Description of mouth shapes used in traditional Japanese sign language by comparison to those of speech utterance

Mouth shapes used in traditional Japanese sign language were described systematically through comparison to those in uttered speech. A framework of mouth shape descriptions that had been proposed by the present authors included (1) projection of mouth shapes of Japanese vowels and semi-vowels to the lip articulation plane of the three-dimensional IPA vowel chart and (2) grouping of discriminating consonants in lip-reading on the IPA articulation matrix. It was transferred to a coordinate consisting of contractions of muscles involved in mouth movement. In traditional Japanese sign language, the mouth shape, when added as a part of facial expression, modifies meaning of the word conveyed by a hand gesture. Those mouth shapes were extracted from conversations among native signers and were symbolized by their respective degrees of closing, rounding, and pulling corners, and by categories borrowed from Japanese vowels and some consonants. Using the extended framework, those mouth shapes that were elected for visual discrimination ranged more widely than those elected to discriminate phonemes aurally. Video pictures were retrieved according to their symbols from an electronic dictionary of 250 basic sign words and 1500 exemplary sentences of their meanings, as edited by the Japanese sign language research group, NRCD.