Table 1.
Eye and head features used in classification models to infer task-induced effects of target discriminability and time pressure
| Metric | Definition | Significance | Supporting Literature |
|---|---|---|---|
| Fixation | |||
| Fixation Frequency | Total fixation count divided by trial time (sec) | Fixation Frequency: Reflects how often attention shifts to specific visual location. Higher frequencies may indicate increased visual samplingor search effort. Fixation Duration: Longer fixations typically reflect deeper processing, uncertainty, or hesitation; shorter durations may indicate more confident or automatic responses. Fixation Duration Proportion: Indicates how much of the trial is spent fixating; higher values suggest greter engagment or deliberation. Target vs. Distractor Fixations: Target-focused metrics reflect goal-directed attention while distractor-focused metrics may indicate inefficient search or difficulty in discrimination | Drew et al., (2017); Over et al., (2007); Reingold and Galhot, (2014); Lu and Sarter, (2019); Huanget al., (2015); Karessli et al., (2017); Iskandarani et al., (2024) |
| Avg Fixation Duration | Average fixation time (sec) | ||
| Fixation Duration Proportion | Sum of all fixation durations divided by trial time | ||
| Target Fixation Frequency | Total target fixation count divided by trial time | ||
| Avg Target Fixation Duration | Average target fixation time (sec) | ||
| Target Fixation Duration Proportion | Sum of all target fixation durations divided by trial time | ||
| Distractor Fixation Frequency | Total distractor fixation count divided by trial time | ||
| Avg Distractor Fixation Duration | Average distractor fixation time (sec) | ||
| Distractor Fixation Duration Proportion | Sum of all distractor fixation durations divided by trial time | ||
| Target Fixations per Target | Total number of target fixations divided by total number of targets | ||
| Distractor Fixations per Distractor | Total number of distractor fixations divided by total number of distractors | ||
| Target Distractor Fixation Ratio | Target fixation preference compared to other fixations | ||
| Saccade | |||
| Saccade Frequency | Total saccade count divided by trial time (sacades/s) | Saccade Frequency: Higher frequency may reflect rapid scanning or uncertainty in search strategy. Saccade Size and Size per Second: Larger or more frequent saccades may suggest a global search strategy while smaller saccades may indicate more focused, precise search behavior. Target vs Distractor Saccade Size: Differentiates the visual distance the eye travels totask-relevant vs. irrelevant stimuli, potentially reflecting discrimination efficiency | Watson et al., (2010); Over et al., (2007); Di Stasi et al., (2011); Velichkovski et al., (2002); Gordonet al., (2024) |
| Avg Saccade Size | Average size of a saccade (dva) | ||
| Saccade Size Per Second | Sum of all saccade magnitudes divided by trial time (°/s) | ||
| Avg Target Saccade Size | Average size of saccade to a target (dva) | ||
| Avg Distractor Saccade Size | Average size of saccade to a distractor (dva) | ||
| Head | |||
| Head Movement Frequency | Total head movement count divided by trial time | Head Movement Frequency and Size: Capture how often and how far users reorient their field of view; higher values may relfect broader or more effortful search strategies. Head Fixation Duration and Proportion: Longer or more frequent head fixations may reflect more focused attention or reduced exploratory behavior. Global Head Movement: Indicates spatial engagement with the scene | Hu et al., (2023); David et al., (2018); Fuller, (1992); Stahl, (1999); Oommen and Stahl, (2005); Freedman and Sparks, (1997) |
| Avg Head Movement Size | Average size of a head movement (degrees of visual angle) | ||
