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Improving Game Experiences
CHI 2015, Crossings, Seoul, Korea
Exploring 3D User Interface Technologies For Improving
The Gaming Experience
Arun Kulshreshth
Department of EECS
University of Central Florida
4000 Central Florida Blvd
Orlando, FL 32816, USA
arunkul@knights.ucf.edu
Joseph J. LaViola Jr.
Department of EECS
University of Central Florida
4000 Central Florida Blvd
Orlando FL 32816, USA
jjl@eecs.ucf.edu
ABSTRACT
We present the results of a comprehensive video game study
which explores how the gaming experience is effected when
several 3D user interface technologies are used simultaneously. We custom designed an air-combat game integrating
several 3DUI technologies (stereoscopic 3D, head tracking,
and finger-count gestures) and studied the combined effect
of these technologies on the gaming experience. Our game
design was based on existing design principles for optimizing the usage of these technologies in isolation. Additionally,
to enhance depth perception and minimize visual discomfort,
the game dynamically optimizes stereoscopic 3D parameters
(convergence and separation) based on the user’s look direction. We conducted a within subjects experiment where we
examined performance data and self-reported data on users
perception of the game. Our results indicate that participants
performed significantly better when all the 3DUI technologies (stereoscopic 3D, head-tracking and finger-count gestures) were available simultaneously with head tracking as
a dominant factor. We explore the individual contribution of
each of these technologies to the overall gaming experience
and discuss the reasons behind our findings.
Figure 1. A user playing the air-combat game we designed. The game
effectively uses stereoscopic 3D, head tracking and finger-count gestures.
tial to improve game performance and the gaming experience.
Such interfaces allow users to use natural motion and gestures
to control the game thereby making the whole gaming experience more immersive and engaging. In the past, researchers
[9, 10, 11, 18, 19] have studied the benefits of these technologies (e.g. stereoscopic 3D, head tracking, gesture based
control, etc.) for video games. But, most of the past work
have been focused on these technologies in isolation and it is
still unknown how the gaming experience will be affected if
several 3DUI technologies are used simultaneously. By designing a game which integrates several 3DUI technologies,
we hope to understand the interplay between the technologies
and its effect on the gaming experience.
Author Keywords
Air-combat game; Finger-Count; Stereoscopic 3D; Head
tracking; User Study; Video Games; Game Design;
Game-play metrics; Player Behavior; User Experience.
Stereoscopic 3D and head tracking are two core technologies for 3DUI applications. Stereoscopic 3D [11, 18, 19] and
head tracking [10, 21, 22], in isolation, have been shown to
provide a better gaming experience along with performance
benefits for some games. Based on these findings, we chose
to use stereoscopic 3D and head tracking for our game design. We chose to design an air-combat game since it had
tasks (e.g. judge the distance of an enemy, find enemy, etc.)
which could benefit from the availability of stereoscopic 3D
and head tracking usage. Furthermore, to enhance depth perception and minimize visual discomfort, our game dynamically adjusts the stereoscopic 3D parameters (convergence
and separation), based on the user’s look direction.
ACM Classification Keywords
H.5.m Information Interfaces and Presentation (e.g. HCI):
Miscellaneous.; K.8.0 Personal Computing: Games
General Terms
Design, Experimentation, Measurement, Performance,
Human Factors.
INTRODUCTION
3D user interface technologies [4] (e.g., stereoscopic 3D,
head tracking, gesture based control, etc.) have the potenPermission to make digital or hard copies of all or part of this work for personal or
classroom use is granted without fee provided that copies are not made or distributed
for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than
ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission
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CHI 2015, April 18 – 23, 2015, Seoul, Republic of Korea
c 2015 ACM 978-1-4503-3145-6/15/04…$15.00
Copyright
http://dx.doi.org/10.1145/2702123.2702138
Additionally, we wanted to include a 3DUI input mechanism
in our game to create a more inclusive 3D user interface experience and chose a gesture-based interface. Initially, we
experimented with several motion sensing devices (e.g. Leap
Motion, Microsoft Kinect, etc.) but these devices failed for
our purposes for two reasons. First, the gestures recognition
125
Improving Game Experiences
CHI 2015, Crossings, Seoul, Korea
accuracy of these devices was not good enough for precisely
controlling the aircraft in our game. Second, users needed to
continuously control the airplane causing fatigue during our
pilot testing sessions (lasting for about 100 minutes). These
factors hindered the overall gameplay experience. However,
finger-count gestures [9] are well studied in the past and have
higher recognition accuracy as well as being easy to use and
fast to perform. These gestures could potentially be used as
shortcuts in video games. The finger count gestures were well
suited for longer use since the user is not using them continuously while playing the game. Therefore, we used these gestures as an alternate to using buttons for switching weapons.
