VOCAL-TRACT AREA FUNCTIONS FOR AN ADULT FEMALE SPEAKER BASED ON VOLUMETRIC IMAGING

Magnetic resonance imaging (MRI) was used to acquire vocal tract shape s of ten vowels /i, I, epsilon, ae, Lambda, a, (sic), o, (sic), u/and two liquid approximants /(sic), l/ for a 27-year-old adult female. The se images were complemented with additional images acquired with elect ron beam computed tomography (CT) of /i/and /a/. Each 3-D shape was co ndensed into a set of cross-sectional areas of oblique sections perpen dicular to the centerline of the vocal tract's long axis, resulting in an ''area function.'' Formant frequencies computed for each area func tion showed reasonable similarity to those determined from the natural (recorded) speech of the imaged subject, but differences suggest that some of the imaged vocal tract shapes were articulated differently du ring imaging than during recording of natural speech, and also that im aging procedures may have compromised some accuracy for a few shapes. The formant calculations also confirmed the significant effect that th e piriform sinus can have on lowering the formant frequencies. A compa rison is made between area functions derived using both MRI and CT met hods for the vowels /i/ and /a/. Additionally, the area functions repo rted in this study are compared with those from two previous studies a nd demonstrate general similarities in shape but also obvious differen ces that can be attributed to anatomical differences of the imaged sub jects and to differences in imaging techniques and image processing me thods. (C) 1998 Acoustical Society of America.