| Head Movement Size Per Second | Sum of all head movement magnitudes divided by trial time (°/s) | ||
| Avg Head Fixation Duration | Average time the head remains below the threshold of a head movement (sec) | ||
| Head Fixation Duration Proportion | Sum of all head fixation durations divided by trial time | ||
| Head Fixation Frequency | Total head fixation count divided by trial time | ||
| Global Head Movement Per Second | Sum of the angular distance the head moved divided by trial time Independent of head movement classification | ||
| Eye | |||
| Avg Eye in Head Angle | Average rotation of the eye within the head (dva) | Eye in Head Angle: Larger angles may reflect reliance on eye movements rather than head shifts. Eye-to-Gaze Proportion: important for undertanding search strategy preference (e.g."eye movers"vs."head movers") | Sidenmark & Gellersen, (2019, 2023); Stahl, (2001a, 2001b); Freedman, (2008); Zangemeister and Stark, (1982); Doshi and Trividi, (2012) |
| Global Eye Movement Per Second | Sum of the angular distance the eye moved divided by trial time. Independent of saccade classification | ||
| Avg Eye to Gaze Proportion | Average proportion of eye contribution to gazeangle. Gaze Angle = Eye Angle + Head Angle | ||
| Kinematic | |||
| Head | |||
| Avg Head Velocity | Average head velocity (°/s) | Velocity: Indicates speed of eye or head movement; higher values may reflect urgency or less deliberate behavior. Acceleration: Measures the rate of movement change. Jerk: Captures abruptnessor smoothness of movement; higher jerk suggests more reactive or less controlled movements. Variability (Standard Deviation): Grater variability across velocity, acceleration, or jerk may reflect less stable or more exploratory search strategies | Di Stasi et al., (2011); Salehi et al., (2024); Hu et al., (2023); Lisberger et al., (1981) |
| Std of Head Velocity | Standard deviation of head velocity (°/s) | ||
| Avg Head Velocity X,Y,Z | Average head velocity around the X, Y, and Z axes (°/s) | ||
| Std of Head Velocity X,Y,Z | Standard deviation of head velocity around the X, Y, and Z axes (°/s) | ||
| Avg Head Acceleration | Average head acceleration (°/s2) | ||
| Std of Head Acceleration | Standard deviation of head acceleration (°/s2) | ||
| Avg Head Acceleration around the X,Y,Z | Average head acceleration around the X, Y, and Z axes (°/s2) | ||
| Std of Head Acceleration around the X,Y,Z | Standard deviation of head acceleration around the X, Y, and Z axes (°/s2) | ||
| Avg Head Jerk | Average head jerk (°/s3) | ||
| Std of Head Jerk | Standard deviation of head jerk (°/s3) | ||
| Avg Head Jerk X,Y,Z | Average head jerk around the X, Y, and Z axes (°/s3) | ||
| Std of Head Jerk X,Y,Z | Standard deviation of head jerk around the X, Y, and Z axes (°/s3) | ||
| Eye | |||
| Avg Eye Velocity | Average eye velocity (°/s) | ||
| Std of Eye Velocity | Standard deviation of eye velocity (°/s) | ||
| Avg Eye Velocity X,Y,Z | Average eye velocity around the X, Y, and Z axes (°/s) | ||
| Std Eye Velocity X,Y,Z | Standard deviation eye velocity around the X, Y, and Z axes (°/s) | ||
| Avg Eye Acceleration | Average eye acceleration (°/s2) | ||
| Std of Eye Acceleration | Standard deviation of eye acceleration (°/s2) | ||
| Avg Eye Acceleration around the X,Y,Z | Average eye acceleration around the X, Y, and Z axes (°/s2) | ||
| Std Eye Acceleration around the X,Y,Z | Standard deviation eye acceleration around the X, Y, and Z axes (°/s2) | ||
| Avg Eye Jerk | Average eye jerk (°/s3) | ||
| Std of Eye Jerk | Standard deviation of eye jerk (°/s3) | ||
| Avg Eye Jerk X,Y,Z | Average eye jerk around the X, Y, and Z axes (°/s3) | ||
| Std Eye Jerk X,Y,Z | Standard deviation eye jerk around the X, Y, and Z axes (°/s3) | ||