ORIGINAL ARTICLE

Adrian David Cheok Æ Kok Hwee Goh Æ Wei Liu

Farzam Farbiz Æ Siew Wan Fong Æ Sze Lee Teo

Yu Li Æ Xubo Yang

Human Pacman: a mobile, wide-area entertainment system basedon physical, social, and ubiquitous computing

Received: 5 December 2003 / Accepted: 19 March 2004 / Published online: 30 April 2004� Springer-Verlag London Limited 2004

Abstract Human Pacman is a novel interactive enter-tainment system that ventures to embed the naturalphysical world seamlessly with a fantasy virtual play-ground by capitalizing on mobile computing, wirelessLAN, ubiquitous computing, and motion-trackingtechnologies. Our human Pacman research is a physicalrole-playing augmented-reality computer fantasy to-gether with real human–social and mobile gaming. Itemphasizes collaboration and competition betweenplayers in a wide outdoor physical area which allowsnatural wide-area human–physical movements. Pacmenand Ghosts are now real human players in the realworld, experiencing mixed computer graphics fantasy–reality provided by using the wearable computers. Vir-tual cookies and actual tangible physical objects areincorporated into the game play to provide novel expe-riences of seamless transitions between real and virtualworlds. We believe human Pacman is pioneering a newform of gaming that anchors on physicality, mobility,social interaction, and ubiquitous computing.

Keywords Collaboration Æ Physical interaction Æ Socialcomputing Æ Wearable computer Æ Tangibleinteraction Æ Ubiquitous computing

1 Introduction

In recent years, the world has seen the proliferation ofhighly portable devices, such as personal digital assis-tants (PDAs), laptops, and cellular telephones. Trends incomputing environment development also suggest that

users are gradually being freed from the constraints ofstationary desktop computing with the explosive expan-sion in mobile computing and networking infrastructure.With this technological progress in mind, we havedeveloped human Pacman, a genre of computer enter-tainment that is based on real-world-physical, social, andwide-area mobile-interactive entertainment. The noveltyof this computer game has the following aspects: first, theplayers physically and immersively role-play the charac-ters of the Pacman and the Ghosts, as if a fantasy com-puter digital world has merged with the real physicalworld. Second, users can move about freely in the realworld over wide area indoor and outdoor spaces whilstmaintaining seamless networked social contact with hu-man players in both the real and virtual world. Third,human Pacman also explores novel tangible aspects ofhuman physical movement and perception, both in theplayer’s environment and in the interaction with thedigital world. In other words, objects in the real world areembedded and take on a real-time link and meaning withobjects in the virtual world. For example, to devour thevirtual ‘‘enemy’’, the player has to tap on the real physicalenemy’s shoulder; to obtain a virtual ‘‘magic’’ cookie, theplayer has to physically pick up a real physical treasurebox with an embedded Bluetooth device attached.

Human Pacman ventures to elevate the sense of thrilland suspended disbelief of the players in this untypicalcomputer game. Each of the novel interactionsmentionedis summarized inTable 1.Wewill proceed by firstly givingthe research background for the human Pacman systemand the previous works that have motivated us. Then, wewill give details on the gaming experience of playing hu-man Pacman, as well as clarifying the design of the actualgame play. Finally, we will give details and experimentalresults of a user study performed on the system.

2 Background

Today’s mainstream entertainment revolves aroundinteractivity. People today enjoy entertainment that they

A. D. Cheok (&) Æ K. H. Goh Æ W. Liu Æ F. FarbizS. W. Fong Æ S. L. Teo Æ Y. Li Æ X. YangMixed Reality Laboratory,National University of Singapore, SingaporeE-mail: adriancheok@nus.edu.sg

