Virtual Reality System for Rehabilitation of Children
with Cerebral Palsy: A Preliminary Study
Pierre Michel
1
, Paul Richard
1
, Takehiko Yamaguchi
2
, Adrien Verhulst
3
,
Eulalie Verhulst
1
and Micka
¨
el Dinomais
1
1
Laboratoire Angevin de Recherche en Ing
´
enierie des Syst
`
emes (LARIS), Universit
´
e d’Angers, Angers, France
2
Faculty of Industrial Science & Technology, Tokyo University of Science, Tokyo, Japan
3
CRENAU UMR CNRS 1563, Universit
´
e de Nantes, Nantes, France
Keywords:
Virtual Reality, Adaptive Game, Rehabilitation, Children, Cerebral Palsy.
Abstract:
We present a non-immersive virtual reality (VR) system for the rehabilitation of children with Cerebral Palsy
(CP). Our objective is to encourage and motivate children to improve their limb motor control while playing
a game. Two tasks are available: (1) intercepting or (2) catching / releasing moving objects using a Kinect
T M
sensor. These tasks are achieved via the control of a virtual character placed in a virtual island. A control-
display ratio is used to virtually increase the child workspace allowing him/her to intercept moving objects
from any direction. In addition, a dynamic difficulty adjustment (DDA) is used to keep a good motivation
level. Furthermore, virtual coach is provided to support and congratulate the children. Twenty healthy children
participated in a preliminary experiment. The aim was (1) to collect control data concerning performance and
workload, and (2) to investigate the effect of the virtual coach. Results show a good usability of the game and
reveal a high ratio of acceptance and enjoyment from the children.
1 INTRODUCTION
Cerebral palsy (CP) is a term that refers to various
motor impairments caused by damage to the central
nervous system during foetal development. Tradi-
tional CP therapies are often of little interest to a
child, affecting his motivation to continue therapeu-
tic activities (Schmidt and Lee, 2005). For example,
Constraint-induced movement therapy (CIMT), often
used to improve upper limb function encourages the
use of the affected hand by restricting the unaffected
hand and asking for intensive movement with the im-
paired upper limb (Hoare et al., 2007). Having the
good arm blocked for long periods of time can gener-
ate frustration and might not be applicable in a long-
term rehabilitation program.
More child-friendly approaches are needed dur-
ing the neuro-development of children with CP. For
example, rehabilitation programs should offer thera-
peutic games that are specifically designed to encour-
age the child to use their affected limb and even both
arms in coordination. The proposed games should be
easy to use and non-intrusive in order to affect chil-
dren movements.
The paper is organized as follows: the next sec-
tion provides a survey of the related work concerning
interactive motor rehabilitation systems and adaptive
games. Section 3 presents an overview of our sys-
tem and its innovative characteristics. In Section 4,
we describe our approach for the auto-adaptation of
the system. Section 5 is dedicated to the experimen-
tal study. Section 6 concludes the paper and discuss
directions for future work.
2 RELATED WORKS
2.1 Rehabilitation Systems
Virtual reality (VR) or Virtual Environments (VEs)
may be described as multi-sensory, interactive and
immersive computer-based 3D environments that
could be used to simulate some aspects of the real
world. VR is now recognized as a powerful tool for
the assessment and rehabilitation of both motor and
cognitive impairments and provides a unique medium
for the achievement of several requirements of ef-
fective rehabilitation: controlled conditions, repeti-
tive practice and feedback about performance (Riva,
306
Michel, P., Richard, P., Yamaguchi, T., Verhulst, A., Verhulst, E. and Dinomais, M.
Virtual Reality System for Rehabilitation of Children with Cerebral Palsy: A Preliminary Study.
DOI: 10.5220/0005720503040311
In Proceedings of the 11th Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications (VISIGRAPP 2016) - Volume 1: GRAPP, pages 306-313
ISBN: 978-989-758-175-5
Copyright
c
2016 by SCITEPRESS Science and Technology Publications, Lda. All rights reserved
2003; Burdea, 2003; Gaggioli et al., 2009; Halton,
2008; Raspelli et al., 2012; Cipresso et al., 2012;
Pallavicini et al., 2013). In addition, VR offers
boundless variations of augmented feedback, objects,
and allow the users immersion in attractive environ-
ments (Cikajlo et al., 2010; Berger-Vachon, 2006) so
that VR remains motivating and entertaining (Rand
et al., 2009).
