Jianwu Dang, Kiyoshi Honda
Acoustic characteristics of the piriform fossa in
models and humans
Abstract:The piriform fossa forms the bottom of the pharynx and acts as a side branch of the vocal tract. Because of its obscure form and function, the role of the piriform fossa has been underestimated in the traditional models of speech production. This study examines acoustic characteristics of the piriform fossa on speech sounds by means of mechanical modeling, in-vivo experiments and numerical computations. Morphological data of the piriform fossa were obtained from volumetric MRI images for four subjects. Replica models of the vertical part of the vocal tract were developed based on the MRI data from one of the subjects. Acoustic measurements were performed on those models with and without inclusion of the fossa. The results showed that the piriform fossa does not only contribute a local zero to speech spectra, but also affects the lower vowel formants. In-vivo experiments were conducted on human subjects by injecting water into the piriform fossa. The antiresonances were identified as a pattern of increasing trough in speech spectra while decreasing air volume of the cavities. Acoustic simulation based on numerical models demonstrated that the effects of the piriform fossa extend down to the first vowel formants, because the fossa is located near the glottal end of the vocal tract. The antiresonances obtained from these experiments were confirmed to be consistent with those in natural speech within 5%.