and steering: Modeling, physiology, and psychophysics

Bonham

Litvak²

2008

Hearing Research

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Current steering and current focusing are stimulation techniques designed to increase the number of distinct perceptual channels available to cochlear implant (CI) users by adjusting currents applied simultaneously to multiple CI electrodes. Previous studies exploring current steering and current focusing stimulation strategies are reviewed, including results of research using computational models, animal neurophysiology, and human psychophysics. Preliminary results of additional neurophysiological and human psychophysical studies are presented that demonstrate the success of current steering strategies in stimulating auditory nerve regions lying between physical CI electrodes, as well as current focusing strategies that excite regions narrower than those stimulated using monopolar configurations. These results are interpreted in the context of perception and speech reception by CI users. Disparities between results of physiological and psychophysical studies are discussed. The differences in stimulation used for physiological and psychophysical studies are hypothesized to contribute to these disparities. Finally, application of current steering and focusing strategies to other types of auditory prostheses is also discussed.

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“…Here, loudness-balanced pTP stimuli with different α were assumed to activate the same number of neurons, as in Goldwyn et al (2010) and Litvak et al (2007). Although there was no evidence that a chosen neuron count corresponded to a particular value on a loudness perception scale, the current levels that activated 100 and 1,000 neurons were assumed to be around the perceptual threshold and most comfortable level, respectively.…”

Section: Computational Modelmentioning

confidence: 99%

“…A computational model that simulates intra-cochlear potential fields and auditory neural response to CI stimulation (Goldwyn et al 2010) was used to investigate loudness and pitch perception with steered pTP mode. Similar models have been used to study loudness growth with standard pTP stimulation (Litvak et al 2007) and simulate current focusing and steering in various modes (Bonham and Litvak 2008). Modeling studies were less time-consuming than testing human CI subjects and could provide valuable insights into human perceptual data, thanks to their capability of adjusting specific CI factors and examining conditions that were difficult to test in real CI users.…”

Section: Introductionmentioning

confidence: 99%

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

Luo

2012

JARO

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The large spread of excitation is a major cause of poor spectral resolution for cochlear implant (CI) users. Partial tripolar (pTP) mode has been proposed to reduce current spread by returning an equally distributed fraction (0.5×σ) of current to two flanking electrodes and the rest to an extra-cochlear ground. This study tested the efficacy of incorporating current steering into pTP mode to add spectral channels. Different proportions of current [α×σ and (1−α)×σ] were returned to the basal and apical flanking electrodes respectively to shape the electric field. Loudness and pitch perception with α from 0 to 1 in steps of 0.1 was simulated with a computational model of CI stimulation and tested on the apical, middle, and basal electrodes of six CI subjects. The highest σ allowing for full loudness growth within the implant compliance limit was chosen for each main electrode. Pitch ranking was measured between pairs of loudness-balanced steered pTP stimuli with an α interval of 0.1 at the most comfortable level. Results demonstrated that steered pTP stimuli with α around 0.5 required more current to achieve equal loudness than those with α around 0 or 1, maybe due to more focused excitation patterns. Subjects usually perceived decreasing pitches as α increased from 0 to 1, somewhat consistent with the apical shift of the center of gravity of excitation pattern in the model. Pitch discrimination was not better with α around 0.5 than with α around 0 or 1, except for some subjects and electrodes. For three subjects with better pitch discrimination, about half of the pitch ranges of two adjacent main electrodes overlapped with each other in steered pTP mode. These results suggest that current steering with focused pTP mode may improve spectral resolution and pitch perception with CIs.

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Loudness growth observed under partially tripolar stimulation: Model and data from cochlear implant listeners

Cited by 81 publications

References 31 publications

Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants

Excitation Patterns of Standard and Steered Partial Tripolar Stimuli in Cochlear Implants

Current focusing and steering: Modeling, physiology, and psychophysics

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

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