ABSTRACT
A long-standing challenge in speech research is obtaining accurate information about the movement and shaping of the vocal tract. Dynamic vocal tract imaging data, recorded in real-time and with no requirement for sustaining postures or repeating utterances, are crucial for investigations into cross-linguistic phonemic inventories, phonetics, and phonological theory. Such data also afford insights into the nature and execution of speech production goals, the relationship between speech articulation and acoustics, and the cognitive mechanisms of speech motor control and planning. Dynamic articulatory data are also important for advancing the knowledge and treatment of speech pathologies and for improving models used in speech technology applications such as machine speech recognition and synthesis. Several articulatory tracking and imaging techniques available today – such as electromagnetic articulography, which tracks positions of coils adhered to articulators; electropalatography, which uses an artificial palate with embedded electrodes to record linguopalatal contact; and ultrasound, which can image partial outlines of the tongue or larynx surface – offer adequate to high temporal resolutions, although they are limited in their spatial resolution and/or vocal tract coverage. New advances in real-time magnetic resonance imaging (rtMRI) of the vocal tract offer an attractive tool that provides dynamic information of adequate to good temporal resolution for imaging the entire midsagittal (or any other) plane of a speaker’s upper airway, capturing not only lingual, labial and jaw motion, but also articulation of the velum, pharynx (epiglottis) and laryngeal structures. The hard and soft palate and the rear pharyngeal wall of the vocal tract, which are nonaccessible or poorly accessible using other techniques, are available using rtMRI. Complementing rtMRI with other types of static MRI data, capturing the full three-dimensional vocal tract and tongue shape during short sustained productions of speech sounds, is also possible. This chapter presents an overview of advances in vocal tract imaging from 2000 to 2017, focusing on rtMRI.
