<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.0 20120330//EN" "JATS-archivearticle1.dtd">
<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Towards the Development of Immersive Virtual Reality Games for Spatial Skills Training</article-title>
      </title-group>
      <contrib-group>
        <aff id="aff0">
          <label>0</label>
          <institution>Departamento de Expresión Gráfica, Diseño y Proyectos Escuela de Ingenierías Industriales, University of Málaga c/ Dr.</institution>
          <addr-line>Ortiz Ramos s/n. Campus de Teatinos. 29071 Málaga</addr-line>
          ,
          <country country="ES">Spain</country>
        </aff>
      </contrib-group>
      <fpage>90</fpage>
      <lpage>97</lpage>
      <abstract>
        <p>The purpose of this paper is to set the foundations for a serious game development to train spatial skills in virtual reality. Spatial competences relevance is highlighted as key indicator for STEM careers, as a requirement under the EHEA for technical studies as in engineering, architecture or chemistry degrees. Through immersive experiences simulated with virtual reality technologies, the objective is improving user capacity to understand and visualize threedimensional objects morphology, identify orthogonal projections, perform rotation and cutting spatial operations as well as being able to assemble sets of parts.</p>
      </abstract>
      <kwd-group>
        <kwd>Spatial Skills Training</kwd>
        <kwd>Immersive Virtual Reality</kwd>
        <kwd>Serious Games</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>Introduction</title>
      <p>
        Since the last 20 years there have been a growing interest on how to increase the
interest and engagement for learning via empowering tools such as videogames.
Several applications have been recognized as potential tools for improving cognitive
processes for mathematics, programming or specific sets of skills such as spatial abilities.
Some examples such as Medal of Honor [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ], Minecraft [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] or Portal 2 [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] have been
proven to help training spatial skills in controlled environments.
      </p>
      <p>
        Despite these results, there are still open discussion on how to enhance cognitive skills
outside laboratory-constrained conditions, meaning applying gamification to academic
environments with serious games, which precise purpose is not only enjoying the
experience but to learn by playing [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ].
      </p>
      <p>
        One of the main focus for research is to identify potential game experiences that can
improve subset of spatial skills as key indicator for STEM careers success [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ].
Following literature on this matter, there are several factors consider when facing a study on
spatial skills training: First, expected higher impact for training low spatial skills
population, that tend to struggle with early courses of STEM careers that will likely result
on failing or dropping from the course. The issue has been addressed particularly for
undergraduates with non-technical education background as well as females, that have
been consistently reported as worse performing on spatial abilities tasks than males [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ],
therefore considered a relevant factor on the gender gap on technical and scientific
degrees. Secondly, students that already possess high level of spatial skills might face
little improvement by training or the so called “ceiling effect”. These factors are to be
translated into key design principles for developing engaging and effective spatial skills
training experience.
      </p>
      <p>Recent growth of virtual reality technology and accessibility to development engines
such as Unity have made possible a proposal where immersive qualities of virtual
reality allow direct interaction with a gamified experience empowering learning process
and motivation for the students, especially those less trained for the competences
required to achieve academic goals.
2
2.1</p>
    </sec>
    <sec id="sec-2">
      <title>Spatial Skills</title>
      <sec id="sec-2-1">
        <title>Spatial Ability Competence &amp; Relevance</title>
        <p>
          Following Gardner’s Multiple Intelligence theory [
          <xref ref-type="bibr" rid="ref7">7</xref>
          ], intellectual coefficient or
capacity cannot be considered a univocal quality such as height or weight, as it is
constructed from eight dimensions or types of intelligence. This theory was a complete
revolution at educational level, driving the attention for multiple research studies on
each of the intelligence areas, one of them being spatial intelligence. The perception of
the visual world and the capacity of making transformations on its representations
depend on this intelligence. The subset of spatial skills is derived from it as the ability to
solve problems between the relation of the environment and the observer – spatial
orientation – or the relation between elements and its transformations – spatial
visualization [
          <xref ref-type="bibr" rid="ref8">8</xref>
          ].
        </p>
        <p>
          On the Science, Technology, Engineering and Mathematics (STEM) aspect, there is
a relevant number of students accessing higher education courses with less trained
spatial skills, this factor impacts negatively on early academic abandon rates [
          <xref ref-type="bibr" rid="ref9">9</xref>
          ]. Thus,
first year subjects for technical degrees introduce methods for thinking spatially and
understand 2D and 3D representations, such as graphic expression, computer assisted
graphics or engineering graphics, where main objective is to solve spatial problems.
