Abstract
Cochlear implants provide individuals who are deaf with access to speech. Although substantial advancements have been made by novel technologies, there still is high variability in language development during childhood, depending on adaptation and neural plasticity. These factors have often been investigated in the auditory domain, with the mismatch negativity as an index for sensory and phonological processing. Several studies have demonstrated that the MMN is an electrophysiological correlate for hearing improvement with cochlear implants. In this study, two groups of cochlear implant users, both with very good basic hearing abilities but with non-overlapping speech performance (very good or very poor speech performance), were matched according to device experience and age at implantation. We tested the perception of phonemes in the context of specific other phonemes from which they were very hard to discriminate (e.g., the vowels in /bu/ vs. /bo/). The most difficult pair was individually determined for each participant. Using behavioral measures, both cochlear implants groups performed worse than matched controls, and the good performers performed better than the poor performers. Cochlear implant groups and controls did not differ during time intervals typically used for the mismatch negativity, but earlier: source analyses revealed increased activity in the region of the right supramarginal gyrus (220–260 ms) in good performers. Poor performers showed increased activity in the left occipital cortex (220–290 ms), which may be an index for cross-modal perception. The time course and the neural generators differ from data from our earlier studies, in which the same phonemes were assessed in an easy-to-discriminate context. The results demonstrate that the groups used different language processing strategies, depending on the success of language development and the particular language context. Overall, our data emphasize the role of neural plasticity and use of adaptive strategies for successful language development with cochlear implants.
Highlights
After their initial development in the 1950s by Djourno and Eryies [1], cochlear implants (CI) provide individuals who are deaf with access to spoken language
Sorted by each person’s most difficult-to-differentiate subtest, the three groups showed a different performance: while control participants performed on a very high level (d’ = 4.25, which equals about 99% correct answers), good performers showed moderate performance (d’ = 1.25, 68% correct answers) and poor performers performed on guessing level (d’ = -0.41, equaling about 47% correct answers)
The neurophysiological analyses demonstrated that the mismatch negativity component (MMN) in CI users is similar in latency and overall amplitude to the MMN of matched controls
Summary
After their initial development in the 1950s by Djourno and Eryies [1], cochlear implants (CI) provide individuals who are deaf with access to spoken language. Young children who were born deaf or became deafened before language development started can–under optimal conditions- even develop language performance within the normal range, enabling them to communicate with people of typical hearing [2]. There is a surprisingly strong variance in language development in these children. We attempt to shed light on phoneme perception in difficult language contrasts in two groups of congenitally deaf or prelingually deafened CI users. Both groups have very good basic hearing abilities, but differ in their language perception performance. Before explaining the differences between the two studies, we will introduce the background and methods in more detail
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