Hisanao Nakadai

Takuya Hirano
email: hirano.takuya@entcomp.esys.tsukuba.ac.jp

Jun ' Ichi Hoshino

Real-time Expression Control System for Wearable Animatronics

Keywords:

The animatoronics is used for the expression of the character with many picture works which includes movies. As for the animatronics mask that the person wears of the lively character, the expression of lively character is truly possible because the actor's performance is reflected directly. In this research, I suggest using an animatronics mask in order to reflect the character's feelings and expressions real time by the actor wearing the mask.Conventionally, it is necessary for the actor to look good with the movements and facial expressions beforehand in order to determine if the actor can intuitively play the character but thinks that an actor can play a character intuitively by using this system.

Introduction

Various characters that we enjoy appear in visual works such as films. One method for presenting those characters is animatronics. This is the combined technology of special effect modeling and mechatronics and is used in various areas such as for the president of Disney World or the creatures in Star Wars. In recent years they are also used in live spectacles combined with projection mapping and provide spectators with a life-like experience. One way of using animatronics is a performer gets into a suit and controls it themselves. This method reflects the body movements of the performer and allows direct interaction with other actors and guests, giving a true sense of presence without using any CGI. But animatronics using suits often involve multiple controlling staff moving parts of the lead character with a remote control in accordance with the performer's movements and it is difficult to match movement with that of the performer playing the character. Detailed acting such as character facial expressions also largely depends on the experience and senses of the controlling staff. This study proposes a combined system that allows for the facial expressions of the performer to be expressed on the character in real-time. This system uses multiple photo reflectors and EOG and verifies expression and gaze. With this it is possible to operate in small spaces and use within animatronics without the need of a camera. This system can sync the body movements and expressions of the performer and allows the performer to intuitively act out a character, making it possible for other actors and guests to achieve a high level of interaction with the character.

System Overview

This study aims to develop a new space-saving and light weight sensor unit that can be used within an animatronic suit and recognize and express the facial expressions of a performer in real-time. This study will develop a sensor unit that recognizes facial expressions and develop an animatronic which expresses the recognized facial expression information.

Development Of Sensor Unit That Recognized Expressions:

A person's face has 22 types of facial muscles which create the various facial expressions of a person when moved in complex ways. The shape of the face's skin surface also changes with change in facial expression. This study recognizes these changes using multiple photo reflectors and estimates the facial expressions of the interior performer. This system also aims to recognize blinking and gaze by combining these with the obtained EOG. (Fig. 1) To obtain the EOG, biological signals obtained from an off-the-shelf myoelectric sensor were processed through a filter (Fig. 1), the moving average was multiplied with a micro-computer (Arduino Mega2560) and treated as the input signal. The myoelectric sensor used was a Grove-EMG Detector from Groove.

Development Of Animatronic That Shows Expressions

An animatronic is developed which actually outputs the facial expression changes of the performer recognized by the sensor unit as facial expressions. Small arms corresponding to each area of the face which create all facial expressions are controlled with the variation amounts estimated by the sensor units as target values. The skin of the animatronic uses silicon (Gel-10) which is used in prosthetic makeup. Gel-10 is an extremely flexible material which allows for rich expression.

Experiments

Fig. 2 shows the experimental results of this proposed method. The facial expression changes are recognized in real-time and reflected in a CG adapter acting as an animatronic. At present, the range of line of sight movement is recognized by being split into three steps. The five expressions of "Joy", "Anger", "Sadness", "Surprise", and "Normal" are recognized. However, complicated movement such as sudden eye movement, diagonal movement, or circular movement is not supported. Although change in five large expressions is recognized, incorrect recognition is prone to occur in between all (a)Gaze recognition.

(b)Facial expression recognition.

Fig. 2. Experimental results.

expressions. There is noise contained in the EOG obtained using the myoelectric sensor primary due to difficulty in obtaining quick and complicated eye movements. While multiple filters and amps are used for noise processing and amplification, the EOG is a biological signal and touch sensor, so it is prone to various types of interference such as being affected by open air or the state of a subject's skin. Thus, it is difficult to process noise with just a LPF or HPF. In addition, an EOG characteristic phenomenon occurs when electrodes have been connected for a long period of time where the drift voltage gradually rises [START_REF] Kuno Yoshiaki | Development of Eye -gaze Input Interface using EOG[END_REF]. It is therefore considered that the regular voltage value in this experiment could possibly have changed due to drift. In the future it will be necessary to revise the noise processing method, implement machine learning, and aim to design a system that is not prone to noise influence. Furthermore, the primary reason for incorrect recognition of facial expressions with this system was that although four photo reflectors were used to recognize five large expression changes, including how someone is regularly, partial changes from "Sadness" to "Anger" and "Sadness" to "Joy" were incorrectly recognized. It is thought that the current sensor is badly positioned and unable to correctly obtain changes in skin shape for facial expressions. In the future we will review the sensor position, increase the number of sensors, and aim to recognize changes in detailed facial expressions that occur in-between expressions.

Conclusion

This paper developed a space-saving and light weight sensor unit that can be used within animatronic suits, aimed to recognize and express the facial expressions of a performer in real-time, and conducted experiments. By using multiple photo reflectors and EOG signals, we were able to recognize simple eye movements (one-dimensional movements) and five large facial expression changes.

In the future we plan to improve the accuracy of recognizing facial expressions and eye movements with sensors and to actually proceed with the production of an animatronic mask which reflects facial expressions. (Fig. 3).

Fig. 1 .

 1 Fig. 1. System Chart and Filter configuration diagram.


Yuki Ueda
email: ueda.yuki@entcomp.esys.tsukuba.ac.jp

Junichi Hoshino
email: jhoshino@esys.tsukuba.ac.jp

Reorientation Method to Suppress Simulator Sickness in Home Video Game Using HMD

Keywords: Virtual reality walking, Redirection, Simulator sickness

While home-use HMD including Oculus Rift has been widely spread in the market today, simulator sickness mainly caused by difference between visual information and body sensation has taken up as a problem. Even though it has been proved that simulator sickness is reduced by reflecting actual physical movement to a VR space, many of approaches ever proposed had various restrictions and mechanisms easy to cause simulator sickness. In the current study, such an approach for moving within a VR space is proposed for home-use HMD that is less likely to cause simulator sickness.

Introduction

With an expectation that home-use HMD including Oculus Rift is to be widely distributed in the market today, VR experience via home-use game machine and the like has become familiar to us. Image experience with a sense of immersion such as VR, however, is known to cause simulator sickness associated with symptoms including tiredness, headache, eyestrain, dizziness and nausea. Since discomfort caused by simulator sickness may turn user's long hours of VR experience into something associated with distress, it is an unavoidable bottleneck for content developers to cope with. While cause of simulator sickness is still in debate, it is believed, in particular, that difference in body sensation between reality and VR space is a major cause [START_REF] Laviola | A discussion of cybersickness in virtual environments[END_REF]. Approaches to make a body move within a VR space by actually moving the body were often proposed but many of them were not applied to VR experience at home because they required large experience space and extensive equipment as well. Further, in such approaches as walking back and forth within a small walking area such as Redirected Walking [START_REF] Razzaque | Redirected Walking[END_REF] and Reorientation Technique [START_REF] Peck | Evaluation of Reorientation Techniques for Walking in Large Virtual Environments[END_REF], there was a problem that the mechanism to correct direction when reached at the end of the walking area caused some restrictions to contents. In the current study, a sequential move approach within VR space is proposed which is less likely to cause simulator sickness without restricting experience environment and contents.

System Overview

With a purpose to achieve visually sequential horizontal movement without any restriction for experience environment and contents while inhibiting simulator sickness, the system has defined the requirements as follows:

① Not to require extensive equipment; ② To be able to realize within a small experience space; ③ Not to restrict contents; ④ To make users actually walk within the VR space to transfer; and ⑤ Not to generate difference in rotation angle during direction correction. In order to meet the requirements above, we have determined to take an approach to give a sensation of continuous walk in a large VR space by walking back and force in a small walking area. Even though restrictions for routes and visual presentation of rotation angle different from reality has been adopted in order to prevent users from recognizing direction correction in previous studies on Redirected Walking [START_REF] Razzaque | Redirected Walking[END_REF] and Reorientation Technique [START_REF] Peck | Evaluation of Reorientation Techniques for Walking in Large Virtual Environments[END_REF], reduction of simulator sickness is tried in the system by intentionally make users notice that they are correcting direction.

By the system consisting of a PC for VR environment drawing, HTC vive as a home-use HMD capable of position estimation, base station and controller for exclusive use of HTC vive and a flat floor for walking, users are able to arbitrarily shift between the following two conditions by operating the controller:

[Movement phase]
Users are able to freely walk within the walking area. Since it is impossible to take a step further when reaching the end of the walking area, it is required to correct the direction by shifting to rotation phase. Besides, the walking area ground was colored by different color from that of surrounding ground in order for users to be able to recognize the walking area.

