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1. Introduction
The prelinguistic stage is between 1 month and 18 or 24 months of age [1]. This period is before the language emergence phase. Communication skills developing in the prelinguistic stage are nonverbal skills that form the main communication ways of children at this period. This phase involves a subtle but systematic developmental transition as children move from the prelinguistic to the linguistic stage. These skills serve as a foundation and predictor for later language development. Therefore, they are important subjects to study in this stage [2, 3]. 
The prelinguistic skills that develop before language acquisition can be classified as means of communication (e.g., eye contact, gestures, vocalization, first words, and facial expressions) [4-9], and communicative functions (e.g., behavior regulation, joint attention, and social interaction [10]. Furthermore, some prelinguistic skills have cognitive bases, like imitation, object permanence, and playing [11-13].
Prelinguistic skills are essential in children’s development because of their association with language acquisition [2, 3]. These skills are the basis of language development, as children with limited prelinguistic skills may face difficulties in language acquisition [14]. As indicated in the study conducted by Luke et al., lower pointing gestures at 12 and 14 months are associated with language development delays [15]. Besides, children’s communication abilities in this stage predict their later language development [16]. That is why some researchers name prelinguistic skills as language predictors [17, 18]. For instance, the predictive value of babbling on subsequent language acquisition has been mentioned in Fasolo, Majorano, and Dodorico’s study. Based on their findings, late talkers have limited phonetic complexity and a lower rate of babbling than typically-developing children [19]. 
There are some factors, such as family history and gender, that might affect the children’s communication skills development [20, 21]. Family history of speech-language disorders is one of the risk factors for these impairments in children up to five years old [22]. Sunderajan and Kanhere [23], Molini-Avejonas et al. [22], Saeed et al. [24], and Conti-Ramsden and Durkin [25] highlighted the higher prevalence of speech-language impairments in children with positive family history. Twin studies [26] and family aggregation studies [27], as well as genetic linkage analyses [28], provided strong evidence of running speech-language impairments in families. 
While girls and boys are similar at birth, there are differences in their verbal abilities under the age of 3 [21]. For instance, girls have a larger vocabulary than boys at 18 to 24 months [29]. Some researchers discuss the influence of social factors on cognitive and language domains [30-33]; however, others debate on the greater male variability hypothesis (i.e., greater variability among males in intelligence compared to females), which might lead to different language abilities in boys [34, 35]. Also, after the discovery of the first gene connected with speech and language disorders, the FOXP2 gene [36], a considerable number of studies focused on gender differences as genetic factors involved in speech and language developments [37-39]. For instance, in a review article, Wermke et al. concluded that the difference between hormones in boys and girls leads to faster language development in girls [40]. 
Few studies have been published about Persian children’s prelinguistic skills. Most of these studies only focus on the expressive language and first words [41-44]. For example, Mahmoudi Bakhtiyari et al. studied expressive lexicon size in Persian children aged 18 to 36 months [45]. Some studies have focused on only one prelinguistic skill [46, 47], and some had a limited number of participants [48, 49]. 
The relation between prelinguistic and linguistic stages increases the significance of studying the prelinguistic skills [17]. Despite the importance of these skills, there are limited studies focused on prelinguistic skills and comparing them in different age groups in Persian-speaking children. The present study aimed to investigate the prelinguistic skills in Persian-speaking children aged 6 to 24 months and compare these children within different age groups and genders. We also studied the effects of family history of speech-language impairments. 

2. Materials and Methods
 This cross-sectional study was conducted in Tehran City, Iran, in 2021. We included 277 Persian-speaking children (124 girls and 153 boys) aged between 6 and 24 months (Mean±SD: 15.81±5.9 months). The children were independently grouped according to their ages. In this study, 49 children aged 6-9 months, 53 children aged 10-12 months, 73 children aged 13-18 months, and 102 children aged 19-24 months. A convenient sampling method was used for the selection of the study participants from Tehran, Iran. The inclusion criteria were normal mental and physical development, having no history or symptoms of neurological problems, brain damage, seizures, or any other disorders, having literate mothers, and no divorced parents. The Persian version of the ages and stages questionnaire was used to check children’s developmental status. It is a reliable and valid tool for assessing the physical and mental development of Persian children [50]. Mothers of the children who withdrew from the study were excluded. After explaining the aim and method of the research, mothers of the children interested in participating were checked regarding the inclusion criteria. Those mothers whose children were eligible to participate in this study provided written informed consent. The researcher-made checklist was sent to the mothers by Email or social media apps like WhatsApp. All participants who received the checklist completed it. The research protocol was approved by the Ethics Committee of the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran (Code: IR.USWR.REC.1400.025). The characteristics of the children are demonstrated in Table 1.




