Effects of gravity on articulation of sustain fricatives

External loads such as gravity play a significant role in shaping movement goals in human physiology. Prior research suggests that body position can affect speech articulation, although findings have been inconsistent. This study investigates how gravity influences the articulation of sustained fricatives by examining tongue shape variability across body positions. Tongue shape during fricative production in both supine and upright positions was measured from 3-D/4-D ultrasound images. Audio was simultaneously captured using a microphone placed approximately 1 m in front of the participant, with a sampling rate of 48 kHz. This analysis, part of a larger study involving 24 participants aged 18–21, examined data from six native speakers of American English (three male, three female) with no history of speech, language, or hearing disorders. Initial results suggest that voiceless alveolar fricatives [s] and [z] exhibit minimal variability across positions, while post-alveolar fricatives [ʃ] and [ʒ] show greater tongue shape variation. No significant gender-based differences were observed. These findings may have implications for speech motor control theory, as well as speech-language assessment tools for individuals with disabilities who may struggle with upright positioning.