Introduction
The prevalence of Hearing Loss (HL) is 4.7 in 1000 live birth in the capitals of Iran provinces. Of them, 2.2 in 1000 have moderate hearing loss (40-65 dB), and 1.5 in 1000 have severe hearing loss [1]. Although the newborn hearing screening can identify HL, and early intervention will provide immediate support, children still need to spend time receiving, adapting, and getting used to the new devices. So, the children spend a portion of critical language acquisition period with distorted or partial language input. Studies indicated that sensory neural HL affects children’s language skills [2, 3], their reading and writing skills during school age [4], and communication skills in their later lives [5]. Plenty of persuasive reasons highlights the necessity of research in language skills of children with HL, such as asymmetry of language profiles in children with mild to severe hearing loss [6, 7, 8, 9, 10], provision of further documents to find out the causality relationship between the severity of hearing loss and morphosyntactic structures [3, 11], and the influence of cognitive factors on language acquisition in children with hearing loss [12, 13, 14, 15, 16, 17, 18]. 
Study objectives
Based on all these arguments, this study was the first on Persian children with Moderately Severe Hearing Loss (MSHL) designed to achieve the following objectives: 
1) Provide a detailed investigation on 14 Persian inflectional morphemes and clause structures in children with Normal Hearing (NH) and children with MSHL; 
2) Find the possible differences between 6-year-old children with MSHL and younger children with NH on the number of morphemes, phrases, and clause structures; 
3) Provide the productivity index of morphemes and clauses; the productivity criteria for morphemes and clause structures were the rules of productivity introduced by Scarborough (1990) “two appearances of each structure of interest” within a 100-utterance language sample [19]. This approach was efficient because only the first two appearances of any structure should be counted, not the total frequency. Besides, if two-thirds of children in each group had a structure in their repertoire, that structure is reported as acquired for that specific group.
4) Investigate the Mean Length of Utterances (MLU) as a general index for morphosyntactic skills.
In this study, we selected children with MSHL because this group of children has access to speech in contrast with children with severe-profound hearing loss. Thus, the study of children with MSHL can show the vulnerability of morphosyntactic structures because of the degree of hearing loss or other possible factors if the features of hearing aids and the frequency of their usage, and the administration of auditory-verbal therapy have been controlled. So, this study investigated the vulnerability of morphosyntactic units in children with MSHL. 
Materials and Methods
Study participants 
The study participants were recruited by convenient sampling method from two specialized institutes of children with HL (Rasa & Payam No). Information sheets and consent forms were sent to the families through the centers. Fifteen families signed the consent forms (Table 1).


