Language development of children before and after cochlear implant activation: a longitudinal study on the contribution of maternal input and acoustic environment

Introduction. In the last twenty years, several studies have assessed the effects that cochlear implants (CIs) have on the linguistic development of children with profound hearing loss. However, contrasting results have been reported about the children's language outcomes and the length of time the children need for recovering the language delay. These findings could be related to a number of complex, interrelated factors, such as age at CI activation, residual hearing, maternal input, and environmental acoustic exposure. To date, few longitudinal studies have been conducted with these children, and, in the case of Italian participants, with small sample sizes. The general aim of the present thesis, which includes three studies, is to assess longitudinally, using direct observations, the language development of Italian children with profound bilateral sensorineural hearing loss and CIs, considering some variables (preverbal linguistic abilities, maternal input and acoustic environment) that could affect language outcomes. Specifically, the sub-aims of this thesis are: 1) to assess the language development of the preverbal skills and the lexical development of children with CIs, compared with two groups of hearing children, paired by chronological age and language level; 2) to assess the relationship between mothers’ linguistic input and the language development of children with CIs, compared with a group of hearing children, paired by chronological age; 3) to investigate the relationship between children’s linguistic development and their exposure to diverse acoustic environments. Method. Twenty children with profound bilateral sensorineural hearing loss and CIs and their mothers were recruited and paired with two groups of hearing children. Specifically, one group is chronological age-matched, and one group was linguistic age-matched (lexical production). In all three studies, the children were video-observed during semi-structured play sessions with their mothers. All video observations were transcribed and coded, according to the different aims of each study. All mothers completed self-report questionnaires on their children's language skills and the mothers of children with CIs also completed two questionnaires on their children's auditory skills. Data on the daily acoustic exposure of children with CI collected by the devices. Results. As regards the first aim (first study), the data showed that children with CIs increased their linguistic production, with language developmental more similar to those of children matched for linguistic level than to those of children matched for chronological age. In fact, the children with CIs showed, at the last observation, similar linguistic outcomes of those of children paired for initial language level. However, it should be highlighted that children with CIs maintained high levels of preverbal communication in parallel with words, even in the last observation, in particular with regard to reduplicated and variegated babbling. Moreover, significant correlations emerged between the children’s preverbal production and their lexical development. As regards the second aim (second study), the data showed that mothers of children with CIs increased the use of higher facilitative language techniques (questions, answers and reformulations) and labelling after CI activation but, at the same time more production of directive phrases (lower facilitative language techniques) than mothers of hearing children. The data also showed progressive increases in the production of initiatives and adequate answers by children with CIs. The data, therefore, seem to show that the mothers of children with CIs are able to match their communication to their children’s language abilities, even if they maintain a higher level of directives. With regard to the third aim (third study), the data have highlighted a relationship between children’s language development and the daily environmental acoustic exposure as reported by data logging three, six and twelve months after the CIs activation, in particular for speech in quiet and speech in noise. Moreover, it was found that speech exposure in noise can negatively moderate children's linguistic outcomes results. Conclusion. The results highlighted the importance of investigating diverse factors that could affect the language development of children with CIs. Understanding the relationship between the children’s prelinguistic skills, maternal input, exposure to different acoustic scenes and linguistic development outcomes can be of fundamental importance in clinical practice. Considering these results, language habilitation programmes perhaps should consider the impact of a wider, and more complex, range of variables on the children's linguistic development. In particular, the findings could help medical staff to identify early the children’s language delays and their early risk indices and help parents to develop better communication strategies, and to plan more effective daily acoustic exposure in supporting their children's language development.