[Rotation phase]

Users rotate on the spot. As foreground is rotated in synchronization with user rotation, the foreground of the users remains fixed in their eyesight. In this case, it is possible to present an eyesight without any difference in rotation angle to users by displaying independent visual background [START_REF] Prothero | The use of an independent visual background to reduce simulator side-effects[END_REF] fixed at global coordinate system making it further possible to give users a sensation that the foreground is rotating along with the body's rotation. Recommended rotating direction and angle guide is displayed for users as shown in Fig. 2.

Experiments

In the current experiment cooperated by 8 persons in their 20's (male: 7, female: 1), a task was imposed to them in which they walk around through five check points set up in the VR space to move a route equivalent of about 45m of distance both by a proposed approach preparing a walking area with a size of 2.0m×1.5m and a movement approach based on a home-use game operation using a normal keyboard/mouse. Overview of VR environment and position of each check point is shown in Fig. 3 and Fig. 4, respectively. The two types of movement approaches were compared by time required for subjects to walk through all of the check points as well as evaluation value of SSQ [START_REF] Kennedy | Simulator sickness questionnaire: An enhanced method for quantifying simulator sickness[END_REF] performed immediately after experiment completion and contents of hearing.

Table 1 below shows mean time required for subject to have completed the task and standard deviation. It has been proved that the proposed system requires much longer time compared with a movement approach by keyboard/mouse. In addition, evaluation values were obtained by SSQ for SSQ (Total Score) as a comprehensive index for motion sickness, SSQ-N (Nausea), SSQ-O (Oculomotor) and SSQ-D (Disorientation). The result is shown in Table 2. The tougher is the symptom, the higher is the evaluation value. As a result of Mann-Whitney U test for each evaluation value, it has been proved that the proposed system shows significant difference in evaluation values of SSQ-TS (Z=2.013, p<0.05) and SSQ-O (Z=2.016, p<0.05) compared with those of the movement approach based on keyboard/mouse.

Keyboard/Mouse

The

Table 1: Comparison of required time

Table 2:Comparison of SSQ results

It has been also revealed from the experiment that the proposed system is superior to the movement approach based on keyboard/mouse in degree of comprehensive motion sickness as expressed by SSQ-TS and degree of eye fatigue as expressed by SSQ-O in case of moving the same route. In the hearing after the experiment, such opinions were obtained that it was impossible for them to follow the movement on the screen by the movement approach based on keyboard/mouse even if operating on their own or that they got tired due to unintended movement. In contrast, there was an opinion for the proposed system that the system is intuitive causing less fatigue because images always moved in synchronization with their own movement. From the experiment results and opinions for it, it is believed that simulator sickness has been relieved in the proposed system by reducing difference in body sensation between the reality and VR space. For the proposed system, however, there was a complaint of feeling sick due to frequent correction of direction. It is understood as caused by the fact that many times of direction correction is required in order to move long distance because of the small walking area in reality. In addition, it is also believed that required time was greatly prolonged for the proposed system due to the frequent direction correction compared with movement approach based on keyboard/mouse. Resolution for the problem may include increase of moving speed within a range that users do not feel difference in the body sensation in addition to expansion of walking area in reality.

Since it took much more time by the system compared with the movement approach based on keyboard/mouse in the current experiment conducted in such a way to move along the same route, we thought it necessary to conduct also such experiments by the same movement speed and experiencing time as well. It is believed because the faster is the movement speed within a VR space the larger is the difference in the body sensation from the reality causing intense simulator sickness and longer time of experience may cause deterioration of simulator sickness. As we also felt a necessity to improve usability aiming at shortening a period of time until getting familiar with the system as well as method of displaying rotating direction not to cause cables to wind around the body in addition to opinions obtained, we would like to work on these challenges in the future.

Fig. 1 . 2 .

 12 Fig. 1. Independent visual background Fig. 2. Rotating direction recommendation guide

Fig. 3 . 4 .

 34 Fig. 3. Overview of VR environment Fig. 4. Positions of check points

proposed system

		Mean	SD	Mean	SD
	Time	46 sec	8 sec	208 sec	54 sec
		Keyboard/Mouse	The proposed system
		Mean	SD	Mean	SD
	SSQ-TS*	38.80	23.28	20.57	15.19
	SSQ-N	27.42	19.34	10.73	12.10
	SSQ-O*	50.22	28.35	23.69	17.13
	SSQ-D	59.16	53.35	36.54	40.55


Yuki Hatori

Shuang Wu

Youchao Lin

Takehito Utsuro
email: utsuro@iit.tsukuba.ac.jp

Mining Preferences on Identifying Werewolf Players from Werewolf Game Logs

Keywords: The Werewolf Game:"Are You a Werewolf ?", Game Logs, Mining

The deception party game "Are You a Werewolf ?" requires players to guess other's roles through discussions that are based on one's own role and other players' crucial utterances. This paper proposes a method to mine the empirical preference data used to identify werewolves from game logs. This involves obtaining an empirical preference related to the practice of divination. In this method, if one of the three players revealing oneself as a seer divines a player as a human, while the other two players divine the player as a werewolf, then it can be judged that the divined player's role is a werewolf.

Introduction

"Are you a werewolf ?" is a party game that was created by the USSR in 1986. It models a conflict between an informed minority, the werewolf, and an uninformed majority, the villagers. The werewolf game has been popular in many countries including Japan where it has inspired several other activities. Some of these related activities include Werewolf TLPT (Werewolf: The live playing theater), a live improvisation where the actors and actresses play the werewolf game, and a TV variety show where comedians, actors, and actresses play the werewolf game.

In the research community of artificial intelligence (AI), the werewolf game is well known as one with imperfect information where certain information is hidden from some players. This is contrary to games that provide players with complete information such as chess, shogi, and go, where computer programs won against a human champion. Within the Japanese research community, the werewolf game has been employed to evaluate the performance of AI systems since 2014 [START_REF] Shinoda | Are you a Werewolf?" becomes a standard problem for general artificial intelligence[END_REF] which has inspired researchers to develop computer-agent programs that actively participate in the werewolf game. The first Artificial Intelligence-Based Werewolf (AIWolf) competition was held in August 2015.

However, in previous studies aiming at developing a computer-agent program that participates in the werewolf game tended to overlook research issues that are closely related to natural language processing and knowledge processing. These higher-level research issues include (i) understanding natural language conversations among the participants, (ii) inferring each player's roles on the basis of their utterances in game-related conversations, and (iii) deciding which player is the werewolf based on high-level inference.

The goal of this paper is to construct an agent that is able to analyze players' utterances and take an active role in the werewolf game. Firstly, we propose a method to mine empirical preferences used to identify werewolf players using game logs1 . We obtain an empirical preference related to the practice of divination where, if one of the three players reveals himself as a seer divines a player as a human, while the other two players divine the player as a werewolf, then it can be judged that the divined player's role is the werewolf.

Mining a Preference based on Conflict of Divination

Among these preferences related to correctly identifying a werewolf, our method employs the act of divination. We especially focus on the case where more than one player reveals themselves as seers yet their divination encounters a conflict. More specifically, we concentrate on the case shown in Fig. 1, where three players reveal themselves as seers, among whom one player divines a player as a human, while the other two players divine the player as a werewolf. Then, as a result of mining a preference to correctly identify a werewolf, in this case, we can judge that the divined player's role is actually a werewolf.

Before we mined the preference introduced above, we first randomly selected 65 game logs from the WolfBBS site. In every game, the seers are assumed to reveal themselves. Thus, in every game, one or more players will reveal themselves as seers. Considering this, in each of the randomly selected 65 games, we examine the result of the first divination (i.e., on the morning of the second day) by the player(s) who reveal themselves as seer(s). Here, the variation of the divination by one or more player(s) who reveal themselves as seer(s) are among the following three: i.e., only a human, only a werewolf, and the mixture of a human and a werewolf. Table 1(a) shows the distribution of those three variations within the 65 games, where it is quite interesting to note that there is no observation of the divination variation as only a werewolf2 . We further concentrate on those 28 games where the variation of the divination is the mixture of a human and a werewolf. Table 1(b) shows the distribution of the detailed variation of the divination, i.e., divination by two players as a human and a werewolf, divination by three players as:

a human, a human, and a werewolf, and a human, a werewolf, and a werewolf.

For each of those three variations, Table 1(b) also shows the rate of the divined player's true role being a werewolf. This result clearly shows that the divined player is always a werewolf when the variation of the divination is a human, a werewolf, and a werewolf. Thus, we successfully mine a 100% correct preference in identifying a werewolf player that is based on the conflict in the divination process.

For the seven cases of the variation of the divination being a human, a werewolf, and a werewolf, Table 2 further examines the variation of the true roles of the three players who reveal themselves as seers. Again, it is quite interesting to note that in all of those seven cases, the possessed divine the player as a human, while the seer and the werewolf divine him/her as a werewolf (i.e., case (c)). The reason why the werewolf tends to take this strategy of following the seer's divination but abandoning the divined true werewolf player is to simply avoid being executed even after the divined true werewolf player is executed and is exposed as a werewolf. Also, a werewolf does not tend to take the strategies in cases (a) and (b) in Table 2 simply because they avoid taking the risk of being exposed as a werewolf but take on the strategy of abandoning the divined true werewolf player (case (b)), or not taking the strategy of divining a human player as a werewolf (case (a)).

