Speech perception in congenitally, pre-lingually and post-lingually deaf children expressed in an equivalent hearing loss value

Abstract

To investigate the speech perception performance of children with a cochlear implant (CI) after 3 and 4 years of follow-up and to study the influence of age at implantation, duration of deafness and communication mode on the variability in speech perception performance. A broad battery of speech perception tests was administered to 67 children with a CI. The results were reduced into one measure: the 'equivalent hearing loss (EHL)'. This outcome measure refers to the performance of a reference group of severely and profoundly hearing impaired children with conventional hearing aids. The population comprised 35 congenitally, 17 pre-lingually and 15 post-lingually deaf children implanted between 1989 and 1999. The population was homogeneous with respect to cognition, residual hearing and support at home as a result of conservative inclusion criteria. During the first 2 years after implantation, post-lingually deaf children showed the fastest rate of improvement in speech perception. After 3 years of implant use, the early implanted pre-lingually deaf children and congenitally deaf children implanted under the age of 6 years caught up with the post-lingually deaf children. Pre-lingually deaf children implanted after a relatively long-duration of deafness tended to show poorer performance than those with a shorter duration. Performance of congenitally deaf children implanted after the age of 6 years was poorer and progress was slower. In the congenitally deaf children, 36% of the variability in performance was explained by duration of deafness, whereas in the children with pre- and post-lingually acquired deafness, communication mode explained 69% of the variance. All children derived benefit from their CI for speech perception tasks, but performance varied greatly. Several children reached EHL levels around 70 dB; their speech perception was equal to that of a child with conventional hearing aids who has 70 dB HL. After early implantation, the levels of performance that were eventually achieved differed no more than 10 dB, irrespective of whether the onset of deafness was pre-lingual or postlingual. In congenitally deaf children, duration of deafness played a major role in speech perception performance, whereas in the children with pre-lingually and post-lingually acquired deafness together, mode of communication was a major factor.