Index of content:
Volume 115, Issue 2, February 2004
- SPEECH PRODUCTION 
115(2004); http://dx.doi.org/10.1121/1.1639325View Description Hide Description
A physiological articulatory model has been constructed using a fast computation method, which replicates midsagittal regions of the speechorgans to simulate articulatory movements during speech. This study aims to improve the accuracy of modeling by using the displacement-based finite-element method and to develop a new approach for controlling the model. A “semicontinuum” tongue tissuemodel was realized by a discrete truss structure with continuum viscoelastic cylinders. Contractile effects of the muscles were systemically examined based on model simulations. The results indicated that each muscle drives the tongue toward an equilibrium position (EP) corresponding to the magnitude of the activation forces. The EPs shifted monotonically as the activation force increased. The monotonic shift revealed a unique and invariant mapping, referred to as an EP map, between a spatial position of the articulators and the muscle forces. This study proposes a control method for the articulatory model based on the EP maps, in which co-contractions of agonist and antagonist muscles are taken into account. By utilizing the co-contraction, the tongue tip and tongue dorsum can be controlled to reach their targets independently. Model simulation showed that the co-contraction of agonist and antagonist muscles could increase the stability of a system in dynamic control.
115(2004); http://dx.doi.org/10.1121/1.1642624View Description Hide Description
Beginning at the age of about 14 months, eight children who lived in a rhotic dialect region of the United States were recorded approximately every 2 months interacting with their parents. All were recorded until at least the age of 26 months, and some until the age of 31 months. Acoustic analyses of speech samples indicated that these young children acquired [ɹ] production ability at different ages for [ɹ]’s in different syllable positions. The children, as a group, had started to produce postvocalic and syllabic [ɹ] in an adult-like manner by the end of the recording sessions, but were not yet showing evidence of having acquired prevocalic [ɹ]. Articulatory limitations of young children are posited as a cause for the difference in development of [ɹ] according to syllable position. Specifically, it is speculated that adult-like prevocalic [ɹ] production requires two lingual constrictions: one in the mouth, and the other in the pharynx, while postvocalic and syllabic [ɹ] requires only one oral constriction. Two lingual constrictions could be difficult for young children to produce.