We refer to them as finger-count shortcuts.
viewing experience and still enhance stereo depth perception
whenever possible.
Wang et al. [24] used face tracking for head gesture recognition. Their evaluation, based on simple game prototypes
they developed, showed that the test participants experienced
a greater sense of presence and satisfaction with their head
tracking technique. However, no performance benefits were
found compared to a button based head control. Yim et al.
[26] developed a head tracking solution using Wiimotes and
their preliminary results show that users perceived head tracking as a more enjoyable and intuitive gaming experience. Sko
et al. [21] explored head tracking for first person shooter
games. Their study showed that head tracking could be useful for games which are designed with head tracking usage
in mind. Kulshreshth et al. [10] explored head tracking for a
variety of games and found it to be useful for a few games depending upon the game type and the gaming experience of the
participants. However, they used commercial games for their
experiment and some of their games may not have been designed with head tracking usage in mind, possibly explaining
why they did not find performance benefits in all the games
they tested.
In this paper, we designed an air combat game (see Figure
1) and conducted a within subjects experiment to evaluate
the effectiveness of simultaneous use of these technologies
(stereoscopic 3D, head tracking and finger-count shortcuts).
We examined the performance data (enemies killed & survival time), head tracking usage data, and self-reported data
on user’s perception of the game.
RELATED WORK
For optimal head tracking usage in a game some design
guidelines have been proposed [10, 22] which includes proper
training for head tracking usage, avoiding awkward head
movements, non-isomorphic head rotations with different
scaling along different directions, natural movements for
tasks and proper calibration of head tracking device. For our
air-combat game, we made use of all these design principles
to optimize head tracking usage.
Stereoscopic 3D has been found useful for games depending
upon the game task involved. Stereoscopic 3D has also been
found to be helpful in playing simple games where a user is
manipulating a single object at a time [6]. Rajae et al. [16]
showed that presence of stereoscopic 3D did not help people
perform better in a shooter game but people experienced a
stronger feeling of presence in stereoscopic 3D mode. Other
researchers [13, 18, 19] have also confirmed increased engagement and preference for stereoscopic 3D games.
Barfield et al. [3] studied the effects of stereoscopic 3D and
head tracking on a wire-tracing task. Their results indicated
that the task time was the same irrespective of display conditions (monoscopic vs stereoscopic 3D) when head tracking was present. People performed best with stereoscopic 3D
when head tracking was absent. McMahan et al. [14] explored the interplay between display fidelity and interaction
fidelity. Their results showed that the performance was best
with low-display low-interaction fidelity and high-display
and high-interaction fidelity. Another experiment involving
a spatial judgment task [15] showed that the participants performed better with head-tracking and best performance was
achieved when both stereoscopic 3D and head tracking was
present. The worst score was achieved with a combination of
monoscopic display and no head tracking. However, none of
these researchers used complex video games for their experiments.
Creating graphical user interfaces (GUI) for stereoscopic 3D
games is a difficult choice between visual comfort and effect. Schild et al. [17] explored GUI design space for a
stereoscopic 3D game in order to design comfortable game
GUIs (e.g., menus and icons). Their results showed that ingame menus look best when displayed at the bottom of screen
with a semi-transparent background. For referencing objects,
they found that it is best to show the referencing information at the same depth as the object itself. Deepress3D is a
flight game [18] which was custom designed keeping stereoscopic 3D viewing in mind. Their game design featured a
stereoscopic specific GUI based on [17] , no real depth illusions in graphics, and optimal parallax budget for stereoscopic viewing. Their results show that the users experienced
an enhanced sense of presence in the stereoscopic 3D viewing
environment.
