## 2 Research Background
### Cognitive Evaluation  
Cognitive assessment involves the analysis of psychological processes such as awareness, understanding, human information elaboration, reasoning, and the use of knowledge, as it concerns human interaction with other system components. The analysis of the MentalWorkload (MWL) is one of the most widely studied topics; it \"emerges from the interaction between the requirements of a task, the circumstances under which it is performed, and the skills, behaviors, and perceptions of the operator\" [32]. MWL assumes that each person has a relatively limited cognitive capacity that deals with auditory, verbal, and visual material; this capacity is likened to a pool from which resources can be drawn to meet the demands of ongoing tasks [33]. Moreover, the response to the same stimuli differs among users, being different in the capabilities of everyone. MWL can positively or negatively affect human performances; in this direction, measuring the MWL means to quantify the mental \"cost\" of performing a task in order to predict the performances [34]. In the design of industrial systems, measuring the MWL can help to identify sources of errors and understand the complexity of a task as perceived by workers. According to [35] the MWL assessment methods are classified into four main broad categories: performance assessment method, self-assessment (or subjective scaling) method, physiological measurements method, and job and task analysis. Examples of common performance parameters are response, reaction time, accuracy, error rate, estimation time, and objective speed [36]. The combination of different methods is necessary to have a clearer picture of the perceived workload, due to the complexity of cognitive processes. Self-assessment measures allow the user to subjectively evaluate the perceived workload needed to accomplish a task, using questionnaires or psychometric scales. This evaluation is based on the personal experience of the interaction with the system and is obtained from the direct estimation of task difficulty. The most used tool for workload subjective assessment, applied in several research studies, is the multidimensional questionnaire NASA Task Load Index (NASA-TLX) that allows the assessment of six different domains (mental, physical, and temporal demands, performance, effort, and frustration) [37; 38; 39]. Such data can be used to understand how the workload varies over time or to compare the operators' perceived workload (e.g., with and without a particular tool, or between different systems). Physiological measures consider physiological responses of the human body that are believed to be correlated with MWL. Indeed, changes in specific parameters, such as heart rate (HR), heart rate variability (HRV), eye activity (like pupil diameter, gaze entropy, and eye movements' velocity), brain activity (EEG), breathing rate (BR), galvanic skin response or electrodermal activity (GSR or EDA), can be indirect indicators of mental workload [40; 41; 42]. However, all the mentioned physiological parameters can be easily influenced by external factors such as physical activity, environment, and psychological elements (such as emotional involvement) that are not related to the analyzed activity [43], so the analysis has to be properly tailored to the specific context. Also, high levels of inter- and intra-individual variability of biometric indices exist, and sometimes it could be difficult to distinguish MWL from stress or mental fatigue.