Evaluating Benifits of Cochlear Implantation in Special Cases

A cochlear implant is an electronic medical device that replaces the functions of a damaged inner ear. Cochlear implants provide young children with immediate benefits in the domain of auditory receptive capabilities that accordingly triggers a cascade of further benefits in several areas: spoken communication, attention and memories skills, educational achievements, social independence, and quality of life. The gains in these different areas depend on several aspects such as age at implantation, the presence of additional disabilities, family and social aspects, and the learning style. Therefore, for a complete evaluation of the benefits provided by cochlear implants, it is necessary to assess, before and after the surgical interventions, not only the patients' perception skills, but also the performance in the other above-mentioned areas, on with hearing impairment has an impact and that are benefited from implantation. Unfortunately, more often than not the evaluation of these children is difficult, mostly when the grade of impairment in some of the above-mentioned areas is mild or profound. Cochlear-implanted children with several and profound grade of deficits, e.g., children with additional disabilities, are frequently unable to perform the tests and the absence of response is interpreted as absence of skills. However, frequently parents and therapist don't agree with the test results and refer better skills. On the other hand, cochlear-implanted children with a mild grade of impairment frequently achieve scores similar to those of normally-developing children mostly in the areas of language, but this only suggests that they have age-appropriate skills in the language tasks assessed by the test. In fact not infrequently therapist and teacher refer that they have different performances than their peers in languages aspects such as grammatical skills or some aspects of knowledge. These facts suggest that the tools that clinicians have at disposal allow the assessment of deficits ranging from middle-moderate to middle-severe grades of impairment, but rarely do they allow the assessment of mild or profound grades of impairment. The aim of the present work was to develop two new tools for the assessment of these two different special cases of cochlear-implanted children, which are at opposite ends of the impairment spectrum. After a general introduction on hearing, deafness and cochlear implantation, Chapter 2 is directed at the evaluation of severe deficits. It has been shown that, in deaf children with additional disabilities, although speech perception and language may develop at a slower pace than in peers, cochlear implantation provides benefits on a larger range of neuropsychological functions, including social and relational skills. These benefits are frequently referred by parents, but rarely objectively measurable by tests. Chapter 2 presents a new evaluation tool aimed at assessing the global benefits offered by cochlear implantation in these special cases. The new tool has been designed as a closed-format questionnaire divided into five areas and is aimed at detecting the frequency of selected behaviours, which occur during everyday activities and that imply specific social, neuropsychological, and perceptual skills. The questionnaire has been administered to the parents of fifty deaf children with additional disabilities, before and at least six months after cochlear implantation. The data show significant improvements in all areas investigated. However, not all skills improve in the same way and only those related to language and communication correlate positively with hearing age, i.e. the time spent with implants. Chapter 2 further discusses improvements in skills for which parents' expectancy is higher, such as preferred communication mode, speech intelligibility, and ability to make a telephone call. The questionnaire has a format simple to use and has been proven sufficiently sensitive to detect changes in each area examined. Being based on observed behaviours in daily activities, it can be useful even in cases where other tests are too complex for these children. Chapter 3 is directed at the evaluation of light deficits. Data on implanted children have shown that their development is not uniform across language domains: some aspects of language seem to receive more benefit from cochlear implantation than others, and more particularly it seems that lexical skills achieve higher levels than grammatical skills. As to the reasons, there are three main theories: the delay of exposure to spoken language before implantation (critical and sensitive periods), the high complexity of grammar due to the close integration with pragmatics, and the fact that hearing with implants, despite offering good access to spoken language, is not equivalent to normal hearing. Nowadays the age of implantation is ever more precocious and children implanted at the age of five-six months will allow us to understand much better the grammatical deficit in these children. In fact we argue that these children will develop normal grammatical skills or that they will have very low grammatical deficits thanks to the exploitation of the period in which the brain is most sensitive to speech perception input, which is also known as sensitive period. However, currently there are no tools that allow assessing this type of light deficits. Chapter 3 presents the development of such a tool to fulfil this need. In addition to the testing tool, for this kind of assessment it is necessary to have at one's disposal normative data. Besides, the analysis of this data, gathered on normal subjects, will also allow us to obtain information about the existence of critical and sensitive periods for grammar in deaf children. The new assessment tool has been developed starting from the concept that the evaluation of low deficit levels is possible by asking subjects to perform grammaticality judgement tasks, in which sequences of preselected stimuli are presented by means of a computer program, and by measuring speed and accuracy of the subjects' responses. The stimuli consist in grammatical and ungrammatical sentences, which are either shown on a computer screen or read out loud to subjects. We completed the first experimentation step of the new tool. It was administered to two groups of subjects with different age and schooling and without deficits. The results show very different performances between the two groups and confirm our hypothesis that normative data matching age and schooling level are necessary and that the choice of stimuli used in the assessment is very important. In summary, the tools developed and the results collected in this thesis demonstrate that with specific and targeted assessment tools it is possible to evaluate much better the benefits received by cochlear implants in special cases, than with generic tools that are suitable mostly for moderate levels of impairment