Lyapunov exponents for japanese vowels in normal adult and cleft palate speakers

Objective: The purpose of this study was to explore the possibility of using Lyapunov exponents (LE) to evaluate the voice and speech in cleft palate (CP) patients. Subjects and Methods: Fifty healthy adults (25 males and 25 females) and 17 adult patients (10 males and 7 females) with repaired CP, who had no hypernasality, were enrolled. Five Japanese vowels were recorded at 44.1 kHz. Nasalance scores were measured simultaneously. The first LE was computed for each 1-second interval, and the mean for the first LE from all intervals (mLE₁) was then calculated. The delay time and embedding dimension were estimated at 13, 40, 34, 27 and 22 points for the vowels /a/, /i/, /u/, /e/ and /o/, respectively, and at 8 points for all vowels. Results: The mLE ₁s for all vowels did not differ between normal males and females. The mLE₁s for /a/ were significantly higher both in males and females with CP than in normal individuals. The correlation coefficient between the mLE₁s and nasalance scores for all vowels was not significant for both normal and CP subjects. Conclusion: The LE seemed to be related to pathological disorders of the vocal cords in CP patients, but was independent of resonance parameters.