Cognitive deafness The deterioration of phonological representations in adults with an acquired severe hearing loss and its implications for speech understanding

Sammanfattning: The aim of the present thesis was to examine possible cognitive consequences of acquired hearing loss and the possible impact of these cognitive consequences on the ability to process spoken language presented through visual speechreading or through a cochlear implant.The main findings of the present thesis can be summarised in the following conclusions: (a) The phonological processing capabilities of individuals who have acquired a severe hearing loss or deafness deteriorate progressively as a function of number of years with a complete or partial auditory deprivation. (b) The observed phonological deterioration is restricted to certain aspects of the phonological system. Specifically, the phonological representations of words in the mental lexicon are of less good quality, whereas the phonological system in verbal working memory is preserved. (c) The deterioration of the phonological representations has a negative effect on the individual's ability to process speech, either presented visually (i.e., speechreading) or through a cochlear implant, as it may impair word recognition processes which involve activation of and discrimination between the phonological representations in the lexicon. (d) Thus, the present research describes an acquired cognitive disability not previously documented in the literature, and contributes to the context of other populations with phonological disabilities by showing that a complete or partial deprivation of auditory speech stimulation in adulthood can give rise to a phonological disability. (e) From a clinical point of view, the results from the present thesis suggest that early cochlear implantation after the onset of an acquired severe hearing loss is an important objective in order to reach a high level of speech understanding with the implant.