In the present study, the mothers were asked to fill the communication skills checklist, which is a researcher-made checklist, and answer some questions about family history of speech-language disorders. This checklist evaluates the means of communication (i.e., eye contact, gestures, vocalization, first words, and facial expressions), communicative functions (i.e., behavior regulation, joint attention, and social interaction), and prelinguistic skills with cognitive bases (i.e., imitation and object permanence). The checklist contains 36 items (33 scored on a 3-point Likert-type scale, and three scored on a 5-point Likert-type scale), according to the psychometric properties of the researcher-made checklist, which was determined before the present study. It is a reliable and valid instrument. All items had the Content Validity Ratio (CVR) higher than 0.79 and the Content Validity Index (CVI) of higher than 0.62. Based on the validity of the age groups, the results of the communication skills checklist demonstrated significant differences between the four age groups. Moreover, based on the previous study, the checklist demonstrated a high association with the “childhood nonverbal communication scale” [51, 52]. The internal consistency determined by the Cronbach α was 0.952 for all the 3-point Likert scored items and was 0.857 for the 5-point Likert scored items. This result indicated a good correlation between these items. The test-retest reliability coefficient was also calculated regarding 50 mothers who filled the checklist for the second time about two weeks later. According to the intraclass correlation coefficient (ICC), the checklist demonstrated excellent reliability (ICC=0.933, P<0.001) [52]. 
After the data gathering, the statistical analysis was performed using the SPSS v. 25. Analysis of variance (ANOVA), Scheffé test [53], the Kruskal–Wallis, and the post-hoc test [54] were used to compare the children’s ability in the four above-mentioned age groups. The difference between the total scores of the two genders was also determined using the Mann-Whitney U test. 

3. Results 
In the present research, 277 children aged between 6 and 24 months were studied. The results of the statistical analysis are described in the following. According to Table 2, the 2-way ANOVA test demonstrated lower scores of the communication skills checklist in children with a positive family history of speech-language impairments. Furthermore, the results illustrated the increase in the scores as children grow up.




This increase is also demonstrated in the scores of gestures (Table 3) and first words (Table 4). Based on the results of the Scheffé test in Table 5, there were significant differences between the age groups.










The Kruskal-Wallis test showed a statistically significant difference in the score of each skill between the different age groups (i.e., eye contact χ2 (3)=15.941, P=0.001; gestures χ2 (3)=160.141, P=0.001; vocalization χ2 (3)=124.231, P=0.001; first words χ2 (3)=179.094, P=0.001; facial expressions χ2 (3)=33.528, P=0.001; behavior regulation χ2 (3)=102.062, P=0.001; joint attention χ2 (3)=77.307, P=0.001; social interaction χ2 (3)=95.188, P=0.001; imitation χ2 (3)=128.707, P=0.001; object permanence χ2 (3)=132.283, P=0.001; play χ2 (3)=136.551, P=0.001). According to the post-hoc test, gestures and first words are specifically different between the four age groups. In other words, the scores of these two skills are statistically different between 6 to 9 and 10 to 12, 6 to 9 and 13 to 18, 6 to 9 and 19 to 24, 10 to 12 and 13 to 18, 10 to 12 and 19 to 24, and 13 to 18 and 19 to 24 months. The Kruskal-Wallis and the post-hoc tests results are presented in Table 6. 











Based on the results of the Mann-Whitney U test in Table 7, the standardized test statistics for eye contact, gestures, vocalization, first words, facial expressions, behavior regulation, joint attention, social interaction, imitation, object permanence, and play were respectively -0.704, -2.621, -2.206, -3.624, -0.300, -1.468, -0.951, -2.154, -2.846, -1.162, and -3.953. P value was only lower than 0.05 in gesture, vocalization, first words, social interaction, imitation, and play skills. 