2.2
        </p>
      </sec>
      <sec id="sec-2-2">
        <title>Training and Assessment</title>
        <p>
          In spatial skills development research studies, measurement tools are used to
quantify results and gains. Enhancing and assessing skills is the main challenge faced by
authors previously as introduced in [
          <xref ref-type="bibr" rid="ref10">10</xref>
          ], where a wide range of measurement tools are
used, from which the most common are standardized tests:
Mental Rotation Test (MRT). Introduced by Vanderberg and Kuse (1978) [
          <xref ref-type="bibr" rid="ref11">11</xref>
          ], this
tests presents 20 exercises to be completed in 20 minutes, where a model figure is
presented. To this model certain rotation transformation is applied and the user has to
choose two from the four possible options. In these exercises, mirror objects are usually
presented as incorrect answers. Spatial rotation and visualization are assessed in this
test.
        </p>
        <p>
          Mental Cutting Test (MCT). Initially developed as higher education access test for
USA in 1930, afterwards adopted in Australia, Germany, Poland or Japan [
          <xref ref-type="bibr" rid="ref12">12</xref>
          ]. It
consists in 25 exercises where guide model is presented on left side and user has to choose
unique correct answer from total five possible results from cutting operation.
        </p>
      </sec>
      <sec id="sec-2-3">
        <title>Differential Aptitude Test: Spatial Rotations (DAT:SR). This test purpose is to pre</title>
        <p>sent a 2D pattern that is to be mentally folded by the student as to result in any number
from the four possible options. There are a total of 50 exercises where spatial
visualization and spatial relations are evaluated.</p>
        <p>
          Purdue Spatial Visualization Test: Rotations (PSVT:R). Developed with the aim of
assessing the ability for solids rotation visualization [
          <xref ref-type="bibr" rid="ref13">13</xref>
          ]. Upper figures show an
example of a three-dimensional object rotation, while on the second row the figure to be
rotated is presented. Unique answer corresponds with the result of applying the same
rotations to the proposed figure. In this rest both mental rotation and spatial
visualization are tested.
        </p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>Immersive Virtual Reality</title>
      <sec id="sec-3-1">
        <title>Definition</title>
        <p>
          Immersive Virtual Reality systems are able to present simulated virtual scenarios
that surround the user in a three-dimensional space. Generally, they will provide a
firstperson perspective based on and synchronized with head position and orientation from
the user. These is achieved through the usage of Head-mounted Displays (HMD) inside
out tracking, as the sensors responsible for monitoring are included in the device [
          <xref ref-type="bibr" rid="ref14">14</xref>
          ].
Since the first introduction of VR HMD in 1963 by Hall and Miller, subsequent
evolutions such as 3D visual display in 1968 by Sutherland [
          <xref ref-type="bibr" rid="ref15">15</xref>
          ], integrated binaural audio or
hand-computer interactions [
          <xref ref-type="bibr" rid="ref16">16</xref>
          ] set the foundations for the technological uprise that
Oculus VR headset produced in 2013. Other VR systems have been explored in
educational applications such as CAVE or semi-immersive virtual reality, but in this paper is
focused on head-mounted displays.
3.2
        </p>
      </sec>
      <sec id="sec-3-2">
        <title>Hardware</title>
        <p>Among current VR HMD we found an increasing number of devices in the market.
For this proposal study we have considered three critical characteristics to be present
in the device:
1. Inside-out tracking and 6 Degrees Of Freedom (6DOF). Yaw (Z), roll (Y) and nod
(X) in addition to head positioning in 3D space.
2. Standalone. Device can be used without being physically connected to a computer,
which enables better mobility for the user.
3. High resolution display. Providing good visual and refresh rate needed for planned
sessions with the experience.</p>
        <p>These guidelines suggest that Oculus Quest 2 device is currently one of the best
options available. Future development will consider these hardware characteristics to
adjust performance appropriately and produce enjoyable and reliable experience.
4</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>Related Work</title>
      <p>
        Considerable amount of research has been performed on games as learning
environments. Similar to the proposal presented in this paper, other researches found that the
level of engagement that videogames create has a positive effect on learning and
training purposes. Key factor for this benefit is the level of immersion and progression that
a game typically demonstrates. It challenges the players to continuously adapt and take
action to complete each level [
        <xref ref-type="bibr" rid="ref17">17</xref>
        ].
