Individual Difference of Relative Tongue Size and its Acoustic Effects

Abstract

This study examines how the speaker’s tongue size contributes to generating dynamic characteristics of speaker individuality. The relative tongue size (RTS) has been proposed as an index for the tongue area within the oropharyngeal cavity on the midsagittal magnetic resonance imaging (MRI). Our earlier studies have shown that the smaller the RTS, the faster the tongue movement. In this study, acoustic consequences of individual RTS values were analyzed by comparing tongue movement velocity and formant transition rate. The materials used were cine-MRI data and acoustic signals during production of a sentence and two words produced by two female speakers with contrasting RTS values. The results indicate that the speaker with the small RTS value exhibited the faster changes of tongue positions and formant transitions than the speakers with the large RTS values. Since the tongue size is uncontrollable by a speaker’s intention, the RTS can be regarded as one of the causal factors of dynamic individual characteristics in the lower frequency region of speech signals.