## 5 Real-Time Evaluation of HRI with BCI
### EEG Signatures of the Three Psychological Effects in HRI  
To achieve this goal, a critical step is to identify the EEG signatures of these effects, which social neuroscientific studies have shed light on. Starting with the neuroscientific findings related to social facilitation, on the one hand, as arousal is a key concept in most social facilitation theories, i.e., the presence of others could increase individuals' arousal level thus facilitating their dominant response [20], an EEG approach which can provide direct information about arousal level [58; 59] bears the potential to measure the extent of the social facilitation effect [60]. Indeed, EEG indicators of arousal such as alpha power, which is negatively linked to arousal level [61; 62; 63; 64], and beta power, which is positively correlated with arousal [65; 66], have already been used in studies on social facilitation [20]. On the other hand, neural correlates of some cognitive processes that may contribute to social facilitation, such as performance monitoring, have been intensively investigated with EEG. Specifically, EEG allows us to identify the event-related potentials (ERPs) instantly following specific events, making it ideal for exploring the fast-changing internal processes involved in social interaction. EEG studies on performance monitoring have paid particular attention to the error-related negativity (ERN or Ne; [67; 68; 69]), which is induced by an erroneous response. Generally, the ERN is believed to reflect how much one cares about the consequence of his action [70]. Enhanced ERNs are reported for errors committed in the presence of peers [71] or under social evaluation [72; 73], proposed to arise from the greater threatening value of errors induced by concerns about being judged by others [74]. The neural substrates of motor resonance recognized by brain imaging studies [75; 76; 77] are called the mirror system. Multiple brain regions involved in motor resonance, such as the ventral premotor cortex and the pars operularis of the posterior inferior frontal gyrus (Brodmann area 44), as well as the rostral inferior parietal lobule, are recognized by brain imaging studies [75; 76; 77]. In EEG research, the event-related synchronization and desynchronization of the mu (8-12 Hz) rhythm have been linked to the activity of the mirror system [78; 79]. The power of the mu rhythm decreases when subjects perform or observe an action, known as mu suppression (see [80] for a review). In the context of motor priming, an EEG study [81] revealed a more significant mu suppression when the relevance of observed movement to the required action to perform is higher. The neural processes involved in joint action (mostly with joint interference paradigms) have also been investigated with EEG. The amplitude of the P3 component is larger for their own No-Go trials in a joint action setting than in an individual condition, suggesting an increased need for response inhibition [82, 83]. Another ERP component related to the joint action task is the stimulus-locked N2 reflecting response conflict. [PERSON] and [PERSON] [84] reported that after nasal oxytocin administration, which has been reported to facilitate social behavior by enhancing self-other integration, participants exhibit larger N2 for Go trials in the joint Simon task compared to the individual setting. [PERSON] et al. [85] investigated differences in the processing of social (i.e., indicating that a co-actor should respond) and nonsocial No-Go (i.e., signaling that neither actor nor co-actor should respond) cues in a joint flanker task. The conflict-sensitive N2 showed a compatibility effect only for social No-Go cues, and the P3b component related to response discrimination and evaluation was larger for social relative to non-social No-Go.