Analysis of high-speed digital video images showed that no apparent constriction or tense appeared in larynx and glottis during the production of geminate consonants. Glottal width for geminate consonants is slightly, but not much, wider than their singleton counterparts. Rather, the degree depends largely on consonant types. However, analysis of photo-electric glottogram showed that an interruption of glottal opening movement and/or abrupt cessation of preceding vowel are suggested to be involved during the production of geminate consonants.
Bibliographic reference. Fujimoto, Masako / Maekawa, Kikuo / Funatsu, Seiya (2010): "Laryngeal characteristics during the production of geminate consonants", In INTERSPEECH-2010, 925-928.