Table 2. Variations of the roles of the three players who reveal themselves as seers and divine (when the three players revealing themselves as seers each divine a player as a human, a werewolf, and a werewolf ) Variation of divination # of games (%) (a) the seer divines the player as a human, the werewolf and possessed divine the player as a werewolf 0 ( 0) (b) the werewolf divines the player as a human, the seer and possessed divine the player as a werewolf 0 ( 0) (c) the possessed divines the player as a human, the seer and werewolf divine the player as a werewolf 7 (100) Total 7 (100)

Conclusion

This paper proposed a method of mining empirical preferences of identifying werewolf players from game logs. In terms of the related work on developing a computer-agent program that participates in the werewolf game, most studies have examined face-to-face werewolf games and analyzed the non-verbal audio cues, physical gestures, and conversational features such as speaker turns (e.g., Chittaranjan and Hung [START_REF] Chittaranjan | Are you a werewolf? detecting deceptive roles and outcomes in a conversational role-playing game[END_REF]).

Fig. 1 .

 1 Fig. 1. An example of a conflict of divination

Table 1 .

 1 Distribution of the variation of divination when one or more players reveal Rate of games where the true role of the divined player being a werewolf when the variation of divination is the mixture of a human and a werewolf

	themselves as seers
	(a) Distribution of the variation of a human and a were-
	wolf in divination
	Variation of divination		# of games (%)
	Only a human			37 (56.9)
	Only a werewolf			0 (0)
	Mixture of a human and a werewolf	28 (43.1)
	Total			65 (100)
	(b) Variation of divination	# of games (%)	# of games where the true role of the divined player being a werewolf (%)
	A human and a werewolf	9 (32.1)		4 (44.4)
	A human, a human, and a werewolf	12 (42.9)		4 (33.3)
	human, a werewolf, and a werewolf 7 (25.0)		7 (100)
	Total	28 (100)		15 (53.6)

We use WolfBBS (http://ninjin002.x0.com/wolff/ (in Japanese) ) werewolf game log data. This is a werewolf game site on the Internet, where the players communicate with each other via a character-based text input communication channel. This werewolf game site keeps a record of the text data of the previous werewolf game logs and makes them publicly available.

This is simply because the werewolves' side usually do not abandon a true werewolf player by divining him/her as a werewolf.


Jacques Barnard

Günther Drevin
email: gunther.drevin@nwu.ac.za

Magda Huisman
email: magda.huisman@nwu.ac.za

A Framework to Determine the Suitability of Software Development Methodologies for the Development of Location-Based Games

Keywords:

To determine the suitability of an SDM (software development methodology) for the development of location-based games, it has to be determined to what degree SDMs address aspects that need to be addressed in the process of developing location-based games. These aspects have been identified from information gathered from the literature and were then validated using a survey. Their importance in the development process was also measured using the survey. A framework that uses these aspects to determine the suitability of SDMs for the development of location-based games was then developed. Applying this framework to a number of existing SDMs it was found, among other, that in general SDMs are well suited for the development of location-based games as far as value to the player is concerned but that they are very lacking when it comes to security and privacy.

Introduction

The gaming industry is expanding rapidly with mobile games becoming an increasingly larger part of the industry. In the 2015 annual report of the Entertainment Software Association (ESA) [START_REF]Annual report. A year of innovation and achievement[END_REF] it was reported that 34% of commuters with a round-trip of more than 3 hours play video games while commuting, with smart phones being used the most (80%) followed by tablets (43%). In 2016 the ESA reported that smart phones were used by 36% of gamers, with PCs being used by 56% of gamers and dedicated game consoles by 53% [START_REF]Sales, demographic and usage data. Essential facts about the computer and video game industry[END_REF].

At the same time the complexity of developing games has increased exponentially [START_REF] Reyno | Model-driven game development: 2d platform game prototyping[END_REF] with one of the elements that contribute to this complexity being the multidisciplinary development process [START_REF] Callele | Requirements engineering and the creative process in the video game industry[END_REF]. The interaction of different specialist areas, such as art, gameplay, sound, control systems, and human factors, with traditional software development, indicates that a specialised software engineering methodology is needed for this domain [START_REF] Callele | Requirements engineering and the creative process in the video game industry[END_REF]. Elements that lead to the complexity of game development are the technical challenges for the developers as well as tools, project size, workflow and other technical aspects [START_REF] Blow | Game development: Harder than you think[END_REF].

This paper focuses on location-based games, which can be defined both as a type of ubigame as well as a type of mobile game. Location-based games make use of the player's location and incorporates it in the game play thereby immersing the player even more into the game world [START_REF] Buzeto | Reconfigurable games: Games that change with the environment[END_REF].

In a previous study unique aspects that need to be addressed during the development of location-based games were identified from the literature and were then validated using a survey. The survey was also used to determine the importance of each of the identified aspects [START_REF] Barnard | A systems development methodology for developing location based games[END_REF][START_REF] Barnard | Aspects that need to be addressed during the development of location-based games[END_REF].

In this paper these identified aspects are incorporated into a framework that can be used to determine the suitability of an SDM for the development of location-based games. A number of SDMs are then evaluated using the framework.

Identified Aspects

A list of 15 aspects was identified from literature that focuses on the development process of games, mobile applications and mobile games. These aspects, as well as their importance (column w), are given in Table 1 [START_REF] Barnard | A systems development methodology for developing location based games[END_REF][START_REF] Barnard | Aspects that need to be addressed during the development of location-based games[END_REF]. The aspects are listed in decreasing order of importance.

The security and privacy aspect scored an average of 7.11, which is lower than the average of 7.33 for all the aspects. From this it would seem that although security and privacy is important to the developers it is not as important as one would expect in the light of security concerns regarding online activity [START_REF] Jain | Addressing security and privacy risks in mobile applications[END_REF][START_REF] Zhu | Mobile app recommendations with security and privacy awareness[END_REF]. To ensure the development of secure location-based games, there should be more emphasis on security and privacy in the development process.

Software Development Methodologies

It is important to understand what SDMs are and how they work in order to develop a framework that can be used to evaluate the suitability of an SDM. An SDM can be defined as the totality of a systems development approach in that it is a set of recommended rules, processes and/or steps that need to be followed [START_REF] Avison | Information systems development: methodologies, techniques and tools[END_REF]. Each of these forms part of the total development process that is usually governed by an underlying philosophy that supports, justifies and incorporates coherent context for a specific development project. Furthermore, an SDM identifies the best procedures, phases, tools, techniques, rules, guidelines, documentation and tasks that are to be used, as well as the best manner to execute each of these.

An SDM in itself consists of four main components, namely a philosophical approach, method, process model and tools and techniques that work together to achieve an integrated process with the objective of improving the development of systems [START_REF] Avison | Information systems development: methodologies, techniques and tools[END_REF][START_REF] Huisman | Deployment of systems development methodologies: Perceptual congruence between is managers and systems developers[END_REF]. These components make it possible to evaluate, analyse, compare and develop SDMs. The philosophical approach defines the perspective through which the system is developed [START_REF] Avison | Information systems development: methodologies, techniques and tools[END_REF][START_REF] Reyno | Model-driven game development: 2d platform game prototyping[END_REF]. The next part of an SDM is the development method and consists of the steps that must be followed during the development process. These steps are executed as specified by the process model. This model therefore dictates the strictness of execution, dependencies and iterations of the steps. Finally, the tools and techniques facilitate the development process [START_REF] Avison | Information systems development: methodologies, techniques and tools[END_REF][START_REF] Huisman | Deployment of systems development methodologies: Perceptual congruence between is managers and systems developers[END_REF].

A number of SDMs were evaluated using the framework developed in this study. The SDMs that were chosen for the study are usually associated with game development, mobile development or mobile game development [START_REF] Abrahamsson | Mobile-D: An agile approach for mobile application development[END_REF][START_REF] Avison | Information systems development: methodologies, techniques and tools[END_REF][START_REF] Beynon-Davies | Design breakdowns, scenarios and rapid application development[END_REF][START_REF] Hunicke | MDA: A formal approach to game design and game research[END_REF][START_REF] Jeong | Development process of mobile application SW based on agile methodology[END_REF][START_REF] Krall | Aspects of replayability and software engineering: Towards a methodology of developing games[END_REF]. Furthermore, each SDM has a different combination of philosophical approach, method, process and set of tools and techniques to better represent SDMs that are used for these types of development. The SDMs used in this study are: Mechanics, Dynamics and Aesthetics framework (MDA) focuses on designing games by breaking the game down into its distinct components; that is rules that lead to the system and in turn lead to fun. After the components have been identified their counterparts for designing the game are identified, namely mechanics that lead to dynamics and in turn lead to aesthetics. The fundamental idea of MDA is that games are more like artifacts than media. -Playability and Re-playability [START_REF] Krall | Aspects of replayability and software engineering: Towards a methodology of developing games[END_REF]:

-
This methodology is based on the design process of the two key factors that contribute to the success of a game, viz. playability and re-playability.

