# Situational Awareness Assessment of Drivers Boosted by Eye-Tracking Metrics: A Literature Review
## 3 Results
### Eye-Tracking Metrics and Oculomotor Events
Eight studies used pupillary measures for oculomotor movements. Reference [12] commented on the need for further research to understand the relationship between pupil diameter and SA and ranked pupil diameter as one of the most important measures for predicting SA when drivers scan their driving scenarios. In addition, ref. [32] measured pupil dilation during a memory task to evaluate the effects of mental workload in SA. Reference [44] developed assessments of driver situational awareness utilizing sensor-based methods, especially focusing on road signs. For this experiment, eye-tracking metrics such as average pupil size, eye blinks, and gaze-related features, including gaze visits and total fixation time, were employed. This method allowed AI systems to predict driver situational awareness in relation to levels 1 and 2 of the Endsley model (perception and comprehension). Reference [45], in their literature review, additionally highlighted that pupil measurements, specifically focusing on pupil diameter, may serve as an indication of the user's emotional arousal. Additionally, ref. [34] established a safety analysis of work zone complexity with respect to driver characteristics by using fixations and pupillary measures and situation awareness, with longitudinal control, lateral control, gaze behavior, and daze behavior in the event of changes in SA because of the involvement of secondary visual tasks, for instance, text entry into a GPS unit in an active work zone and a lower perception of hazards. Similarly, ref. [46] reported a relationship between the increase in pupil diameter and situations perceived as risky, showing that danger provokes a stress response that  
Figure 7: Proportion of eye-tracking measures over the total papers reviewed. can be represented in terms of pupil diameter. However, it is not possible to establish this conclusively since videos on monitors were used in the experiment, and the pupil is sensitive to changes in light. Nonetheless, it is possible to measure whether these hazardous situations can be qualified as more dangerous than the nonhazardous situations from oculomotor metrics such as pupil diameter [46]. In addition, ref. [47] considered the effects of pre-takeover visual engagement or takeover request (TOR) warning and risk perception and revealed a correlation between the change in pupil diameter and visual attention--the more dispersed the visual attention, the greater the SA. Other metrics included the blink rate, pupil position, and gaze angle, each of which was utilized in six studies. For instance, ref. [39] studied the role of an in-vehicle digital voice-assistant in conditionally automated vehicles; they stated that drivers could trust driving by an automatic vehicle and tend to fall asleep, thereby suspending the process of becoming alert, as measured by the rate and duration of saccades, as well as the pupil diameter. Reference [48] examined the implications of uncertainty communication for automation and saccades and fixations with eye tracking. They reported that, presumably, operators could adjust their gaze behavior to the level of uncertainty. Reference [49] explored gaze prediction for drivers and used the probability for motion hypotheses and an approach based on a dynamic Bayesian network of fixations and saccades considering human gaze motion characteristics. Similarly, metrics such as smooth pursuit direction, blink rate and duration, pupil dilation, gaze velocity, and peripheral vision were used in studies on driver's gaze prediction in dynamic environments and in the study on driver distraction. In Figure 8, we provide an overview of the eye-tracking metrics systematically categorized and identified within the context of this review. Orange bars indicate the primary metric associated with each distinct oculomotor event. In a majority of the studies, the assessment of SA in drivers was based on the deployment of metrics related to gaze fixation, gaze direction, pupil measurements, and saccades.