Present address: X. Yang4 Engineering Drive, Singapore, 117576

Pers Ubiquit Comput (2004) 8: 71–81DOI 10.1007/s00779-004-0267-x

can control, and experience, in which they are fully in-volved [1]. In fact, not only do they want such enter-tainment, they also want to enjoy it together with familyand friends. As shown in [2], one of the top reasons whypeople like to play games is that it is usually a socialactivity people can enjoy with others. Social gaming hasgained popularity since the introduction of networkedgames [2]. Networked games overcame the barrier ofdistance, enabling real people to play against each otherover large areas. After all, there is no opponent like alive opponent, since no current computer model willrival the richness of human interaction [3]. Nevertheless,even in networked computer games, social interactionbetween players is limited since natural interactions,such as behavioral engagement and cognitive states, arelost. Thus, by bringing players into physical proximityfor interaction, human Pacman brings networked socialcomputer gaming to a new ground because humansenjoy being physically together, and socially interactingwith each other [4]. Essentially, human Pacman bringsthe exciting interactive aspects of networked gaming,and merges it with the real physical world, to allow aseamless real-time networked social contact betweenhumans in both the real and virtual worlds simulta-neously.

Human Pacman also has aspects derived from pio-neering work that has been developed in ubiquitousgaming. Multi-player mobile gaming is demonstrated inPirates! [5]. Pirates! implements the game on PDAs withproximity-sensing technology to incorporate a player’scontextual information (such as physical co-location ofplayers and objects in the world) into the game’s contextas important elements of the game’s mechanics. How-ever, visual and sound effects of game play are limited bythe relatively low computing power of PDAs. Aug-mented Reality (AR) and Virtual Reality (VR) cannotbe implemented, therefore, immersive experience is ra-ther limited due to the flat 2-D display used on PDAs.The E3 project [6] examines the essential elements of freeplay, and multi-user social interaction. It focuses on

human-to-physical interaction and human-to-humaninteraction. However, it does not explore a large-scaleconfiguration where users walk around. In the CityWidePerformance project [7], mobile players use handheldPDAs with global positioning systems (GPS) and wire-less communications to access a virtual world whenmoving through the physical world. These mobileplayers compete and collaborate with online players in anetworked game. Similar to Pirates!, visuals are limitedto a 2-D display on the handheld computer, and thetracking resolution of players is rather large.

In the pre-computer age, games were designed andplayed out in the physical world with the use of real-world properties, such as physical objects, our sense ofspace, and spatial relations. Nowadays, computer gamesfocus the user’s attention mainly on the computer screenor a 2-D/3-D virtual environment, thereby, constrainingphysical interactions. However, there seems to be agrowing interest in physical gaming and entertainment,even in industry. Commercial arcade games haverecently seen a growing trend of games that requirehuman–physical movement as part of interaction. Forexample, dancing games such as Dance Dance Revolu-tion and ParaParaParadise [8] are based on playersdancing in time with a musical dance tune and movinggraphical objects (see Fig. 1). However, these systemsstill force the person to stand in more or less the samespot, and focus on a computer screen in front of them.Nevertheless, the underpinning philosophy is similar.One of the goals for human Pacman is to bring physicalgaming into computer entertainment.

Even though human Pacman uses AR techniques aspart of its interface, it is only for providing a compre-hensive user interface for the players. There have beenprevious works which focused on using AR in enter-tainment. AR2 Hockey [9] is a system that allows twousers to hit a virtual puck on a real table, as seenthrough a head-mounted display (HMD). AquaGaunt-let [10] is a multi-player game where players fight withstrange invaders coming from the virtual world, through

Table 1 Detailed descriptions of the features of human Pacman

Feature Details

Physical gaming Players are physically role-playing the characters of Pacman and Ghosts; with wearable computers donned,they use free bodily movements as part of interaction between each person, between the realand virtual world, and among objects in the real wide-area landscapes and virtual environments

Social gaming Players interact both directly with other players when they are in physical proximity, or indirectly via thewireless LAN network by real-time messaging. There is a coherent networked social contact among playersin both the real and virtual worlds, as well as throughout their boundaries. People from all around the worldcan also participate in the human Pacman experience by viewing and collaborating in real time over theinternet with the physical human Pacmen and Ghosts who are immersed in the physical-real-world game

Mobile gaming Players are free to move about in the indoor\outdoor space without being constrained to the 2D\3D screenof desktop computers

Ubiquitouscomputing

Everyday objects throughout the environment seamlessly have a real-time fantasy digital world linkand meaning. There is automatic communication between wearable computers and Bluetooth devicesembedded in physical objects used in game play

