Review of eye-related measures of drivers’ mental workload

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The assessment of mental workload could be helpful to road safety especially if developments of vehicle automation will increasingly place drivers into roles of supervisory control. With the rapidly decreasing size and increasing resolution of cameras as well as exponential computational power gains, remote eye measurements are growing in popularity as non-obtrusive and non-distracting tools for assessing driver workload. This review summarizes literature on the relation between eye measurement parameters and drivers’ mental workload. Various eye activity measures including blinks, fixations, and saccades have previously researched and confirmed as useful estimates of a driver's mental workload. Additionally, recent studies in pupillometry have shown promise for real-time prediction and assessment of driver mental workload after effects of illumination are accounted for. Specifically, workload increases were found to be indicated by increases in blink latency, PERCLOS, fixation duration, pupil dilation, and ICA; by decreases in blink duration and gaze variability; and with mixed results regarding blink rate. Given such a range of measures available, we recommend using multiple assessment methods to increase validity and robustness in driver assessment.