Playability and re-playability can be described in terms of six aspects: social reasons, challenge, experience, mastery, impact, and completion. These six aspects of playability and re-playability are used to weigh game features and adjust the design phase of the methodology. -Player-Centred game design [START_REF] Sykes | Player-centred game design[END_REF]:

The basis for this method is that games differ from business applications in that a business application is developed to satisfy the requirements for which the client asked, whereas games are not developed to satisfy the requirements of a client. This complicates the development process, as the game should satisfy different types of game requirements without having been specifically developed for a specific group of direct clients. This is why this method of game design focuses on the players of the game.

Evaluation of SDMs

Each of the SDMs chosen for this study was analysed and measured against the aspects identified earlier. Each SDM was awarded a score, which was based on the extent to which the SDM supports all of the the aspects. The results of the evaluation are presented in Table 1. It should be noted that the first author, as well as three independent mobile games developers did the evaluation of the SDMs. The developers were given a blank copy of Table 1 and were asked to score, as a percentage, the extent to which each of the SDMs support each of the aspects in the development process.

Inter-Coder Reliability

To determine to what extent the four evaluators scored the aspects for each SDM the same, Krippendorff's alpha was used. The norm for a very good reliability is α >= 0.8, while 0.8 > α >= 0.67 indicates a good reliability and α < 0.67 should be rejected [START_REF] Hayes | Answering the call for a standard reliability measure for coding data[END_REF]. The Krippendorff's alphas that were obtained are given in the last line of Table 1. Each of the Krippendorff's alphas in the table represents the reliability of the evaluators' scores with regard to all of the aspects for each of the SDMs. The Krippendorff's alphas are between 0.706 and 0.828 with an average of 0.734. This confirms good inter-coder reliability for the scoring of the aspects and SDMs.

Results of Evaluating the SDMs

The summarised results of the evaluation of the SDMs across the aspects are given in Table 1. The weight (w) for each aspect is the importance that the aspect received in the survey. In the first row of each aspect the average scores given by the evaluators for each of the SDMs are given as percentages. The second row of each aspect gives the weighted scores of each of the SDMs for that aspect. The calculations for the framework are discussed below.

Using the weight (w) assigned to an aspect and the average score for an SDM, the framework can be used to score the suitability of each SDM for each aspect. This suitability is in the form of a weighted score and is obtained by multiplying the weight (w) for an aspect by the average score that each SDM received for that aspect. For example: the suitability of SDLC for Playability is the weight w = 8.81 multiplied by the average score of 8.75 giving the weighted score of 77.1 as shown in Table 1 .

Table 1 also indicates the suitability that an SDM has for all the aspects, as well as the suitability all the SDMs have for a single aspect. Both these suitabilities are given as percentages. The suitability of an SDM for the development of a location-based game is the sum of the weighted scores that the SDM received for each of the aspects. These suitability scores are shown as percentages in Table 1. As can be seen in Table 1, the SDM that was most suitable, with a score of 63%, was Playability and Re-playability, with Mobile-D the least suitable with a score of 32%.

Also given in Table 1 is the degree, on average, to which the SDMs address the different aspects. This value is given in the last column of the table and is the average of the scores assigned by the evaluators. As can be seen in Table 1 the aspect, value to the player, received the highest score (88%), while the aspect, security and privacy, scored the lowest (20%). It is critical that the SDM ensures that the games developers incorporate security and privacy in the development of location-based games.

By evaluating the results of the framework, it is clear that there are a number of inadequacies in the available SDMs. The framework shows this by indicating that the highest suitability percentage for any of the SDMs was 64%. Although the highest scoring aspect across all the SDMs in this framework scored 88%, there are still a number of inadequacies that need to be addressed in the development of location-based games.

Conclusions and Future Work

Aspects that need to be addressed during the development of location-based games were identified from the literature and were then validated using an online survey to gather information from the gaming industry to determine the importance of each aspect. These aspects were then incorporated into a framework, which was used to evaluate a number of SDMs.

It was also noted that security and privacy was not regarded as an important aspect in the development process of location-bases games. An example of where more attention to security could have prevented players from getting into harm's way is the recently released Pokémon GO game [19,[START_REF] Summers | UK children's charity says 'Pokémon GO' needs more safety features[END_REF]. The issue of online safety of children has also been raised by the ESA [START_REF]Annual report. A year of innovation and achievement[END_REF].

The result of this study is a framework that can be used to determine the shortcomings of current SDMs for the development of location-based games and can therefore be used as a guide in the development of an SDM that is more suited for the development of location-based games.

  Traditional Systems Development Life Cycle [2, 21]: The Traditional Systems Development Life Cycle (SDLC), or Waterfall model, was one of the first SDMs used to develop information systems and was later adapted and used to develop games.

-Scrum

[START_REF] Keith | Agile game development with Scrum[END_REF]

: The Scrum framework is part of the agile development methodology family along with Extreme Programming and Feature Driven Development.

-MASAM

[START_REF] Jeong | Development process of mobile application SW based on agile methodology[END_REF]

: Mobile Application Software Based on Agile Methodology (MASAM) is an agile methodology that focuses on rapid application development. The key goal of this methodology is simple development and fast deployment of new mobile applications. -Mobile-D [1]: Mobile-D is based on Extreme Programming, Crystal Methodologies and Rational Unified Process and is considered to be an agile development approach. This methodology focuses on developing a mobile application in the shortest possible time. -RAD with DSDM Atern [5, 9]: Rapid Application Development (RAD) focuses on developing and delivering high quality systems in the shortest possible time and at the lowest cost. RAD has been implemented as a new methodology, RAD Dynamic Systems Development Method (DSDM). -MDA Framework [14]:

Table 1 .

 1 Suitability analysis results

		w	SDLC Scrum MASAM Mobile-D RAD MDA Playability& Player Aspect
								Re-playability centered suitability
	Playability	8.81 8.75	20	12.5	12.5	16.25 41.25 93.75	58.75	33%
			77.1	176.2 110.1	110.1	143.2 363.4 825.9	517.6
	Player	8.70 67.5	55	83.75	87.5	84.5 86.25 95.75	95	82%
	Experience		587.3 478.5 728.6	761.35	735.2 750.4 833.0	826.5
	Usability	7.93 75.25 66.25 75	22.5	84.25 84.5 90	88.75	73%
			596.7 525.4 594.8	178.4	668.1 670.1 713.7	703.8
	Value to	7.67 78.75 82.5 88.75	90	87.5 88.75 93.75	93.75	88%
	Player		604.0 632.8 680.7	690.3	671.1 680.7 719.1	719.1
	UI Design	7.47 17.5	55	81.25	20	78.75 86.25 73.75	77.5	61%
			130.7 410.9 606.9	149.4	588.3 644.3 550.9	578.9
	Development	7.37 11.25 87.5 52.5	86.25	88.75 13.75 56.25	86.25	60%
	Team		82.9	644.9 386.9	635.7	654.1 101.3 414.6	635.7
	Re-Playability 7.34 7.5	23.75 10	5	12.5 56.25 95	73.75	35%
			55.1	174.3 73.4	36.7	91.8 412.9 697.3	541.3
	Learnability	7.15 7.5	15	47.5	7.5	41.25 50	57.5	55	35%
			53.6	107.3 339.7	53.6	295.0 357.5 411.1	393.3
	Efficiency	7.11 81.25 7.5	5	6.25	47.5 10	7.5	7.5	22%
			580.1 53.6 35.7	44.6	339.2 71.4 53.6	53.6
	Security &	7.11 77.5	8.75 5	7.5	43.75 5	5	11.25	20%
	Privacy		551.0 62.2 35.6	53.3	311.1 35.6 35.6	80.0
	Availability & 7.07 10	5	70	2.5	87.5 2.5 7.5	7.5	24%
	Accessibility		70.7	35.4 494.9	17.7	618.7 17.7 53.0	53.0
	Cognitive	6.90 68.75 10	56.25	5	42.5 77.5 87.5	86.25	54%
	Support		474.4 69.0 388.1	34.5	293.3 534.8 603.8	595.1
	Compatibility 6.62 81.25 7.5	6.25	55	18.75 26.25 25	10	29%
			537.9 49.7 41.4	364.1	124.1 173.8 165.5	66.2
	Adaptability	6.40 71.25 20	51.25	5	13.75 81.25 82.5	82.5	51%
			456.0 128.0 328.0	32.0	88.0 520.0 528.0	528.0
	Organisational 6.23 50	78.75 50	50	78.75 18.75 53.75	81.25	58%
	Structure		311.5 490.6 311.5	311.5	490.6 116.8 334.9	506.2
	Suitability
	of SDM		47% 37% 47%	32%	56% 50% 63%	62%
	α		0.726 0.743 0.709	0.706	0.828 0.763 0.738	0.733


Natsumi Mori

Takehito Utsuro
email: utsuro@iit.tsukuba.ac.jp

Generating the Expression of the Move of Go by Classifier Learning

Keywords: Entertainment Computing, Go, Classifier Learning, Move, Expression

The ancient Chinese board game, Go, with its simple rules yet highly complex strategies, requires players to encircle more territory than their opponent. However, owing to the rise in the capabilities of Goplaying software and a lack of Go instructors in Japan, there is a need for a software that actively assists human players in learning the high-level strategies required to win the game. This study focuses on generating a review for each consecutive player's move. This paper studies how to generate an expression for each move based on the distribution of the stones on the board. To this task of generating the expression for each move in a game of Go, we apply a classifier learning technique.

