# Situational Awareness Assessment of Drivers Boosted by Eye-Tracking Metrics: A Literature Review
## 3 Results
### Eye-Tracking Metrics and Oculomotor Events  
Appendix A succinctly encapsulates the collective scholarly contributions of authors within the realm of the investigated eye-tracking metrics, as delineated and covered within this comprehensive literature review. The importance of their contributions has been reported in the literature [9; 21]. Eye tracking has been increasingly used in studies on human behavior since 2002, perhaps following one of the largest studies on human behavior in the analysis of gaze patterns carried out by [40], with a significant rise in the field of study of driver behavior in 2013 [41]. Similarly, the use of eye tracking as an objective method and its rise as the commonly used method in studies on SA has witnessed a significant rise [9]. Among the selected studies in this review, 41 studies dealt with the use of eye tracking to investigate SA in drivers. In these studies, a total of 36 distinct oculomotor events--events pertaining to activities governed by the ocular motor system, facilitating the preservation of visual stability, and orchestrating gaze-oriented motions--were discerned and cataloged. For categorizing the metrics, we considered the classification and studies of [21] and [9], which were used as a reference. The oculomotor events that we examined are fixation, saccade, smooth pursuit, blinking, pupillometry measures, gaze, peripheral vision, tremors, microssaccade, and drift, with their respective metrics. Figure 7 shows the proportion of eye-tracking measures in relation to the comprehensive scope of this review. Among the 41 studies incorporated within the review, 31 studies used the fixation metric as the fundamental component to study SA; 29 used count fixation and 25 used duration fixation for SA measurement; 17 studies used gaze direction; and 8 studies used the amplitude and rate of the saccade. These studies revealed a direct relationship between physiological measures obtained through eye tracking and its emergence as the commonly used method in studies assessing SA. For instance, ref. [12] built a prediction model named light gradient boosting machine from the data collected with eye tracking to predict SA during the takeover transition period in conditionally automated driving; they recreated simulated driving scenarios with videos and by using PreScan 8.0.0. They found that fixations, followed by pupil diameter and saccades, had the highest importance in predicting SA. Reference [21] reported in their review that distracted drivers had higher fixation durations and lower fixation counts on the mirror or speedometer. Figure 6: Participants by gender and types of vehicles. Likewise, ref. [32] observed that in a traffic scenario at an intersection in which the participants were instructed to memorize information and to build an understanding of the situation, commonly, participants fixed deflated spatial locations associated with the relevant information (level 3 of SA); in addition, when retrieving information associated with other road users, participants made considerably more saccades between empty locations on the screen. Furthermore, ref. [31] examined instances in which drivers exhibited diminished awareness when approaching and entering a roundabout. They used three distinct eye-tracking devices and relied on metrics such as fixation duration, fixation count, and gaze direction to reveal that drivers, on average, allocated approximately 28.36% of their temporal focus to non-driving-related areas (NDRAs). Likewise, ref. [42] revealed consistency between fixation count and fixation duration on an object and showed that SA during simulated automated driving might be attributed to visual fixation patterns for various traffic scene elements. Similarly, ref. [43] investigated the safety implications of environment self-explaining design on drivers' situational awareness; it was noted that drivers exhibited the highest percentage of fixation number and fixation duration while traversing the yellow-green adorned sidewall tunnel.