Morphological characteristics of male and female hypopharynx: A magnetic resonance imaging-based study

Studies with three-dimensional (3D) vocal tract visualization using magnetic resonance imaging (MRI) have suggested that hypopharyngeal cavities, i.e., laryngeal cavity and bilateral piriform fossa, may be the acoustic loci to express speaker characteristics in male speech sounds. Previous studies mainly investigated the hypopharynx in males but few for females. This study explored the hypopharynx morphological characteristics for the subjects in both genders by MRI. 3D numerical vocal tracts at vowels were reconstructed from the MRI datasets of three male and four female Chinese subjects. Geometrical measurements were conducted for the hypopharyngeal cavities. Morphological observations and statistical analyses revealed both commonalities and differences between the male and female subjects. The laryngeal cavity shapes in females were found similar to males resembling a Helmholtz resonator rather than a simple straight closed tube, and the bilateral piriform fossa cavities showed an asymmetry: the right is longer and wider than the left in both genders. As for the cavity size across vowels, for both the male and female subjects the laryngeal cavity and piriform fossa in /i/ were observed larger than those in /a/. To summarize gender characteristics, the female subjects were characterized by the smaller laryngeal cavity and piriform fossa compared with males.