# Decoding Humor-Induced Amusement via Facial Expression Analysis: Toward Emotion-Aware Applications
## 2 Material and Methods
### Videos  
#### 2.3.1 Stimuli Selection  
For this experiment, we established three distinct categories for the videos: neutral, funny, and very funny. We made this decision based on the recognition that humor is a complex and subjective construct, and may prove challenging to quantify on a continuous scale. By discretizing the videos into these three categories, we aimed to more effectively capture the qualitative aspects of humor, and facilitate the identification of patterns and relationships between the features and the level of amusement elicited. All of the videos utilized in this experiment were selected based on two pilot studies which are elaborated upon below. They ranged in duration from 8 to 12 s, with an overall average length of 10 s. In instances where it was necessary, black frames and any accompanying musical background were removed from the videos to ensure consistency and accuracy in the analysis.  
Humorous Stimuli. Humorous videos (available here) were pretested in an online pilot study in 2017 including 205 participants (141 women, age = 34.77 \(\pm\) 14.22; range) and grouped into funny and very funny categories based on ratings. Participants viewed 94 humorous videos and rated each of them using sliders in terms of arousal (from \"very relaxed/calm\" to \"very excited\"), pleasantness (from \"very unpleasant\" to \"very pleasant\") and funniness (from \"not funny\" to \"very funny/hilarious\"). We computed the mean and variance of arousal, pleasantness, and funniness ratings by video across participants. These ratings were then used as features into an unsupervised k-means classifier to split the videos into two categories: funny and very funny. The categories were generated based on the mean ratings of each video but also depend on the variance of the participants' ratings. The weight of each video being proportional to the variance of ratings across participants. A video leading to greater agreement across participants, and thus to a lower variance, was assigned greater weight in the model. The first cluster consists of 51 videos with high arousal (m = 4.90 \(\pm\) 0.44), high pleasantness (m = 6.13 \(\pm\) 0.37) and high funniness (m = 5.41 \(\pm\) 0.50). The second cluster contains 43 videos with low arousal (M = 4.43 \(\pm\) 0.41), low pleasantness (M = 5.26 \(\pm\) 0.44) and low funniness (M = 4.13 \(\pm\) 0.45). The two clusters were significantly different in terms of arousal (t (92) = 5.363, \(p\) < 0.001), pleasantness (t (92) = 10.330, \(p\) < 0.001) and funniness (t (92) = 13.132, \(p\) < 0.001). To achieve a balanced experimental design, the very funny video with the lowest scores was dropped and seven \({}^{9}\)gag videos with averaged ratings were added to the funny category.  
Neutral Stimuli. In a second pilot experiment in 2020, 40 participants (28 womenage = 24 \(\pm\) 5.32 years) rated 50 neutral videos to control for their arousal and pleasantness using non-graded scales. These videos mainly consisted of scenery, everyday activities (ex: walking, biking, meeting) and animals. All videos were rated with low arousal (mean = 4.09 \(\pm\) 0.73) and neutral pleasantness (neither negative nor positive) (mean = 5.35 \(\pm\) 0.74). These videos were included in the present study as the neutral group.