Zoom out Search Issue

ManualsBrandsContents Manualsaudio & home theatreZoom in

Digital Object Identifier 10.1109/MSP.2014.2371671

Date of publication: 12 February 2015

ochlear implantation is a life-changing intervention

for people with a severe hearing impairment [1]. For

most cochlear implant (CI) users, speech intelligibility

is satisfactory in quiet environments. Although mod-

ern CIs provide up to 22 stimulation channels, infor-

mation transfer is still limited for the perception of fine

spectrotemporal details in many types of sound. These details con-

tribute to the perception of music and speech in common listening

situations, such as where background noise is present. Over the

past several decades, many different sound processing strategies

have been developed to provide more details about acoustic signals

to CI users. In this article, progress in sound coding for CIs is

reviewed. Starting from a basic strategy, the current commercially

most-used signal processing schemes are discussed, as well as

recent developments in coding strategies that aim to improve audi-

tory perception. This article focuses particularly on the stimulation

strategies, which convert sound signals into patterns of nerve stim-

ulation. The neurophysiological rationale behind some of these

strategies is discussed and aspects of CI performance that require

further improvement are identified.

INTRODUCTION

The CI is the most successful man-made interface to the human

neural system; i.e., a machine–brain interface. The auditory nerve

is stimulated electrically, which leads to a partial restoration of

auditory perception for people who have a severe hearing impair-

ment. The understanding of speech by CI recipients in quiet envi-

ronments can be very good, but is considerably worse than that of

normal-hearing (NH) listeners in realistic listening situations. Typ-

ically, the presence of background noise greatly reduces the perfor-

mance of CI systems. For example, the signal-to-noise ratio

required for many CI users to attain 50% speech understanding is

about 15 dB higher than that of NH listeners.

Currently, more than 300,000 people worldwide with severe

hearing impairment, of whom 80,000 are young children, have

received CIs. The proportion of children with CIs (two years old and

younger) is increasing due to the increasing deployment of neona-

tal hearing-screening programs in many countries. Early implanta-

tion can give profoundly deaf children access to important

information to process auditory signals and master spoken

[

Jan Wouters, Hugh J. McDermott, and Tom Francart

]

EARPHONES—IMAGE LICENSED BY INGRAM PUBLISHING

[

From electric pulses to hearing

]

Sound Coding

in Cochlear Implants

THE WORLD’S NEWSSTAND

THE WORLD’S NEWSSTAND