Experimental assessment of the tongue incompressibility hypothesis during speech production

The human tongue is an important organ for speech production. Its deformation and motion control the shape of the vocal tract significantly and thereby the acoustic properties of the speech signal produced. Thus, much effort in the speech research community has been directed towards its biomechanical modeling. A common assumption incorporated into many models of the human tongue is the tissue incompressibility hypothesis: the tongue is considered a muscular hydrostat and therefore its volume should remain constant regardless of its posture. To the best of our knowledge, experimental assessment of the constant volume hypothesis during actual speech production is limited. In this work, the aim is to experimentally assess the incompressibility hypothesis during actual speech production using a dataset of volumetric Magnetic Resonance (MR) images of 17 subjects sustaining contextualized continuants (27 continuants per subject). A seeded region growing based algorithm is used to segment the tongue and calculate its volume. Then, the intra-subject variability of the tongue volume along the different tongue postures is examined. Within the accuracy of our tongue volume measurements, our empirical results seem consistent with the incompressibility hypothesis.