## 3 Results and Discussion
### MRI/fMRI-Based Hyperscanning Research
#### 3.3.1 Cognition  
The cognition application is the most common area for research when using MRI/fMRI hyperscanning (15, 71.4%). These studies analyzed neural synchrony between participants who engaged in various activities, with communication, eye contact, and joint attention being common activities of interest. Six studies looked at neural synchrony during communication and speech [150; 151; 152; 153; 154]. Three studies evaluated neural synchrony in pairs by recording eye-contact [155; 156; 157]. One unique study in particular used online video chat between two participants to analyze the neural activity associated with real-time eye contact (in person) versus non-real time eye-contact (video chat). Three studies used computer games to analyze social interaction [28; 158; 159]. [PERSON] et al. [39] used charades to map information flow between two brains during gestural (non-verbal) communication. They measured the neural activity between the participant guessing and the participant acting out the word to understand the role of the putative mirror neuron system when not taking part in verbal interactions. Two studies used a movie to measure neural synchrony between subjects while observing social reactions in a movie [160; 161]. _Setting and Orientation._ The most common experimental methods included pairs of participants positioned side-by-side in a lab setting. Twelve of the fifteen experiments done by MRI/fMRI in the cognition category were performed in a lab (80%), while the other three studies were done in a natural setting. For example, [PERSON] et al. [160] used fMRI to reveal between-subject correlation of fMRI activity in the right hemisphere and frontal cortical areas while watching a movie. During this study, \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Application** & \multicolumn{2}{c}{**Experiment Paradigm**} & \multicolumn{1}{l}{**Reference**} \\ \hline \multirow{7}{*}{\begin{tabular}{l} Cognition \\ (15, 71\%) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} Setting \\ \cline{3-4} \end{tabular} } & Lab (12) & [28; 38; 39; 150; 152; 153; 154; 155; 156; 157; 158; 159] \\ \cline{3-4}  & & \multicolumn{2}{c}{Natural (3)} & [151; 160; 161] \\ \cline{3-4}  & & \multicolumn{2}{c}{Face-to-Face (3)} & [154; 156; 157] \\ \cline{3-4}  & & Side-by-Side (12) & [28; 38; 39; 150; 151; 153; 155; 158; 159; 160; 161] \\ \cline{3-4}  & & \multirow{2}{*}{Group Size} & n = 2 (12) & [28; 38; 39; 150; 151; 152; 153; 155; 158; 159; 160; 161] \\ \cline{3-4}  & & \multirow{2}{*}{\begin{tabular}{l} Group Size \\ \(\mathrm{n}>2\) (3) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} n = 2 (12) \\ \(\mathrm{n}>2\) (3) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} [28; 38; 39; 150; 151; 152; 153; 155; 158; 159; 160; 161] \\ \end{tabular} } \\ \hline \multirow{3}{*}{\begin{tabular}{l} Decision- \\ (4, 19\%) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} Setting \\ \(\mathrm{Orientation}\) \\ \end{tabular} } & Lab (4) & [8; 17; 162; 163] \\ \cline{3-4}  & & \multirow{2}{*}{\begin{tabular}{l} Orientation \\ \(\mathrm{Group Size}\) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} n = 2 (4) \\ \end{tabular} } & [8; 17; 162; 163] \\ \cline{3-4}  & & & \multirow{2}{*}{\begin{tabular}{l} Setting \\ \(\mathrm{Face-to-Face (1)}\) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} Lab (2) \\ \(\mathrm{[164]}\) \\ \end{tabular} } \\ \cline{3-4}  & & & \multirow{2}{*}{\begin{tabular}{l} Face-to-Face (1) \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{l} [164] \\ \(\mathrm{[165]}\) \\ \end{tabular} } \\ \cline{3-4}  & & & \multirow{2}{*}{\
\begin{tabular}{l} Side-by-Side (1) \\ \end{tabular} } & [165] \\ \cline{3-4}  & & & \multirow{2}{*}{
\begin{tabular}{l} Group Size \\ \(\mathrm{n}=2\) (2) \\ \end{tabular} } & [164; 165] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of 21 fMRI/MRI-based hyperscanning research. participants watched the first 72 min on an LCD screen with surround sound in a dimly lit room (to simulate a movie theater).