A Modeling Study of the Effects of Vocal Tract Movement Duration and Magnitude on the F2 Trajectory in CV Words

Abstract

Purpose: This study used a computational vocal tract model to investigate the relationship of diphthong duration and vocal tract movement magnitude to measures of the F2 trajectory in CV words. Method: Three words (bough, boy, and buy) were simulated on the basis of an adult female vocal tract model, in which the model parameters were estimated from audio recordings of a female talker. Model parameters were then modified to generate 35 simulations of each word corresponding to 7 different durations and 5 movement magnitude settings. In addition, these simulations were repeated with vocal tract lengths representative of an adult male and an approximately 6-year-old child.Results: On the basis of univariate analysis, measures of frequency predicted changes in magnitude, and temporal measures predicted changes in speaking rate consistent with the hypothesis. The combined effects of duration and magnitude showed that F2 was more sensitive to changes in magnitude at shorter word durations compared with longer word durations. This finding held across words and vocal tract length. Conclusions: Results suggest that there is an interaction between duration and magnitude that affects the slope of the F2 trajectory. The next step is to relate kinematics to F2 trajectory output using real speakers.T he trajectory of the second formant (F2) has been studied as an index of gesture overlap in studies of speaking rate and contrastive stress as well as studies of disordered speech production (cf. Liss & Weismer, 1994;Tjaden & Weismer, 1998;Weismer & Berry, 2003;Weismer, Tjaden, & Kent, 1995). F2 trajectories have shown a reasonable correlation with presumed articulatory movement during transitions; however, determining specifically how rate and movement magnitude individually contribute to F2 trajectory measures has been inconclusive (Liss & Weismer, 1994;Tjaden, 1999;Tjaden & Weismer, 1998;Weismer & Berry, 2003).Coarticulation is thought to be reflected in measures of the F2 transition and thus can be a useful measure for studying speech production in populations with speech disorders. Weismer, Kent, Hodge, and Martin (1988) devised a definition to index the beginning and end of F2 transitions by marking F2 transition onsets (points in time at which a 20-ms segment occurs in conjunction with a 20-Hz minimal change) and transition offsets (points in time at which a 20-ms segment does not co-occur with a change of 20 Hz or more), allowing investigators to obtain a measure of slope. Steeper F2 slope and F2 onset values that are close to the steady-state target vowel frequency are considered indicators of articulatory overlap. For example, in vowel F2 trajectories that increase in frequency following a consonant release, higher F2 onset values and steeper F2 slope values are believed to suggest more overlap between neighboring consonant-vowel gestures.Several studies have investigated the effect of speaking rate changes on F2 onset and F2 slope produced by typical adult speakers; for example, Tjaden and Weismer (1998) and Weismer a...

Neuromechanical Modelling of Articulatory Movements from Surface Electromyography and Speech Formants

“…It is well known that the opening of the ONPT in its mid-front section is directly influencing the position of the first formant, and this situation is dominant over the front-back positions of the tongue in most sounds. 25,51,52 Therefore, it will be assumed that for front vowels most of the neuromotor masseter force will produce vertical acceleration observed as a correlate on the first and second formant kinematics. The problem to be faced now is that the vertical force produced by the masseter is not accessible, and has to be estimated indirectly, having (5) into account.…”