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Research Article

Effects of stimulation rate on modulation detection and speech recognition by cochlear implant users

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Pages 123-132 | Received 13 May 2010, Accepted 26 Sep 2010, Published online: 11 Nov 2010
 

Abstract

Abstract

Objective: This study investigated the effect of low to moderate electrical stimulation rates (275, 350, 500 and 900 pps/ch) on modulation detection ability of cochlear implant subjects, and the relationship between modulation detection and speech perception as a function of rate. Design: A repeated ABCD experimental design for the four rate conditions was employed. A sinusoidally amplitude modulated acoustic signal was presented to the audio input of a research processor. Stimuli were presented at an acoustic level that produced electrical levels close to the subjects' most comfortable level (MCL) of stimulation and at an acoustic level 20 dB below this. Study Sample: Ten postlingually deaf adult users of the Nucleus CI24 cochlear implant participated. Results: Acoustic modulation detection thresholds (MDTs), averaged across the subject group, were significantly better for rates of 500 pps/ch compared to the other rates examined for stimuli presented at MCL. In addition, there was a significant relation between speech perception in noise and acoustic MDTs at MCL. Conclusions: The benefits obtained in speech perception and modulation detection as a function of rate were attributed to an increased electrical dynamic range as a function of stimulation rate, at least for rates up to 500 pps/ch.

Sumario

Objetivo: Este estudio investigó el efecto de las tasas de estimulación eléctrica, leves a moderadas, (275, 350, 500 y 900 pps/canal) sobre la capacidad para detecctar la modulación por parte de sujetos con implante coclear y la relación entre la detección de la modulación y la percepción del lenguaje como función de la tasa. Diseño: Se empleó un diseño experimental de ABCD repetido para las cuatro condiciones de tasa. Se presentó una señal acústica de amplitud sinusoidalmente modulada en la entrada de audio de un procesador de investigación. Los estímulos fueron presentados a un nivel acústico que produjo niveles eléctricos cercanos al nivel de estimulación más confortable (MCL) de los sujetos y a un nivel acústico 20 dB por debajo de éste. Muestra Del Estudio: Participaron diez adultos sordos post-lingüísticos usuarios de un implante coclear Nucleus CI24. Resultados: Los umbrales acústicos de detección de la modulación (MDT), promediados en todo el grupo de sujetos, fueron significativamente mejores para las tasas de 500 ppps/canal, comparado con las otras tasas examinadas para estímulos presentados en el MCL. Además, existió una relación significativa entre la percepción del lenguaje en ruido y los MDT acústicos en el MCL. Conclusiones: Los beneficios obtenidos en la percepción del lenguaje y la detección de la modulación, como función de la tasa, fueron atribuidos a un incremento de los rangos dinámicos eléctricos, como función de la tasa de estimulación, al menos para tasas de hasta 500 pps/chanal.

Acknowledgements

The authors would like to express appreciation to the research subjects who participated in the study. The study was supported by University of Melbourne.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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