Emotions are the driving force to human behavior, controlling how humans form preferences, make decisions, and create memories (Walter, 2020). There are two kinds of emotional responses affect (automatic) and conscious (cognitive) (Sharp et al., 2019). Many of the emotions that humans experience are in the category of affect and happen unconsciously and uncontrollably. They are formed from quick judgments based on context and past experiences (Posey, 2019). These affect, unconscious emotions may have resulted from evolution and the reptile brain. Hundreds of years ago, the reptile brain responded to the environment to protect itself from predators and had to make quick judgments on what was safe and what was dangerous. This left humans, centuries later, with the instinct of making unconscious emotional decisions to protect themselves (O'Mahony, 2020; Posey, 2019).

     People may assume that this information does not apply to them and that their decisions are logical and conscious. However, research has proven that most decisions are made unconsciously and emotionally (O'Mahony, 2020; Posey, 2019; Weinschenk, 2020). So much so that if an individual has damage to the brain's parts that controls emotion, that person will have trouble making simple decisions (Posey, 2019; Walter, 2020). 

     This information is invaluable to designers, specifically user experience (UX) designers. UX designers work to enhance users' experiences as they interact with interfaces (electronic or physical). They can be hired to help stakeholders increase website visitation or product purchasing. To meet these requirements, designers need to understand what drives their users to make decisions. Since emotions are one of the primary motivating factors to decision-making, designers must consider emotion as part of the design process. The idea of designing with the inclusion of emotions is commonly referred to as emotional design (Dahlström, 2019; Walter, 2020). 

     This literature review will discuss and synthesize the current scholarly publications on the topic of emotional design. It will review the effects of positive and negative emotions and the three levels of processing pertaining to emotional design. Additionally, it will review the current tools available for creating an emotional experience, as well as areas for future research. This research will inform user experience designers on the best practices for incorporating emotions into their future designs.

Literature Review

Emotional Design 
     Emotional design involves designing an optimal user experience with a strong consideration of the users' emotions (Dahlström, 2019; Walter, 2020) to create a lasting emotional bond between the user and the interface (Alonso-García et al., 2020). To correctly identify what emotions are appropriate to trigger at a given moment, one first needs to comprehend the characteristics and functions of positive and negative emotions. Both positive and negative emotions are involved with memory. When an experience triggers an emotion, that emotion aids in the formation of memories, and this memory can then be retrieved in the future to determine the repetition of that behavior (Walter, 2020). Therefore, it is crucial to ensure that users experience positive emotions to increase behavior repetition. 

     Research has proven that when individuals experience positive emotions, they are more successful at solving problems, comprehending information (Plass et al., 2020), and staying engaged (Karpinski, 2021), which aids in learning and a better user experience. For example, in his book, Walter (2020) stated that happy users can creatively solve problems and are more tolerant of errors. On the flip side, Posey (2019) has found that negative emotions can alter perception, decrease motivation, and increase the likelihood of error. For example, when a user is stressed, they may have trouble completing simple tasks and are more prone to and less tolerant of errors (Weinschenk, 2020). 

     As seen with Yerkes–Dobson law, stress can sometimes be used positively to increase the aroused individual's focus and performance level. According to this law, different arousal (another name for excitement, fear, and stress) levels can result in different behavioral outcomes. When people experience low levels of arousal, such as a low level of stress and fear, it increases their attention and focus, enabling them to complete a task more effectively. However, at a certain threshold, arousal can lead to attention paralysis and an increase in errors (Weinschenk, 2020). 

     Before beginning the design process, it is crucial to determine the user groups of the product. This will allow designers to choose the appropriate tools to elicit the desired emotions. Users' emotions can be influenced by cultural background and past experiences (Stevens, 2020; Sharp et al., 2019). Additionally, the typical emotional state of the users who are interacting with an interface must be considered (Sharp et al., 2019; Weinschenk, 2020). For example, someone coming on to Care First or another medical service page may be experiencing stress and interact with an interface considerably different from someone who is calmly shopping for clothing (Weinschenk, 2020). To gain an understanding of the user’s background and past experiences, designers can conduct research and field studies and apply that to their designs. 

     With the understanding of positive and negative emotions and the importance of determining and knowing one's users, one can begin designing an optimal emotional experience. Donald Norman, a strong advocate for emotional design, instructs designers to create this emotionally engaging experience by considering the three processing levels: visceral, behavioral, and reflective (Aslam & Brown, 2020; Alonso-García et al., 2020). All three levels include emotional responses and should be considered throughout the design process (Aslam & Brown, 2020; Pavliscak, 2018). 

