# Affective Stroking: Design Thermal Mid-Air Tactile for Assisting People in Stress Regulation
## 1 Introduction
### Scope of Our Research  
A substantial number of haptic technologies have been developed to simulate the sensation of stroking, yet the exploration of combining mid-air and thermal tactile technologies remains relatively limited. Also, few cases use the combination to simulate affective touch to assist stress regulation. A large number of blank areas have yet to be verified. We emphasize mid-air and thermal tactile technologies for stress regulation due to their experiential and material qualities, such as convenience to proceed, comfort, subtlety, ability to direct attention, gradual nature, and privacy. We believe that combining mid-air and thermal feedback can create a comfortable and pleasant stroking experience, further helping usersalleviate anxiety and support stress regulation. Compared to other affective touch gestures, such as hugging or patting, which require more complex hardware, stroking demands lower technical complexity. Additionally, stroking can maximize the potential of mid-air technology by simulating a gentle and soothing tactile experience, which is more effective for alleviating stress and anxiety. For the body part selection, we chose the forearm. The forearm is the most extensively studied body part, providing a solid foundation of previous research [38; 39; 40; 41; 42; 43; 44; 45; 50]. Moreover, it is one of the most commonly and easily touched body parts, offering significant potential for developing various corresponding devices. This paper explores affective touch technologies based on mid-air technology, combining thermal sensation for personal stress regulation. We defined research questions as follows:  
* How can designs utilize mid-air and thermal tactile technology to create a sensation of being caresed and evoke positive feelings in users?
* What are the effects and impacts of this technology on participants' stress regulation?
* What are other potential applications or scenarios that can adopt this technology?  
To address these questions, we developed a haptic stroking simulation device. Initially, we evaluated the device to determine the suitable intensity and velocity settings for delivering comforting and pleasant stroking sensations. Subsequently, we conducted a between-group experiment and semi-open interviews with 49 participants. They were randomly divided into either the Stroking Group (SC) or the Control Group (CC). We hypothesized that the computer-mediated stroking device for stress regulation could help to assist people in reducing stress, compared to those who did not use our designed device. After experiencing the stress induction phase, participants who interacted with our haptic device showed a significant reduction in anxiety based on the State-Trait Anxiety Inventory (STAI). The heart rate variability (HRV) feature of those participants also altered, indicating reduced stress and increased relaxation, although the difference was not statistically significant. Our contributions are as follows:  
1. We introduce a novel method that creates subtle stroking sensations by combining mid-air and thermal feedback technologies, thereby exploring new design possibilities offered by haptic sub-modalities;
2. We explore design insights of computer-mediated affective stroking, which contributes to the expansion of the design space for stress regulation technologies;
3. We summarize promising design solutions for practical application scenarios, which refine future research and design in mid-air and thermal tactile technologies.