      </p>
      <p>
        Videogames are no longer considered a negative influence on educational growth,
in fact, it is now proven that games provide tools for encourage critical thought. This is
especially valuable when knowledge is abstract or depends on virtual representations,
such as science or technology. Serious games are presented as valid tool for teaching
problem-solving skills combining scientific contents with game mechanics linking
virtual reality with real world experiences, providing an experience that can be repeatedly
played and otherwise impossible to experiment [
        <xref ref-type="bibr" rid="ref18">18</xref>
        ].
      </p>
      <p>
        In relation to spatial abilities training, there are several proposals consisting on
providing immersive virtual reality games that allows users to locate in a simulated
scenario where different tasks are presented with different objectives. In Indy [
        <xref ref-type="bibr" rid="ref19">19</xref>
        ], a
collaborative treasure hunting trial is presented in an industrial facility environment.
These game offers the challenge of finding specific elements hidden by instructors as
to train professionals and familiarize with the industrial building structure. Not only
spatial orientation is target metrics in this experience but also foster communication
between workgroups in order to coordinate every player and achieve common goal.
      </p>
      <p>
        In the area of standardized tests, there are also gamification proposals such as [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ],
for improving spatial skills through MCT. It presents some gamification mechanics
applicable to a test-based application with scoreboards shared between users as to
compare and reward competitivity. Virtual reality environments are usually used as a tool
for digitalized standardized tests, good example can be PSVT:R in [
        <xref ref-type="bibr" rid="ref21">21</xref>
        ] and [
        <xref ref-type="bibr" rid="ref22">22</xref>
        ]. Some
applications refer to positive effects on spatial memory for retrieving key aspects of
certain elements located in the simulated space or Memory Palace, work from [
        <xref ref-type="bibr" rid="ref23">23</xref>
        ]
highlights this effect of using VR in contrast to traditional desktop application.
      </p>
      <p>
        Spatial Skills evaluation is mentioned one of the challenges that researchers usually
face in training courses, for this regard VR game Homeworld Bound: Redux is
presented as an experience that combines gathering and resource mechanics and building
strategies with spatial transformations for players abilities development [
        <xref ref-type="bibr" rid="ref24">24</xref>
        ]. From this
experience, promoting creative modes and avoid using simple 3D objects such as
symmetric or regular polyhedrons is recommended for challenges tasks that keeps the user
engaged for spatial problems solving.
      </p>
      <p>
        Another phenomenon studied in this field is embodied cognition in relation to spatial
intelligence. This involves physical interfaces combined with virtual simulations so the
user can physically interact with a mockup controller influencing or controlling
elements of the simulation. In [
        <xref ref-type="bibr" rid="ref25">25</xref>
        ], authors present a VR experience where embodied
cognition is the main mechanic for performing spatial puzzles, involving different
changeable first person perspectives to acknowledge position and scale of the model as to
improve spatial orientation.
      </p>
      <p>Interesting mechanics and gamified strategies are extracted to be evaluated as
possible elements of the experience to be developed in order to train and assess spatial
skills. From previous studies, it is acknowledged that main target is to consistently
provide an engaging experience, that enables data gathering for a pre-post test of a
experimental and control group.</p>
    </sec>
    <sec id="sec-5">
      <title>Serious Game for Spatial Skill Development</title>
      <p>
        For the proposed VR Spatial Skills Training experience, Unity game engine is
selected as a low learning curve software and it is already integrated with Extended
Reality Toolkit for Oculus platform. This package provides basic set of interactions for
virtual reality that can be modified to adjust development requirements. Since the aim
is to produce a Serious Game for training, game mechanics are present to motivate users
taking spatial exercises presented as levels, that will increase in difficulty. Not only
visual stimuli will be included, audio and haptic for controller-based experience are
considered to play key role in the game. Sound effects may indicate if correct action
was taken, the start and end of a timer countdown. Haptics, such as controller vibration,
will be used as to indicate boolean interactions such as grab or leave object, with light
vibration or once player navigate to an option from the main menu. It is important
showing players the reason behind a wrong choice, the system should tell correct
solution right after wrong answer is provided [
        <xref ref-type="bibr" rid="ref20">20</xref>
        ].
