Articulator movement contributions to formant trajectories in diphthongs

Abstract

Our purpose was to learn about the relative contributions of lip aperture and protrusion as well as tongue height and advancement to the trajectories of F1 and F2 during diphthongs produced by 20 speakers. Audio and kinematic signals were recorded with an NDI Wave system. Audio segments were analyzed with PRAAT to extract the F1 and F2 histories during the diphthongs. These were time-aligned with the kinematic records in MATLAB. Because time-series data violate the assumptions of traditional correlation and regression analyses, novel methods were developed to represent the relative contributions of individual articulator movements to F1 and F2 changes. All movement and formant tracks during diphthong transitions were converted to z-scores and overlaid on a common time scale. Absolute difference scores between kinematic (predictor) variables and acoustic (dependent) variables were summed along each plot to reflect the strength of the contribution of each movement to the acoustic outcome. The lowest difference sums reflected the closest alignment between a movement and a formant track. Results revealed differences in the relative contributions of the tongue and lips for each diphthong, suggesting that formant patterns during diphthongs may be difficult to interpret in a straightforward way in terms of articulator movement.