A Systematic Review of Emoji: Current Research and Future Perspectives

Use Motivation

Simplicity, convenience and conduciveness to emotional expression are the main motivations attracting users to use emoji. Specifically, emoji can help users to express themselves, relax their mood (Kaye et al., 2016) and build their own identity (Ge and ACM, 2019). As contextualization cues (Al Rashdi, 2018), emoji are used in communication to promote interaction (Gibson et al., 2018), including establishing emotional tone, reducing discourse ambiguity, enhancing context appropriateness (Kaye et al., 2016) and intensifying or weakening speech acts (Sampietro, 2019). In addition, emoji are also used to greet (Aull, 2019), and to maintain and enhance social relations while strengthening communication within a platform (Monica Riordan, 2017b). However, some researchers point out that emoji may also be maliciously used for deception (Njenga, 2018).

Diversity of Emoji Use

In the process of using emoji, the differences between individual characteristics, platforms, cultural backgrounds, and contexts may lead to different understandings. Emoji are also used for some specific topics, such as in sexually suggestive contexts (Thomson et al., 2018). This paper systematically summarizes the differences of emoji in terms of individual diversity, cultural diversity, platform diversity, and their inefficiency in use.

Platform Diversity

Platform diversity is one of the important factors affecting emoji use. The presentation style of emoji on different operating system platforms and the architectural specifications of different network platforms will affect users' preferences for emoji.

Although emoji use Unicode, the presentation style of emoji in IOS, Android, Microsoft and other systems is different due to the influence of different developers (as shown in Table 4). Studies have found that emoji on the IOS platform are more aesthetically attractive, familiar, clear and meaningful than those on the Android platform (Rodrigues et al., 2017). This difference in platform display will lead to misunderstanding and divergence in terms of emoji's emotional and semantic interpretation during cross-platform use (Tigwell and Flatla, 2016). In addition, researchers have studied different network platforms such as Twitter, Facebook and Instagram, and found that users of different platforms have their unique preferences when using emoji. The most popular emoji in one platform may not be popular on other platforms. For example, users tend to use emoji more frequently and positively on Facebook than on Twitter (Tauch and Kanjo, 2016). At the same time, some researchers focus on more marginal community platforms like Gab. In the face of the same event, Gab users tend to publish positive emoji to express irony in text with negative connotations, while Twitter users tend to use emoji to express suspicion (Mahajan and Shaikh, 2019). However, some researchers believe that the use of emoji is generally consistent on all platforms, except for e-mail, which is not suitable for using emoji (Kaye et al., 2016).

Table 4

Emoji differences on major platforms.

	Face with tears of joy	Red heart	Pleading face	Fire	Smiling face with heart-eyes	Smiling face with smiling eyes	Smiling face with hearts	Thumbs up	Thinking face
IOS
Android
Windows

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Source https://emojipedia.org/.

The Emotional Functions of Emoji

Because they are non-verbal cues with rich emotional meanings, emoji are an important medium for interaction and emotional communication on the Internet.

Emoji can express or enhance emotions (Gülşen, 2016). Jaeger and Ares (2017) analyzed 33 facial emojis and found that most emoji can express one or more emotions. The rich emotional meaning of emoji makes them a key area for researchers who analyze their emotions and develop emoji emotional lexicons. By artificial annotating, Petra et al. (2015) divided emojis into positive, negative and neutral according to their emotional distribution, and found that most emojis were positive, but there were also some emojis which can express irony or satire (Vanin et al., 2013). Due to the subjectivity of human annotating, some researchers have proposed the automatic construction of emoji lexicons. Fernandez-Gavilanes et al. (2018) automatically constructed an emoji lexicon based on the official definitions in emojipedia.

Because of their rich emotional meanings, emoji are often used to express emotions in online communication. In general, users tend to use emoji in positive messages and to use them less in sad or angry messages (Cheng, 2017). Different emoji affect people's attention and responses in divergent ways (Hjartstrom et al., 2019). Although both facial and non-facial emoji can express emotions (Riordan, 2017a), facial emoji outperform non-facial emoji (Jaeger et al., 2019). Using non-facial emoji can bring about positive emotions, especially joy, but it can't change the valence of the message (Riordan, 2017b). Different combinations of emoji also have subtle differences in emotional expression, for example, López and Cap (2017) found that when combining frog emoji or hot beverage emoji with other emojis, there will be subtle but observable emotional changes.

Computer Science

Research in the field has focused on using emoji for emotional analysis of UGC data, the conversion of emoji to other expression modality, and using emoji for optimizing computer systems.

Communication

In the field of communication, research on emoji mainly focuses on two aspects: one is emoji's emotional and linguistic functions in CMC, the other is how different factors, such as individual characteristics, cultural background and system platform, influence users' preferences for emoji use.