However, only 10 children with HL were evaluated since the other five children had profound HL. 
All children had sensorineural HL and used bilateral hearing aids since their HL had been detected. The age of diagnosis for 50% of children was at birth, and the other half was around 30 months. All children received hearing aids six months after diagnosis. They have received auditory-verbal therapy in their institutes every week for one to two years. Based on the audiometric classification of Bess and McConnell (1981), all children showed MSHL at the speech frequencies of 500, 1000, and 2000 Hz that includes a hearing range from 56 to 70 dB SPL [19]. All children used their hearing aids always except for bath and sleep, and they could successfully repeat all six sounds in the Ling test. All children with MSHL were monolingual and spoke Persian. According to fathers’ jobs and their mothers’ education (50% had a university degree and the other half had a high school diploma), children with MSHL were from moderate Socioeconomic Status (SES) backgrounds. 
The average number of digits was four in forward recall and three in the backward recall. In word recall, the average number of monosyllable words that they could remember was four; however, when the number of syllables increased, children could remember fewer words. Two out of 10 could not do the backward digit recall test. Eighty percent of mothers estimated their children’s intelligibility as “somewhat intelligible in conversation”, 20% considered their children “mostly intelligible in conversation”.
Five kindergartens in Semnan were selected randomly from north, south, west, east, and center. All children received an invitation flier and a consent form. A total of 109 signed consent forms were returned. However, language samples of 88 children with NH were analyzed, and the remaining were excluded due to the short length of language samples. Their mothers, the kindergartens’ board, and the health centers, according to their routine evaluation, confirmed the other 88 children’s health. Mothers provided all information regarding children’s health, language development, and HL situation. The Speech-Language Pathologists (SLPs) asked for information about the mother’s educational level and the parents’ jobs to have a rough estimation of socioeconomic status. 
Study procedure
The time duration to collect language samples was six months. Language samples were collected using 20-minute interaction between each child and a speech therapist. To get a natural language sample, the context of the interaction was free play. The speech therapists were allowed to ask questions to motivate children for more talk, but there was no pressure or force on children [19]. 
Transcription, segmentation, and structure allocation were based on a systematic procedure known as P-LARSP. This procedure is an adaptation of Language Assessment, Remedy, and Screening Procedure (LARSP) [20, 21] for Persian-speaking children [22].
Another speech therapist that had enough knowledge about Persian grammar transcribed the whole interaction. The first three minutes of each language sample were taken out to eliminate a potential warm-up effect; then, a hundred analyzable utterances were selected according to P-LARSP [22, 23]. 
For reliability purposes, another speech therapist blinded to the study transcribed, segmented, and extracted all inflectional morphemes from 10 samples (10%). The reliability between two speech therapists was calculated through a point-by-point procedure. Discrepancies in segmenting, identifying, labeling, and allocating 14 inflectional morphemes were discussed, and over 98% of the agreement was obtained on all transcripts. 
Participants and methods
We chose free play as our context to elicit language samples, so the SLPs used age-appropriate toys (for example, dolls, dollhouses, furniture, animals, and cars) in interactions. All groups of children had access to similar toy sets on the floor. Different types and sizes of cars, dolls, and farm animals were available to provide obligatory context. The child began the play and could pick any toy set and shift among them. If a child did not want to play with any toy set, the toy set was still where the child left them in case the child wanted to get back to them or combine the toys. All the sessions were audio-recorded using a Stereo IC Recorder (ICD-PX440 model made by SONY, China) for transcription and later checks.
Results
Demographic information
In children with NH, over 45% of mothers had a university degree, and the others had a high school diploma. All parents had NH, monolingual in Persian, and at the time of this study had annual income noticeably more than the approved range for Iranian general workers. Children’s age and gender are presented in Table 1. 
A detailed description on 14 Persian inflectional morphemes 
While most of the inflectional morphemes showed an increasing number with age in children with NH, plural marker, object markers, past participle inflection, indefinite marker, and ezafe marker had fluctuating trends (Table 2). 


Differences between children with MSHL and NH
The number of 14 inflectional morphemes, the total number of them, MLU, and the percentage of 1-word utterances in children with MSHL were close to figures obtained from language samples of children with NH aged 24-36 months (Table 2). For half of the 14 inflectional morphemes, the differences between children with MSHL and children with NH were statistically significant.
Using the Bonferroni test, the significant differences were obtained for verb/complement+personal pronoun,/mi/as a tense marker, MLU, total number of affixes, and percentage of 1-word utterances between children with MSHL and children with NH aged between 49 and 60 months (Table 3).


Productivity of morphemes and clause structures
Regardless of hearing status, definite and indefinite markers and comparative and superlative inflections did not reach the productivity criterion. Children with MSHL did not show imperative prefix, plural, object markers, and Ezafe marker in their repertoire (Table 4). 


Some of the absent morphemes might be a consequence of clause and phrase structures that children used. Children with MSHL used significantly fewer numbers of clause structures from stage V compared with the oldest group of children with NH (P=0.002) (Table 6), and types of their clause structure repertoire were similar to those of children with NH aged between 24 and 36 months (Table 5).