Few virtual rehabilitation systems have been de-
veloped for motor rehabilitation using full-body in-
teraction. For example, Kizony et al., (Kizony et al.,
2003) proposed IREX, based on a video-capture sys-
tem. A single camera is used for vision-based track-
ing to capture the users movements. The captured
video images can be displayed on a connected TV
screen, corresponding in real time to his movements.
Its suitability has been investigated for use during mo-
tor or cognitive rehabilitation (Rand et al., 2004). The
Cybex Trazer
T M
employs a single infra-red beacon
which is mounted on a belt worn around the waist of
the user. The user’s motion is captured by monitor-
ing the sensor’s position by the tracker bar (Fitzgerald
et al., 2007). The EyeToy
T M
game uses a single cam-
era to capture the users movements. Interaction with
an on-screen user avatar can only track movements in
a single plane and is not able to record body move-
ments (Fitzgerald et al., 2007). For a review, a review
see Adamovich et al., (Adamovich et al., 2009).
Some research used others interaction techniques
to rise the motivation of children with CP in their mo-
tor rehabilitation exercises. For example using VR
devices with Wii
T M
or with Kinect
T M
, the children
showed improvement in the motor rehabilitation with
VR devices (Sharan et al., 2012; Deutsch et al., 2008;
Ortiz-Gutirrez et al., 2013; Chang et al., 2013). In-
deed Chang, Han and Tsai (2013) asked two teenagers
to move their arms in front of a screen. When they
made correct movement a song was broadcast and a
cartoon character was displayed. In our study, to sup-
port children’s motivation, we propose to use a virtual
coach and found the rehabilitation process on a play-
ful approach.
2.2 Adaptive Games
Dynamic Difficulty Adaptation (DDA), also known
as Dynamic Game Balancing (DGB), is the process
of automatically changing parameters, scenarios, and
behaviours in a video game in real-time, based on
the player’s ability, in order to avoid them becoming
bored (if the game is too easy) or frustrated (if it is too
hard) (Huang et al., 2010). In recent years, studies
have used different approaches to handle DDA. For
example, Parnandi et al., (Parnandi et al., 2013) pro-
posed an approach based on control theory’s princi-
ples. They used variation of actual and desired arousal
of the user as the variation error to minimize. They
conducted an experiment on 20 subjects through a
Car-racing application. Hocine and Goua
¨
ıch (Hocine
and Goua
¨
ıch, 2011), described an approach based on
prior assessments of the capability of the user. The
adaptation is done through an ability zone, which con-
tains information on the difficulty to do a given task
at given position. They conducted an experiment on 8
subjects through a reaching-task application.
Goua
¨
ıch et al., (Goua
¨
ıch et al., 2012) proposed
a digital pheromone approach based on the ant al-
gorithm introduced by (Dorigo and St
¨
utzle, 2004).
The adaptation is done through an ability zone up-
dated regarding users performance. They conducted
an experiment on 10 subjects through a reaching-task
application. Arulraj et al., (Arulraj, 2010) proposed
a differential learning approach for NPC. The agent
learning-rate reduces with time, while being impacted
by users performance. The approach feasibility has
been tested using the Minigate game. Andrade (An-
drade and Ramalho, 2005) and Tan (Tan et al., 2011)
both proposed a Reinforcement Learning (RL) ap-
proach for NPC. Andrade implemented it by using
the Q-learning algorithm, the adaptation being done
by choosing the action-value which fit the level of
the user. The approach feasibility has been tested
using a fighting application. Tan implemented it by
using Adaptive Uni-Chromosome Controller (AUC)
and Adaptive Duo-Chromosome Controller (ADC)
algorithms, the adaptation is being done by activating
controller’s behaviour which fit the level of the user.
Figure 1: Screen shot of the rehabilitation game.
3 SYSTEM DESCRIPTION
The goal of our research is to develop an innovative
interactive virtual rehabilitation system which enables
children with CP to play while improving their motor
Virtual Reality System for Rehabilitation of Children with Cerebral Palsy: A Preliminary Study
307
(a)
(b)
(c)
Figure 2: Interaction techniques : (a) using the game-pad
only, (b) using the game-pad and the TrackIR
T M
, (c) and
(d) using the kinect
T M
and the TrackIR
T M
.
control of the limb. This requires the use of a non-
intrusive motion capture device such as the Microsoft
Kinect
T M
and the possibility to increase the children
workspace allowing him/her to reach and intercept
any moving objects. The proposed approach enables
a modifiable control-display ratio together with dy-
namic difficulty adjustment (DDA) capabilities used
to keep children motivation.
