Sound Processing and Language in Children with Mild to Moderate Hearing Loss

Background to the study

We have known for some time that having a permanent severe or profound hearing impairment in childhood often leads to marked delays and deficits in the acquisition of spoken and written language. Indeed, it was an awareness of this fact which led to specialist education programmes for the deaf, and which spurred the development of hearing aid and cochlear implant technologies. Much less is known about how having a permanent mild or moderate hearing loss (MMHL) in childhood affects language development. Nevertheless, recent research suggests that the language abilities of this group are mixed; whereas many go on to acquire completely normal language abilities, others show substantial impairments. The aim of this project was to investigate why some children with MMHL have impaired language.

One factor that might account for the individual differences of children with MMHL is the way in which sounds are processed in the brain. Some researchers think that even subtle deficits in sound processing can lead to marked impairments in language development. However, this theory is quite controversial, and researchers have been debating the extent to which deficits in sound processing might lead to language problems. A few years ago we tried to test this theory, by examining the sound processing and language skills of children with MMHL. We found that, on average, children with MMHL performed more poorly than their normally hearing peers on a range of tasks used to assess sound processing. However, on average, they had language abilities that were appropriate for their age. We interpreted this as evidence that deficits in processing sounds do not necessarily lead to difficulties in language [1, 2].

However, the research described above had a number of shortcomings. First, sound processing skills were assessed when children were not wearing hearing aids. Nevertheless, many children with MMHL do wear hearing aids, and much of the sound processing they do takes place with them on. Second, there are a number of reasons why children with MMHL might perform poorly on a sound processing task. Research has shown that children with hearing loss often need to put more effort into tasks that require them to listen. These shortcomings mean that we may have underestimated the sound processing skills that children with MMHL use in the real world. Therefore, it remains possible that sound processing skills might better predict the language outcomes of children with MMHL, if we measure them in a different way.

In a series of experiments, we examined in more detail the sound processing and language skills of children with MMHL. In order to assess whether children with MMHL have deficits in processing sounds in the real world, we tested their sound processing both while they were wearing their hearing aid(s) and while they were not. To assess whether poor performance was due to the extra effort required for them to listen, we also measured sound processing using a task that did not require any active listening. Finally, to assess whether deficits in sound processing lead to language impairments in children with MMHL, we measured their performance on a wide range of language tests. For all tasks, the performance of children with MMHL was compared to that of normally hearing children of the same age (8 – 15 years).

References

[1] Halliday L.F. & Bishop, D.V.M. (2005). Frequency discrimination in children with mild to moderate sensorineural hearing loss. Journal of Speech, Language, and Hearing Research, 48, 1187 - 1203.

[2] Halliday L.F. & Bishop, D.V.M. (2006). Is poor frequency modulation detection linked to literacy problems? A comparison of specific reading disability and mild to moderate sensorineural hearing loss. Brain and Language, 97, 200 - 213.