Shiraz E-Med J. 2017 July; 18(7):e13094. Published online 2017 May 14. doi: 10.5812/semj.13094. Research Article Evaluation of Formant Frequencies in Persian Speaking Children with Different Degrees of Hearing Loss Ehsan Naderifar, 1 Ali Ghorbani, 2 Negin Moradi, 3,* Hossein Ansari, 4 Ozra Aghadoost, 5 Faezeh Asadollahpour, 5 and Martina Ozbic 6 1 Musculoskeletal Rehabilitation Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran 2 Department of Speech Therapy, Tehran University of Medical Sciences, Tehran, Iran 3 Assistant Professor, Musculoskeletal Rehabilitation Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran 4 Health Promotion Research Center, Zahedan University of Medical Sciences, Zahedan, IR Iran 5 PhD Student of Speech and Language Pathology, Tehran University of Medical Sciences, Tehran, Iran 6 Faculty of Education, University of Ljubljana, Slovenia * Corresponding author: Negin Moradi, Assistant Professor, Musculoskeletal Rehabilitation Research Center, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Tel: +98-9166312518, E-mail: neginmoradist@gmail.com Received 2017 January 16; Revised 2017 February 21; Accepted 2017 April 19. Abstract 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 pro- found). 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 presum- ably 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. Keywords: Acoustic Analysis, Formant Frequency, Hearing Loss, Vowel 1. Background A traditional voice assessment is based on perceptual analysis. However, objective (acoustic) measurements are an important aspect of a voice assessment. Acoustic anal- yses are recommended to provide objective data, more ac- curate diagnosis, and document the effectiveness of artic- ulation therapy (1, 2). The acoustic features of the voice are related to the function of the auditory system. The auditory system acts as an important sensory component so that speech output is received again as an input through acoustic feedback (3). Hearing is one of the most important factors that effects voice because it provides the main feedback for articula- tory control (4) and influences moment-to-moment and delayed control of speech (5, 6). A normal auditory feed- back system is important for controlling and monitoring aspects of speech, including voice, articulation, and flu- ency (7). Individuals with hearing loss (HL) due to defects in au- ditory input are unable to develop the appropriate mo- tor control needed for phonation mechanisms and speech production (4, 5). These impairments (such as imprecise vowel and consonant production) can effect the acoustic characteristics of voice and the intelligibility of speech (4, 8, 9). Vowels are a critical factor for intelligibility of speech (10-12) and are involved in both prosodic and segmental features of speech (13, 14). The corner vowels (“a,” “i,” and “u”) are more important than other vowels, because they represent a wide range of production situations of the tongue (15). Persian vowels are divided to 2 groups, based on the position of the tongue (front vs. back): front vowels include “i”, “e”, and “æ”, and back vowels include “u”, “o”, and “a”. Vowels, based on tongue height, are divided to 3 groups, high (“i” and “u”), low (“æ” and “a”), and mid-high (“e” and “o”) (16). According to Ansarin (2004), these 6 vow- els are symmetrically distributed in a vowel space plot so Copyright © 2017, Shiraz University of Medical Sciences. 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