Table 1.

Physiological signals, EEG, and eye movement-related metrics and explanations.

Hierarchy	Indicator	Description	Equipment
Psychological	Heart rate	Heart rate is increased with elevated activity levels, stressful conditions, and stimulation but decreased by quiet and relaxed states (Pham et al., 2021).	ErgoLAB Finger Biosensing Smart Wearable Finger Sensor ErgoLAB Wrist Biosensing Smart Wearable Wrist Sensor ErgoLAB Chest Biosensing Smart Wearable Chest Strap Sensor
	Respiratory rate	An index of the balance between sympathetic and parasympathetic activity. A high respiratory rate is typically associated with stress, anxiety, and tension. A low respiratory rate is usually associated with relaxation and meditative states (Pham et al., 2021).
	Low-frequency/high-frequency ratio	A higher ratio suggests dominance of sympathetic activity (stress or arousal), whereas a lower ratio indicates higher parasympathetic activity (relaxation) (Immanuel et al., 2023).
Electroencephalography	α-EEG	Increased alpha activity is commonly observed when an individual is in a relaxed, meditative state, or during quiet wakefulness with eyes closed (Laufs et al., 2003).	ErgoLAB EEG Wearable Hydrogel Electrode EEG Device
	β-EEG	High beta activity is associated with heightened cognitive activity, attention, stress, and anxiety (Palacios-García et al., 2021).
	β/α	A higher β/α ratio often indicates increased stress and anxiety levels, whereas a lower ratio suggests a more relaxed state (Palacios-García et al., 2021).
Eye-tracking	Average pupil diameter	An increase in pupil size (pupil dilation) is often associated with a higher cognitive load, increased attention, and stress or arousal. Conversely, pupil constriction can indicate a state of relaxation or low cognitive demand (Beatty and Lucero-Wagoner, 2000).	Tobii Pro Glasses2 wearable eye tracker
	Fixation frequency	Higher fixation rates can indicate sustained attention and detailed processing of visual information, whereas lower fixation rates might suggest distraction or a broader, less focused scan of the environment (Holmqvist et al., 2011).
	Saccade frequency	A higher saccade rate can indicate exploratory behaviour and the search for new information, often associated with increased cognitive load or stress. A lower saccade rate may indicate focused attention and fewer transitions between visual targets (Holmqvist et al., 2011).

EEG, electroencephalographic activity.