## 3 Results
### Physiological Assessment of Mental Workload
#### 3.6.3 Ocular Measures
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Features** & **Description** & **Employed in** \\ \hline Blink rate & \begin{tabular}{c} Blink frequency per minute or second. Higher blink rates can be \\ associated with higher mental demand or fatigue, while lower blink \\ rates can be associated with higher visual demand or attention. \\ \end{tabular} & [40; 52] \\ \hline Blink duration & \begin{tabular}{c} Closure time duration of a blink. Lower blink duration may be \\ associated with higher visual demand, while higher blink duration can \\ be provoked by tiredness or fatigue. \\ \end{tabular} & [40] \\ \hline Pupil size & \begin{tabular}{c} Diameter or area of the pupil. Pupil size in adults can range between 2 \\ mm and 8 mm in diameter. Higher pupil size can be associated with higher mental demand. \\ \end{tabular} & [43; 45; 52] \\ \hline Fixation rate & \begin{tabular}{c} The number of fixations, usually in a certain area of interest (AOI). The \\ number of fixations approximates visual attention allocation. More \\ fixations can equate to less efficient search or increased visual effort, \\ thus, a higher mental workload. \\ \end{tabular} & [40; 43; 45] \\ \hline Fixation duration & \begin{tabular}{c} The time spent gazing at a position. A longer fixation duration describes \\ issues related to extracting information (i.e., more processing time), or it \\ indicates that the target is more appealing. \\ \end{tabular} & [40; 43; 45] \\ \hline Saccade rate & \begin{tabular}{c} The number of saccades, usually in a certain AOI. A higher number of \\ saccades can be associated with higher visual effort and, thus, higher \\ mental workload. \\ \end{tabular} & [43; 45] \\ \hline Saccade duration & \begin{tabular}{c} The length of time from the start to the end of a saccade event (i.e., \\ shifting from one fixation to another). \\ \end{tabular} & [43] \\ \hline Saccade amplitude & \
\begin{tabular}{c} The measure of visual arc degrees of movement from one fixation to the \\ next. Saccade amplitude usually drops as mental workload increases. \\ \end{tabular} & [43] \\ \hline Saccade velocity &
\begin{tabular}{c} The speed of the saccade (degrees/time) is usually measured \\ considering the peak velocity. \\ \end{tabular} & [43] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Common ocular measures and respective definitions (adapted from [45]). with more complex tasks. Similar results were found by [45], who reported that the rates of fixations and saccades increased as cognitive load increased, not only while participants learned how to perform an assembly task but also while they had to resume it as well. In contrast, both of these rates decreased throughout a shift as participants got used to the assembly task. However, a relation between increased fixation rate and increased mental workload was not reported by [40], who employed this metric as well. Some contradictory results highlight how different tasks can have varying effects on physiological responses, an issue that should be considered in future investigations [40; 64]. Moreover, limitations of ocular measures also include significant variability among individuals due to personal differences, such as ocular characteristics and levels of experience, which can impact the accuracy and consistency of the collected data [45].