      </p>
      <p>A design principle related to spatial operations is that each task or beforementioned
standardized test (MRT, MCT, PSVT and combination of all three) will be presented
as a challenge with progression in the shape of unlockable levels. This sense of
progression will be presented through user interface through progression bars to show
students how many levels have been completed and remain to unlock next one. In this
regard difficulty will increase as player will face higher levels. At the end of every
level, scoreboards are presented to show player’s performance in comparison with
others, to promote competitivity and compare results for each task completed. In order to
ensure replayability, new game modes are to be introduced such as Time Trial, where
tasks are to be completed within a time limit and Treasure Hunt, where players have to
locate through limited spatial operations a key to the next level located inside a 3D
model.</p>
      <p>Duration of each level should not be superior to 5-10 minutes per player. This way,
mental exhaustion is avoided, which helps student’s expectation for next session as well
as to ensure experimental phase can be adapted to an undergraduate academic course.
For gains evaluation, results from playing the VR experience are to be logged in
network shared file so researcher directly exports to data sheet and prepare statistical
analysis.
6</p>
    </sec>
    <sec id="sec-6">
      <title>Future line of Research</title>
      <p>In the upcoming phase, the experience will be developed and tested for fine tuning
and usability matters. Then, start of the tests are planned for next academic course in
2022. The main goal is to start the measurements with different user groups.
Implementing real-time activities in VR game complemented with theory sessions in
engineering graphics course is expected to lead to better results in spatial tasks as well to
improve performance at higher level in students from the experimental group than in
control group. It is also interesting to perform Likert scale and usability questionnaires
for user feedback on improving experience’s immersion and usability for future
experimentation.
7</p>
    </sec>
    <sec id="sec-7">
      <title>Conclusions</title>
      <p>In this paper, relevance of spatial competences for higher education STEMs careers
is highlighted. Currently there is a need for training spatial skills in early years of
technical degrees as it is a required competence, is also an indicator for academic success
and may help reducing gender gap differences on performance and early abandon rates.</p>
      <p>
        A new VR Training game is presented as concept of an application whose goal is to
engage and motivate users who would like to improve their visual skills by completing
engaging exercises presented as levels, especially those with lower level of spatial
abilities [
        <xref ref-type="bibr" rid="ref26">26</xref>
        ].
8
      </p>
    </sec>
  </body>
  <back>
    <ref-list>
      <ref id="ref1">
        <mixed-citation>
          1.
          <string-name>
            <given-names>J.</given-names>
            <surname>Feng</surname>
          </string-name>
          ,
          <string-name>
            <surname>I. Spence</surname>
          </string-name>
          , and
          <string-name>
            <given-names>J.</given-names>
            <surname>Pratt</surname>
          </string-name>
          <article-title>: Playing an action video game reduces gender differences in spatial cognition</article-title>
          .
          <source>Psychological Science</source>
          , vol.
          <volume>18</volume>
          , no.
          <issue>10</issue>
          , pp.
          <fpage>850</fpage>
          -
          <lpage>855</lpage>
          , (
          <year>2007</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref2">
        <mixed-citation>
          2. C. Carbonell-Carrera,
          <string-name>
            <given-names>A. J.</given-names>
            <surname>Jaeger</surname>
          </string-name>
          ,
          <string-name>
            <given-names>J. L.</given-names>
            <surname>Saorín</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Melián</surname>
          </string-name>
          , and J.
          <string-name>
            <surname>de la</surname>
          </string-name>
          Torre-Cantero:
          <article-title>Minecraft as a block building approach for developing spatial skills</article-title>
          .
          <source>Entertainment Computing</source>
          , vol.
          <volume>38</volume>
          , no.
          <source>March</source>
          , (
          <year>2021</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref3">
        <mixed-citation>
          3.
          <string-name>
            <given-names>V. J.</given-names>
            <surname>Shute</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Ventura</surname>
          </string-name>
          , and
          <string-name>
            <given-names>F.</given-names>
            <surname>Ke</surname>
          </string-name>
          <article-title>: The power of play: The effects of Portal 2 and Lumosity on cognitive and noncognitive skills</article-title>
          .
          <source>Computers and Education</source>
          , vol.
          <volume>80</volume>
          , pp.
          <fpage>58</fpage>
          -
          <lpage>67</lpage>
          ,
          <year>2015</year>
        </mixed-citation>
      </ref>
      <ref id="ref4">
        <mixed-citation>
          4.
