## 5 Discussion
), most participants agreed that both game modes were not boring (i.e., a score of 0 on a Likert scale [0: nothing; 1, 2, 3, 4, and 5: high]), irrespective of the EEG sensor used in the experiments, i.e., the Unicorn sensor (non-tailored mode and tailored mode: 78.79% of the participants) and the Bitalino sensor (non-tailored mode: 80% of the participants, and tailored mode: 85% of the participants). [PERSON]'s exact tests did not show any significant associations between the game modes and boredom. With reference to RQ6 (Which game mode is the most entertaining to play? ), most of the participants ranked the non-tailored game mode with the highest score (5) of the Likert scale [0: nothing; 1, 2, 3, 4, and 5: high], irrespective of the EEG sensor employed in the experiments (i.e., Unicorn: 45.46% of the volunteers, Bitalino: 55% of the volunteers). [PERSON]'s exact tests did not show any significant associations between the game modes and entertainment. With respect to RQ7 (Which game mode has the fastest game response time to control commands? ), most participants that used the Unicorn sensor to collect the EEG signals considered the tailored game mode the game mode with the fastest game response time to control commands. Specifically, 63.64% of the participants rated the tailored game mode with a high score (4) of the Likert scale (1: slow; 2, 3, 4, and 5: fast). On the other hand, most participants that used the Bitalino sensor in the experiments considered both game modes to offer a fast response time. In particular, 35% of the participants ranked both game modes with a high score (4) of the Likert scale. Additionally, [PERSON]'s exact tests did not reveal any significant associations between the game modes and game response time. Finally, regarding the last RQ (Is there any significant association between the game modes and the players' opinion variables (favorite game mode, ease of play, frustration, boredom, entertainment, and game response time)? ), [PERSON]'s exact tests showed significant associations between the game modes (non-tailored, tailored) and the following players' variables: ease of play when the Unicorn sensor was used to collect the EEG in the Likertscale values (1, 2, 3, 4), \(p\) value = 0.009341; and frustration when the Unicorn sensor was used to collect the EEG in the Likert scale values (0, 1, 2, 3), \(p\) value = 0.0466. Although studies have analyzed emotions in games according to [PERSON] et al. [35], few studies have performed this in serious games with DDA for upper limb rehabilitation. Specifically, studies have employed the system usability scale questionnaire to assess the system usability of games with DDA for hand [29] and arm rehabilitation [31]. Similarly, the GEQ questionnaire has been used to assess the participants' engagement during the playing of a serious game with DDA and the same game without DDA for hand rehabilitation [30]. This study reported no significant difference between the game modes in terms of the GEQ scores. Another study has used EMG, ECG, and electrodermal activity to adjust the game difficulty of a serious game for arm rehabilitation [32]. Furthermore, this study [32] used the NASA-TLX questionnaire to assess the participants' affective state. The authors reported no significant difference between the two strategies for adjusting the game difficulty in terms of the workload induced by the participants. It is important to remark that this study used a questionnaire and EEG signals to determine the participants' engagement and preferences. As can be seen, further research could focus on using other biosignals (e.g., respiration, electrocardiogram, and electrodermal activity) to determine the participants' engagement.