Introduction

With the recent, well-known success of the computer Go program AlphaGo [START_REF] Silver | Mastering the game of Go with deep neural networks and tree search[END_REF] that beat a high-level professional without handicaps, computer-based Go programs now represent a serious challenge to professional human players. Therefore, from an entertainment and educational perspective, developing software particularly designed to teach human players high-level techniques is an important task. This is an especially pressing task because, at present, Japan has only a small number of professional Go players who are capable of teaching amateurs. Furthermore, there is a need to develop high-level software that can play so-called "customer" Go, where the software analyzes a human player's habits and predicts their next moves, allowing them to win on purpose while concealing the fact that they won with the aid of the software.

Based on those arguments, this paper aims at developing a software which assist human players to learn high level techniques on the move of Go. Within various functions of such a software of assisting human players to learn the techniques of the game of Go, this paper focuses on the task of generating a review for each move in a game of Go 1 . It is strongly required to develop such a software of generating a review for each move in a game of Go mainly because it can assist amateur human players to learn high level techniques on the move of Go. Then, according to such a requirement on developing a software of generating a review for each move in a game of Go, this paper more specifically proposes to generate the expression for each move in a game of Go from the pattern of the stones on the Go board. Furthermore, to this task of generating the expression for each move in a game of Go, we apply a classifier learning technique.

In related research, Ikeda et al. [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] propose generating expressions of the shape of a particular move based on the pattern of the stones on the board by applying a classifier-learning technique. Out of the overall types of expressions of a move, Ikeda et al. [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] concentrated on generating those based on the shape of a move but failed to analyze strategic moves. Thus, one of the major contributions of the present study compared to Ikeda et al.'s [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] research is that it investigates expressions based on the shapes of moves while also taking strategic moves into account. Furthermore, in terms of the features of the classifiers used to generate an expression for each move, in addition to lower-level features, most of which have been studied by Ikeda et al [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] (see section 3.1), the current study illustrates the effects of higher-level features (examined in detail in section 3.2). Finally, in section 4, we show the optimal combination of features for each expression required to achieve the best-possible performance in a game, an aspect that was overlooked by Ikeda et al. [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF].

Expressions of Go Moves

Expressions Based on the Shape of the Move

Expressions based on the shape of a particular move are typically identified by considering the static local pattern of the stones on the board. As illustrated in section 2.3, we focus on the 10 most frequent expressions for the shapes of moves listed in Table 2. For each of these 10 expressions, Fig. 1 shows a typical example of a move; the black stone with a white triangle within it represents the last move with the expression of its shape.

Expression for the Strategic Move

As we mentioned in the previous section, the expressions for the shape of a move are typically identified by considering the static local pattern of the stones on the board. On the other hand, expressions for strategic moves are typically identified by considering a much broader view of the patterns of the stones. Each of these expressions of strategic moves represents fairly characteristic situations encountered throughout the whole-state transition within a game. Moreover, from the perspective of the overall time-series state transition of the moves within a game, a move's time-series sequences can be approximately segmented by strategic moves. Therefore, each strategic move is typically played separately from the previous moves. As mentioned in section 2.3, we focus on the three most frequent expressions for the strategic moves listed in Table 2. A detailed description of each of these three expressions is given below.

-Protect-represents that the move by the current player is intended to protect one's own stones from the opponent using various strategies. -Approach move-represents that the move by the current player is intended to start approaching the opponent's stone. -Invasion-represents that the move by the current player is intended to invade an area occupied by the opponent.

Fig. 2 illustrates examples of two of these three expressions for strategic moves as well as typical situations in which ambiguities against those for the shape of the move are present. In short, a particular move and the pattern of the stones on the board can be interpreted as strategic when considering it more seriously and trying to react to it as much as possible; conversely, it can also be interpreted as simply representing the shape of a particular move when it is considered less seriously, for example, by ignoring the opponent's move and attempting not to react to it. However, in both of the cases shown in Fig. 2 considering the pattern of the stones on the board more seriously and interpreting these moves as strategic is the correct approach.

The Dataset

The dataset used to evaluate the classifier for generating the expressions of the moves from the pattern of the stones was constructed from the SGF-move coordinates file as well as the game review text. We first collected these data from reviews of Go games available in newspaper articles over a period of 5 years. This included 60 game reviews played on a 19 × 19 size board and comprising 9,209 moves in total. Then, as shown in Table 1, from each SGF-move coordinate file and the game review text for each move, its order, coordinates (x, y), as well as expression were manually extracted. However, from the total number of moves, the expression for each move is available to a certain extent. This amounts to 1,207 moves out of a total of 9,209 moves. Of these 1,207 moves, 238 types of expressions were manually extracted and within this set, only 34 types were

• • • 1 (16,4) • • • • • • 2 (4,4) • • • • • • 3 (16,17) • • • • • • 4 (4,16) • • • • • • 5 (6,
• • • • • • • • • • • •
observed more than or equal to 10 times. Then, these 34 types of expressions (with 667 moves in total) were employed as the overall resource for evaluating the classifier for generating the expression of particular moves. These 34 expressions can be further classified into 21 expressions based on the shape of the move at 478 moves (71.7% of the 667 moves) and the remaining 13 expressions for strategic moves at 189 moves (28.3% of the 667 moves). Then, as shown in Table 2, the 10 most frequent expressions for the shape of the move as well as the 3 most frequent expressions for the strategic move were selected (422 in total) as the positive/negative samples of the training/test dataset.

Features

The features examined in this study comprise lower-level features aimed at identifying the shape of a particular move as well as higher-level features that seek to identify strategic moves specifically.

Lower Level Features of a Particular Move's Shape

Most of the lower-level features examined here have been studied in previous work [START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] on generating expressions for the shape of a move.

F L 1 : Coordinates of a Move

The x and y coordinates of a move are used as two features, which are denoted as F L 1 .

F L 2 : Number of Stones

The number of stones on the board when a move is made is used as a feature that represents the order of the move from the beginning of the game. This feature is denoted as F L 2 . As shown in Fig. 3, the distance from a stone used in a particular move to the closest board edge is used as a feature and is denoted as F L 3 .

F L 4 /F L 5 : Distance to the Closest Current Player's/Opponent's Stone

As shown in Fig. 4, the distance from the stone resulting from a move to the closest current player's or an opponent's stone is used as a feature and these are denoted as F L 4 or F L 5 respectively. In terms of the distance measurement used for these features, that used by previous research [START_REF] Coulom | Computing Elo ratings of move patterns in the game of Go[END_REF][START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF] is employed. Thus δx and δy denote the differences of the x and y coordinates of the two stones, respectively:

distance(δx, δy) = δx + δy + max( δx , δy )

In our implementation of these features, feature values over six are ignored. As shown in Fig. 5, the distance from the closest current player's or opponent's stone to the board edge is used as a feature. This denoted as F L 6 or F L 7 , respectively.

Higher-Level Features for Strategic Move

In addition to employing the features of lower levels to identify the shape of a particular move, this section presents features of higher levels that specifically aim to identify strategic moves. This study uses the following type of higher-level features. As shown in Fig. 6, the higher-level features is the distance to the stone of the previous move or the move before the previous move, which is denoted as F H 1 or F H 2 , respectively. Strategic moves are typically characterized in terms of the time-series sequences of the current player's moves. As illustrated in Fig. 2, the overall sequence of time-series state transitions of moves within a game can be approximately segmented by strategic moves, each of which is typically played apart from the previous move as well as the move before the previous move. Therefore, these features of the distance between the current and previous moves are typically intended to express such time-series factors within a game. Furthermore, in our implementation of these features, instead of the distance measurement presented by equation (1) in the previous section, the following definition of the distance is employed, where δx and δy denote the differences between the x and y coordinates of the two stones, respectively:

distance(δx, δy) = δx + δy (2)
This is because these features are required to be sensitive to a much broader area on the board compared to those of F L 4 and F L 5 , aiming at identifying the shape of a move, but not a strategic move.

The Procedure

In the evaluation of the classifier for generating the expression of a particular move from the pattern of stones on a Go board, for each of the 13 expressions listed in Table 1, we train a binary classifier with all of the samples of the expression (as listed in Table 2) as positive samples. An equal number of negative samples are randomly selected from the pool of negative samples that is constructed by removing all the positive samples from the 422 samples listed in Table 2. The classifier for each binary classification is implemented using the decision tree's2 module of the scikit-learn toolkit [START_REF] Pedregosa | Scikit-learn: Machine learning in Python[END_REF]. The parameters of the lower bound of the number of training samples within each node of the decision tree (in the range from 1 to 7) as well as the upper bound of the depth of the decision tree (in the range from 2 to 8) are tuned through a preliminary round of a 10-fold cross-validation with a random split into the training and test sets. This is also implemented through a module of the scikit-learn toolkit. The final evaluation results are obtained through another round of 10-fold cross-validation with the two parameters optimally tuned as above.

