Evaluation of Formant Frequencies in Persian Speaking Children with Different Degrees of Hearing Loss

Background: This study compared formant frequencies in vowel production among children with different degrees of hearing loss (HL) and normal hearing. Methods: This study was carried out on 40 children with different degrees of HL (moderate, moderate to severe, severe, and profound). Forty age (7 to 9 years old) and gender (22 males and 18 females) matched children with normal hearing were included. After collecting acoustic data during vowel production (/a/i/,/u/) for 3 seconds, the mean of the F1 and F2 were selected using the Praat software. The data were analyzed using analysis of variance (ANOVA) and Dunnett’s Post Hoc test. Results: Several differences in formant frequencies were confirmed with ANOVA tests. The results from Dunnett’s post hoc test showed that the F2 value of /a/ and /i/ in the control group were significantly different from all groups with HL (P < 0.05). However, the F1’s of the control group in all 3 vowels were significantly different only from the profound group. Conclusions: There was little distinction between vowels of HL children, and their vowel space had become centralized presumably due to limited auditory feedback, relative invisibility of the articulatory gestures needed for vowel production, and similar tongue position for all vowels. The second formant tended to be affected more than the first formant because less audibility and the difficulty of its learning through vision.