Tangible interaction Throughout the game, people interact in a graspable and tangible manner. For example, players need tophysically pick up objects to collect them digitally, or to tap on the shoulder of other players to devour them

Outdoor wide-areagaming arena

Large outdoor areas can be set up for the game whereby players carry out their respective missions for therole they play. This could even be linked throughout cities

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some egg-shaped objects, into the physical space. Thesegames are played in a small and restricted area, withlimited movement, and little interaction with physicalspace. There is no exploration of the physical environ-ment that the player is in. In [11], Starner created a newmobile experience by introducing AR to wearablecomputing. An important mobile AR game is ARQuake[12], which is an AR extension of the popular computergame, Quake. Using a wearable computer equipped withGPS, ARQuake can be played indoors and outdoors.However, it is a single-player game with practically nosocial interaction.

3 System design and game play

Human Pacman features a centralized client–serverarchitecture that is made up of four main entities,namely, a central server, client wearable computers,helper laptops, and Bluetooth-embedded objects. Anoverview of the system is shown in Fig. 2. Wireless LANserves as a communication highway between the wear-able computers, the helper computers (laptops), and theserver desktop computer.

The physical location and players’ status updates aresent from the client wearable computers to the serverevery 10–21 ms, depending on the processing load on the

client. The server maintains up-to-the-minute playerinformation (location, status, etc.), and presides over anycommunication between the Bluetooth objects and thewearable computers. The software flow of the server codeis given in Fig. 3. Since the wearable computers weredeveloped in the lab for this research, we proceed to dis-cuss its detailed configuration, as summarized in Fig. 4.

At the heart of the whole system is a Desknote A980system with a 3 GHz processor and an NVidia GeForce4video card. Twiddler2 acts as a handheld keyboard andmouse input device for the system. The video input of thesurroundings is obtained from a Firefly digital firewirecamera. The Cy-Visor video see-through HMD displaysthe processed video. Data from the InertiaCube2 (whichhas been fastened onto the HMD) is obtained and usedto track the user’s head motion with a dynamic accuracyof 3�. Data obtained from Point Research’s DRM-IIImodule helps in determining the position of the userthrough the direct use of its GPS data, or indirect esti-mation with the dead-reckoning method using its step-counting data, which has an accuracy of 2–5% of thetotal distance traveled. Bluetooth communication ismade with the TDK Bluetooth USB Adaptor. A touch-sensor circuit designed and built in our laboratory usingcapacitive touch sensors, QT160, is used to sense thetouching of the backpack by the enemy player, or thetouching of Bluetooth-embedded objects by Pacmen.

With the software architecture mentioned as thebackbone of the game engine and the hardware as en-abling tools, we proceed to describe the game play ofhuman Pacman1. The main concepts of the game arefirst given in terms of team collaboration, ultimate gameobjectives, and the essential nature of the game’s play-ground, named Pac-World. Then, we move on to presentthe details on the players’ roles as Pacman, Ghost, andHelper, respectively. We end this section by givingexamples of several actual game play situations.

3.1 Main concepts: team collaboration, ultimate gameobjectives and the nature of Pac-World

The players are assigned to two opposing teams, namelythe Pacman team and the Ghost team. The former

Fig. 2 Top-level system design overview of human Pacman

Fig. 1 A player of the ParaParaParadise arcade game

1Videos introducing human Pacman are available online at http://mixedreality.nus.edu.sg/research-HP-videos.htm .

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consists of two Pacmen and two Helpers; correspond-ingly, the latter consists of two Ghosts and two Helpers.Each Pacman or Ghost is in coalition with one Helper,promoting collaboration and interaction between theusers. Since a Helper player is essentially participating inthe game play remotely by using a computer terminalover a wireless LAN, human Pacman can effectively beexpanded to include online players anywhere on Earthwho can view and collaborate, via the Internet, with realhuman Pacmen and Ghosts who are immersed in thephysical playground.