We also provided the figures for phrase structures in different stages, revealing that children with MSHL used significantly fewer numbers of phrases from stages II & III compared with the oldest group of children with NH (Pphrase stage II=0.005 and Pphrase stage III=0.002). 
Discussion and Conclusion
The present study indicated that some grammatical morphemes known as definite and indefinite markers and comparative and superlative inflections are not so common in the context of free play, according to findings from children with NH. Similar data were obtained for children with MSHL, although children with MSHL did not produce enough samples of the object, plural, and Ezafe markers, as well as the imperative prefixes. In the matter of numbers, children with MSHL used significantly lower numbers of the 14 inflectional morphemes, the tense marker/mi/, and verb/complement+personal pronoun compared with the oldest group of children with NH. Thus, regarding the number of inflectional morphemes, children with MSHL who were 5-6 years old were comparable to those with NH below four years old. However, the types of their inflectional morphemes repertoire were restricted and not similar to any inflectional morphemes repertoire of any age group of children with NH. Such findings highlight the delay that children with MSHL show in their use of inflectional morphemes. 
We observed that children with MSHL had lower MLU than children with NH. Such findings provide further evidence that the presence of MSHL places children at risk for delayed grammatical development. Although we did not investigate the factors other than MSHL that made such effects, a possible explanation for such findings might be the quality and quantity of intervention and age of diagnosis. At this point, it is impossible to draw firm conclusions about the protective nature of early intervention because the details of the intervention that each child received were not clear. As a longitudinal project may provide a proper response, we think this is worthy of further analysis. 
The significant differences between children with MSHL and children with NH on the different grammatical structures reveal persistent risk in this aspect of children’s language. Our findings support the findings of Norbury et al. [24]. They found that their study participants demonstrated verb morphology problems. Since our participants were older than their participants, our results indicate that some language difficulties did not resolve by age. Koehlinger et al. in 2013 [2] reported similar findings. It is worthy of mention that both of these English studies found that their participants had higher rates of difficulties with verb morphology than the usual rate that might be expected in the general population. However, we found that children with MSHL had problems with both noun and inflectional verb morphemes; even noun inflectional morphemes were the place of more issues than verb ones. Such differences could be a result of language differences. 
The three inflectional morphemes that children with HL used significantly less than those of younger children with NH were both verb and noun bound morphemes: verb/complement+personal pronoun and prefix/mi/as a present tense marker. These morphemes were in the initial and final positions of the words, so it is not possible to explain such findings with the lower energy that they might carry. The noticeable number of complement+personal pronouns in children with HL is an assertive finding that shows children with HL can use such inflections but is not as common as younger children with NH. Probably cognitive factor has some impression in this case since when the word syllable increases, children with MSHL could remember fewer words. Therefore, children with MSHL probably choose simpler forms of sentences to overcome this insufficiency in their working memory.
The delay in producing inflectional morphemes is in line with findings reported by English studies [10, 25, 26,  27]. These English studies report the effects of late diagnosis on children’s morphology skills. However, in the present study, two-thirds of children who produced those morphemes belonged to the early and late-diagnosed children. Another interpretation goes back to the length of utterances that children with MSHL used compared to younger children with NH. Over 40% of utterances that children with MSHL used were 1-word. This finding left speech therapists with only 60% of utterances that could be categorized in stages II to V. Even in clause structures, children with MSHL used significantly fewer numbers of clause structures in stage V. This another factor reduces the number of possible inflectional morphemes. The fewer phrase structures in stages II and III could be considered another point that affected the number of inflectional morphemes. 
Conclusion
The present study results could support the claim that disruption of the auditory input, especially in the early ages of life, can delay the development of language skills, specially morphosyntactic features, even in mild to severe degrees of HL [10, 24]. A comprehensive look into clause structures and inflectional morphemes left us with a possible theory that despite all efforts to detect children as early as possible and provide enriched interventional programs for them, some children with MSHL have simpler language structures than their peers with similar degrees of HL and younger children with NH. The results showed some persistent delays in morphology that may limit children from conveying specific concepts. Future studies should determine what factors may decrease the effectiveness of early detection and intervention programs since the degree of HL is not the only explanation about children’s grammatical outcomes. Given the present findings, the language abilities of children with MSHL should be monitored throughout early childhood. Grammatical aspects such as MLU, complex utterances, and inflectional morphemes would be appropriate measures for monitoring because these morphosyntactic structures appear to be sensitive to differences across groups. 
Study limitations
The current research was limited in some areas, such as the number of participants with HL, the number of language samples, and communication partners. Future studies may overcome such problems with a larger sample of children with HL, at least two language samples in different settings, and various communication partners. Besides, according to P-LARSP, utterances with grammatical issues would not receive further morphosyntactic analyses. Future studies may analyze error patterns in this group of children.

Ethical Considerations
Compliance with ethical guidelines
This study received approval codes from the Human Research Ethics Committee of Semnan University of Medical Sciences (Code: IR.SEMUMS.REC.1397.015).

Funding
This research was sponsored by the Student Research Committee of Semnan University of Medical Sciences (Grant No.: 1243 & 1383) and the Vice Chancellor for Research and Technology of Semnan University of Medical Sciences (Grant No.: 1476).

Authors' contributions
Conceptualization: Masoomeh Salmani and Ms Sepideh Seyed; Methodology: Masoomeh Salmani, Ms Sepideh Seyed, Sara Moradi, Zohreh Shirkavand, Sahar Sadati, and Maryam Sadat Tabatabayi; Supervision, project management: Masoomeh Salmani.

Conflict of interest
The authors declared no conflict of interest.

Acknowledgments
We would like to express our gratitude to the children and their families for contributing to this study. The authors are grateful to the Student Research Committee of Semnan University of Medical Sciences and Semnan University of Medical Sciences for the financial support. 



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