Visceral Level 
     The visceral level is at the lowest level of processing, and according to many sources, this is where the unconscious and automatic emotional responses take place (Alonso-García et al., 2020; Pavliscak, 2018; Sharp et al., 2019). This processing level occurs when users are first interacting with an interface and are presented with some form of stimulus that elicits an emotional response such as trust, fear, or joy (Alonso-García et al., 2020; Dahlström, 2019). It is often associated with first impressions (Dahlström, 2019) that lead to attitude and mental model formation (Alonso-García et al., 2020). This makes the visceral level a crucial point for adverse emotion prevention. If the user's mental models do not align with the interface's conceptual model, this can lead to frustration during the behavioral level (Weinschenk, 2020).

     When designing for the Visceral level of processing, one needs to consider what design elements can elicit the hardwired positive emotions and avoid the negative ones. Many sources have found that an interface's look and feel can affect the emotional outcome (Alonso-García et al., 2020; Dahlström, 2019; Pavliscak, 2018; Walter, 2020). People naturally experience joy and pleasure from interacting with aesthetically pleasing and beautiful designs (Pavliscak, 2018). This beauty can surface by creating symmetry in designs and organizing the information in a way that is considered beautiful, such as using the golden ratio (Pavliscak, 2018).

     Research has also proven that users view interfaces that look confusing as untrustworthy, while simple and clear interfaces are deemed as trustworthy (Walter, 2020). A designer can avoid creating a confusing interface and build trust with its users by limiting unnecessary information and implementing optimal information architecture (for example: using information hierarchy and the gestalt principles). Designers can also build trust in their users by utilizing the babyface bias (Plass et al., 2020; Walter, 2020). This bias states that people are hardwired to see the proportions of a baby (large forehead, big eyes, small nose (Walter, 2020), and round face (Plass et al., 2020) as "innocent, trustworthy, cute, and lovable" (Walter, 2020, para. 8). Therefore, incorporating the proportions of a babyface into a design creates trust and love between users and the interface. 

     This information coincides with the findings of Plass et al. (2020), who conducted a study to determine the effects of shape and color on emotions. Plass et al. found that round shapes lead users to feel more positively than shapes with sharp edges due to the babyface bias. This study also found that warm colors were more likely to invoke positive emotions than neutral and cool colors (Plass et al., 2020). These findings can be applied to an interface by implementing warm-colored and rounded buttons rather than cool-colored and squared buttons.  

     According to Stevens (2020), the above findings of the positive effects of warm colors may not hold true for all colors in every context. Stevens explains how the usage of color to elicit emotion can be tricky to implement due to the different cultural meanings behind color and the mixed messages that color can invoke. For example, the cultural meaning behind yellow in Germany is envy which differs from the meaning of yellow in Egypt of happiness. Yellow can also elicit different kinds of emotions. For example, yellow can cause one to feel happy in specific contexts and to feel cautious and frustrated in other contexts (Stevens, 2020). Taking all of this into consideration can affect the mood and personality of a design and the emotions that will be triggered as a result.

     Additionally, many sources agree that visual artifacts such as pictures can elicit strong emotions (Sharp et al., 2019; Walter, 2020; Weinschenk, 2020). This emotional response stems from the desire for human connection and interaction (Walter, 2020; Weinschenk, 2020). Pictures are also effective emotional triggers due to the existence of mirror neurons. Humans naturally mirror the emotions that they see (Sharp et al., 2019; Weinschenk, 2020), so if the image on the interface has a woman smiling and having a great time, this can cause the user to smile back and feel a sense of happiness. This can be used as a tool to elicit any kind of emotions from the users.

Behavioral Level
     The behavioral level is the second level of processing and refers to how one feels while interacting with an interface (Alonso-García et al., 2020; Pavliscak, 2018). In design, it is often associated with a product's usability (Dahlström, 2019; Pavliscak, 2018). For example, if a product is inconstant and challenging to use, it can cause users' frustration. On the other hand, an easy-to-use and intuitive interface can elicit pleasure and joy. It has been found that the behavioral level of processing can be influenced by both the visceral and reflective levels (Pavliscak, 2018). For example, if a user is evoked with positive emotions on a visceral level, this can lead them to solve problems creatively and click buttons at the behavioral level. The reflective level can influence behavior by driving users to revisit and use an interface due to the meaning that they have assigned to the interaction.

