Introduction
According to Grosjean (2010), more than half of the world's population is bilingual (2). This highlights the need to study different aspects of bilingualism. Due to the contemporary period’s sweeping social and cultural changes, many researchers believe bilingualism is considered normal and exceptional monolingualism. It was believed that bilingualism and learning two or more languages, especially in the early years of a person's life, would confuse and impair a person's cognitive and linguistic abilities, and in many respects, would confuse the individual. However, recent research  has reinforced the notion that learning two languages has not only  a negative cognitive and non-cognitive effect but also improves individuals' brain functions and helps people outperform in cognitive and non-cognitive tasks than their peer monolinguals (1). Different theories about the advantage of being bilingual predict that bilinguals should show superior performance in different cognitive tasks due to increased executive control functions. Although there is no consensus on this, some studies have shown that even if there is a difference in essential cognitive functions between bilinguals and monolinguals, this is not necessarily always the positive effect of bilingualism (5). Recently, accumulating research shows that bilingualism affects cognitive processes. Bilingual advantages were reported in executive functions, theory of mind, metalinguistic knowledge, socio-pragmatic abilities, and some linguistic functions, including grammatical judgments (6). The present research examined the evidence for bilingual advantages in spatial perspective-taking and self-regulation. The main question of this research is whether bilingual and monolingual individuals differ in their ability to choose a spatial perspective and self-regulating.
Methods
Azeri Turkish-Persian bilinguals and Persian monolinguals attended this study. Participants were asked to self-report their language proficiency (listening comprehension and speaking skills) in Persian and Turkish on a scale of zero to ten using a self-assessment questionnaire. Participants’ self-reported measures of language proficiency (speaking, comprehension, and reading) revealed that they were proficient in Turkish and Persian. Of the 39 participants, 21 participants spoke Persian at home. Factors such as age and education were controlled as disruptive factors that could lead to individual differences. The participants performed a visual task used in Hegarty (2004) (24). Then, to measure the ability of spatial perspective-taking, a spatial perspective-taking task designed by Hegarty et al. was used. This task has twelve visual items, in each of which the participant must visualize himself in different spatial situations and determine the degree of angle of the objects in question relative to the imagined position for himself. A second task was used to measure the dependent variable of self-regulation. For this purpose, we used an unsolvable puzzle (17). The participants were required to visualize themselves in different spatial situations and recognize the angle of the objects in relation to the visualized position. Moreover, unsolvable puzzles were presented to both groups in order to measure their self-regulation. In the last task, the more time a participant spent to find the answer, the higher the self-regulation score he/she obtained. This means that participants who ponder more on the unsolvable puzzle task have a higher ability to self-regulate.
Results
As stated above, this study investigated the ability of spatial perspective-taking of bilingual and monolingual individuals. This research used the spatial perspective-taking task to assess the spatial perspective-taking ability of Turkish-Persian bilinguals and Farsi monolingual speakers. Mann-Whitney test and Kendall correlation coefficient test at the significance level of 5% were used to evaluate the significance of the relationship between the variables. The difference in self-regulation between the two bilingual and monolingual groups was significant. This study found that the monolingual participants had lower scores in self-regulation, and bilingual participants spent more time solving the puzzle and got a higher score. The relationship between spatial perspective-taking and bilingualism was not significant, though the differences observed in the mean and standard deviations in two groups of bi- and monolinguals are considerable. The results of the self-regulatory ability of monolingual and bilingual participants showed that most people who use both Turkish and Persian languages have higher scores in the self-regulatory task compared to their monolingual peers. In other words, monolingual people, on average, had less self-regulation ability, and the scatter of scores in this group was lower than bilingual people. Thus, the results of the present study are in line with the results of studies that found the effect of bilingualism on individuals' self-regulatory ability.
Conclusion
The results showed that there was an association between bilingualism and performance in self-regulation tasks. Although Kendall correlation coefficients test between possible pairs of the variables related to the ability of spatial perspective-taking and bilingualism were not statistically significant, the bilingual participants spent less time on the spatial perspective-taking task, indicating the participants' ability of spatial perspective taking was higher than average. The statistical results did not show a significant difference between the scores of spatial and self-regulatory selection tests. However, careful attention to the means and data scatter of the studied variables indicates that people with lower scores in self-regulation tests, on average, have more ability to select landscape. In addition, it was observed that there is a significant relationship between the three scores of "total duration of spatial selection test," "total duration of self-regulation test," and the dominant language of people at home. Also, an essential finding of this test was that Persian monolingual participants tended mainly to the right in orientations, while Turkish-Persian bilinguals tended mainly to the left in orientations. A closer look at the direction of the hints may provide useful information on the relationship between bilingualism and map-based spatial orientation. The statistical results did not show a significant difference between the scores of spatial and self-regulated landscape selection tests. However, careful attention to the means and data scatter of the studied variables indicates that people with lower scores in the self-regulatory test, on average, have more ability to select perspective. In addition, it was observed that there is a significant relationship between the three scores of "total duration of the spatial perspective-taking task," "total duration of self-regulation test," and the dominant language of people at home.
Ethical Considerations
Compliance with ethical guidelines
The researchers obtained informed consent from the participants, and all procedures followed were in accordance with the ethical standards.
Authors’ contributions
Mehdi Purmohammad: Conceived the presented idea and contributed to experimental design. Azadeh Derakhshan: Designed the experiment, collected the data, and reported the results. Farzaneh Safavimanesh: Conducted the data analysis and contributed to experimental design
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Acknowledgments
We would like to thank all participants who attended this study.
Conflict of interest
The authors declare no conflicts of interest.

Keywords: Bilingual, Monolingual, Spatial perspective taking, Self-regulation

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