Evaluation Results

Table 3 shows the optimal combination of features as well as the optimal performance achieved by the combination of these particular features for each expression. Overall, for most expressions, including both those of the shape of a move as well as the strategic moves, optimal combinations of features tend to include F L 4 /F L 5 (the distance to the closest current player's/opponent's stone). F L 6 (the distance from the closest current player's stone to the board edge), and F H 1 /F H 2 (the distance to the stone from the previous/before the previous move). These features typically represent the characteristics of the patterns of stones on a Go board. Other features such as F L 1 (the coordinates of a move), F L 2 (the number of stones on the board), and F L 3 (the distance to the closest board edge) typically contribute little to achieving the optimal performance. This is mainly because such features represent the physical layout of the stones on the board that are not critically sensitive to detecting the expression of a move. Notably, the higher-level features are more effective in the identification of the shapes of moves rather than those of strategic moves. This is because even in the binary classification task of a single expression for the shape of the move and the others, negative samples comprise not only other expressions for the shape of a move but also all the expressions for a particular strategic move. These results provide important clues for devising new types of features in future work.

Conclusion

This study aims to develop a software that assists human players in learning high-level Go strategies by focusing on generating a review for each individual move in a game of Go. In particular, this study proposes generating an expression for each move based on the pattern of stones on the board. Furthermore, to this task of generating the expression for each move in a game of Go, we applied a classifier learning technique. In terms of future work, we aim to scale up the dataset to allow more accurate evaluation of the results and evaluate other types of classifiers such as support vector machines.

Fig. 1 .

 1 Fig. 1. The most frequent 10 expressions for the shape of a move (expression for each last move)

Fig. 2 .

 2 Fig. 2. Examples of the ambiguity of the expressions for shape and strategic moves

Fig. 3 .F L 3 :

 33 Fig. 3. F L3: distance to the closest board edge

Fig. 4 .

 4 Fig. 4. F L4/F L5: distance to the closest current player's/opponent's stone

Fig. 5 .F H 1 /F H 2 :

 512 Fig. 5. F L6 / F L7: distance from the closest current player's/opponent's stone to the board edge

  Fig. 6. F H1/F H2: distance to the stone of the previous/move before the previous move

Table 1 .

 1 Generating the training/test dataset of the expression of the Go move from the SGF-move coordinates file and the game review text

	Game review text (English translation)	Order of the move	Coordinate the move (x, y) of	Expression of the move

Table 2 .

 2 Numbers of positive samples in the dataset for each expression of the moves

	Type of move and expression	ID Expression	# of positive samples
		1	attachment	60
		2	connection	57
		3	hane	42
		4	cut	37
	Expression for the shape of the	5	peep	30
	move	6	extend	29
		7	jump	25
		8	block	25
		9	ate	21
		10	extension	19
		11	protect	29
	Expression for a strategic move	12 approach move	25
		13	invasion	23
	total			422

Table 3 .

 3 Evaluation results (%)

	Type of the
	move and the expression	ID Binary classification	Evaluation results	Optimal features
		1	attachment/rest	95.0	F L4, F L6
		2	connection/rest	86.1	F L4, F L5, F L6, F H2
		3	hane/rest	89.5	F L4
	Expression for the shape of a move	4 5 6 7	cut/rest peep/rest extend/rest jump/rest	84.2 81.7 95.0 91.7	F L2, F L4, F L6 F L2, F L6, F H1/F H2 F L6, F L7 F L4
		8	block/rest	82.5	F H1
		9	ate/rest	83.3	F L7, F H2
		10	extension/rest	87.5	F L6
			Average	87.6	-
	Expression for a strategic move	11 12 approach move/rest protect/rest 13 invasion/rest	71.7 95.8 94.2	F L1, F L2 F L4 F L6
			Average	87.2	-
		Average	87.5	-

Yoshikawa et al. [5] studied the protocols of the game of Go with respect to the relations between the player's skill and the use of Go terms.

In this study, we applied decision trees as the classifier for identifying and generating the expression of moves as it was employed successfully by Ikeda et al.[START_REF] Ikeda | Machine-learning of shape names for the game of Go[END_REF].


Jan Smeddinck
email: smeddinck@tzi.de

Dmitry Alexandrovsky

Dirk Wenig
email: dwenig@tzi.de

Michel Zimmer

Waldemar Wegele

Sylvia Juergens

Rainer Malaka
email: malaka@tzi.de

Hoverboard: A Leap to the Future of Locomotion in VR!?

Keywords: Locomotion, Virtual Reality (VR), Motion-Based Control, Natural User Interface, Hoverboard, Leaning, Whole-Body Interface, Gaming

Locomotion in virtual reality (VR) remains challenging due to limitations of common input methods. Sedentary input devices may endanger immersion, real-tovirtual world perception dissonance can lead to simulator sickness, and physical input devices such as framed walking dishes are often complex and expensive. We present a low-cost, easy to use, easy to manufacture, and easily portable device for locomotion in VR based on a hoverboard metaphor. Building on related work and our own iterative VR locomotion system designs we hypothesize that hoverboarding can provide a compelling and intuitive method for short-and long-distance locomotion in VR with a potential to reduce simulator sickness due to consistent and stable locomotion that corresponds well to the physical proprioception of the users while navigating VR. We discuss design iterations of our device prototypes, promising results from an early explorative evaluation, as well as ongoing continued work.

Introduction

Virtual reality (VR) is expected to play an important role as a key new interaction modality for mainstream applications in entertainment computing, education, computer-supported cooperative work, and beyond. Due to the strong notion of physical presence and location in VR, applications require novel physical locomotion interfaces for navigation in virtual worlds which allow the user to travel long distances that cannot be bridged in reality while using the system due to physical constraints as well as due to constraints with tracking technologies.

In VR applications that present larger spaces and invite users to change locations, for example in many simulators or games, using traditional controllers, such as gamepads, or keyboard and mouse, is often cumbersome and unintuitive, since the input does not map well the impression of first-person movement that player-view camera translations in VR induce [START_REF] Wang | Comparing Isometric and Elastic Surfboard Interfaces for Leaning-based Travel in 3D Virtual Environments[END_REF]. In many cases, a disconnect between the input method which leads to a specific sensory experience (including the vestibular system) for the user and the resulting displayed action can contribute to problems with VR sickness [START_REF] Klatzky | Spatial Updating of Self-Position and Orientation During Real, Imagined, and Virtual Locomotion[END_REF] and challenge immersion [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF].

Modern VR systems offer "room-scale" tracking of physical motion (e.g., the HTC Vive), allowing the user to walk around in a small area. For traveling longer distances, there are approaches such as teleportation [START_REF]HTC Vive Support[END_REF], walking-in-place (WIP) [START_REF] Walther-Franks | Suspended Walking: A Physical Locomotion Interface for Virtual Reality[END_REF], or using walking dishes [START_REF] Ohnishi | Motion Control for Advanced Mechatronics[END_REF], treadmills [START_REF] Iwata | Gait Master: A Versatile Locomotion Interface for Uneven Virtual Terrain[END_REF], or spheres [START_REF] Medina | Virtusphere: Walking in a Human Size VR "Hamster Ball[END_REF]. All of these approaches have specific advantages and disadvantages. They are either not fully immersive, or uncomfortable, or they require a complex or expensive hardware setup.

This motivated our iterative design exploration of further suspension devices following the original suspended walking system [START_REF] Walther-Franks | Suspended Walking: A Physical Locomotion Interface for Virtual Reality[END_REF], targeting increased comfort, ease of use, lowered cost, immersion, reduced VR sickness, and facilitating faster and further locomotion. The resulting most favorable setup of a suspended wooden board (see Fig. 1, top) induced the emergence of the hoverboard metaphor and was integrated in a fully interactive VR locomotion prototype that was subjected to an early evaluation. The outcomes, while promising, indicated room for improvements, motivating iterations towards a followup modified hoverboard concept that is not suspended and targets increased portability, stability, and control.

This work contributes to the development of full-body interfaces for locomotion in VR with use cases in gaming and beyond. The publication of these latebreaking developments is meant to inform researchers and developers that may currently pursue similar challenges in the booming area of VR.

Related Work

In the past, there have been commercial devices for body-based input that became popular for arcade of casual games. Instead of a VR setup the systems often realize visual output on a display, allowing users to reference the stationary environment around the display, thus motion sickness is not an issue. Sickness due to unconstrained movement in VR [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF] is such a notable problem that most (even top-level) current VR games radically confine movement (e.g. Space Pirate Trainer) or use considerable workarounds, such as teleporting (e.g. Rec Room). Many acclaimed VR experiences (e.g. Elite Dangerous) are based on metaphors that match well with a seated computer desk setting and thus do not induce require physical locomotion. Some games use a "moving platform" (e.g. Hover Junkers), since standing on a surface that moves around the VR space matches better with actual proprioception if VR is used while standing, even if the floor is stable and does not move.