Finger-Count menus were first proposed for multi-touch surfaces [1] and were later adapted for distant displays [2], using
the Kinect as the gestural input device. But, the Kinect based
implementation was slow for practical use. Another implementation [9] improved the selection time of this technique
by using a faster finger recognition algorithm resulting in an
average selection time of under a second. Their study showed
that Finger-Count shortcuts have a high accuracy and are layout independent. Finger-Count gestures could also be used as
shortcuts in video games. Our game these finger-count shortcuts for switching between weapons.
Stereoscopic 3D benefits can only be expected if the stereoscopic vision is not accompanied by distortions (e.g., contradicting depth cues, ghosting/cross-talk, exaggerated disparity) [27]. While stereoscopic 3D has shown some positive
benefits depending on the task, it also has shown to cause negative symptoms as well, such as eyestrain, headache, dizziness, and nausea [8]. Ware [25] proposed dynamic adjustment of stereoscopic parameters to minimize visual discomfort and optimize stereo depth. Our game design also dynamically adjusts stereoscopic 3D parameters (convergence and
separation), based on user’s look direction, for a comfortable
126
Improving Game Experiences
CHI 2015, Crossings, Seoul, Korea
Figure 2. Air-combat game screenshot
Figure 3. Joystick Controls for the air-combat game
None of the work mentioned above evaluated the affects of
using several 3DUI technologies together in complex gaming
environments like in modern video games. To the best of our
knowledge, our work is the first to systematically explore the
combined affect of several 3DUI technologies in a custom
designed game with several design optimizations specific to
each technique.
implementing finger-count shortcuts, we used the Intel’s perceptual computing SDK.
Stereoscopic 3D features
Dynamic Stereo. Currently, most stereoscopic 3D games fix
convergence and separation values for optimal depth budget
throughout the game. But, this approach reduces stereo depth
when a large object (e.g. gun in FPS games, cockpit in aircombat, etc.) is present in front of the game camera. The reason being the fact that stereo parameters have to be optimized
to keep that large object always in focus. However, when the
player’s head is rotated, that nearby object is not in the players
view and stereo depth could be increased. In case of our aircombat game, we optimized stereo parameters under two conditions. First, when the user is looking sideways (left/right)
and second, when the user is zoomed into the scene. In both
these cases, the user is not looking at the cockpit in front.
When the player’s head is rotated sideways (left/right), the
separation is increased with linear scaling proportional to the
heads rotation and the convergence is not changed. When a
user zooms in the scene the field of view (FOV) of the camera is reduced proportional to the head’s displacement. Thus,
in case of zooming, the separation is increased with linear
scaling proportional to the camera’s FOV. At the same time,
the convergence is linearly decreased with the camera’s FOV
to keep both the crosshair and background in focus. These
dynamic parameters ensured a comfortable stereoscopic 3D
experience and provided better depth perception for this aircombat game.
DESIGN FACTORS
As mentioned in the introduction, we chose to design an aircombat game since it had tasks which could benefit from
availability of stereoscopic 3D, head tracking usage, and
finger-count gestures. Furthermore, an air-combat game
scene has a lot of depth and using stereoscopic 3D would
make the game more immersive. The design of this game
includes several optimizations, based on past work, specific
to stereoscopic 3D [11, 17, 18, 20] and head tracking [10, 21,
22].
Air-Combat Game
The player has to control an aircraft , using the Logitech extreme 3D Pro joystick, in first person view and shoot enemies
(see Figure 2 for a screenshot of the game). The game has five
different kind of enemies, each marked with a different color,
and five different kind of weapons. The color of the crosshair
indicates the color of the currently selected weapon. Each
enemy can be killed only with a weapon of the same color
and thus requires a user to frequently switch weapons while
playing the game. A radar is also available which shows 2D
positions of the enemies around the aircraft. To be consistent with the color scheme, the radar uses the same color as
the enemy to display its position. The game also featured 3D
sound effects for aircraft, weapons and explosions (when enemies are shot dead). An enemy could also be locked (except
for yellow and green enemies) by holding the crosshair over
it for a short period of time (about two seconds).
