Functions of the muscles of the tongue during speech

Abstract

To investigate the functions of tongue muscles during speech, three methods were combined: conventional MRI, to identify the musculature; tagging snapshot MRI, to visualize the displacement of tissues and measure contractions of muscles; and electromyography (EMG), to observe muscle activities. Five Tokyo-dialect speakers produced sustained phonations of five Japanese vowels. (Sessions of five English speakers are also planned to observe English vowels and consonants.) Muscle contractions of four regions of genioglossus (GG1-4, anterior to posterior), styloglossus (SG), vertical (V), superior and inferior longitudinal (SL, IL) were measured. The functional units of GG seemed to be overlapped with each other: GG3-4 to make the highest point of the tongue higher, working against V; GG2-4 to move the most posterior point anteriorly; and GG1-3 to move the highest point anteriorly, working against SG. SL contributed to groove formation. IL contributed to ‘‘landslide’’ formation in /o/ by keeping the lower half of the tongue forward against the posterior pull on the upper half by SG. EMG potentials from GG were higher in the supine than in the upright position, suggesting that there may be a system to generate different neural command patterns in relation to the direction of gravity. [Work supported by NIH DC-00865 to Haskins Laboratories, by St. John’s University, and by a Grant-in-Aid for Scientific Research (No. 01440071) from the Japanese Ministry of Education, Science, and Culture to the Department of Speech Physiology, Faculty of Medicine, University of Tokyo.]