the connection is less clear. In a review of a net selection of six studies performed between 1992 and 2012, Cysneiros, Leal, Lucena, and Muniz (2016) concluded that there was a positive relationship between expressive and receptive communication, but that there was a serious lack of quality research on this association. The complexities involved in this issue may stem from the multifactorial nature of influences on speech and language performance by CI users (Cosetti & Waltzman, 2012; Gillis, 2018; Lazard, Vincent, et al., 2012).
3.3.8 Word and Sentence Processing
A relatively large percentage of research at the word (in the sense of vocabulary) and sentence levels involves children. Whereas children with CIs have a reduced receptive and expressive vocabulary compared to their NH peers, as was found in a recent meta‐analysis (Lund, 2016), there is some evidence that grammatical skills lag behind their lexical skills. For instance, in a sentence repetition task, they substituted more words and omitted more articles than hearing‐age matched NH controls, whereas their vocabulary was normal (Caselli, Rinaldi, Varuzza, Giuliani, & Burdo, 2012). Half of the 70 school‐aged Dutch children with CIs studied by Boons et al. (2013) had developed linguistic skills on a par with their NH peers. Whereas vocabulary was on average at age‐appropriate levels, CI children had difficulty with salient morphology (for example, the comparative ‐[ər] and the superlative ‐[stə]), with formulating sentences according to the CELF test (creating sentences using word and picture cues; Kort, Compaan, Schittekatte, & Dekker, 2010) and with retelling stories based on picture cues. Four‐ to seven‐year‐old children with CIs had a mean length of utterance (MLU, a measure of grammatical complexity) in spontaneous speech below the norm. At the age of seven, this was still 55%. Moreover, they had more errors in finite verb morphology and subject–verb agreement. Age at implantation, but not hearing level, was found to predict results. Scores did not clearly improve over time, except for finite verb morphology. This indicates that CI children have extended delay in their grammatical development.
In a study by de Hoog et al. (2016), of 39 CI children, 12.9% performed at a level that is comparable to the norm on picture naming, which is a test of expressive vocabulary, and 10.4% on picture selection, which tests receptive vocabulary. For sentence completion, testing morphosyntactic proficiency (e.g., plurals and verb tenses), this was 20.7% and in picture selection, testing grammatical knowledge in word order tasks, they scored 28.4%. The authors note that the relatively low scores may be due to the fact that only a little over 51% of their cohort used spoken language in education. Lexical language skills were best predicted by age at testing, phoneme perception abilities, and auditory word closure scores, which involves identifying words based on partial information. The best predictors of morphosyntactic skills were the lexical skill scores, auditory memory for words, and auditory word closure. In a recent review, Ruben (2018) concluded that many, but not all, CI children reached age‐appropriate receptive and expressive language skills between 3 and 10 years after implantation, with more promising results for earlier implantations. This conclusion is seemingly at odds with Boons et al. (2013), and highlights the need for further thorough investigation of the effects of CI listening on language development.
In conclusion, the above studies show that CI children have delayed development of many aspects of morphosyntax, despite a relatively normal vocabulary. Their development is influenced by more fundamental abilities such as phoneme perception and auditory memory, as well as by age at implantation. Existing literature indicates that they have a reasonable chance of catching up with their NH peers several years after implantation.
3.3.9 Higher‐Order Communication
While a central goal of cochlear implantation is to improve expressive and receptive communication competence and performance of the structure of speech and language, that is, the formal aspects of language, such as phonology and grammar, it is of special interest to study how successfully CI users practice and apply language along with other pragmatic aspects of communication, since that is ultimately what affects quality of life (Fortunato‐Tavares, Befi‐Lopes, Bento, & de Andrade, 2012). This involves skills such as intelligibility, discourse strategies, nonverbal communication and communicative initiative. Fewer studies are devoted to this than to objective language and speech perceptual measures.
Sarant et al. (2018) reviewed research using parental reports showing that, on a general level, cochlear implantation, relative to pre‐implantation, enhances communication skills and social relationships for children suffering from severe to profound hearing loss. A large majority of parents surveyed by Nelson, Herde, Munoz, White, and Page (2017) reported that they were satisfied with their choice of CI for their children because it allowed them to communicate orally with them, their family and the rest of the hearing community. They also indicated that it provided for school performance that could be on par with hearing peers, although hearing in noise was found to be problematic. This motivation for implantation by parents is consistent with other research, although signed communication is seen as a useful support for oral communication (Hyde & Punch, 2011). Advantages have also been reported for adults. Patients over 40 years old reported that implantation had improved their general and physical health, as well as, to a lesser extent, their social interaction (Ramos et al., 2013). Furthermore, in a review, Mayer and Trezek (2017) found that only 3 out of 14 studies observed reduced literacy development in students with CIs.
These merits of implantation do not, however, mean that the everyday communication skills of CI recipients were commensurate with their NH counterparts. For children, they were found to be comparable to those of peers with moderate to severe hearing loss using amplification (Meister et al., 2015). Intelligibility was observed to be reduced and to correlate with measures of psychosocial development, among which functional communication, which was itself impaired (Boonen, Kloots, & Gillis, 2019; Freeman, Pisoni, Kronenberger, & Castellanos, 2017); however, see also Li et al. (2018) and Sarant et al. (2018). Reduced abilities in everyday communication in quiet and in noise were reported for a group of 339 children (Cupples et al., 2018).
Holt et al. (2017) found that adults with CIs, in a task where interlocutors were asked to direct each other around a map, used repetition of directives more often than information requests, as a request for clarification, and also fewer acknowledgments than NH counterparts. Moreover, their final rise excursions for questions, which were normally large, as opposed to statements, which were normally small or non‐existent, was opposite to those of the control participants. This shows that their usage and realization of pragmatics in language was essentially different from NH controls.
The above literature suggests that CIs improve non‐objective higher‐order communication relative to the pre‐implant period, but that many aspects of the pragmatics of communication deviate from those of NH peers. Many issues are yet to be thoroughly investigated. Sarant et al. (2018) argued that impaired prosocial behavior that can be observed in CI children may be due to issues, some of which have been reported, for children with hearing loss, such as reduced access to speech due to, for instance, a late onset of acquisition, difficulty with hearing in noise, poor quality of speech input, reduced amount of overhearing or eavesdropping, reduced child‐directed input or parental attention, increased listening effort, and shame in expressing oneself. Children (n = 188) with delayed expressive and receptive oral language development spent less time communicating with their parents and had reduced sustained attention, as revealed by the percentage of time dedicated to playing, during free play than their NH peers (Barker et al., 2009). According to the authors, the results supported the hypothesis that attention deficits, and not communication skills, mediated the effect of language problems on behavior, which opens up new avenues of investigation for the study of the long‐term effects of cochlear implantation on the higher‐order communication of children.
3.4 Auditory Brainstem Implants
A device that is essentially similar to CIs is the auditory brainstem implant (ABI). ABI systems were developed to address the auditory communication needs of patients with neurofibromatosis type‐2 (NF‐2), but have also been used with non‐tumor patients, and sometimes children, when cochlear implantation is contraindicated