Emoji make up for the lack of non-verbal cues in CMC, and play an auxiliary role in conveying emotion (Gülşen, 2016), expressing semantics (Walther and D'Addario, 2001), and promoting interpersonal communication (Gibson et al., 2018). For example, Jaeger and Ares (2017) analyzed the emotional attributes expressed by 33 facial emojis, and found that most emoji contained one or more emotional meanings. Based on their emotional distribution, Petra et al. (2015) classified emojis into positive, neutral and negative and found that most emojis express positive emotions. Similar studies have found that users tend to use more emoji more in positive messages than negative messages. Both facial and non-facial emoji exhibit a great deal of ability when it comes to expressing emotions (Herring and Dainas, 2018; Jaeger et al., 2019). At the same time, different combinations of emojis can enrich the meanings of emotional expression. López and Cap (2017) studied how emotions change when different combinations of emojis were used. More research in this area is referred to in section The Emotional Functions of Emoji of this paper.

Individual use of emoji is influenced by many factors. The existing research can be divided into three categories: individual characteristics, cultural background and system platform. First, the use of emoji is strongly influenced by demographic characteristics such as gender and age of users. Women use them more frequently and men use them more abundantly (Tossell et al., 2012; Prada et al., 2018). Women use emoji more in public communication, but less in private communication (Li et al., 2018). In terms of social cognition, emoji with stronger emotional meanings are considered more appropriate and lovely for women than for men, while emoji with weaker emotional meanings but friendlier meanings are considered more appropriate for men (Derks et al., 2008a). Secondly, the use of emoji is closely related to the user's cultural background. Users in different countries will use emoji with specific national or ethnic meanings (Gaspar et al., 2016). Finnish users introduce “sauna,” Hindus use “Happy Diwali” and Pakistanis use Namaz symbols for emoji design. Users in different countries tend to use emoji differently. Chinese people use emoji and emoticons more often than Spaniards (Lin and Chen, 2018). Emoji show a high degree of contextual sensitivity and different language types influence the use of emoji. For example, the use of emoji displays a strong correlation among English-speaking countries, while displaying lower correlation among other languages (such as Italian and Spanish) (Barbieri et al., 2016b). Finally, different system platforms also lead to differences in emoji usage. Although emoji has a Unicode in the operating system platform, users show emoji differently in IOS, Android and Microsoft operating systems due to the limitation of these software's developmental compatibility (Cramer et al., 2016). Different social networking platforms such as Twitter, Facebook, Gab and Instagram also have their own particular patterns of emoji usage. For example, users tend to use emoji more frequently and positively on Twitter than on Facebook (Hall and Pennington, 2013). Gab users tend to use positive emoji to express negative emotions, thus showing irony (Settanni and Marengo, 2015). More research is referred to in section Diversity of Emoji Use of this paper.

Marketing

Due to their visual and emotional attributes, emoji can be used in marketing activities. Emoji play an important role in attracting attention, stimulating social interactions and enhancing the experience of consumers, along with their willingness to purchase (Das et al., 2019). So it is hardly surprising that emoji are frequently used in consumer interactions (Lee et al., 2014; Negishi, 2014). Furthermore emoji are also used to depict consumer emotions (Li et al., 2014). Their dominance in emotional expression makes them an effective tool to measure user's emotions.

Textual paralanguages like emoticons and emoji, can influence the cognition and behavior of consumers in marketing activities (Luangrath et al., 2017; Manganari and Dimara, 2017; Urumutta Hewage et al., 2018), for example, the presence of emoji on food packaging can influence children's dietary choices (Siegel et al., 2015; Luangrath et al., 2017). It has been found that using emoji can enhance the explanatory power, attractiveness, creativity and innovation of marketing activity. With the introduction of emoji in online marketing, more young people are attracted (Yakin and Eru, 2015). Ge and Gretzel (2018) indicate that social media influencers (people who take on the dual roles of marketer and active user of social media) can initiate online interaction by presenting emoji individually or in combination, which can attract consumers to participate in interactions.

Emoji can also be a way of reflecting consumers' emotions, describing user's profiles (Moreno-Sandoval et al., 2018), and especially monitoring the emotions users feel toward products, brands, and services (Rathan et al., 2017, 2018; Phand et al., 2018; Moussa, 2019). It has been found that gender, age and frequency of usage do not affect consumers' ability to describe and distinguish stimuli with emoji (Jaeger et al., 2018b), and certain emojis can help consumers better differentiate product samples (Schouteten et al., 2019). In addition, emoji and emoticons are considered simple and intuitive ways to express food-related emotions (Vidal et al., 2016). Marketers use emoji questionnaires as a common tool to measure user's emotions (Jaeger et al., 2017b, 2019), especially children's food preferences and emotional responses (Gallo et al., 2017; Swaney-Stueve et al., 2018; Lima et al., 2019).

