Elsevier

The Lancet

Volume 356, Issue 9228, 5 August 2000, Pages 466-468
The Lancet

Articles
Determinants of speech perception in children after cochlear implantation

https://doi.org/10.1016/S0140-6736(00)02555-1Get rights and content

Summary

Background

Cochlear implants provide access to the speech signal in those profoundly deaf children who derive no material benefit from acoustic hearing aids. Speech perception after implantation can vary widely—we have analysed the contribution of several factors.

Methods

We examined 40 children with mean age at implantation of 52 months who were either born deaf or became deaf before 3 years. All patients received the same multichannel implant system and were followed up for 5 years. We used connected discourse tracking (CDT) as the measure of speech perception. The effect of five potential predictors (age at implantation, number of inserted electrodes, origin of deafness, mode of communication, and socioeconomic group) on speech perception was analysed.

Findings

The mean number of words per minute perceived increased from 0 before implantation to 44·8 (SD 24·3) 5 years after implantation. Repeated-measures ANOVA showed that children significantly progressed over time (p=0·001). Age at implantation was a significant covariate (p=0·01) and mode of communication was a significant between-individuals factor (p=0·04).

Interpretation

Young age at intervention and oral communication mode are the most important known determinants of later speech perception in young children after cochlear implantation. Early identification of candidate children necessitates implementation of universal neonatal screening programmes for hearing impairment.

Introduction

Most children with impaired hearing can hear speech through acoustic hearing aids. However, some profoundly deaf children cannot, and as a consequence, their ability to develop spoken language and intelligible speech is severely restricted. For these children, cochlear implants are the only means of hearing speech and thus developing spoken language. Cochlear implants differ from hearing aids because they bypass the damaged inner ear and directly stimulate the residual auditory nerve fibres in the cochlea. An implant system has two components: an external component worn on the body and resembling a walkman, and an internal receiver that is surgically implanted behind the ear. The speech processor, which is either worn on the body or at ear level, converts speech into electronic signals and has a transmitter coil to send these signals to the implanted receiver package. The receiver package then carries electronic signals along several electrodes that can selectively stimulate the auditory nerve fibres in the cochlea.

Initially, only children who had lost their hearing after acquisition of spoken language were judged candidates for implantation, but the procedure has proven effective for the much larger group of children who are deaf from birth. Cochlear implants do not restore normal hearing, but are individually programmed to provide the recipient with hearing sensitivity within the speech range. Several years are needed for a child to learn to interpret what is heard through an implant and combine it with lip-reading to understand conversational speech. Worldwide, over 10 000 children have been the recipients of a cochlear implant. In Britain, the National Health Service (NHS) commits about £10 million yearly to the immediate and long-term management of implanted children, which is about a fifth of the annual NHS expenditure on permanent hearing-impairment in childhood.1

The primary measure of benefit from cochlear implantation is the ability to perceive speech. Previous studies have shown that a wide range of speech perception abilities are achieved by implanted children.2, 3, 4, 5, 6, 7 We aimed to explore this variability to identify the contribution of several possible predictors on the ability of these children to perceive speech.

Section snippets

Methods

We did this prospective and longitudinal study in one paediatric cochlear-implant centre. The children underwent extensive audiological testing to confirm lack of benefit from acoustic hearing-aids. Wearing hearing aids, all children had hearing losses greater than 60 dB from 500 Hz to 4 KHz, which is equivalent to unaided thresholds greater than 100 dB. Our study was confined to those children who were born deaf or who lost their hearing in the first 3 years of life. Only children who were

Results

Table 1 shows the results of CDT before implantation and at 3, 4, and 5 years after implantation. Age and mode of communication were significantly related to CDT results at 5 years after implantation (table 2). The correlation analysis at 3 and 4 years also showed significant correlations of CDT results with these factors. Number of inserted electrodes, origin of deafness, and social class did not correlate with CDT results. Repeated-measures ANOVA showed that children significantly progressed

Discussion

Contemporary cochlear implant systems provide substantial auditory information to children with profound hearing impairment who are unable to benefit from conventional hearing aids.2, 3, 4, 5, 6, 7 Development of appropriate test materials for young implanted children has proved a major challenge. In this study, we selected CDT as the measure of speech-perception since it closely simulates the real-life situations in which children need to understand speech in conversation. The results clearly

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