Neural Correlates of Speech Processing in Prelingually Deafened Children and Adolescents with Cochlear Implants

Abstract

Prelingually deafened children with cochlear implants stand a good chance of developing satisfactory speech performance. Nevertheless, their eventual language performance is highly variable and not fully explainable by the duration of deafness and hearing experience. In this study, two groups of cochlear implant users (CI groups) with very good basic hearing abilities but non-overlapping speech performance (very good or very bad speech performance) were matched according to hearing age and age at implantation. We assessed whether these CI groups differed with regard to their phoneme discrimination ability and auditory sensory memory capacity, as suggested by earlier studies. These functions were measured behaviorally and with the Mismatch Negativity (MMN). Phoneme discrimination ability was comparable in the CI group of good performers and matched healthy controls, which were both better than the bad performers. Source analyses revealed larger MMN activity (155–225 ms) in good than in bad performers, which was generated in the frontal cortex and positively correlated with measures of working memory. For the bad performers, this was followed by an increased activation of left temporal regions from 225 to 250 ms with a focus on the auditory cortex. These results indicate that the two CI groups developed different auditory speech processing strategies and stress the role of phonological functions of auditory sensory memory and the prefrontal cortex in positively developing speech perception and production.

When Hearing Is Tricky: Speech Processing Strategies in Prelingually Deafened Children and Adolescents with Cochlear Implants Having Good and Poor Speech Performance

“…Difficult contrasts (e.g., the vowels in /bu/ and /bo/) were not predefined, but rather separately established for each participant on the basis of behavioral measures. This research complements and contrasts with earlier data on easy-to-discriminate contrasts in the same population [6]. Before explaining the differences between the two studies, we will introduce the background and methods in more detail.…”

“…Children with cochlear implants often miss a great amount of hearing experience before implantation leading to less exposure to the phonemes of their native language. With strong relations between phonological awareness and higher order language abilities as word decoding, reading or communication mode [16–20], it is not surprising that prelingually deafened CI users with very good or poor language development do also show strong differences in phoneme discrimination [6]. …”

“…Even though source localization of ERP components does not provide the spatial accuracy of fMRI and PET, it is recommended for CI users because of strong safety concerns with fMRI (due to the metallic and magnetic components of the implant) as well as the invasive character of PET. Source localization with distributed models for ERP data of CI users has been successfully used before [6,40] and is applied frequently to other areas of language processing (e.g. [41–43]).…”

Neurocognitive factors in sensory restoration of early deafness: a connectome model

“…For example, verbal short-term memory tests (eg, digit or letter spans) that assess sequential processing and memory of linguistic stimuli showed developmental delays in many people with a cochlear implant. 74,75,78 However, poor performance on verbal memory span tests can reflect either language or sequential processing deficits (or both). On the other hand, spatial, design, or tactile sequential processing and learning tasks are not constrained by language and allow for assessment of more domain-general nonverbal memory and sequential processing deficits.…”

“…10 Although delays and disturbances in sequential processing have been reported in some people with a cochlear implant on tests of spatial memory and fingertip tapping, 9,81 this is not always the case, particularly with spatial memory tests. 74,75,78 As with executive functioning, large individual differences in sequential processing skills within the population with cochlear implants necessitate an individualised patient-centred approach to assessment.…”