In normal speech, oral sounds resonate in the oral cavity, and nasal sounds such as m, and n resonate in the nasal cavities. The velopharyngeal sphincter closes for oral sounds and opens for nasal sounds. The studies presented in this thesis sought to advance the assessment, control and modification of oral-nasal balance in speech. While the research was carried out in normal speakers, the intention was to create knowledge that will ultimately improve the assessment and behavioural treatment of speakers with oral-nasal balance disorders due to cleft palate. The first study (de Boer and Bressmann, 2016 a) was a retrospective analysis of normal speakers simulating different disorders of oral-nasal balance (hypernasality, hyponasality and mixed nasality). The recordings were analyzed acoustically using Long Term Averaged Spectra. The simulations produced distinctive spectra enabling the creation of formulas that predicted the oral-nasal balance well above chance level. The second study (de Boer & Bressmann, 2017) explored the role of auditory feedback in the regulation of oral-nasal balance in speech. In an altered auditory feedback paradigm, speakers of Canadian English compensated more for increased nasality than decreased nasality. This suggested that the speakers were less critical of a lack of nasality (hyponasality) than excess nasality (hypernasality). The third study (de Boer, Marino, Berti, Fabron, & Bressmann, 2016) investigated how voice focus affects oral-nasal balance in normal Brazilian speaking individuals. Participants read stimuli with their normal voice, a backward focus and a forward focus. The mean nasalance scores of the stimuli in the backward focus and normal speaking conditions were significantly lower than in the forward focus condition. The results confirmed that speaking focus influences oral-nasal balance in normal speakers, which could be useful for the development of new approaches of behavioural therapy. The research presented expands our understanding of oral-nasal balance control and lays the groundwork for new ways of clinically assessing and managing oral-nasal balance disorders.
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- Atmospheric sciences;Climate change;Environmental science; Speech therapy;Acoustics