# Affective Stroking: Design Thermal Mid-Air Tactile for Assisting People in Stress Regulation
## 2 Materials and Methods
### Computer-Mediated Stroking Design
#### 2.2.3 Mediated Stroking Design Decisions  
Shapiro-Wilk normality tests showed that most participants' ratings are normally distributed (\(p\) > 0.05). Ratings also met [PERSON]'s Test of sphericity (\(p\) > 0.05). Firstly, Intensity had statistically significant effects on the ratings of continuity and authenticity. It had no statistically significant effects on the ratings of comfort and pleasantness. The ratings for continuity were 4.87 \(\pm\) 0.29 for PWM_200 and 5.59 \(\pm\) 0.28 for PWM_255. The ratings for Authenticity were 4.28 \(\pm\) 0.37 for PWM_200 and 4.88 \(\pm\) 0.36 for PWM_255. Compared to PWM_200, PWM_255 provides greater power output. Therefore, with increased airflow, the perception becomes more pronounced, resulting in better scores across all evaluation metrics. Secondly, Duration had statistically significant effects on the ratings of continuity, comfort, and pleasantness. It had no statistically significant effect on the ratings of authenticity. Post hoc LSD comparisons showed that there was a significant difference between 1.5 s and 2.5 s on continuity (\(p\) = 0.03), comfort (\(p\) = 0.01), and pleasantness (\(p\) = 0.003). Since the air generated a gentle sensation, the 2.5 s interval provided a longer blowing duration, resulting in a more sustained and stable airflow. This made the perception more pronounced, leading to higher scores across all evaluation metrics. Thirdly, the two-way interaction of Intensity \(\times\) Duration had statistically significant effects on the ratings of continuity (F (2, 18) = 5.42, \(p\) = 0.01), authenticity (F (2, 18) = 8.07,  
Figure 3: Fans around the outer and upper sides of the arm, blowing air pressure on the forearm. \(p=0.001\)), and comfort (F (2, 18) = 5.23, \(p=0.01\)). However, it had no statistically significant effect on the ratings of pleasantness (F (2, 18) = 2.11, \(p=0.15\)). Figure 4 shows the results. The two-way interaction of Moving Direction x Intensity and the two-way interaction of Moving Direction \(\times\) Duration did not reveal any significant effects on any of the measured variables. The three-way interaction was not found significant on any dependent variable. From the study, we can see the intensity of the airflow affects the perception of the stroking force. In our experiment, users felt that the stroking was closer to a gentle human touch when the force was generated by the PWM_255 setting. Additionally, the duration of the interval influences the airflow output, altering the perceived stroking force. The longer the duration is, the stronger the perceived force is. In our study, the 2.5 s interval provided better results across all evaluation metrics. However, due to the varying speeds in real stroking, the 2.5 s interval setting was felt slower. On the other hand, the 1.5 s interval setting resembles the speed of a real human stroking more closely. We also found that the user's perception of stroking primarily depends on the stroking force and the speed. The higher airflow intensity closely resembles the feeling of actual stroking. Blowing duration also affects the real-stroking perception, but not as important as the intensity. In our study, each fan operated sequentially to create a continuous tactile sensation, with the airflow rhythm being consistently maintained across different stroking parameter sets. The participants could tell the difference in the stroking direction. However, they told us that the Direction of the stroking did not lead to any differences in perceived continuity, perceived authenticity, perceived comfort, and perceived pleasantness for them because the blowing rhythm was fixed. Considering the above findings, we finally chose PWM_255 as the intensity parameter, with a 1.5 s interval for a fast-stroking effect and a 2.5 s interval for a slow-stroking effect. Figure 4: The two-way interaction of Intensity \(\times\) Duration on four metrics: (**a**) perceived continuity; (**b**) perceived authenticity; (**c**) perceived comfort; and (**d**) perceived pleasantness.