          <string-name>
            <surname>M.</surname>
          </string-name>
          <article-title>Romero: Serious Games para el desarrollo de las competencias del siglo XXI. RED</article-title>
          . Revista de Educación a Distancia, no.
          <issue>34</issue>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>22</lpage>
          , (
          <year>2012</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref5">
        <mixed-citation>
          5.
          <string-name>
            <given-names>J.</given-names>
            <surname>Wai</surname>
          </string-name>
          ,
          <string-name>
            <given-names>D.</given-names>
            <surname>Lubinski</surname>
          </string-name>
          , and
          <string-name>
            <given-names>C. P.</given-names>
            <surname>Benbow</surname>
          </string-name>
          <article-title>: Spatial Ability for STEM Domains: Aligning Over 50 Years of Cumulative Psychological Knowledge Solidifies Its Importance</article-title>
          .
          <source>J. Educ. Psychol.</source>
          , vol.
          <volume>101</volume>
          , no.
          <issue>4</issue>
          , pp.
          <fpage>817</fpage>
          -
          <lpage>835</lpage>
          , (
          <year>2009</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref6">
        <mixed-citation>
          6.
          <string-name>
            <surname>C.</surname>
          </string-name>
          <article-title>A. Lawton: Gender, Spatial Abilities, and Wayfinding</article-title>
          . in Handbook of Gender Research in Psychology, Chrisler, New York, NY: Springer New York, pp.
          <fpage>317</fpage>
          -
          <lpage>341</lpage>
          (
          <year>2010</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref7">
        <mixed-citation>
          7.
          <string-name>
            <given-names>H.</given-names>
            <surname>Gardner</surname>
          </string-name>
          , Estructuras de la mente. La Teoría de Las Inteligencias Múltiples. (
          <year>1994</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref8">
        <mixed-citation>
          8.
          <string-name>
            <surname>M. G.</surname>
          </string-name>
          <article-title>McGee: Human spatial abilities: Sources of sex differences</article-title>
          ,
          <source>Praeger</source>
          . (
          <year>1979</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref9">
        <mixed-citation>
          9.
          <string-name>
            <given-names>D. H.</given-names>
            <surname>Uttal</surname>
          </string-name>
          and
          <string-name>
            <given-names>C. A.</given-names>
            <surname>Cohen</surname>
          </string-name>
          <article-title>: Spatial Thinking and STEM Education</article-title>
          . When, Why, and How?, vol.
          <volume>57</volume>
          , no.
          <source>October</source>
          <year>2017</year>
          . (
          <year>2012</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref10">
        <mixed-citation>
          10.
          <string-name>
            <given-names>R.</given-names>
            <surname>Gorska</surname>
          </string-name>
          and
          <string-name>
            <surname>S.</surname>
          </string-name>
          <article-title>Sorby: Testing instruments for the assessment of 3-D spatial skills</article-title>
          .
          <source>ASEE Annu. Conf. Expo. Conf. Proc.</source>
          ,
          <string-name>
            <surname>June</surname>
          </string-name>
          (
          <year>2008</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref11">
        <mixed-citation>
          11.
          <string-name>
            <given-names>S. G.</given-names>
            <surname>Vanderberg</surname>
          </string-name>
          and
          <string-name>
            <given-names>A. R.</given-names>
            <surname>Kuse</surname>
          </string-name>
          <article-title>: Mental Rotations, a Group Test of Three-Dimensional Spatial Visualization</article-title>
          .
          <source>Percept. Mot. Skills</source>
          , vol.
          <volume>47</volume>
          , no.
          <issue>2</issue>
          (
          <year>1978</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref12">
        <mixed-citation>
          12. CEEB:
          <article-title>Special Aptitude Test in Spatial Relations (MCT)</article-title>
          .
          <article-title>(</article-title>
          <year>1939</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref13">
        <mixed-citation>
          13.
          <string-name>
            <surname>G. M. Bodner and R. B. Guay</surname>
          </string-name>
          :
          <article-title>The Purdue Visualization of Rotations Test</article-title>
          . Chem. Educ., vol.
          <volume>2</volume>
          , no.
          <issue>4</issue>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>17</lpage>
          , (
          <year>1997</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref14">
        <mixed-citation>
          14. W. S. Alhalabi:
          <article-title>Virtual reality systems enhance students' achievements in engineering education</article-title>
          .
          <source>Behav</source>
          . Inf. Technol., vol.