Stereoscopic 3D Specific GUI Elements. Based on [17], we
optimized our game GUI for stereoscopic 3D usage. All the
2D GUI elements (timer, game stats, etc.) were rendered
at screen depth to allow them to be in focus throughout the
game. The radar was displayed at the bottom of the screen
and was also rendered at screen depth. The chart displaying the correspondence between finger-count gestures and
weapon colors was a 3D object rendered at the same depth as
the aircraft to be visible all the time without being occluded
by other 3D objects in the scene.
The head of the player can be controlled either by using head
tracking (a TrackIR 5 device was used) or a combination of
the hat switch and buttons on the joystick (see Figure 3). To
switch weapons one can use finger-count shortcuts or buttons on the joystick (one button is assigned for each weapon).
To avoid any confusion each button is clearly marked with a
color on the joystick. In case of finger-count shortcuts, a chart
was displayed at the top of the screen indicating the correspondence between finger-count gestures and weapon colors.
The game was implemented using the Unity3D game engine
and the Air Strike Starter Kit from the Unity Asset Store. For
Optimal Depth Cues. The game minimized the impact of
monocular depth cues. All the enemy ships were colored instead of textured. No dynamic light sources were used and
shadows (a known depth cue) were disabled.
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Improving Game Experiences
CHI 2015, Crossings, Seoul, Korea
distance from display. In the past, non-isomorphic rotations
seem to have helped in rotation tasks [12] when head tracking is present. We used non-isomorphic rotation scaling for
left and right rotations to allow users to see more area on both
sides of the plane without rotating his head too much. We
thought this would help them quickly scan a large area of the
game environment for finding potential enemies.
Disable Post-processing Image Effects.
Some postprocessing image effects (e.g. halo effect for lights) do not
work well with stereoscopic 3D rendering since these effects
are rendered only for one eye making it uncomfortable to look
at. Hence, we did not use any post-processing image effects
for our game.
Minimized 3D Glasses Flicker. Excessive motion in front of
the display may sometime cause the 3D glasses to flicker due
to loss of sync signal [11]. In our case head tracking was
used only for head rotations & zooming and all other motions were restricted. In case of head rotation, the head position does not change and the head rotation is also limited
(about 40 degrees each side). When a user zooms in, the head
moves towards the Nvidia IR emitter. Thus, in both these
cases the head motion is minimal and does not interfere with
3D sync signal loss. Furthermore, we noticed that Nvidia 3D
vision 2 glasses were flickering when used together with the
Creative Senzeye3D depth camera (used for detecting fingercount gestures). We suspect that there was some interference
between IR blaster inside the camera and the 3D sync signal from Nvidia IR emitter causing the glasses to loose sync
signal. However, older Nvidia 3D vision glasses worked fine
without any flickering issues. Hence, we used older Nvidia
3D vision glasses instead of newer 3D vision 2 glasses for
our experiments.
Why Five Enemies and Five Weapons?
As part of our experiment, we wanted to evaluate the performance of finger-count shortcuts, as a fast way to switch
weapons, compared to buttons. Since the user were using one
hand to control the plane, only one hand was available for
finger-count gestures. This limits the number of finger-count
gestures to five. This motivated us to keep five different kind
of enemies. Moreover, we wanted people to use these gestures frequently throughout the game play session. Thus, we
designed five different kind of weapons and added a restriction that each enemy can be killed only by a specific weapon.
USER EVALUATIONS
We conducted an experiment with our air-combat game to
evaluate the combined effect of stereoscopic 3D, head tracking, and finger-count shortcuts on the gaming experience.
Additionally, we also looked at the effects of individual technologies to be able to understand their contribution to the
overall gaming experience. Based on previous findings in related work and our analysis of the game, we have the following hypotheses:
Head Tracking Features
Natural Head Movements. People are used to rotating their
head for looking around. We mapped head tracking to use
these natural movements for looking through the sides of the
plane and zooming in. Thus, it is very easy to understand the
head tracking usage for our air-combat game.
Hypothesis 1 (H1) : The combined usage of stereoscopic
3D, head tracking and finger-count shortcuts im …
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