## 3 State-of-the-Art Technologies for Emotional Management
### Expressing Emotions  
Once the system recognises the emotion in a person, it should make a decision about which emotion and through which sensory channel it should reply. To achieve that, the system should offer the necessary tools to express that emotion. In the case of IVEs, the system tools to express emotions include avatars, with verbal and body language ability, as well as virtual content, such as 3D models and audio, as potential transmitters of emotions. Therefore, emotional responses could be expressed by one of the following elements:  
Figure 5: Several studies employed the OCC model to generate emotions for embodied characters; image source [57]. * Non-verbal language: [PERSON] [64] concluded that, in the case of face-to-face communication, the three parts of a message (words, tone of voice and body language) should be coherently supportive of one another. In fact, 7% of our acceptance and empathy for a message emitted face to face depends on our acceptance of the choice of words, 38% depends on the use of voice (tone, volume) and 55% depends on over-gesticulation or facial structure. Because of this, when expressing emotions, non-verbal language has an important impact. Virtual Reality environments allow both non-verbal communication, due to the use of avatars with full-body movements, and verbal communication in real time, although they usually lack a complete system for non-verbal signals [65]. In [66], the authors highlight the lack of interaction paradigms with facial expression and the almost nonexistence of significant control over environmental aspects of non-verbal communication, such as posture, pose and social status. Several research works have focused on defining how human beings express emotions with their body and face. Although studies similar to [PERSON] [67] state that one of the main aspects of non-verbal communication when communicating emotions is facial emotional expressions, body movements are also considered essential to accompany words [68]. To generate believable avatars, it is imperative that an animation motor is developed based on these studies. On the one hand, in the area of facial animation, there is diverse research. A lot of these studies are based on [43]. [PERSON] and [PERSON] developed FACS which stands for Facial Action Coding System. It is an exhaustive system based on human anatomy that captures all visually differentiable facial movements. FACS describes this facial activity by means of 44 unique actions called Action Units (AUs), which categorise all possible head movements and eye positions. On the other hand, the body animation in the field of Affective Computing has been less researched than that of facial expression [69], although some studies were found focused on body positions and the movement of the hands in non-verbal expressiveness [70; 71]. Nowadays, most of the work related to body animation is based on data collected by systems of motion capture (mocap). Mocap is a popular technique for representing human motion based on tracking markers corresponding to different regions or joints of the human body [72]. Nevertheless, this kind of studies can exclusively be used when an avatar has anthropomorphous appearance. In the case of other types of emotional agents with no human shape, the way to provide them with some tools for non-verbal communication could be to modify their shape [73], colour [74], or to apply some changes to the way they move. Following this last approach, there is research that analyses the effect that amplitude, acceleration and duration of movements have on different emotions [75]. Other studies analyse the variation of heart rate [76] and respiratory rate [42] to link each rhythm variation to its corresponding emotion. * Verbal Language: Dialog Systems and Digital Storytelling: [PERSON] and [PERSON] [77] confirmed that non-verbal channels are important not only for tansmiting more information and complementing the voice channel but also for regulating the conversational flow.