          <volume>35</volume>
          , no.
          <issue>11</issue>
          , pp.
          <fpage>919</fpage>
          -
          <lpage>925</lpage>
          , (
          <year>2016</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref15">
        <mixed-citation>
          15.
          <string-name>
            <given-names>I. E.</given-names>
            <surname>Sutherland</surname>
          </string-name>
          :
          <article-title>A head-mounted three dimensional display</article-title>
          .
          <source>in AFIPS '68 - Proceedings of the Fall Joint Computer Conference</source>
          , vol.
          <volume>1</volume>
          , pp.
          <fpage>757</fpage>
          -
          <lpage>764</lpage>
          (
          <year>1968</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref16">
        <mixed-citation>
          16. T. G. Zimmerman,
          <string-name>
            <given-names>J.</given-names>
            <surname>Lanier</surname>
          </string-name>
          ,
          <string-name>
            <given-names>C.</given-names>
            <surname>Blanchard</surname>
          </string-name>
          ,
          <string-name>
            <given-names>S.</given-names>
            <surname>Bryson</surname>
          </string-name>
          , and
          <string-name>
            <given-names>Y.</given-names>
            <surname>Harvill</surname>
          </string-name>
          <article-title>: Hand Gesture Interface Device</article-title>
          .
          <source>Proc. - Graph. Interface</source>
          , pp.
          <fpage>189</fpage>
          -
          <lpage>192</lpage>
          , (
          <year>1987</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref17">
        <mixed-citation>
          17.
          <string-name>
            <surname>J. Hamari</surname>
            ,
            <given-names>D. J.</given-names>
          </string-name>
          <string-name>
            <surname>Shernoff</surname>
            ,
            <given-names>E.</given-names>
          </string-name>
          <string-name>
            <surname>Rowe</surname>
            ,
            <given-names>B.</given-names>
          </string-name>
          <string-name>
            <surname>Coller</surname>
            ,
            <given-names>J.</given-names>
          </string-name>
          <string-name>
            <surname>Asbell-Clarke</surname>
          </string-name>
          , and T. Edwards:
          <article-title>Challenging games help students learn: An empirical study on engagement, flow and immersion in gamebased learning</article-title>
          .
          <source>Comput. Human Behav</source>
          ., vol.
          <volume>54</volume>
          , pp.
          <fpage>170</fpage>
          -
          <lpage>179</lpage>
          , (
          <year>2016</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref18">
        <mixed-citation>
          18. M. T. Cheng, H. C. She, and
          <string-name>
            <given-names>L. A.</given-names>
            <surname>Annetta</surname>
          </string-name>
          <article-title>: Game immersion experience: Its hierarchical structure and impact on game-based science learning</article-title>
          .
          <source>J. Comput. Assist. Learn.</source>
          , vol.
          <volume>31</volume>
          , no.
          <issue>3</issue>
          , pp.
          <fpage>232</fpage>
          -
          <lpage>253</lpage>
          , (
          <year>2015</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref19">
        <mixed-citation>
          19.
          <string-name>
            <given-names>A.</given-names>
            <surname>Mas</surname>
          </string-name>
          ,
          <string-name>
            <surname>I. Ismael</surname>
          </string-name>
          , and
          <string-name>
            <surname>N.</surname>
          </string-name>
          <article-title>Filliard: Indy: A virtual reality multi-player game for navigation skills training</article-title>
          .
          <source>2018 IEEE 4th VR Int. Work. 3D Collab. Virtual Environ. 3DCVE</source>
          <year>2018</year>
          , no.
          <source>March</source>
          , pp.
          <fpage>1</fpage>
          -
          <lpage>4</lpage>
          , (
          <year>2019</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref20">
        <mixed-citation>
          20.
          <string-name>
            <given-names>R.</given-names>
            <surname>Toth</surname>
          </string-name>
          ,
          <string-name>
            <given-names>M.</given-names>
            <surname>Zichar</surname>
          </string-name>
          , and
          <string-name>
            <surname>M.</surname>
          </string-name>
          <article-title>Hoffmann: Gamified mental cutting test for enhancing spatial skills</article-title>
          .
          <source>11th IEEE Int. Conf. Cogn. Infocommunications, CogInfoCom 2020 - Proc.</source>
          , pp.
          <fpage>299</fpage>
          -
          <lpage>304</lpage>
          , (
          <year>2020</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref21">
        <mixed-citation>
          21.
