“…Therefore they can be used as a valuable source of independent and unique information about effort and fatigue effects in ER, alongside changes in ER efficiency itself. These indicators include, for example, a stimulus proceeding negativity (EEG evoked potential, Moser et al, 2017 ), pupil dilation (Strauss et al, 2016 ; Scheffel et al, 2021 ), the activity of particular brain regions detected in fMRI (e.g., Dörfel et al, 2014 ; Ellard et al, 2017 ), as well as fNIRS studies (Lu et al, 2019 ; Azhari et al, 2020 ), but also subjective self-reports of effort and fatigue (Wong et al, 2017 ; Visser et al, 2018 ). Interestingly, digital biomarkers of mental fatigue, like smartphone-based gaze detection, are also being developed (Tseng et al, 2021 ).…”