Acoustic properties of turkish alveolar and post-alveolar fricatives of children with cleft lip and palate

Cleft lip and palate is one of the common birth defects. It may result in anatomical and physiological problems, feeding and dental problems, and hearing and speech problems. Velopharyngeal incompetence is one of the speech characteristics that can be seen in the speech of people with cleft palate. As the velopharyngeal port doesn't work accurately, the air pressure coming from the lungs escapes into nasal cavity instead of coming into oral cavity and the speech becomes hypernasal. In this kind of a speech, the obstruent sounds (e.g. fricatives and plosives) are weakened. The aim of this study is to analyse the acoustic properties of Turkish fricatives of children with cleft lip and palate having hypernasality. For this purpose, duration, center of gravity (COG), skewness and kurtosis values of sibilants (/s, z, ʃ, Ʒ/) were measured. Each sibilant was located word initial position within a sentence. 4 children with cleft palate with hypernasality and 4 children without cleft palate were participated in the study (4 male, 4 female). All the participants were Turkish native speakers and their age range was 10-12. For the statistics, Open Source Statistics Software R was used, and in R, linear mixed model was applied. It has been seen that duration of target sounds is longer for the people with cleft palate having hypernasality. Moreover, for these participants COG is found lower than the participants without hypernasality. Although skewness doesn't show any discrepancy for both groups, kurtosis is lower for the people with cleft palate having hypernasality. It has been found that hypernasality has an effect on the duration, COG and kurtosis of target sibilant sounds. All results have shown that children with hypernasality need more time, and prefer back articulation in order to create the intra oral pressure; however, they can create enough turbulence required for fricatives. Key Words: Hypernasality, cleft lip and palate, fricatives, spectral moments, acoustics.