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We live in a world of language and we communicate with each other using language (Fromkin et al., 2007). Deafness occurs when a person cannot understand speech through hearing, even when the sound is amplified. The degree of hearing loss is measured according to the sensitivity of deaf people’s ears to the sounds (Ganji, 2017) and then those people are asked to use hearing aids or do cochlear implantation surgery (Ebrahimi, 2006). Children have the opportunity to hear others’ speech during normal speech development while children with hearing impairment lose much of the auditory input, which may hinder speech development (Tseng et al., 2011 as cited in Serry and Blamey, 1999; Blamey et al., 2001; Peng et al., 2004; Bouchard et al., 2007). Different factors will affect speech development. One of these factors is DISABILITY, any disorder in hearing will affect speech and subsequently will cause problems in communication (Amiri et al., 2014). Some speech characteristics of children with hearing loss are different from each other and different from normally hearing children (Kord et al., 2012). GENDER is another factor affecting speech. While analyzing vowels produced by Azari speakers, Mirahadi et al. (2018) proved that men produce some vowels different from women.
Vowel space is a vowel quadrilateral which is used to shows the first and the second formants. Phoneticians put vowels in the vowel space according to their position in the oral cavity, which was first introduced by Essner (1947) and Joos (1948) (as cited in Harrington & Cassidy, 1999). The first formant will increase as we go down the vowel space, it shows highness of tongue while producing vowels in the oral cavity. The second formant shows anterior or posterior position of tongue in the process of production of vowels in the oral cavity and will increase as we go to the left side of the vowel space (Hayward, 2013: 227, 228 & 502).
The present study aims to compare the vowel space of hearing aided, cochlear implanted, and normally hearing children, with DISABILITY and GENDER as factors, in order to investigate the difference between the vowels produced by these children (Their average age was 10 years and 4 months and their participation in the study was optional, after getting permission from their parents.) and find out more effective hearing aid tools among two groups of children with DISABILITY (They did not have any mental or physical problems except hearing impairment and took part in language therapy classes for about 450 hours.), the group which makes vowels similar to normally hearing children will prove the effectivity of the hearing aid tools. So, the results will be useful for language therapists while helping children learn how to pronounce vowels.
Therefore, the participants, 5 girls and 5 boys in each group, were asked to repeat thirty-six CVC framed words. Each word consists of one of the stops [p, b, t, d, k, g] in the onset and offset of the pattern and one of the Persian vowels [æ, e, o, a, i, u] in the center. Then the words were recorded using a Shure microphone in PRAAT software. After that, the first and the second formants of each vowel were measured and by using SPSS software the data was analyzed.
The results showed that the effect of DISABILITY on the first formant of vowels [æ, a, i, u] and the second formant of vowels [a, e, o, u] was significantly different (p < 0.050). The results of a Post Hoc Bonferroni test showed that children with DISABILITY produced vowels [u, i, e, ᴂ] in a lower place in the vowel space comparing to normally hearings. Cochlear implanted children produced vowel [a] in a lower place and vowel [o] in a higher place in the vowel space comparing to normally hearings. Hearing aided children produced vowel [a] in a higher place in the vowel space comparing to normally hearings. All vowels in cochlear implanted children and vowels [ᴂ, a, e, i, u] in hearing aided children were produced in an anterior place in the vowel space comparing to normally hearings.
The results also proved that the effect of GENDER on the first formant of vowel [a] and the second formant of vowel [i] was significantly different (p < 0.050). The results of a Post Hoc Bonferroni test revealed that the mean of the first formant of vowel [a] in girls was more than boys and the mean of the second formant of vowel [i] in girls was less than boys.
It is also important to mention that hearing aided children had the smallest vowel space among three groups of participants while the vowel space of cochlear implanted children was not so different from the vowel space of normally hearings. So, language therapists have to try more to teach vowels to the children who use hearing aids comparing to the children who are cochlear implanted.

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Although the hearing skills of children with hearing loss are improved with the help of hearing aids, cochlear implants, and speech therapy, they have difficulties understanding and producing language because of their delayed hearing onset. Considering that these children go to school with their hearing peers, it is needed that their oral language performance be compared with the hearing students. Hence, the present study analyzed and compared the oral language skills of children with hearing loss having hearing aids and cochlea implants, with their hearing counterparts. For this purpose, 39 children aged 6-8 years were examined by the Told-p:3 test. The participants included 16 hearing children, 13 children with cochlear implants, and 10 children with hearing aids. The data were analyzed using Kruskal-Wallis and Mann-Whitney U tests. The results showed no significant difference in syntactic and semantic skills of children having hearing aids and cochlear implants. However, the findings indicated a significant difference between hearing children and children with hearing loss ones having hearing aids and cochlear implants in their semantic and syntactic skills. Therefore, it is needed that children with hearing loss go through verbal-auditory rehabilitation training until they reach the hearing level of hearing children. Neglecting this issue can have detrimental effects on their educational achievements and future job performance.

1.  Introduction

Today, in the Iranian context, children with any kind of physical-motor and hearing disabilities go to public schools to study with other students if they have normal IQs. Although the language skills of hearing-loss children are improved with the help of hearing aids, cochlear implants, and speech therapy, because the onset of hearing in these children is delayed and given that the education of hearing-loss children is done in public schools, it is necessary that the quality of oral language and, consequently, the quality of the written language of deaf children in comparison with their hearing peers be carefully examined. Therefore, in the present study, the quality of oral language in hearing-loss children with their hearing counterparts has been analyzed and compared.

2. Method
In this study, oral language of hearing and hearing loss children was compared from two aspects of listening and speaking. For this purpose, 39 children aged 6-8 years, including 16 hearing children, 13 children with cochlear implants, and 10 children with hearing aids were examined by using the told-p3 test. Deaf children had pre-lingual deafness and had received hearing aids or cochlear aids before the age of two, and have gradually been able to speak with auditory-verbal rehabilitation training. The Told-p3 test was used for data collection. The collected data were analyzed using descriptive statistics for all variables. For inferential statistics, the Kruskal-Wallis test was used to examine the difference between the means in all three groups of children, and then the Mann-Whitney U test was used to compare the groups.

3. Results
The gathered data were analyzed using SPSS. Descriptive and inferential statistics were used for data analysis. The results showed no significant difference in syntactic and semantic skills of children having hearing aids and cochlear implants (P.>0.05). However, the findings indicated a significant difference between hearing children and children with hearing loss ones having hearing aids and cochlear implants in their semantic and syntactic skills (P.<0.05). These children had a significantly worse performance than that of hearing children in receiving and understanding the meanings of words and sentences, providing verbal definitions of words and recognizing them, and understanding and applying the forms.

4. Conclusion
The findings of the study showed no significant difference in the quality of oral language between children with cochlear implants and hearing aids. However, there was a significant difference between hearing children and the two groups of hearing-loss children in the quality of oral language in terms of listening and speaking. Accordingly, because deaf children have poorer performance than that of hearing children, not paying enough attention to this issue can have detrimental effects on their educational achievements and future job performance.  Therefore, the policy of teaching hearing-loss children in public schools along with hearing peers needs more reflection by educational policymakers. It is suggested that hearing loss children be helped by different interventions and rehabilitation programs before they start their education with their hearing peers.