A considerable body of research explores the design space of traveling through virtual environments. Bowman et al. [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF] provide a broad overview of techniques and devices. Stationary controls that are used in VR experiences with considerable locomotion mainly result in visual cues disregarding vestibular perception/feedback. This negatively affects a user's sense of presence and spatial awareness and also contributes to the risk of simulator sickness [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF][START_REF] Ruddle | For Efficient Navigational Search, Humans Require Full Physical Movement, but not a Rich Visual Scene[END_REF]. Involving a user's body in the interaction loop, providing multimodal feedback, can arguably help overcome these issues [START_REF] Wang | Comparing Isometric and Elastic Surfboard Interfaces for Leaning-based Travel in 3D Virtual Environments[END_REF][START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF][START_REF] Ruddle | For Efficient Navigational Search, Humans Require Full Physical Movement, but not a Rich Visual Scene[END_REF][START_REF] Harris | Human Joystick: Wiileaning to Translate in Large Virtual Environments[END_REF][START_REF] Kruijff | On Your Feet! Enhancing Self-Motion Perception in Leaning-Based Interfaces through Multisensory Stimuli[END_REF][START_REF] Marchal | Joyman: A Human-scale Joystick for Navigating in Virtual Worlds[END_REF].

Hence, it is not surprising that a number of research projects have investigated interfaces that implement a walking metaphor. While many methods, such as walking in place [START_REF] Slater | Taking Steps: The Influence of a Walking Technique on Presence in Virtual Reality[END_REF], walking dishes and spheres [START_REF] Medina | Virtusphere: Walking in a Human Size VR "Hamster Ball[END_REF], or treadmills [START_REF] Iwata | Gait Master: A Versatile Locomotion Interface for Uneven Virtual Terrain[END_REF] draw on walking motions that require users to actively carry their own weight, alternative suspended walking interfaces that utilize hanging harnesses have also been introduced [START_REF] Walther-Franks | Suspended Walking: A Physical Locomotion Interface for Virtual Reality[END_REF]. Such walking-based methods offer an intuitive approach to locomotion in VR and can support immersive experiences [START_REF] Slater | Taking Steps: The Influence of a Walking Technique on Presence in Virtual Reality[END_REF][START_REF] Williams | Evaluation of Walking in Place on a Wii Balance Board to Explore a Virtual Environment[END_REF]. However, they suffer from shortcomings around latency, tracking accuracy, discomfort, restricted freedom of motion, or unnatural leg movements. Furthermore, they only work well with small virtual environments. Once a user is to explore large areas, techniques that involve walking, become exhausting [START_REF] Harris | Human Joystick: Wiileaning to Translate in Large Virtual Environments[END_REF]. Thus, other modalities, or mixed methods for traveling mark interesting venues for further exploration.

As one example, related work suggests the application of interfaces that rely on devices that are sensitive to weight shift, mapping a user's leaning motion to the direction and/or the speed of the device. Similar approaches have been discussed employing a "flying carpet" metaphor [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF]. The Joyman [START_REF] Marchal | Joyman: A Human-scale Joystick for Navigating in Virtual Worlds[END_REF] is an isotonic [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF] VR locomotion interface that provides stability through resistive force that increases with displacement. A circular platform with a safeguard is connected via springs to a base. The inclination is measured with an inertia sensor. Along with the device the authors provide a translation model for the inclination of the device to a realistic control of virtual vehicles. Compared with a joystick, users completed navigation tasks significantly faster with the joystick, but had more fun and felt more present with Joyman. The interface encourages exaggerated leaning motions over the limit of balance. While this can be a fun way to navigate through some extreme sport games, such gestures appear inappropriate for regular navigation tasks. However, if the visual and auditory feedback presented in VR adequately corresponds to the movements that are enacted on the surface, such input schemes can provide close real-world-to-VR perceptive consistency.

Related work on vestibular feedback comparing a Wii Fit Balance Board as an isometric (i.e. non-displacing [START_REF] Bowman | 3D User Interfaces: Theory and Practice[END_REF]) device with an isotonic device (the Reebok Core Trainer Tilt Board) found that, while no sig. diff. in performance between these two devices existed, participants preferred the isotonic interface, perceiving it as more joyful and realistic [START_REF] Wang | Comparing Isometric and Elastic Surfboard Interfaces for Leaning-based Travel in 3D Virtual Environments[END_REF].

Hoverboard System Design

Based on related work and our own prior experience with suspension devices for locomotion in VR [START_REF] Walther-Franks | Suspended Walking: A Physical Locomotion Interface for Virtual Reality[END_REF], an iterative design process was carried out to further investigate alternative suspended movement setups for locomotion in VR. The developments were motivated by the challenges around alternative techniques discussed above. Early informal evaluations with convenient subjects showed that the prototype devices pictured in Fig. 1 could support entertaining VR experiences, when test participants were asked to act out user generated gestures for direction control when using the setups while watching a VR video of moving down a rail that changed directions. In comparison, two alternative concepts of suspended walking and suspended flying were dismissed for reasons of discomfort and setup complexity when considering an interactive integration with a VR test application, and the third concept employing a hoverboard metaphor (Fig. 1) was chosen as first candidate for an interactive evaluation due to favorable ratings of comfort and ease of use.

Hardware Design

The hoverboard setup originally consisted of a wooden board attached by ropes to a roofmounted hold, allowing for rotation around the horizontal or vertical axis. A smartphone was attached to the bottom of the board as a readily available integrated sensor device with wireless network connectivity. Although this could easily be replaced by a dedicated embedded device for further developments, this setup allowed rapid iteration, benefitting from the integrated accelerometer, gyro, and compass for a high accuracy rotation detection [START_REF] Anjum | Activity Recognition using Smartphone Sensors[END_REF]. A belt at waist level was added for safety reasons prior to testing the setup with users.

Software Design

A small android app employs the acceleration sensors and transfers the orientation data via Wi-Fi. For a simple, low-cost, and replicable approach, the Unity game engine was chosen to drive a VR test application. The design of the VR environment was deliberately kept simple (Fig. 2). It contains a virtual representation of the board that moves along hovering above a corridor or track for depth reference at a constant speed that was set to approximate 25 km/h. The level contains a series of crosses that are placed along the virtual track and can be collected by the user to induce steering movements and to measure precision. When a cross is collected, the counter in the HUD increases and the user hears a jingle sound. The application also plays a simple background music tune for ambience.

Incoming rotation values are interpolated to avoid jitter in movements and mapped to the rotation around vertical or horizontal axis of the virtual board according to the physical manipulation of the real wooden board. The application allows for a forward, as well as for a sideways stance orientation. The system was used in conjunction with an Oculus DK2.

Evaluation

An exploratory evaluation was carried out to capture first impressions regarding the general usability, user experience, and acceptance of the suspended locomotion method. It included four trials with different stance orientation (sideways vs. forward stance) and different perspectives (first-person vs. third-person), lasting about three minutes per trial. The users participated in an interview comparing the conditions and discussing the perception of the general approach regarding aspects of fun, precision of control, the level of immersion, the occurrence of motion-sickness, and a comparison to the applicability of traditional input methods (such as keyboard and mouse) for controlling similar locomotion in VR.

Outcomes

Four convenient subject casual gamer participants with an average age of 23 years were recruited for the study. None had used a VR headset However, one participant immediately reported VR sickness, which is not a rare occurrence when working with translational movement in VR. The participant did not complete the study and is thus not considered in the following results and analysis. None of the remaining participants reported sickness. Problems due to latency in tracking and smoothing were not observed. The remaining three subjects (1m, 2f) all reported the interactions to be a fun experience. P1 and P3 explicitly related their impression to the control modality. Although no common preference could be isolated regarding the stance, the individual favorites appeared to correspond to the stance of their favorite stance-related sports. The third-person perspective was noted to provide a better impression of the orientation of the board. All felt immersed noted that they find the game boring without the hoverboard control scheme. P2 and P3 highlighted the role of whole-body input. P1 and P3 noted that they felt they had precise control of the board (P3 collected most crosses). P3 also commented on the performance and showed notable increases across trials. P1 and P2 attempted to collect crosses with imaginary virtual representations of their real (untracked) body parts (e.g. hands). P2 showed very pronounced movement, at one time shouting "this is great; I would immediately buy this".

Discussion & Limitations

Overall, these exploratory evaluation results point towards a positive interaction experience. However, the evaluation is limited due to the low number of participants. Future evaluations should also consider using more immersive (real game) test applications, comparing to other control modalities, comparing the effect of controlling different objects that are not immediate representations of the input board, and controlling for the impact of first time VR experiences. In practical terms the most apparent limitation of the setup was a restricted portability, together with the need to provide hand holds due to fast rotations around the horizontal axis. This inspired the development of a follow-up prototype.