          <string-name>
            <surname>D. F. Ali</surname>
            ,
            <given-names>M.</given-names>
          </string-name>
          <string-name>
            <surname>Omar</surname>
            ,
            <given-names>M.</given-names>
          </string-name>
          <string-name>
            <surname>Mokhtar</surname>
          </string-name>
          ,
          <article-title>and</article-title>
          <string-name>
            <surname>A. N. M.</surname>
          </string-name>
          <article-title>Nasir: Application of virtual learning in the teaching of engineering drawing to enhance students' mental rotation skills</article-title>
          .
          <source>Proc. 1st Int. Conf. Innov. Sci. Technol</source>
          .
          <source>(IICIST</source>
          <year>2015</year>
          ), vol.
          <volume>1</volume>
          , no.
          <source>January</source>
          , pp.
          <fpage>469</fpage>
          -
          <lpage>472</lpage>
          , (
          <year>2015</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref22">
        <mixed-citation>
          22. T. Guzsvinecz, É.
          <string-name>
            <surname>Orbán-Mihálykó</surname>
            ,
            <given-names>E.</given-names>
          </string-name>
          <string-name>
            <surname>Perge</surname>
            , and
            <given-names>C.</given-names>
          </string-name>
          <article-title>Sik-Lányi: Analyzing the spatial skills of university students with a virtual reality application using a desktop display and the gear VR</article-title>
          .
          <source>Acta Polytech. Hungarica</source>
          , vol.
          <volume>17</volume>
          , no.
          <issue>2</issue>
          , pp.
          <fpage>35</fpage>
          -
          <lpage>56</lpage>
          , (
          <year>2020</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref23">
        <mixed-citation>
          23. B. Berki:
          <article-title>Better Memory Performance for Images in MaxWhere 3D VR Space than in Website</article-title>
          .
          <source>9th IEEE Int. Conf. Cogn. Infocommunications, CogInfoCom 2018 - Proc., no. CogInfoCom</source>
          , pp.
          <fpage>281</fpage>
          -
          <lpage>284</lpage>
          , (
          <year>2018</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref24">
        <mixed-citation>
          24. H.
          <string-name>
            <surname>Wauck</surname>
            ,
            <given-names>B. S.</given-names>
          </string-name>
          <string-name>
            <surname>Woodard</surname>
            ,
            <given-names>Z.</given-names>
          </string-name>
          <string-name>
            <surname>Xiao</surname>
            ,
            <given-names>T. W.</given-names>
          </string-name>
          <string-name>
            <surname>Li</surname>
            , and
            <given-names>B. P.</given-names>
          </string-name>
          <string-name>
            <surname>Bailey</surname>
          </string-name>
          :
          <article-title>A Data-Driven, PlayerCentric Approach to Evaluating Spatial Skill Training Games</article-title>
          .
          <source>CHI Play 2020 - Proc. Annu. Symp. Comput. Interact. Play</source>
          , pp.
          <fpage>349</fpage>
          -
          <lpage>361</lpage>
          , (
          <year>2020</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref25">
        <mixed-citation>
          25.
          <string-name>
            <surname>J. S. K. Chang</surname>
          </string-name>
          et al.:
          <article-title>Evaluating the effect of tangible virtual reality on spatial perspective taking ability</article-title>
          .
          <source>SUI 2017 - Proc</source>
          .
          <year>2017</year>
          Symp. Spat. User Interact., pp.
          <fpage>68</fpage>
          -
          <lpage>77</lpage>
          , (
          <year>2017</year>
          )
        </mixed-citation>
      </ref>
      <ref id="ref26">
        <mixed-citation>
          26.
          <string-name>
            <surname>H. C. Wauck</surname>
            ,
            <given-names>E. D.</given-names>
          </string-name>
          <string-name>
            <surname>Mekler</surname>
          </string-name>
          , and W.-T. Fu:
          <article-title>A Player-Centric Approach to Designing Spatial Skill Training Games</article-title>
          .
          <source>In Proceedings of the 2019 CHI Conference on Human Factors in Computing Systems</source>
          , New York, NY, USA: Association for Computing Machinery, pp.
          <fpage>1</fpage>
          -
          <lpage>13</lpage>
          (
          <year>2019</year>
          )
        </mixed-citation>
      </ref>
    </ref-list>
  </back>
</article>