     When designing for the behavioral level of processing, it is crucial to consider the design best practices for designing a usable, learnable, and enjoyable interface (Dahlström, 2019; Pavliscak, 2018). For example, ensuring consistency and implementing affordances can allow users to achieve their goals and feel pleasure (Sharp et al., 2019). Additionally, proper labeling, appropriate use of the gestalt principles, and information hierarchy can also allow users to find the information they seek and feel pleasure. The opposite is true for all of these scenarios. If users cannot achieve their desired goals, they can feel frustrated or stressed from the interaction (Sharp et al., 2019) and reflect (at the reflective level of processing) those feelings into the entire experience. 

     Providing users with empathetic feedback can also elevate their behavioral experiences. Designers can use feedback to inform their users of their successes or failures while helping their users feel understood (Sharp et al., 2019). For example, if a user has finished a transaction and receives a note "we are so happy that you purchased from us," this will tell them that their transaction went through while making them feel as if someone else is excited for them.   Understanding what users prefer doing can also lead to pleasure during behavior and limit negative emotions. A study has found that people are happier when they are busy (Weinschenk, 2020). Therefore, designing an interaction that allows users to click and swipe rather than stay on one page for a significant amount of time can elicit joy and prevent boredom. Research has also found that people naturally like positive surprises (Pavliscak, 2018; Weinschenk, 2020). So, implementing surprise coupons or unexpected feedback can also create an enjoyable experience for the users. 

Reflective Level 
     The reflective level is the highest of the three processing levels and involves some form of cognitive thought (Alonso-García et al., 2020; Sharp et al., 2019). At this point, users ascribe persisting meaning to their interactions (Alonso-García et al., 2020; Aslam & Brown, 2020) and form an emotional attachment to the interface and the corresponding brand or company. During reflection, users think about their interaction and how it fits in with their lives and values (Dahlström, 2019; Sharp et al., 2019). For example, Apple has given over the message of privacy that has allowed them to remain popular despite the high competition levels. They have done this by dropping subtle messages of privacy throughout their designs (Walter, 2020).

     When designing for the reflective level, designers must determine what message they want to give over to users and what creates a lasting impression. Research has proven that people remember events more positively after they occur and that the end is the most memorable (Walter, 2020; Weinschenk, 2020). These finding indicate that users need something positive to remember as well as a positive end to their experience. A designer can create this experience by implementing a peak moment at the end of an interaction. 

     It has been found that implementing peak moments in a user interaction can have a lasting effect on the overall experience and strongly contribute to the lasting impression (Walter, 2020). For instance, when a person is completing a complex task or the main task, this can be considered a peak moment. These peak moments are typically charged with some emotion such as anticipation, excitement, or stress. If the designers use this moment to give positive feedback, such as "you did it" with a smiley face, this can elevate this peak moment into something truly memorable. 

     This strategy was successfully implemented in MailChimp, by having users high five with a monkey hand after completing their task. Users were typically feeling happy or relieved at this point. The interaction of the high five elevated that moment to such an extent that people started to associate MailChimp with that hand. It became part of the brand personality and identity and led Mailchimp to produce and sell shirts with a printing of this monkey hand (Walter, 2020). Mailchimp successfully used a behavioral principle of surprise at the appropriate time to lead users to process this emotion at the behavioral and reflective levels.

     Determining the precise occurrence of these peak moments can be difficult, but it can be approximated using journey maps. Journey maps can allow designers to determine what users may do and feel at a given moment, enabling them to give over a specific message to evoke specific emotions (Walter, 2020).  Like a story, these maps can determine the different beginning, middle, and end points for their users. This information can be used to leverage a desired experience that takes their users on an emotional journey (Dahlström, 2019; Walter, 2020).

     The use of emotional design has been around for decades. One of the popularly known examples of a failed attempt of emotional design ranged back to the early 1990s with Clippy the personified personal assistant. Clippy was distracting for users and therefore was a failed attempt at eliciting positive emotions (Sharp et al., 2019). The research in this field has grown tremendously and has led to advancements in emotional design. Presently, a well-designed interface will have more subtle uses of emotional design that does not interfere with the task. With the further development in artificial intelligence (AI), there is room for a tremendous amount of growth in emotional design (Pavliscak, 2018)

Future Research  
     Tools to aid in emotional design have continued to develop over the years. Designers used to rely on customer journey maps, field studies, and other tools to aid them. In recent years automated facial coding and emotional AI were introduced to designers, giving them other outlets to determine users' feelings (Sharp et al., 2019). The focus on determining the benefits and drawbacks of the different emotional design tools is out of the scope of this literature review. However, it will need further analysis in the future in order to leverage the potential of emotional design.