The game takes place in a virtual island. Figure 1
shows a screenshot of the rehabilitation game. The
avatar is controlled (arms only) in real-time by the
child facing the visual display. The goal is to animate
the avatar in order to intercept, or catch and release
the virtual objects. A Kinect
T M
sensor is used to get
the 3D motion data from the child’s arms.
The user may intercept or catch and release the
virtual objects
1
using virtual hands
2
. While the
virtual character’ arms are moving is 3D space, both
the virtual hands and the approaching objects are con-
strained in a vertical plane. Thus, the subject does
not have to manage the depth. In addition, as previ-
ously mentioned, to allow the children with motor dis-
ability to perform the task, a control-display ratio has
been implemented (amplification of movements). An
important aspect is that a control/display ratio (less
than 1/1) could be used to encourage the children with
CP not to use his/her ”good” hand, but rather his/her
paretic hand.
In order to keep the children motivation to play the
game and keep exercising, we constantly display the
score
3
on the upper right corner of the screen. At
the bottom of the screen, a scroll bar is displayed to
inform the children about the current difficulty level
of the game.
The system proposes different menus to set-up the
game parameters. The first menu, illustrated in Fig-
ure 2 (a), allows to set the value of the control/display
ratio for both the right and the left hands
1
. We could
also set-up the affine transform parameters
2
. Then,
we could select different avatars (boy, girl, animated
or not). We can display a circle around the avatar to
illustrate the hands movement constraint and also set
and display the collision area (on both hands) used for
intercepting the objects
4
. Finally, we can save the
parameters and load any set-up
5
.
The second menu, illustrated in Figure 2 (b), is
mainly used to select the task
1
: intercept or catch
and release, and select with which hand
2
the child
have to use to perform the task (right hand, left hand,
any of them, or with both hands joined). We can also
set the task’s parameters
3
such the size, velocity, or
frequency of occurrence (spawn interval) of the ob-
jects (Figure 5).
The third menu, illustrated in Figure 2 (c), is used
GRAPP 2016 - International Conference on Computer Graphics Theory and Applications
308
to select the set of objects that will have to be caught
1
. Is this menu, we can also choose a level of dis-
traction
2
, ranging from a static white background
to a fully dynamic virtual island including moving ob-
jects and sounds. This menu also allows to set the way
(manually or automatically) the difficulty level
3
will
be changed and the way the task will be displaced in
the island after each session
4
. In addition the system
allows to set the area from which the moving objects
will approach the avatar. For example, in the Figure 3,
the main direction (red line) can be tuned to a given
angle. In addition, a range (width) around this main
direction can be tuned manually on the circle around
the avatar.
Figure 3: Setting the area for the approaching objects.
3.1 Control/Display Ratio
The Control/Display (C/D) ratio is the ratio between
the amplitude of movement of the user’s real arm
and the amplitude of movements of the virtual cur-
sor (Dominjon et al., 2005). The C/D ratio may be
used to increase the user’s physical workspace allow-
ing him/her to move in a larger workspace. Since pa-
tients with impaired motor functions have a limited
(hopefully increasing) ranges of movement, a C/D ra-
tio may help them to perform task as the people with-
out any impairment.
3.2 Dynamic Difficulty Adaptation
In order to maintain the child’s attention and moti-
vation to an acceptable level, we implemented a Dy-
namic Difficulty Adaptation (DDA) protocol. We pro-
posed that the game difficulty is dependant of (1) the
task parameters, (2) the game ambiance, and (3) the
interaction technique used to perform the task. In the
context, we propose to use a virtual coach (Figure 6)
to support, congratulate or advise the child after each
game session.
Figure 4: Task-Difficulty-Automaton.
Figure 4 shows the automaton related to the evo-
lution of the task’s difficulty. In this automaton, TP
0
is the initial state vector of the parameters. This pa-
rameters are tuned according to the user’s personal
profile. If the user performance (score), is less that
30% or more that 80% of catches, then the TP
0
state
switches to the TP
1
(difficulty is decreased) or TP
1
(difficulty increase) states respectivelly. The task dif-
ficulty could then be further decreased (TP
2
) or in-
creased TP
2
or returns to the initial state (TP
0
) ac-
cording to the same given thresholds. This approach
will keep the child motivated, because if the game is
too easy or too difficult he/she will not keep playing.
