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

Document Type

Article

Abstract

Most cochlear implant strategies utilize monopolar stimulation, likely inducing relatively broad activation of the auditory neurons. The spread of activity may be narrowed with a tripolar stimulation scheme, wherein compensating current of opposite polarity is simultaneously delivered to two adjacent electrodes. In this study, a model and cochlear implant subjects were used to examine loudness growth for varying amounts of tripolar compensation, parameterized by a coefficient sigma, ranging from 0 (monopolar) to 1 (full tripolar). In both the model and the subjects, current required for threshold activation could be approximated by I(sigma)=Ithr(0)(1-sigmaK), with fitted constants Ithr(0) and K. Three of the subjects had a "positioner," intended to place their electrode arrays closer to their neural tissue. The values of K were smaller for the positioner users and for a "close" electrode-to-tissue distance in the model. Above threshold, equal-loudness contours for some subjects deviated significantly from a linear scale-up of the threshold approximations. The patterns of deviation were similar to those observed in the model for conditions in which most of the neurons near the center electrode were excited.

Medical Subject Headings

Acoustic Stimulation; Cochlear Implantation; Electric Stimulation; Electrodes; Equipment Design; Humans; Loudness Perception (physiology); Models, Biological; Neurons (physiology); Psychophysics (methods); Reproducibility of Results; Speech Perception (physiology)

Publication Date

8-1-2007

Publication Title

The Journal of the Acoustical Society of America

E-ISSN

1520-8524

Volume

122

Issue

2

First Page

967

Last Page

81

PubMed ID

17672645

Digital Object Identifier (DOI)

10.1121/1.2749414

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