An articulatory study of fricative consonants using magnetic resonance imaging

Magnetic resonance images of the vocal tract during sustained production of the fricatives /s, sh, f, θ, z, yog, v, edh/ by four subjects are analyzed. Measurements of vocal-tract lengths and area functions, and morphological analyses of the vocal tract and tongue shapes for these sounds are presented. Interspeaker differences in area functions are found to be greater in the pharyngeal cavity than in the buccal cavity with the nonstrident fricatives exhibiting greater differences than the strident ones. The anterior tongue body of the alveolar stridents exhibit concave cross-sectional shapes while that of the postalveolars show a relatively raised tongue body with flat or slightly convex cross-sectional shapes. The concave tongue shapes of the alveolars result in a more abrupt area function behind the constriction when compared to that of the postalveolars. Laminality or apicality of articulation is found to be speaker dependent. Moreover, a greater degree of anterior medial grooving and lateral lingua-palatal contact is found in apical alveolar fricatives than in laminal ones. The posterior tongue body of all fricatives shows concave cross-sectional shapes. Voiced fricatives are characterized by larger pharyngeal volumes than the unvoiced fricatives due to tongue-root advancement. Tongue-shape asymmetries are found to be subject and, in some cases, sound dependent.