4. Discussion
The present study aimed to assess prelinguistic skills in Persian-speaking children aged 6 to 24 months and compare the skills between different age groups and the two genders. Also, we studied the effects of family history of speech-language disorders on children’s prelinguistic development. The prelinguistic skills assessed in this study were means of communication (i.e., eye contact, gestures, vocalization, first words, and facial expressions), communicative functions (i.e., behavior regulation, joint attention, and social interaction), and prelinguistic skills with cognitive bases (i.e., imitation and object permanence).
The analysis revealed the statistically significant differences between the scores of 6 to 9 months, 10 to 12 months, 13 to 18 months, and 19 to 24 months groups, indicating that these prelinguistic skills develop as children grow up. 
According to the results, there is a difference in the frequency of eye contact between different age groups. These results are consistent with those of Brooks and Meltzoff [4], Dawson et al. [55], and Berger and Cunningham [56]. Eye contact, an essential skill affecting information processing, should be developed in children to facilitate learning [57]. 
According to our findings, gestures develop as children grow up. This increase in ability in the perception and expression of gestures from 6 to 24 months can be attributed to mothers’ performance. Mothers in the early years of their children’s life usually use gesture-word combinations [58, 59]. Moreover, with the emergence of communicative functions in children, especially joint attention, the use of some direct gestures such as pointing increases since pointing is one of the most common forms of communication in joint attention [60, 61]. However, our findings of gestures are consistent with the studies conducted by Bates et al. [62], Crais et al. [63], Tomasello et al. [64], Masur et al. [58], and Iverson et al. [59]. Babaei et al. concluded that gestures remain stable in Iranian children from 12 to 18 months. This difference might be due to the small number of samples in that study [48]. 
There is a difference between the results of the age groups in vocalization. These findings are consistent with Davis and Macneilge’s paper. According to their findings, children use labial and alveolar consonants more than the others in their primary babblings. As children develop, the consonants become more varied, and when they reach 14 to 20 months of age, they use different consonants like nasal consonants [65]. 
Based on the results, children express more words as they grow up, which is consistent with studies conducted by Brooks and Kempe [66], Mahmoudi Bakhtiyari et al. [45], and Tardif et al. [67]. Children’s first words are important issues to be assessed in the prelinguistic stage. Surprisingly, children who were late to express first words were more at risk for future language problems than children who were not [68]. Vocabulary spurt, an acceleration in the rate of expressing new words, happens between 19 to 18 months of age [69, 70]. The age of this apparent growth is also consistent with our findings. 
The ability to express and perceive facial expressions and emotions are different between age groups. This finding is consistent with the studies conducted by Herba and Phillips [71], Cole [72], McClure [73], and Thompson [74]. 
Based on the results, there is a difference between the communicative functions scores in the age groups. Children’s ability in response to and initiation of joint attention, behavioral regulation, and social interaction was different between the age groups, which is consistent with the studies conducted by Mundy et al. [75], Carpenter et al. [76], and Papousek [77]. However, the results are not consistent with Babaei et al.’s study because they consider the development of joint attention stable from 12 to 15 months of age. The difference is assumed to be due to the various methodologies [49]. 
The ability to imitate, which is the base of the mind theory [78], is different among the age groups. This finding is consistent with the papers published by Jones [79], Wang et al. [80], and Oostenbroek et al. [81]. The difference between the age groups in object permanence ability, which is another skill with cognitive bases, is remarkable and is consistent with Gopnik et al.’s study [82]. 
According to O’Grady and Dusing, play skill develops in children as they age and become more complicated. For example, exploratory kind of play decreases, but functional, representational, and symbolic plays increase in children as they grow up [83]. The results of studies conducted by Nwokah et al. [84], Casby [85], and Bruce et al. [86] are consistent with the present study. 
In addition to the difference between the results of the age groups, children with a negative family history of speech-language disorders had higher communication skills checklist scores. This finding is consistent with other studies [25-28], such as the study conducted by Molini-Avejonas et al., which considered positive family history a risk factor for speech-language impairments in children [22]. 
Our findings revealed the statistically significant differences between the two genders in gesture, vocalization, first words, social interaction, imitation, and play. As Jacklin and Baker [30] and Eagly et al. [31] indicated in their papers, there are some differences in the acquisition of language and its basic skills between the girls and boys based on social factors. For instance, Bornstein et al. reported that Argentinian, French, and American mothers tend to have more exploratory plays with boys and more symbolic plays with girls. Also, they often vocalize while playing exploratory plays with boys and use words and sentences while playing with girls [32, 33]. Besides, girls tend to have fewer exploratory games in comparison to boys. These social factors, which have some effects on girls and boys, might be a reason for the different performance of the two genders. 

5. Conclusion
In conclusion, children develop their communicational skills in the prelinguistic stage as they grow up. In this regard, the scores of eye contact, gestures, vocalization, first words, facial expressions, behavior regulation, joint attention, social interaction, imitation, object permanence, and play are different between 6 to 9 months, 10 to 12 months, 13 to 18 months, and 19 to 24 months age groups. A positive family history of speech-language impairments also might be a risk factor for children’s prelinguistic developmental issues. Furthermore, some prelinguistic abilities have different developmental patterns between girls and boys. We also faced some limitations in this study. Due to the spread of COVID-19, we used the convenience sampling method. Furthermore, the socioeconomic status of the families was not considered. It is suggested to conduct studies on families with different socioeconomic classes.


Ethical Considerations
Compliance with ethical guidelines
The research protocol was approved by the Ethics Committee of the University of Social Welfare and Rehabilitation Sciences, Tehran (Code: IR.USWR.REC.1400.025).

Funding
This research did not receive grants from funding agencies in the public, commercial, or non-profit sectors.

Authors' contributions
All authors equally contributed to preparing this article.

Conflict of interest
The authors declared no conflicts of interest.

Acknowledgments
The authors wish to thank all participants in this study. The present paper was extracted from the Master’s thesis of the first author in Speech-Language Pathology at the University of Social Welfare and Rehabilitation Sciences, Tehran, Iran.

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