## 4 Discussion  
The results on whether athletes differ in their gaze behavior if the stimuli are presented in situ or by video presentation (Q1) show a significant effect of this factor in the identified studies [8; 14; 25; 29]. The fixation duration, fixation location, or the number of fixations may differ between the two types of study designs because of the modified depth perception in the video presentation [48]. In addition, the eye movements carried out by the test persons or athletes (concerning accommodation, vergence) differ in the in situ and the video presentation. The possible action or reactions in response to the sequence also significantly influenced the pupil movements and the participants' visual search strategy ([14]; Q2). [PERSON] et al. [49] discuss the nature of the relation between expertise and perception-action coupling using ideas from ecological psychology [11] and the framework of representative task design by [PERSON] [12]. [PERSON] et al. [49] gives an example of perception-action coupling: \"When analyzing the pickup of information used in the return of serve in tennis, participants should be exposed to the in-situ actions of an opponent and ball-flight while being allowed to use the attended information for action\". In the video simulation, the perception is separated from the real action. The research approaches usually allow a rudimentary response to the shown stimuli (e.g., [14]). The separation of perception and action gaze behavior or visual information pickup is different from reality. In comparing different perspectives on the same game situation (Q3), differences in gaze behavior and visual search strategy could be identified [31]. These differences appear to be determined by the available information. For example, the aerial view shows more details on the open space because of the depth of the perspective. This information leads to a different search strategy to find the best decisions for the given game situation. The results of the reviewed studies reveal many reasons for using VR in gaze behavior studies: (a) There are significant differences in gaze behavior between 2-D or video screen projection and in situ representation [8; 14; 25; 28; 29] and also between the different perspectives of the presentation [30; 31]; (b) In the current literature, no significant differences between the in situ representation and the representation of the scenes in VR or 3-D are reported ([36]; Q4); (c) On the VR display, scenes and stimuli can be shown that cannot be shown in reality or that cannot be shown in a standardized manner ([37; 50]; and (d) In addition to the VR presentation, supplementary examination methods that require a stationary or safe workplace can be used (eye-tracking: [39]; EEG: [40]). In scientific studies, however, the fatigue caused by the (a) vergence-accommodation conflict should be considered in developing the research design and interpreting the results. Another aspect which is lacking consideration is the perception-action paradigm in the context of sports situations. Most sporting movements and gaze movements require movement by the athlete himself. This means that the athlete moves in order, for example, to take a better angle to the opponent or teammate. Immersive designs consider this problem by using artificial locomotion (continuous forward movement) or teleporting (\"jumping\" from one location to another) [51]. However, using these techniques in the sports context is questionable because the complexity of motor control would be expanded. The player must learn how to move with a controller (teleporting) instead of just using his legs when moving more than just one or two meters. In addition to the few studies that can be reported, the review has another limitation: the studies report findings of different sports (e.g., tennis, soccer). Gaze behavior could differ between these sports situations, which must be considered when interpreting the results.