Computer-based speech therapy using visual feedback with focus on children with profound hearing impairments

Abstract: This thesis presents work in the area of computer-based speech therapy using different types of visual feedback to replace the auditory feedback channel. The study includes diagnostic assessment methods prior to therapy, type of therapy design, and type of visual feedback for different users during different stages of therapy for increasing the efficiency. The thesis focuses on individual computer-based speech therapy (CBST) for profoundly hearing-impaired children as well as for computer-assisted pronunciation training (CAPT) for teaching and training the prosody of a second language. Children who are born with a profound hearing loss have no acoustic speech target to imi¬tate and compare their own production with. Therefore, they develop no spontaneous speech but have to learn speech through vision, tactile sensation and, if possible, residual hear¬ing. They have to rely on the limited visibility of phonetic features in learning oral speech and on orosensory-motor control in maintaining speech movements. These children constitute a heterogeneous group needing an individualized speech therapy. This is because their possibilities to communicate with speech depend not only on the amount of hearing, as measured by pure-tone audiometry, but also on the quality of the hearing sensa¬tion and the use the children through training are able to make of their functional hearing for speech. Adult second language learners, on the other hand, have difficulties in perceiving the phonetics and prosody of a second language through audition, not because of a hearing loss but because they are not able to hear new sound contrasts because of interference with their native language. The thesis presents an overview of reports made concerning speech communication and profound hearing impairment such as studies about residual hearing for speech processing, effects of speech input limitations on speech production, interaction between individual deviations and speech intelligibility, and speech assessment methods of phonetic realizations of phonological systems. Finally, through several clinical evaluation studies of three Swedish computer-based therapy systems, concerning functionality, efficiency, types of visual feedback, therapy design, and practical usability for different users, important recommendations are specified for future developments.