## 1 Introduction  
Since well-developed spatial skills are necessary for several jobs, mainly for those that are related to engineering [1], they are considered to be essential in the present day. Fortunately, as they are cognitive skills, they can be improved through time [2]. It is imperative that training of spatial skills should be included in the studies of engineering students [3]. Through the years, several paper-based geometric problems that can improve spatial ability were created in the literature. In this paper, three such tests are focused on: the Mental Rotation Test (MRT) [4], Mental Cutting Test (MCT) [5], and the Purdue Spatial Visualization Test (PSVT) [6]. Although their numbers are still scarce, new versions of these spatial ability improving tests are recreated in virtual or augmented environments [7; 8; 9; 10], and some even include gamification elements [11; 12]. Building such virtual/augmented versions of these tests is quite complex: according to [PERSON] and [PERSON], a virtual system is created of five various parts: software/database(s), the VR engine behind it, tasks, I/O devices, and the users themselves [13]. Due to its complexity, the design of virtual environments can influence human-computer interaction because users can be immersed and human-computer interfaces can be redefined [14; 15]. There is no perfect human-computer interaction for virtual reality applications because the interaction type varies from application to application [16]. As can be observed, design is quite important in virtual environments. According to [PERSON] et al., users perform better in dynamic environments [17], while the study of [PERSON] et al. concludes that the blur, and fade effects as well as \"standard environments\" can positively influence users [18]. Using a head-mounted display can also enhance the performance of users in virtual reality [19], and user characteristics can also influence the results on tests [20], even their completion times as well [21]. However, distances from objects are typically underestimated in virtual environments [22], however binocular disparity and a carefully adjusted camera should be provided to increase the presence of the users [23]. This means that with a carefully designed virtual environment, spatial skills can be improved [24; 25; 26; 27; 28]. Among others, investigation of human-computer interaction in virtual worlds is part of the Cognitive InfoCommunications (CogInfoCom) environment [29; 30; 31; 32; 33; 34] which was used for this and the authors' previous studies: spatial skills are also investigated in it [11; 12; 35], and the optimal user-centric virtual environment--to enhance the spatial skills of users--was also found [36]. Based on the literature and previous research, the display parameters and devices are in interaction with the various users: every factor has some influence on the correct answers reached on the spatial ability tests. Even the characteristics of users affect current answers [9; 19; 37], and completion times [21]. However, what about the display parameters? Do they affect test completion times? To find an answer to this question, a previously developed spatial ability measuring virtual environment was used [38]. While the application logs user results and information about the tests, display parameters--such as the virtual camera type, its field of view (FoV), rotation, contrast ratio, and the existence of shadows--can be controlled in the application. For the measurements, participants either used a desktop display or the Gear VR head-mounted display. 240 participants tested with the former, and 61 with the latter. Their completion times were evaluated using linear regression analysis. According to the results, a combination of 75\({}^{\circ}\) FoV, 45\({}^{\circ}\) camera rotation, and 3:1 contrast ratio has the largest increase in completion times--even when this combination is inside a quartet or a quintet.