3.2.1 Interaction Technique
The interaction technique parameters could also im-
pact the task difficulty. These parameters are: (1) the
control/display ratio (ratio between the child move-
ments and avatar movements), (2) the feedbacks
(sounds from collision with the moving objects or
haptic feedback), (3) movement constraints (in our
case 2D projection of 3D movements), and (4) time
delay between the child movements and the avatar
movements.
3.2.2 Virtual Coach
The behaviour of the virtual coach is the following.
At the beginning of the game, the coach tell the story,
explain the goal of the game and the task. Then he dis-
appears from the screen. At the end of each session,
the virtual coach appears to (1) congratulate the child
in case of a good score (more than 80% of catch), (2)
advise the child in case of a bad score (less than 30%
Virtual Reality System for Rehabilitation of Children with Cerebral Palsy: A Preliminary Study
309
Figure 5: Diagram for task parameters.
Figure 6: Illustration if the virtual coach.
of catch), or (3) to support the child if the score is
between these two thresholds.
4 USER STUDY
4.1 Aim of the Study
The aim of this study is twofold. Firstly, we want
to collect control data with healthy children in order
to have a baseline for comparison with CP children.
These data are related to performance (score) but also
to the usability of the system, the enjoyment, the task
and the game-play. Secondly, we would like to inves-
tigate the effect of the virtual coach on both perfor-
mance data and subjective data.
4.2 Method
4.2.1 Design and Procedure
Twenty children from a primary school in Angers
(France) participated in the study. The task consisted
Figure 7: Experimental set-up.
in catching a total of 200 objects (fruits: pineapple,
banana, kiwi and apple) during four sessions (50 ob-
jects in each session). The children were split in two
groups of 10 children each. The first group performed
the task in condition C
1
(without the virtual coach),
while the second group performed the task in condi-
tion C
2
(with the virtual coach). Children were al-
lowed to get a rest of 5 minutes between sessions.
The fruits were launched randomly from starting
point above the avatar’s shoulders (direction was set
to 0 degree and width was set to 90 degrees). The
control/ratio display was set to 1/1. The task difficulty
was kept constant throughout the experiment. Thus,
the objects always moved at a constant velocity of 0.2
m.s
1
. The children have to use their dominant hand.
The task took place in a different position for each
session. Concerning the sounds, a tropical forest am-
biance was displayed including birds, monkey, etc.
The assertions submitted to the children in the
main questionnaire were the following:
1. I had a lot of fun playing the game,
2. I found the game interesting,
3. I found the game boring,
4. The game caught my attention,
5. I found this game somehow complicated,
6. I liked the graphics of the game,
7. I liked the sounds of the game,
8. I liked the game scenario,
9. I liked the character that caught the fruits.
4.2.2 Apparatus
The experimental set-up is illustrated in Figure 7.
The system is composed of a 60 LCD TV monitor,
a laptop, and a Microsoft XBox 360 Kinect
T M
sen-
sor. Each child was placed in front of the screen, at
GRAPP 2016 - International Conference on Computer Graphics Theory and Applications
310
the center of the Kinect’s workspace. The Kinect
T M
SDK v1.8 for Windows was used for motion tracking.
In order to measure children performance, we
recorded the total number of caught objects in each
sessions. To get subjective data about the system us-
ability, preference, enjoyment, task, and game-play, a
non standardized questionnaire was used (seven Lik-
ert scale). The children were also asked about the time
they spend in playing video games. We also used the
NASA Task Load Index (TLX) to assess the task’s
mental, physical and temporal demand, user’s per-
ceived performance, effort and frustration. Finally,
we observed the children while performing the task
and noted his/her comments, strategies and specific
behaviours.
4.3 Results and Discussion
Results about performance are illustrated in Figure 8.
We observed that the scores (number of fruits caught)
obtained in both conditions are quite good. Indeed,
we obtained a mean score of 39.18 (std : 1.1) for the
C
1
condition and a mean score of 42.45 (std : 0.50)
for the C
2
condition.