     After reviewing the current literature on emotional design, it is clear why user experience designers would benefit from implementing these design principles into their work. As mentioned earlier, emotions are the driving force of human decision-making. These emotions are primarily unconscious, and once set off, can affect a user's behavior and thought processes. These emotional experiences have the potential to create loyal users and a pleasurable experience. Therefore, it is crucial to follow these appropriate guidelines for achieving that emotional connection.

     As compiled from this research, the consideration of visceral, behavioral, and reflective processing can help designers achieve that pleasurable experience. UX designers can utilize the visceral level to create an impactful first impression that leads users to interact with their site. They can create a memorable onboarding experience that emotes trust, joy, and calmness to their users. This can be done by creating an aesthetically pleasing interface and including a careful choice of images, colors, shapes, and organization.  

     UX designers can maintain their users' attention by connecting with them on a behavioral level by creating a seamless user experience with clear affordances and information architecture. If designed well, this level will allow users to complete a task successfully and to feel a sense of joy and pleasure. The behavioral level can be elevated by including behaviors and notions that users enjoy, such as surprises and staying busy.

     The behavior and visceral levels can be driven to the next level by considering the reflective level. The reflective level communicates the meaning and values that designers wish to convey to the users and is what the user remembers the most about the experience. Designers can do this by carefully timing out their peak moments and determining what emotions are appropriate to elicit at what time. It is at this point that the designers utilize the emotion mapping tools such as user journey maps to create a lasting impression and emotional bond with their users.

     In conclusion, user experience designers would befit from considering emotions in their everyday designs. Designers have a strong desire to help their users receive an optimal user experience and to achieve what they want. Users want an optimal user experience and an interaction that they love and that they feel like doing. Implementing emotional design would satisfy the needs of both designers and users. This research has proven that emotions are not simply the feeling in one's mind. They are the drivers to an individual's decision, to the users' decisions. By implementing the three levels of processing into their future work, UX designers can elevate their design skills and create a memorable and lasting user experience.

Alonso-García, M., Pardo-Vicente, M.-Á., Rodríguez-Parada, L., & Moreno Nieto, D.    (2020). Do Products Respond to User Desires? A Case Study. Errors and                           Successes in the Design Process, under the Umbrella of Emotional Design.                     Symmetry, 12(8), 1350.  APA 7th                   Edition (American Psychological Assoc.) 

Allison Posey. (2019). Engage the Brain : How to Design for Learning That Taps Into the   Power of Emotion. ASCD.  

Aslam, H., & Brown, J. A. (2020). Affordance Theory in Game Design. O'Reilly Online  Learning.                                      theoryin/9781681737539/chapter-09.html. 

Dahlström, A. (2019). Storytelling in Design. O'Reilly Online Learning.                                                       in-design/9781491959411/side-04.xhtml. 

Karpinski, E. (2021). Put Happiness to Work: 7 Strategies to Elevate Engagement for      Optimal Performance. O'Reilly Online Learning.                                                                                                         to/9781260466737/ch1.xhtml. 

O'Mahony, K. (2020). The Brain-Based Classroom. O'Reilly Online Learning.                                                        based classroom/9781000330663/xhtml/Ch03.xhtml. 

Pavliscak, P. (2018). Emotionally Intelligent Design. O'Reilly Online Learning.                                          intelligentdesign/9781491953136/ch02.html. 

Plass, J. L., Homer, B. D., MacNamara, A., Ober, T., Rose, M. C., Pawar, S., … Olsen, A. (2020). Emotional design for digital games for learning: The effect of expression, color, shape, and dimensionality on the affective quality of game characters. Learning and Instruction, 70, 101194.                                                        

Sharp, H., Preece, J., & Rogers, Y. (2019). Interaction Design, 5th Edition. O'Reilly Online Learning.

Stevens, R. (2020). Powered by Design. O'Reilly Online Learning. 

Walter, A. (2020). Designing for Emotion. O'Reilly Online Learning. 

Weinschenk, S. (2020). 100 Things every designer needs to know about people. Peachpit Press/New Riders.  
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