Magnetic Resonance Imaging Research on Explications of the Book Hunminjeongeum Mid-Sound /·/(천, 天, Heaven) /ㅡ/(지, 地, Earth)/ㅣ/(인, 人, Human)

The mid-sound (vowels) chapter of Hunminjeongeum Haeryebon identifies three main letters— ‘•(heaven), ㅡ (earth), and ㅣ (human)’—as the foundation for all vowels, with their forms originating from pictographic principles. The document employs specific phonetic expressions such as “tongue contraction” and “deep sound,” suggesting that these letters were deliberately designed to reflect the configuration of the vocal tract during phonation. Building upon the first author’s previous CT imaging findings, we conducted real-time magnetic resonance (MR) imaging techniques to examine these articulatory principles of Hunminjeongeum. Our investigation included MR imaging examinations and acoustic analyses of 11 Jeju dialect speakers (ages 70–80 years old) who maintain the historical ‘•’ vowel sound. MR imaging analysis confirmed differences in tongue contraction degrees and sound depth across three vowels. Furthermore, the comparative analysis of acoustic data and MR images revealed how the first and second formant values differ among three vowels. We hope this research endeavor could be recognized for its value in demonstrating that Hangeul (or Hunminjeongeum) were designed with remarkable phonetic precision, capturing the essential configurations of the vocal tract—a finding that highlights the scientific sophistication underlying this 15th-century writing system.