# Situational Awareness Assessment of Drivers Boosted by Eye-Tracking Metrics: A Literature Review
## 4 Discussion
The eye-tracking metrics, such as peripheral vision, pupil diameter, rate of saccades, and general fixation, suggest differences in the SA of drivers in observation windows of 7 s. They concluded that dispersed visual attention has a positive correlation with better SA. Studies such as those of [62] support and validate the idea that SA in humans is related to the fixation of their eyes on relevant objects [11], and various studies revealed a positive relationship between eye-tracking metrics and SA [9]. Regarding distraction, reference [21] presented the research of [PERSON] and [PERSON] (2000), who studied the relationship of SA with eye tracking to identify patterns in driver distraction. The review reported that higher fixation durations, higher pupil dilations, and lower fixation counts in the display of the vehicle or mirror are related to driver distraction. Likewise, the review also explained how fixations allow us to understand the visual perception processes and how much of the visual gaze is retained. Concerning remembered information and mental workload, reference [32] studied the count and duration of the fixations and their relation with different information retrieval patterns through the gaze; they also examined how the metrics are related to the information remembered by the driver and the behavior, as a part or due to the mental interpretation of the trajectory traversed rather than based on retrieving individual pieces of information. Other studies [30; 34; 54] explored the safety analysis of work zone complexity and the influence of different attention allocation strategies under mental workloads on SA based on the metrics of count and duration of fixations, diameter and position of the pupil, and gaze direction. These studies showed that an increase in the complexity of the driving zones increases the mental workload and decreases SA. Furthermore, the mental workload can increase by 37% if a secondary visual task is involved; this has immediate repercussions on the gaze behavior, leading to a lower perception of risks and a lower level of safety perception of the situation. Additionally, ref. [50] made an interesting statement regarding the construction of new adaptable systems that include the human-machine relationship with SA. They reported the ability of the operator to be prepared to \"fallback-ready user\", even performing secondary tasks and recovering awareness in the main operation by studying SA with real-time data from eye trackers. Likewise, reference [12] built a prediction model of SA during takeover transitions in conditionally automated driving with only eye-tracking data. In terms of the metrics used, specifically, 89% of authors using at least three commonly employed eye-tracking metrics, such as gaze fixation, pupil diameter, and saccades, found eye tracking to be an objective indicator of SA. Fixations were the most utilized metric in the experiments, aligning with studies such as the one conducted by [12]. It was found that within the relationships with the measurement of situational awareness in drivers, at the perceptual level (level 1), an excessive number of fixations might be associated with difficulty in gathering information during demanding tasks. Additionally, it was observed that distracted drivers had higher fixation durations. Furthermore, the mean fixation time of eye movement was noted to have the potential to measure situational awareness, as presented by [54]. Combining saccades with fixations is the second most used metric for measuring SA, although saccade amplitudes were found to be negatively correlated with SA, as reported by [12]. However, it is crucial to consider the limitations of using eye-tracking metrics. Certain metrics may excel in measuring perception (level 1 of SA) but may have less relevance to comprehension (level 2) and projection (level 3), as presented in the research by [59]. In terms of the scientometric analysis, eye-tracking-related research on physiological measures of SA has experienced a rapid surge since 2015.