Abstract
Individuals with Down syndrome（DS）frequently show poor intelligibility of speech. Ishida（1999）reported that their word intelligibility is more reduced than expected by that of monosyllables. Therefore, we assessed tongue movements during speech production through vocal acoustic analysis and auditory impressions in individuals with DS. Voices pronounced by 7 individuals with DS and 10 normal adults were acoustically compared between using a simple vowel（/i/, /o/, /a/） or compound vowels（/io/, /oi/, /ao/, /oa/）in Japanese words. As a result, the transitions of the second formant（F2）between /i/ and /o/ for compound vowels in DS were significantly decreased compared to those in normal adults. This result suggests limited articulation in individuals with DS, especially horizontal movement of the tongue, when they utter continuous vowels. This may be related to the poor intelligibility of their words.
