Description of the Features and Vibratory Behaviors of the Nyquist Plot Analyzed From Laryngeal High-Speed Videoendoscopy Images

Facilitative playback-based subjective measures offer a more reliable evaluation of the vocal fold vibration than those derived from direct inspection of video playback. One of the measures is a Nyquist plot, which presents the analyzed cycle-to-cycle vibratory information in a graphical form. While the potential is evident, the information of the features of the Nyquist plot, which the evaluation is based on, is still incomplete. The current identified features and their vibratory behaviors may be inadequate to guarantee accurate interpretation of the findings. The present study aims to address this issue by examining the features of the Nyquist plot and their vibratory behaviors. A total of 56 young normophonic speakers, that is, 20 males and 36 females were recruited as the participants. Each of them underwent laryngeal high-speed videoendoscopy to record the images of the vocal fold vibration, which were then analyzed to generate the Nyquist plots. The features were identified by inspecting the properties of the plot points forming the Nyquist plots. For each identified feature, its vibratory behaviors were examined. The results revealed four features: rim contour depicting the longitudinal phase difference; left edge shape signifying the glottal configuration, phase closure, and closed phase duration; rim width and rim pattern visualizing the regularity of glottal areas and the regularity of the intracycle variations, respectively. The findings present a more complete reference of the features and their vibratory behaviors that is pertinent for the Nyquist plot interpretation.