However, some researchers point out that although emoji show more discriminability and simplicity than emotional words in emotional measurement, their multiple meanings could pose a barrier to the survey. Therefore, emoji questionnaires can't directly replace the existing text-based forms of sentiment survey directly. They can, however, act as a complement to the current form (Jaeger et al., 2017a, 2018a).

Behavioral Science

In the field of behavioral science, research on emoji focuses on three aspects: motivation, preference and influencing factors. There has been abundant research focusing on the motivations behind emoji usage. This research has found that emoji are used for managing and maintaining interpersonal relationships (Chairunnisa and Benedictus, 2017; Riordan, 2017b; Albawardi, 2018), expressing oneself (Kaye et al., 2016), constructing personal identity (Ge and ACM, 2019), facilitating communication and enhancing interaction (Gibson et al., 2018) in interpersonal communication. As a contextual cue, emoji can help users establish an emotional tone, reduce the ambiguity of semantic expression and improve appropriateness relative to context (Kaye et al., 2016). There are two aspects of emoji usage preference. One is users' selection of emoji content and the other is the degree to which there is a match between emotions expressed by emoji and real sentiments. For example, users in different countries introduce elements which are representative of their countries into emoji (Sadiq et al., 2019); and users of one social networking platform prefer to use positive emoji in negative texts to express irony (Kaye et al., 2016).

Linguistics

In the field of linguistics, research focuses on the pragmatic functions of emoji and the possibility that they could become an independent language. Emoji have been identified as having semantic properties, and can be used both as an independent language and as a component of a paralanguage providing users with a means of communication and promoting speech acts and interaction (Jibril and Abdullah, 2013; Alshenqeeti, 2016; Na'aman et al., 2017). There are pros and cons regarding whether emoji can become an independent language. Some researchers believe that emoji possess visual rhetoric and text functions and have more subtle semantics and for this reason deem that emoji can independently express meaning (Jibril and Abdullah, 2013; López and Cap, 2017). An application was developed to verify the possibility of emoji-first communication (Khandekar et al., 2019). Other researchers think emoji can't be regarded as an independent language because their meaning largely depends on surrounding text, and only when they are combined with the text can complete semantics be expressed (Zhou et al., 2017).

Psychology

Studies in this field mainly focus on two aspects. One is the relationship between individual psychological characteristics and emoji usage, and the other is the introduction of emoji into the scale design and the implementation of new psychological measurement tools. Emoji usage was found to be closely related to some psychological traits such as the big five personality traits, self-monitoring, emotional stress, and others (Derks et al., 2008a; Hall and Pennington, 2013; Li et al., 2018). For example, research has shown that frequency of emoji use correlates with emotional stability, extroversion and agreeableness in the big five personality traits, but not with conscientiousness and openness (Li et al., 2018). At the same time, some studies have attempted to introduce emoji into psychometric scales and have achieved good results in actual measurements (Marengo et al., 2017; Phan et al., 2019).

Medicine

In the field of medicine and public health, studies on emoji mainly focus on correcting personal behavior and improving doctor-patient communication. Emoji can be used to guide people's behavior regarding health, and it has been shown that using emoji can reinforce correct behavior when it comes to hand hygiene monitoring (Gaube et al., 2018). Furthermore, using emoji can improve communication between doctors and patients and also enhance patients' abilities to manage their own health (Balas et al., 2012; Troiano and Nante, 2018). Some researchers suggest developing a set of emoji specifically to be used for patient care, which could help patients better understand and communicate the challenges they face in health management (Skiba, 2016). In addition, emoji can be used for the identification and prediction of mental illness due to their strength in emotional expression. Marengo et al. (2019) has introduced emoji into the process of depression assessment and found that accuracy of identifying depression was significantly improved.

Factors Influencing User Preferences in Emoji Use

At present, research focuses on the description of users' preference for emoji, but fails to go deeply into the underlying reasons. Emoji such as “heart” () and “tears of joy” () were found to be more popular, but whether their popularity is related to specific cultural traits has not been studied. Users' preferences for emoji are influenced by many factors such as contextual information, interpersonal relationships, familiarity with emoji and personal interpretations other than official definitions, which are all worthwhile factors to explore.

Sticker's Impact on Emoji

The emergence and widespread use of stickers has impacted the status of emoji, and some research has begun to improve the user experience of stickers (Shi et al., 2019). Whether stickers will replace emoji is an interesting topic for researchers. Under the impact of stickers, how to further enhance emoji's performance in emotion and semantic expression and improve user experience is also a direction worth exploring.