Spatial spread of neural excitation in cochlear implant recipients: comparison of improved ECAP method and psychophysical forward masking

Cohen, Lawrence T.; Richardson, Louise M.; Saunders, Elaine; Cowan, Robert

doi:10.1016/s0378-5955(03)00096-0

Cited by 205 publications

(306 citation statements)

References 27 publications

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“…A forward masking subtraction method (e.g., Abbas et al 1999) was used to remove electrical stimulus artifacts while preserving neural responses. To determine the spread of neural excitation for steered pTP stimuli, the ECAP spatial profile (e.g., Cohen et al 2003) was measured by keeping the steered pTP-mode probe on EL8 (i.e., pTP EL8, α = 0 , pTP EL8, α = 0.5 , and pTP EL8, α = 1 ) while moving the MP-mode masker along the electrode array from EL1 to EL16. Both probe and masker used a biphasic cathodic-leading, charge-balanced pulse.…”

Section: Ecap: Stimuli and Proceduresmentioning

confidence: 99%

“…The spatial profile of ECAP (e.g., Cohen et al 2003;Hughes and Abbas 2006) shows the spread of excitation for the probe by assessing the spatial and temporal interactions between the neurons activated by the masker and probe (due to the neural refractory effects). While ECAP patterns have been studied extensively for MP stimuli, those for focused TP stimuli have only been reported by Zhu et al (2012) to be irregular with multiple peaks.…”

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: Ecap: Stimuli and Proceduresmentioning

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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“…However, it must be emphasized that electrode spacing is an extremely complex issue and many other factors must be considered in defining the optimum electrode spacing. Many investigators have noted extensive channel interactions in CI users (Cohen et al 2003;Stickney et al 2006), and closer electrode spacing might exacerbate this problem. Computer modeling studies also suggest that dynamic range and spatial selectivity for apical electrodes (1.5 cochlear turns) are often limited due to cross-turn stimulation (Briaire and Frijns 2006).…”

Section: Frequency-position Map Of Human Sgmentioning

confidence: 99%

“…Several studies have shown that estimates of intracochlear electrode positions based on analysis of either 2D radiographs or CT scans are more accurate than those based on absolute insertion depth, as reported during surgery (Marsh et al 1993;Cohen et al 1996;Xu et al 2000). Furthermore, Boex et al found that using rotational insertion angles, rather than absolute insertion depths, to estimate electrode frequencies resulted in less discrepancy between pitch sensations and the frequencies predicted by Greenwood_s function.…”

Section: Electrode Insertion Distances and Sg And Oc Place Frequenciementioning

confidence: 99%

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

Stakhovskaya

Sridhar

Bonham

et al. 2007

JARO

356

357

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The goals of this study were to derive a frequencyposition function for the human cochlear spiral ganglion (SG) to correlate represented frequency along the organ of Corti (OC) to location along the SG, to determine the range of individual variability, and to calculate an Baverage^frequency map (based on the trajectories of the dendrites of the SG cells). For both OC and SG frequency maps, a potentially important limitation is that accurate estimates of cochlear place frequency based upon the Greenwood function require knowledge of the total OC or SG length, which cannot be determined in most temporal bone and imaging studies. Therefore, an additional goal of this study was to evaluate a simple metric, basal coil diameter that might be utilized to estimate OC and SG length. Cadaver cochleae (n = 9) were fixed G24 h postmortem, stained with osmium tetroxide, microdissected, decalcified briefly, embedded in epoxy resin, and examined in surface preparations. In digital images, the OC and SG were measured, and the radial nerve fiber trajectories were traced to define a series of frequency-matched coordinates along the two structures. Images of the cochlear turns were reconstructed and measurements of basal turn diameter were made and correlated with OC and SG measurements. The data obtained provide a mathematical function for relating represented frequency along the OC to that of the SG.Results showed that whereas the distance along the OC that corresponds to a critical bandwidth is assumed to be constant throughout the cochlea, estimated critical band distance in the SG varies significantly along the spiral. Additional findings suggest that measurements of basal coil diameter in preoperative images may allow prediction of OC/SG length and estimation of the insertion depth required to reach specific angles of rotation and frequencies. Results also indicate that OC and SG percentage length expressed as a function of rotation angle from the round window is fairly constant across subjects. The implications of these findings for the design and surgical insertion of cochlear implants are discussed.

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“…A more straightforward way to explain the variable perceptual data is to directly estimate the excitation patterns of steered pTP stimuli with different α in each subject. This can be achieved by measuring the forward masking patterns of steered pTP stimuli using psychophysical methods (e.g., Chatterjee and Shannon 1998; Kwon and van den Honert 2006b; Srinivasan et al 2010;Landsberger et al 2012) or using electrically evoked compound action potentials (e.g., Cohen et al 2003;Hughes and Stille 2008).…”

Section: General Discussion and Summarymentioning

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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Spatial spread of neural excitation in cochlear implant recipients: comparison of improved ECAP method and psychophysical forward masking

Cited by 205 publications

References 27 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

Frequency Map for the Human Cochlear Spiral Ganglion: Implications for Cochlear Implants

Current Steering with Partial Tripolar Stimulation Mode in Cochlear Implants

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