## 3 Results
### Characteristics of the Selected Studies  
Using VOSviewer, authors' keyword co-occurrence network maps were generated to visually explore key research areas [53]. To ensure consistency in keyword representation, variations in formatting--such as acronyms, capitalization, and spacing--were standardized. For instance, occurrences of human-robot collaboration and EEG in different formats were uniformly converted to human-robot collaboration and electroencephalogram, respectively. It is important to note that four papers did not provide author-defined keywords, and as a result, they were not included in this visualization. The network visualization of this bibliometric map, derived from the available bibliographic data, is presented in Figure 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Publication** & **Sample Size** & **Task Category** & **Workload Measure** & **Collected Data** \\ \hline \multirow{3}{*}{[46]} & \multirow{3}{*}{JP} & \multirow{3}{*}{24} & \multirow{3}{*}{Blasting} & \multicolumn{2}{c}{Performance} & \multicolumn{2}{c}{Time-based measures} \\ \cline{5-6}  & & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX} \\ \cline{5-6}  & & & & & \multicolumn{1}{c}{Physiological} & \multicolumn{1}{c}{EEG (PEN, Pe)} \\ \hline \multirow{3}{*}{[47]} & \multirow{3}{*}{JP} & \multirow{3}{*}{4} & \multirow{3}{*}{Assembly} & \multicolumn{2}{c}{Performance} & \multicolumn{2}{c}{Number of errors/mistakes; Time-based measures} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX} \\ \hline \multirow{3}{*}{[48]} & \multirow{3}{*}{JP} & \multirow{3}{*}{22} & \multirow{3}{*}{Inspection} & \multicolumn{2}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subological} & \multicolumn{1}{c}{Cardiac activity; EDA; Temperature; ACC} \\ \hline \multirow{3}{*}{[49]} & \multirow{3}{*}{CP} & \multirow{3}{*}{11} & \multirow{3}{*}{Problem-solving} & \multicolumn{2}{c}{Performance} & \multicolumn{2}{c}{Number of errors/mistakes} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX; TRUST} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subbiological} & \multicolumn{1}{c}{EEG} \\ \hline \multirow{3}{*}{[50]} & \multirow{3}{*}{CP} & \multirow{3}{*}{43} & \multirow{3}{*}{Assembly} & \multicolumn{2}{c}{Performance} & \multicolumn{2}{c}{Number of errors/mistakes} \\ \cline{5-6}  & & & & \multicolumn{1}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX; TAM; Perceived control} \\ \cline{5-6}  & & & \multicolumn{1}{c}{Subbiological} & \multicolumn{1}{c}{HR} \\ \hline \multirow{3}{*}{[51]} & \multirow{3}{*}{JP} & \multirow{3}{*}{17} & \multirow{3}{*}{Inspection} & \multicolumn{2}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX; BWS} \\ \cline{5-6}  & & & \multicolumn{1}{c}{Subbiological} & \multicolumn{1}{c}{HR} \\ \hline \multirow{3}{*}{[52]} & \multirow{3}{*}{JP} & \multirow{3}{*}{16} & \multirow{3}{*}{Agricultural tasks} & \multicolumn{2}{c}{Subjective} & \multicolumn{1}{c}{NASA-TLX; NARS; RAS} \\ \cline{5-6}  & & & \multicolumn{1}{c}{Subbiological} & \multicolumn{1}{c}{OM; Spine kinematics} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._In Figure 2, keywords are identified by a label inside a circle, with two items being connected by lines between their respective circles. The weight of the keyword determines the size of its respective label and circle, with larger labels and circles corresponding to heavier keywords, e.g., keywords with higher reoccurrence amongst papers. Furthermore, in terms of co-occurrence linkages, the proximity between two items indicates their correlation with each other: the stronger the relation, the closer two keywords are to one another. Analyzing the total incidence number at once reveals the correlation between all the keywords found in the papers.