Instrumental Analysis of Speech Production

Speech production involves precisely timed and controlled movements of various parts of the orofacial system. Those movements modulate the airstream entering the various supralaryngeal cavities from the larynx, and give rise to an acoustic waveform. Characterizing the articulatory events that take place to produce speech sounds is a challenging endeavor. Sometimes movements can be inferred from perceptual identification (both auditory and visual) by the clinician. Other techniques such as acoustic analysis can also help determine the articulatory gestures from which a given speech sequence originates. However, the extraordinary flexibility of the speech production system usually makes this method problematic. Different combinations of articulatory positions give rise to similar acoustic‐perceptual outputs. This phenomenon, referred to as “ motor equivalence ,” is a necessary characteristic of speech production as it allows speakers to produce intelligible speech despite various changes in speech conditions: increased speech rate, loudness, and competing demands induced by coarticulation, among others. People with speech disorders use this property of the motor system to compensate for various deficits and limitations. In‐depth investigation of the articulatory strategies they use to produce speech can reveal alternative strategies. Over the years, several instrumental techniques and tools have been designed to track the movements and shape of the orofacial articulators. In this chapter, we will focus on the supralaryngeal articulators, namely the jaw, tongue, soft palate, and lips. Instrumental analyses of the laryngeal system are addressed in Chapter 36 (this volume) Depending on the accessibility of the structure being studied (the lips are more easily accessible to the experimenter than the tongue, for instance), different tools will be used, each of which has different degrees of invasiveness. Furthermore, whether the experimenter's goal is to assess the speaker's specific speech production characteristics at the evaluation stage or to compare production strategies at different points in time during therapy will have a substantial impact on the kind of instrument that can be used. Finally, and maybe most importantly, the specific type of disorder, its severity and the target population will dictate the pool of instrumental techniques that can be used to investigate speech production mechanisms. For the sake of clarity, we have grouped the techniques in five categories, depending on the targeted process: (i) muscle contraction measurement, (ii) point tracking systems to measure supraglottal articulatory displacement, (iii) image tracking systems, (iv) tongue‐to‐palate contact tracking, and (v) airflow measurement (aerometry).