The vowel system of Italian subjects with Down Syndrome. A spectro-acoustic approach

In this study we will present the first acoustic analysis on Italian vowel system concerning adults with Down Syndrome. These subjects show scarce speech intelligibility and a remarkable alteration of phonological structure, as documented in the international literature. A large presence of phonetic errors has been already reported for Down people in many languages. Nevertheless, the phonetic aspects received little attention by researchers. In this regard, the acoustic vowel space of ten Italian young adults with Down Syndrome was investigated as compared to a control group of subjects with the same chronological age. Frequential values of the first two formants, and the Euclidian distance of each vowel to the Centroid were measured. Experimental findings showed, only for Down people, high rate of vowel errors and a reduced vowel space. The ellipses of vowels were always wide and strongly overlapped. The overlapping of formant distributions, particularly evident in connected speech, lowered the degree of intelligibility, determining a degraded speech production.