Updated Prototype

Although the interaction method discussed above appeared promising, the setup is not easily portable. Thus, we developed a smaller device that utilizes an isotonic hoverboard interaction metaphor. It consists of two identical wooden boards that are connected by springs (Fig. 3). Again, a smartphone attached to the bottom side of the top board provides the inclination data to the host computer. For this prototype, the springs are chosen to bear a 70-80 kg person allowing an inclination up to 10° in each direction. The springs can easily be swapped for different bodyweights and different maximum inclinations. One major advantage over the previous swing version is that it allows not only a leaning motion, but also to move freely on the board, which aims at facilitating improved tilting control.

Discussion and Future Work

The current prototype will be iterated to be fit for interactive demo use as well as to support further evaluations regarding the question of how the degrees of freedom can best be mapped to movement in VR, possibly combining velocity/speed and turning. Furthermore, a hydraulic suspension could support different weight ranges without requiring a manual swapping of the springs. We envision that the hoverboard concept can be used in entertainment computing applications as a simple and fun input device, tackling challenges of locomotion and travelling longer distances in virtual worlds. Hoverboard is as a simple, cheap, and easy to build device. As a physical input technique based on the user's body balance, it can be employed in fall prevention, for training core stability or a sense or space and time. It could also be used for spatial data exploration, e.g. traveling through detailed visualizations of the organs of a human body, or exploring large tags clouds or image collections, as well as to navigate geo-mapping environments such as Google Earth or StreetView. The hoverboard implements relative positioning (similar to a computer mouse or joystick) and, to allow for high immersion, it reacts to user input with dampened acceleration. This has advantages from the point of the user experience but presents problems regarding core usability metrics, such as time efficiency [START_REF] Marchal | Joyman: A Human-scale Joystick for Navigating in Virtual Worlds[END_REF]. Therefore, we primarily envision application scenarios where efficiency is not a primary concern.

In many cases stationary controls are not well suited for immersive traveling in VR. Based on recent research we presented two iterations of full-body interfaces for locomotion in large virtual environments that are based on a hoverboard metaphor. First evaluation results promise a positive user experience and good control. Our latest prototype is a portable lowcost and easy to prepare device that promises to provide more precise control due to isotonic increasing resistance with increased stability, allowing for further explorations of the applicability of leaning for rotation and/or acceleration for long-range locomotion in VR.

Fig. 1 .

 1 Fig. 1. Intermediate prototype from the iterative design process for a range of suspended setups for locomotion in VR.

Fig. 2 .

 2 Fig. 2. Playful VR test application. Implemented in Unity3D.

Fig. 3 .

 3 Fig. 3. The updated springboard iteration of the hoverboard device.

Acknowledgments

This research is partially funded by the German Federal Ministry of Education and Research (BMBF). We thank the University of Bremen Spiele AG for support with the latest prototype.


Toshiaki Takita

Kazuhisa Akimoto

Junichi Hoshino
email: jhoshino@esys.tsukuba.ac.jp

Reading Aloud Training Game for Children with Auto Evaluation of Oral Reading Fluency

Keywords: Read aloud training, gamification, evaluation of oral reading fluency

Reading aloud is an important study method of acquiring information and building knowledge from text. This article proposes an objective and automatable method that evaluates fluency of children's reading by reflecting the evaluation by those who are experienced in book reading (to children), and presents the outcomes of building an automatic evaluation system on the fluency of reading with that method.

Introduction

Upon obtaining information and building knowledge, reading aloud is a basic and important learning method. It has been indicated that there is a correlation between children's fluency in reading aloud and their reading comprehension [START_REF] Reutzel | Effects of fluency training on second grader's reading comprehension[END_REF]. It has been also indicated that, by enhancing children's fluency of reading aloud, their reading comprehension can be also enhanced [START_REF] Stayter | Fluency and the understanding of texts[END_REF]. Therefore, it can be said that it is important to enhance children's fluency in reading aloud.

In this article, by reflecting the evaluation of reading fluency by those who are experienced in book reading, an objective and automatable evaluation method on children's reading fluency was proposed, and using that method, an automatic reading fluency evaluation system was built. Upon building the system, it was designed to be capable of enhancing children's reading fluency in their reading practices with the automated evaluation system without having a teacher with them. In the evaluation experiment of the proposed system, the actual system was used by children, and a questionnaire survey was conducted on both children and their parents. As a result, it was revealed that the proposed system was easy to use, and it enhanced children's motivation for reading aloud, resulting in the enhanced reading fluency, not only in the material they practiced on, but also in other materials as well.

Game Design

The proposed system aimed to be a system that could motivate children to practice reading, and to help enhance their reading fluency. By implementing the proposed system in a terminal, it would allow children to practice their reading aloud and have it evaluated anytime without having a teacher or parents around. In order to realize such system, three requirements were set: 1) being capable of enhancing children's reading fluency, 2) being capable of motivating them to practice reading aloud, and 3) being easy to use.

The reading-aloud game consists of three functions: the reading-aloud practice function, practice recording function and the raising game function. The screenshot of the reading-aloud practice function is sown in Fig. 1. A line of the text is displayed in the screen each time, and children read it aloud one by one. Once they have completed reading the whole text, it will display their scores of reading aloud as shown in Fig. 2, using the automated fluency evaluation system that would be described later in this article. The evaluation uses three patterns of 1) 'not fluent', 2) 'neither' and 3) 'fluent'. These marks are shown in a, b and c in Fig. 2.

The reading-aloud practice recording function keeps record of reading-aloud practices. This function consists of switchable two different screens: visualized display of the number of practices and the evaluations as shown in Fig. 3, and text-written displays of the dates and evaluations as shown in Fig. 4.

The raising game function is created for the purpose of motivating children to practice reading aloud. They can raise a 'character' with their scores and the number of times they are evaluated. They can play with this character, going on adventures in response to the number of times they practiced.

Automatic Evaluation of Oral Read Fluency

As the evaluation of reading fluency, S'IPA proposed in [START_REF] Takita | Fluency of reading reading by children Automatic evaluation index[END_REF] was used. S'IPA averages the time duration of each phoneme recorded in advance in children's readings, and took the difference from what was recorded during the automatic evaluation. This is defined in the following formula. 'IPA' is the time it takes to read the i-th phoneme, comma or period, and 'IPAi, x' is the time the reader 'x' took to read the i-th phoneme, comma or period. 'L' indicates the numbers of phonemes, commas and periods in the reading material. The detailed explanations on 'S'IPA' will be referred in [START_REF] Takita | Fluency of reading reading by children Automatic evaluation index[END_REF].

The evaluation of reading fluency was automatically conducted by quantifying the reading fluency using S'IPA, setting the threshold values. When the result was below the lower threshold value, it is defined as 'fluent', when it is in-between the two thresholds, it is 'neither', and when it is higher than the higher threshold, it is defined 'not fluent'.

In [START_REF] Takita | Fluency of reading reading by children Automatic evaluation index[END_REF], taking into account the close correlation with the fluency, the applicability of the reading fluency evaluation index was verified that indicated that S'IPA was best applicable. In addition, it suggested that CIPA and C'IPA that used average time length of each phoneme in model reading materials are the index adequately applicable to evaluate the reading fluency.

Experiments

After having 8 children participate in the reading-aloud practice for a week, an evaluation experiment was conducted by having a questionnaire survey on both children and their parents. By having the parents evaluate children's reading before and after the practice according to the items of Table 3, the improvement of fluency was observed in all the reading materials as shown in Table 2. Among the reading materials, significant improvement was observed in the material A and C, and those children who practiced reading with the proposed system not only improved in fluency of reading in the practiced material, but also in other materials as well. From this result, it was suggested that the proposed system was capable of enhancing children's general fluency of reading.

Moreover, the usability of the system was asked to the children. The content of the questions and the obtained answers were shown in Table 1. All the question items received favorable answers as shown in Table 1, and it was revealed that they found the proposed system easy to use, and were motivated to practice reading.

Table1 Questionnaire and choices

Table2 Questionnaires about oral reading practice and the proposed system Table3 Result of oral reading fluency evaluation Furthermore, as a questionnaire survey was conducted on the parents, it was reported that there were children who practiced reading-aloud proactively everyday, or who raised hands to speak during Japanese class, as well as those who became better in reading aloud in short time. However, since the system offered only one reading material this time, it was reported that some children got bored after a while.

Conclusion

In this article, an automatic evaluating system on the fluency of reading aloud was developed, using the evaluation index that reflected the evaluation by experienced book readers (to children). In the children's fluency evaluation, the feature amount S'IPA that compared the time duration of each phoneme read by a child with the average time duration of the preliminarily recorded reading. The evaluation experiment of the proposed system revealed that it was capable of enhancing the fluency of children's reading. Moreover, children were able to use the proposed system easily, and became motivated to engage in reading aloud proactively.

On the other hand, as the system offered only one reading material, it would be necessary to have multiple materials to keep children interested.

Fig 1 :Fig 3 :

 13 Fig 1:Record of oral reading practice1 Fig2:Record of oral reading practice2