Vibratory phase difference of normal phonation: HSDI analyzed with laryngotopography
Laryngotopography described in Chapter 16 of Volume I is a high-speed digital imaging (HSDI) technique developed by the authors, to show spatial characteristics of vocal fold (VF) vibrations by pixel-wise discrete Fourier transform for brightness curve. Analysis of phonations at a conversational frequency was focused on phase differences (PD) in the anterior-posterior (longitudinal) direction, and in the left-right (lateral) direction. In longitudinal PD, posterior-to-anterior opening type was significantly frequent in young females (all subjects, 43%; young females, 94%; and p<0.001), while anterior-to-posterior opening type was significantly frequent in elderly males (all subjects, 39%; elderly males, 88%; and p<0.001). There were no age- or gender-related differences in lateral PD (all subjects, 65%; and p=0.880).