Title: Effect of F2 (second resonance of the vocal tract) compression on overall speech intelligibility in speakers with Down syndrome
Legend: Figure displaying the intelligibility scores of speakers with Down syndrome as a function of their formant frequencies F1-F4 (resonances of the vocal tract), for the low vowels /æ/ (as in ‘hat’ shown in blue) and /ɑ/ (as in ‘hot’ shown in red). F2 panel is emphasized to draw attention to the most obvious formant differences between the low-front /æ/ and low-back /ɑ/ vowels with intelligibility. Pronounced F2 compression, associated with reduced functional front/back movement of the tongue, is related to reduced speech intelligibility.
Citation: Vorperian, H. K., Kent, R. D., Lee, Y., & Buhr, K. A. (2023). Vowel production in children and adults with Down syndrome: Fundamental and formant frequencies of the corner vowels. Journal of Speech, Language, and Hearing Research, 66(4), 1208–1239. https://doi.org/10.1044/2022_JSLHR-22-00510
Purpose: Atypical vowel production contributes to reduced speech intelligibility in children and adults with Down syndrome (DS). This study compares the acoustic data of the corner vowels /i/, /u/, /æ/, and /ɑ/ from speakers with DS against typically developing/developed (TD) speakers.
Method: Measurements of the fundamental frequency (f o) and first four formant frequencies (F1-F4) were obtained from single word recordings containing the target vowels from 81 participants with DS (ages 3-54 years) and 293 TD speakers (ages 4-92 years), all native speakers of English. The data were used to construct developmental trajectories and to determine interspeaker and intraspeaker variability.
Results: Trajectories for DS differed from TD based on age and sex, but the groups were similar with the striking change in f o and F1-F4 frequencies around age 10 years. Findings confirm higher f o in DS, and vowel-specific differences between DS and TD in F1 and F2 frequencies, but not F3 and F4. The measure of F2 differences of front-versus-back vowels was more sensitive of compression than reduced vowel space area/centralization across age and sex. Low vowels had more pronounced F2 compression as related to reduced speech intelligibility. Intraspeaker variability was significantly greater for DS than TD for nearly all frequency values across age.
Discussion: Vowel production differences between DS and TD are age- and sex-specific, which helps explain contradictory results in previous studies. Increased intraspeaker variability across age in DS confirms the presence of a persisting motor speech disorder. Atypical vowel production in DS is common and related to dysmorphology, delayed development, and disordered motor control.
About the Lab: The Vocal Tract Development Laboratory (VTLab) uses a combination of imaging, acoustics, and vocal tract modeling to understand the lifespan changes of the vocal tract anatomy in typically and atypically developing individuals, and to examine the relation of anatomic changes to speech acoustics.
Investigator: Houri K. Vorperian, PhD