## 3 Results and Discussion
### NIRS/NIRS-Based Hyperscanning Research
#### 3.2.1 Cognition  
NIRS and fNIRS hyperscanning have been used for cognitive applications in numerous experimental tasks. These experimental tasks include computer games [114; 115; 116; 117; 118], verbal communication [26; 119; 120], music [37; 116; 121], gift exchange [122], photography [123], singing [124], the Prisoner's Dilemma Game [125; 126], and puzzles [127]. Using cooperative and competitive computer games, [PERSON] et al. [117] examined the neurobiological underpinnings of emotional bond formation and a child's development of emotional regulation. Furthermore, given the increased prevalence of virtual communication, another study [26] investigated the neural difference between face-to-face communication and other forms of communication, such as through a computer. For example, the most recent fNIRS hyperscanning  
\begin{table}
\begin{tabular}{l l l l} \hline \hline
**Application** & **Experiment Paradigm** & **Reference** \\ \hline \multirow{4}{*}{Cognition (28, 47\%)} & \multirow{2}{*}{Setting} & Lab (25) & [10; 18; 19; 25; 27; 34; 57; 72; 73; 74; 75; 76; 77; 78; 86; 88; 89; 91] \\ \cline{3-4}  & & Natural (3) & [23; 87; 90] \\ \cline{2-4}  & \multirow{2}{*}{Orientation} & Face-to-Face (11) & [10; 27; 34; 78; 79; 82; 84; 86; 89; 90] \\ \cline{3-4}  & & Side-by-Side (17) & [18; 19; 23; 25; 57; 72; 77; 80; 81; 83; 87; 88; 91] \\ \cline{3-4}  & \multirow{2}{*}{Group Size} & n = 2 (23) & [10; 18; 19; 25; 27; 34; 57; 72; 74; 76; 76; 77; 78; 79; 80; 90] \\ \cline{3-4}  & & n \textgreater{} 2 (5) & [23; 75; 87; 88; 91] \\ \hline \multirow{4}{*}{Decision-Making (16, 27\%)} & \multirow{2}{*}{Setting} & Lab (12) & [16; 29; 36; 42; 92; 93; 94; 95; 96; 97; 98; 99; 100; 101] \\ \cline{3-4}  & \multirow{2}{*}{Orientation} & Face-to-Face (9) & [3; 36; 42; 93; 94; 96; 99; 100; 101] \\ \cline{3-4}  & & Side-by-Side (9) & [3; 6; 16; 29; 92; 95; 97; 98; 100; 101] \\ \cline{3-4}  & \multirow{2}{*}{Group Size} & n = 2 (13) & [3; 6; 16; 29; 36; 42; 93; 95; 99; 101] \\ \cline{3-4}  & & n \textgreater{} 2 (5) & [3; 92; 94; 100; 101] \\ \hline \multirow{4}{*}{Motor Synchronization (14, 23\%)} & \multirow{2}{*}{Setting} & Lab (13) & [41; 102; 103; 104; 105; 106; 107; 108; 109; 110; 111; 112; 113] \\ \cline{3-4}  & \multirow{2}{*}{Orientation} & Natural (1) & [58] \\ \cline{3-4}  & & Face-to-Face (6) & [41; 68; 105; 108; 112; 113] \\ \cline{3-4}  & & Side-by-Side (8) & [102; 104; 106; 107; 109; 110; 111; 111; 112; 113] \\ \cline{3-4}  & \multirow{2}{*}{Group Size} & n = 2 (14) & [41; 68; 102; 113; 114; 115; 116; 117; 118; 119; 120; 121; 122; 123; 124; 125; 126; 127; 128; 129; 130; 131; 132; 133; 134; 135; 136; 137; 138; 139; 14  
study for applications in cognition explored the effect of prosocial behavior through all-female pairs engaging in a gift exchange task [122]. The results showed that a greater interpersonal engagement between two individuals can lead to significant increase in the coordination of behavioral activities.  
_Setting._ Out of the seventeen studies, two were conducted in a natural setting [37; 120], while the majority (15) were conducted in a lab setting. For example, [PERSON] et al. [117] tested the coherence between parents and children pairs while they played a cooperation-or-competition game in the lab.  
_Orientation._ Eight studies oriented participants side-by-side [37; 114; 115; 116; 117; 121; 122] while nine studies had participants face each other [123; 124; 125; 126; 116; 118; 120; 123; 127] to complete experimental tasks.  
_Group Size._ Three studies had participant group sizes greater than two [127; 120; 119], but a majority (13) organized participants into pairs. Some studies only selected male participants [114; 118; 121], others selected only female participants [116; 122], and the remaining studies included both male and female participants.