Humans communicate in various ways, and we speak our thoughts directly or by using indirect expressions according to the conversational situation and our age. In such an indirect expression method, figurative language is often used, and figurative languages include metaphors, similes, proverbs, and idioms.

Early studies on metaphors said that understanding metaphors develop from a su-perficial level of understanding literal meanings to grasping abstract metaphors [1] and that metaphors cannot be understood from a physical and psychological perspective until age 9 [2]. Winner, Rosenstiel, and Gardner [3] studied subjects who developed metaphor skills beyond age 14. Recently, however, there has been an increasing trend in studies showing that metaphoric ability develops from in-fancy and that metaphorical language is used from the early stage of language development [1,4–6]. In addition, the Har-vard School centered on Chukovsky [7] said that metaphorical ability is only a human's natural ability apart from language ability, while Garder & Winner [8] explained that human metaphor ability is separate from general language ability, general perceptual process, and general conceptualization process [9]. This was explained as a metaphorical characteristic of right hemisphere damage.

These researchers report that young children tend to interpret metaphors as letters, which is not related to language development but rather to processing factors unrelated to metaphors, lack of experience in understanding the world, and im-maturity of cognitive function [5].

This study aims to discover the development of metaphor reasoning comprehension of infants aged 4, 5, and 6 in the early stages of language development and to analyze the correlation between metaphor reasoning development and language development.

This study investigated metaphor and reasoning comprehension ability in preschool children. When comparing the ability of preschoolers to understand metaphorical reasoning according to gender and age, metaphor and reasoning understanding increased with age, but there was no difference between ages. In addition, boys showed higher scores than girls, but there was no statistical significance. In particular, factors such as higher language and contextualization ability were required to understand metaphorical language. According to prior studies, the development of metaphor understanding has reported that infants aged 2 to 3 have already begun to recognize or understand behavior-based metaphors [10], and such early metaphors are gradually used in language [11]. Metaphor identification and comprehension, on the other hand, were considered to develop continuously [12,13]and generally assumed to begin at about the age of five to six. Since metaphor comprehension depends on chronological age and mental age [14,15], it was speculated that children aged five to six begin to understand easier metaphors by con-structing separate categories based on simple perceptual grounds and processing them literally [13]. By age eight, children in early school can generally construct a combined cate-gory built on multiple perceptual grounds and interpret metaphors based on immediate physical similarities. School-age children aged 9 to 11 could understand more difficult metaphors by forming relational categories based on the perceptual and conceptual ground, and by the early adolescence of 11 to 12, they could understand more accurate and higher conceptual metaphors in the course of school age [16]. A recent study of metaphor identification and comprehension development in school-age children revealed that these abilities consecutively increased with age. They found that early ado-lescents (11-year-olds) demonstrated significantly higher metaphor comprehension scores than those of 7-year-olds and 9-year-olds, while younger age groups (7-year-olds vs. 9-year-olds) did not differ [13].

In the same way, in the current study, the development of metaphor reasoning comprehension in preschool children also showed an increase with age but no significant differences between 4-year-olds and 6-year-olds. Although the number of participants in the 4-year-old group was small compared to other age groups, our study showed no significant difference in metaphor comprehension scores between the 4-year-old and 5-year-old groups, so it is believed that understanding of metaphor inference already begins at age 4.

On the other hand, inconsistent results were reported for gender differences in metaphor understanding. Boys were considered superior to girls at 3 to 6 [17], while there was no significant difference between genders aged 7 to 10. In the current study, boys scored higher than girls at 4 to 6 in the preschool age, but there was no difference according to gender.

In addition, children tended to understand metaphors and reasoning better by using familiar objects, situations, materi-als, or words they already know with more experience in ev-eryday life.

In this study, the context of the picture was provided and pointed out among the three pictures, and children aged 4 to 6 showed the most errors in understanding the meaning literally rather than the implied meaning or metaphor of the sentence. In other words, children of this period responded positively to their experiences or much-learned metaphorical expressions. However, metaphorical languages such as proverbs and reasoning show a literal interpretation, which is inferred to be related to personal knowledge, experience, and higher cognitive skills. Several factors have been mentioned why preschoolers struggle to understand metaphorical language. It was pointed out that young children mainly have limited vocabulary and world knowledge [18] and text/non-text distortion [19], while dependence on contextual cues makes understanding metaphorical language challenging.

Regarding the factors that affect metaphor language comprehension in preschool children, vocabulary acquisition development had a significant positive correlation with metaphorical reasoning comprehension. The development of metaphor comprehension is constrained primarily by limitations on children's conceptual knowledge, linguistic skill, and information-processing ability [20]. Therefore, it is believed that the vocabulary development of preschool children in our study influenced the semantic development of metaphors.

Interpreting metaphors requires accepting two different labels for entities: literal labels and new figurative labels. children had problems identifying that “A is like B.” As shown in Figure 4, in “The water tastes as sweet as honey,” most children chose the honey picture. Although all children in this study had normal vocabulary development, young children tended to interpret metaphors literally. In order to perform this task, it is necessary to understand the semantic relationship between A and B based on the understanding of each word and to use it to infer the meaning of the entire sentence.

Children also had problems understanding nominal indi-cators, such as “X is a Y” or “Youngman is a bookworm.” Young-man is a bug, but Young-man still requires one to understand that he is a person. Our study showed that children aged 4 to 6 struggled with metaphor as a second label. In this study, the average correct response rate of items with “X is a Y” (9, 24, 42,77) was 18%.

In addition, most preschool children in this study showed difficulty understanding proverbs. For 78 items, items 39, 45, 51, 53, 54, and 62 are proverbs; their correct response rate had an average of 13%. In understanding metaphors, children of this period were found to have the most errors in literally interpreting idioms or figurative language. For example, children often interpreted idioms literally, such as “Cheol-soo has wide feet” and “I turned on the light in my eyes,” by pointing out pictures with wide feet or pictures with fire in a person's eyes.

A recent study also found that even in school-age children with typical language development, the younger they were, the more literal they answered [21]. Therefore, these results support the tendency of preschool children in this study to interpret metaphorical understanding simply as the word meaning.

Another study investigated the word inference ability of children with typical language development and SLI aged 5-8 [22]. They found a significant correlation between verbal, analytical reasoning capability and receptive & expressive vocabulary, sentence compression, and nonverbal IQ. Our findings are also consistent with previous studies that vocabulary acquisition seems to predict the development of metaphor language comprehension in preschool.

The limitation of this study was that our study measured the ability to understand metaphors in a relatively small number of children in a specific region. Specifically, 4-year-old children did not include a more significant number of children than other groups, as the number of questions was 78, making it difficult for children to concentrate on the test, with the test including a part of high levels of metaphorical reasoning items that 4-year-old children could not understand. Therefore, in future studies, it is necessary to understand the development of metaphorical reasoning in preschool children, including a wide range of regions and many children. In addition to vocabulary knowledge, it will also help understand the development of metaphor language comprehension in the preschool years by looking at correlations with other factors such as sentence comprehension, meta-linguistic awareness, cognitive ability, and information processing speed that affect the metaphor comprehension process in early young children.