The geometry of the articulatory region that produces a speech sound

It is known that some speech sounds are produced by more than a single vocal tract shape. Here, we study to what extent individual articulators (e.g. the tongue tip) are constrained by a given acoustic frame. We use parametric and nonparametric methods for articulatory inversion and quantify the error incurred by inversion methods, and the dimensionality and multimodality of the inverse region in articulatory space that corresponds to a speech sound.