A statistical analysis (MannWhitney U test) re-
vealed that the difference between the C
1
condition
(no avatar) and the C
2
condition (with avatar) is not
significant (U= 25.5, p-value= 0.068). However, we
could consider this results as a trend and state that the
avatar somehow affect the children performance.
Results revealed that the children enjoyed playing
the game (6 points). We observe that the results of
the main questionnaire are not significantly different
between the 2 groups and are very similar for both the
C
1
condition and the C
2
condition.
The children found the game interesting (5.7
points for both conditions) and stated the the game
(6.0 points for the C
1
condition and 5.75 for the C
2
condition). They stated that they liked the graphics
(5.7 points for the C
1
condition and 6.0 for the C
2
condition ) and the sounds (5.9 points for the C
1
con-
dition and 6.05 for the C
2
condition ) of the game.
The children liked the scenario (5.9 points for the C
1
condition and 5.85 for the C
2
condition ), the child
character (6.2 points for the C
1
condition and 6.1 for
the C
2
condition).
The children who had the virtual coach had two
more assertions:
I liked the virtual coach,
I found the coach useful.
The first question obtained in average 5.45 (std :
0.69) points overs the 7 points of the likert scale. The
second question obtained in average 6 (std : 0.82).
Figure 8: Number of fruits caught vs. condition C
1
and
condition C
2
(dash line).
Thus, the presence of the virtual coach was very ap-
preciated by the children. More interesting, they
found it useful for the task. Observation during the
experiment confirm that the children liked the avatar.
Results from the Nasa TLX questionnaire are il-
lustrated in Figure 9 (a) and (b). We observe in Fig-
ure 9 that the results are about the same for both con-
dition C
1
and C
2
excepted for the question 3 con-
cerning the temporal demand where statical differ-
ence was found (U= 80, p-value= 0.04).
This result reveals that the children who per-
formed in C
2
condition felt less intensity and pace in
the game. Thus, the intervention of the virtual coach
at the end of each session allowed the children to get
some rest. Results from the NASA TLX question-
naire also reveal that the game does not involve a high
mental demand. Indeed, the rating for mental demand
was 44.5 (std : 15.71) for C
1
condition and 54.0 (std
: 14.87) for C
2
. However, and this is not very surpris-
ing, the physical demand was rated higher (about 60
for both conditions). Concerning the children perfor-
mance self estimation, we observed that it was rather
high for both conditions: 66.5 (std : 10.29) for C
1
condition and 73.5 (std : 10.01) for C
2
. Similarly,
the children felt developing rather a same level of ef-
fort: 55.0 (std : 14.72) for C
1
condition and 50.0 (std
: 15.63) for C
2
. Finaly, the children felt a rather low
frustration at the end of the experiment: 14.50 (std :
6.43) for C
1
condition and 12.0 (std : 3.50) for C
2
condition.
5 CONCLUSION AND FUTURE
WORK
In this paper, we presented VR system for the reha-
bilitation of children with Cerebral Palsy (CP). The
Virtual Reality System for Rehabilitation of Children with Cerebral Palsy: A Preliminary Study
311
(a)
(b)
Figure 9: Results for the Nasa TLX questionnaire (dash
lines correspond to the C
1
condition ) : (a) rating of the
6 criteria of the Nasa TLX questionnaire, and (b) between
subjects comparison.
system is non-intrusive and includes interesting char-
acteristics such as Dynamic Difficulty Adjustment
(DDA) and a control/display ratio. A Kinect
T M
sen-
sor allows the user to control a 3D avatar and inter-
cept or catch and release moving objects. Further-
more, virtual coach is provided to support the child.
Twenty healthy children participated in a preliminary
experiment. The aim was to collect control data con-
cerning performance and workload, and to investigate
the effect of the virtual coach on both performance
and subjective data. Results show a good usability of
the game and reveal a high ratio of acceptance and
enjoyment. In the near future, experiments with both
healthy children and children with cerebral palsy (CP)
will be carried out to investigate the effect of the con-
trol/display ratio on performance. The DDA proto-
col will be extended to integrate both behavioural and
physiological data.
ACKNOWLEDGEMENTS
This work was supported by the Institut des Sciences
et Techniques de l’Ingnieur d’Angers (ISTIA) and by
the ENJEU[X] project, funded by the Region Pays de
la Loire, France. We wish to thank all children who
participated in the study.
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