Acoustic Analysis Of Compensatory Articulation In Cleft Palate Speech

Cleft palate is one of the common congenital malformations. The ratio of cleft palate in newborns is about 1:1000. With the improvement of living standards, health care becomes one of the most important services in peoples’ lives. Therefore, the study of articulation in children with cleft palate (i.e. cleft palate speech) in order to find methods to improve the articulation level of children with cleft palate has important significance.Cleft palate speech is one type of pathologic speech which is caused by cleft palate. Glottal stop and pharyngeal fricative are the most common abnormal productions of cleft palate speech. In this study, we investigated the acoustic characteristics of these two abnormal productions and extracted their acoustic features which were used to objective detection.(1) Acoustic features in time domain and frequency domain of glottal stops which closures in the glottis substitute typical obstructions along the vocal tract in cleft speech were investigated in this study. It showed that there were two kinds of glottal stops and there was significant difference between them in time domain. The first four moments were calculated for the burst and the subsequent early portion of stop consonants. The results show that the first moments were lower for glottal stops than normal alveolar stops. That is, there was less acoustic energy in the high frequencies for glottal stops than alveolar stops, due to the larger cavity anterior to the closure at the glottis than at the alveolus. We also found that the spectral energy of glottal stops spread over a wider frequency range, indicated by the greater second moments. Positive skewness showed that the spectral distributions were asymmetric with the head towards low frequencies and the tail towards high frequencies.(2) Acoustic features of pharyngeal fricatives which produced as substitutes for fricative consonants by speakers with cleft palate were investigated in this study. We found that the consonant durations of pharyngeal fricatives were longer than the ones of fricatives which produced in the front of mouth. One-third octave analysis was used to represent the acoustic characteristics of pharyngeal fricatives as an auditory spectrum. The results showed that pharyngeal fricatives had higher amplitude below four thousand hertz and lower amplitude above four thousand hertz than normal fricatives. This finding might be due to the fact that constriction places for pharyngeal fricatives were posterior than those for normal fricatives produced in the front of the mouth.(3) A logistic regression model was adopted here as the binary classifier to determine whether a speech sample was a kind of abnormal production of cleft speech. Classification accuracys acceptable for clinics were obtained for glottal stops and pharyngeal fricatves, respectively, after k-fold cross-validations and optimal choices of a few acoustic features.