## 5 Experiment
### Participants and Their Responses  
Players who agreed to participate in the experiment were given anonymous access to our experimental game. Their performance data were uploaded to our database as they played. At the end of each round, they were required to complete our GUESS questionnaire built into the game, and the answers were also uploaded to our database. Internet access was required to play the game. Our experiment consisted of two phases. In both phases, the participants were entirely different. A total of 80 people participated in the experiment, with 40 in each phase. However, some players completed only part of the game, and some did not fill out the final survey. After counting, with 40 players in phase one, we can identify 17 players with 70 GUESS responses from Group A, 16 players with 72 GUESS responses from Group B, and seven players who only completed their first assigned level, with an enemy volume of 0.5, and our GUESS questionnaire at the end of the level. In phase two, all 40 players participated, and we collected 136 GUESS responses. Regarding the final survey, we received 38 responses in phase one and 34 responses in phase two. In both phases, no player informed us that they adjusted the system volume during the tutorial level. In addition, the final survey revealed that our participants came from various backgrounds: 48 university students, 22 non-students, and two users from AMT. They came from six different countries: the United States, China, Italy, Japan, Turkey, and Venezuela (listed in alphabetical order). Regarding gender, 62.5% of participants were male (phase one: 31, phase two: 19), 23.75% were female (phase one: 6, phase two: 13), 1.25% identified as other (phase one: 0, phase two: 1), and 12.5% preferred not to say or were unknown (phase one: 1, phase two: 1). Regarding age, 91.7% of our players were aged 18 to 29 (phase one: 35, phase two: 31), 6.94% were aged 30 to 39 (phase one: 2, phase two: 3), and 1.39% were over 40 (phase one: 1, phase two: 0). Regarding FPS ability, we used a scale of 0 (unfamiliar), 1 (somewhat familiar), and 2 (very familiar) to represent their proficiency. The results showed that 18.1% were unfamiliar (phase one: 7, phase two: 6), 43.1% were somewhat familiar (phase one: 18, phase two: 13), and 38.9% were very familiar (phase one: 13, phase two: 15). Although we cannot accurately determine the maximum decibel output of our players' devices, based on the players' age groups and their familiarity with FPS games, we can assume that there is no significant difference in the perception of audio in FPS games between players in both phases. Table 2 presents the responses and provides detailed insights into the distribution characteristics of the players in both phases. Based on the general information provided by the final survey, the \(p\)-value of the Shapiro-Wilk test (phase one: \(5.201\times 10^{-6}\); phase two: \(8.693\times 10^{-6}\)) shows that the player distributions in both phases with respect to the FPS ability do not follow a normal distribution. As the respondents from the two phases involve different groups of people, we used the Mann-Whitney U test to assess the significance in difference between the respondents from the two phases. The \(p\)-value of the Mann-Whitney U test is 0.67, i.e., not statistically significant. This situation demonstrates that, despite consisting of different individuals, their abilities are similar. Therefore, comparing the GUESS values between phase one and phase two is dependable. After the data cleaning process, using the fraudulent respondent detection mechanisms for our GUESS questionnaire described in Section 4.5, we were left with valid data. In phase one, we received 100 out of 142 valid GUESS questionnaire responses, each a set of answers, from 30 players, and in phase two we received 111 out of 136 such responses from 29 players. For the final survey, we identified one duplicate response from phase one and five fraudulent respondents from phase two, which we removed.