# Affective Stroking: Design Thermal Mid-Air Tactile for Assisting People in Stress Regulation
## 1 Introduction
### Studies About Affective Touch
#### 1.2.2 Using Mid-Air and Thermal Technology to Influence Affections  
Existing technologies have limits for displaying haptic renderings, such as affective touch. The tactile sensations produced by vibration devices are relatively simplistic, often requiring visual assistance to understand the specific haptic gestures [48; 49]. Additionally, both vibration and mechanical devices generate noticeable noise [43], which affects the ability of mediated touch to provide a similar experience to human-to-human touch and thus could result in less authentic and skewed emotional expressions. Emerging trends in contactless haptic interfaces are gaining attraction, utilizing mid-air technologies, such as air-jet [50; 51] and acoustic radiation pressure [52; 53; 54; 55], to generate tactile stimulation without physical contact with the user. [PERSON] et al. emphasized a significant impact of the air jet's intensity and movement speed on assessments of valence, arousal, and dominance [50]. [PERSON] et al. suggested that spatial, directional, haptic characteristics, such as frequency, intensity, and duration of the haptic stimulation, were important factors in generating haptic sensations by employing mid-air tactile stimulation [52]. [PERSON] et al. found that users could directly experience the applications without the need to wear any devices, enhancing the speed and hygiene of the experience [53]. What is more, mid-air tactile is a new promising technology used for stress regulation. [PERSON] et al. assessed how users perceive haptic stimuli created by air vortex rings applied to the cheek and examined their impact on physiological responses. The findings indicate that specific stimuli may help alleviate stress [51]. In the field of VR, researchers have explored the effect of combining mid-air technology with thermal haptics to create a better immersive experience [55].  
Researchers have also found a fundamental link between temperature and intimacy [56], social connections [57], social closeness [58], trust [59], and a warm personality [60]. Furthermore, psychotherapy research shows that warm hands in clients are linked to emotional security [61]. Participants thought these thermal sensations were comfortable and felt like human touch. In the HCI community, thermal touch technologies created thermal sensations of heat or cold. Many studies have shown that temperature affects both the valence and arousal of emotions [62; 63; 64]. Warm stimuli are perceived as more pleasant/positive compared to cold stimuli, and both emotional valence and arousal are influenced by modifying the rate or degree of temperature change [62]. Using thermal tactile for stress regulation has become more and more popular. Some works have focused on using heat to guide participants to pay attention to themselves [65] and engage in physical meditation [66] or relaxation [67]. [PERSON] et al. designed a personalized thermal tactile module for affect regulation following stress induction in participants [68]. The results showed that thermal tactile feedback effectively helped regulate stress and anxiety, playing a crucial role in the process. Individuals use the perceptual attributes of thermal patterns, along with emotional interpretations and metaphors, to attribute familiar meanings to thermal patterns. However, presenting temperature strokes is technically challenging. [PERSON] introduced a haptic device designed to generate a stroking sensation on the forearm by simultaneously applying pressure and thermal feedback. The compact and soft device employs micro blowers and inflatable pouches to create a pressure sensation while utilizing water to provide thermal feedback. According to a user study, it effectively simulated a thermal stroking sensation, and it was observed that cooler temperatures enhanced the perceived pleasantness of the stroking [69].