Ever since its introduction by Namco to Japanesearcade fans in 1979, Pacman has gone through numer-ous stages of development. Yet, the ultimate goal of thegame remains fundamentally unchanged. We havedesigned human Pacman to be in close resemblance tothe original Pacman in terms of game objectives so thatthe players’ learning curves are very much leveled to thepoint where they can pick up the game in very little timeand enjoy the associated familiarity. Basically, the goalof the Pacman team is to collect all virtual plain cookiesand hidden special cookies in Pac-World whilst avoidingthe Ghosts. On the other hand, the aim of the Ghostteam is to devour all Pacmen in Pac-World. To add tothe excitement of the game play, after ‘‘eating’’ a specialcookie, a Pacman gains Ghost-devouring capability and,henceforth, can attack her enemy for a limited period oftime.

Pac-World is a fantasy world existing simultaneouslyin physical reality, in AR and VR modes. Pacmen andGhosts, who are walking around in the real world withtheir networked wearable computers and HMD, view

the world in AR mode. Helpers, on the other hand, canview it in VR mode since they are stationed in front ofnetworked computers. Most importantly, there is a di-rect and real-time link between the wide-area physicalworld and the virtual Pac-World at all times, thus,providing the users with a ubiquitous and seamlessmerging of the fantasy digital world and the realisticphysical world. As seen in Fig. 5, where the 2-D map ofthe selected game play area on our university campusand the 3-D map of Pac-World are shown side-by-side,we have converted the real world to a fantasy virtualplayground by ingraining the latter with direct physicalcorrespondences. This is done with the help of the dead-reckoning module (DRM-III) and inertia sensors(InertiaCube2).

The real-time position of each mobile user is sentperiodically to the server through the wireless LAN.Upon receiving the position data, the server sends anupdate to each wearable computer detailing the positionof the other mobile players, as well as the positions of all‘‘non-eaten’’ plain cookies.

3.2 Pacman, Ghost, and Helper

Pacman has to physically move within the game area tocollect all virtual plain cookies overlaid in the real world,as seen through her HMD (see Fig. 6). In addition, shehas to find and collect special cookies in the virtual Pac-World. These are directly linked and represented byBluetooth-embedded objects, shown in Fig. 7. Thiscreates a sense of presence and immersion within thevirtual Pac-World, as well as a feeling of active partici-pation in the real world.

The Ghost can devour a Pacman by tapping on acapacitive sensor attached to a Pacman’s shoulder.Likewise, a Ghost can be devoured by Pacmen endowedwith Ghost-devouring powers. Such tangible physicalinteraction between humans, commonly found in tradi-tional games such as hide-and-seek and the classic‘‘catching’’ game, is now revived in this computer gam-ing arena.

Each Pacman and Ghost will be assigned a partnerHelper who acts as an intelligence, advisor, and coor-dinator in her quest to achieve her goal. To enhance thegaming experience for both Pacmen and Ghosts, theseplayers in the physical world with wearable computersare not able to see enemy mobile units (the positions ofthe enemies are not shown on the virtual map, and there

Fig. 3 Flowchart of server code

Fig. 5 Two-dimensional map of game area and its corresponding3-D map of Pac-World

Hardware Components of Wearable Computer

Backpack

Desknote

Touch Sensor DRM-III Wireless

LAN card

Cy-Visor HMD

Inertia Cube

Twiddler

Firefly

Battery

Fig. 4 Detailed configuration of the wearable computer system

74

is no AR labelling on them) and hidden special cookies.The Helper, who is in VR mode and sees all, guides herpartner by messaging her with important information, asshown in Fig. 8. This promotes collaboration andinteraction between players through the internet.

3.3 Actual game play

Collection of plain cookies Pacman collects a cookie bywalking through it. Such a physical action is reflectedvisually in Pac-World through the disappearance of thecookie in both the AR and VR mode. In Fig. 9, the topimages show the HMD view of the Pacman player as shecollects a cookie. When she walks through the cookie,the cookie disappears. This collection is also reflected inreal time in the virtual Pac-World (seen by the Helpers)and the Pac-World map (seen by both Pacmen andGhosts) through the disappearance of the cookie in thecorresponding location.

Ghosts cannot collect cookies. Although a Ghost isnot able to see the enemy Pacman on the map, the dis-appearance of cookies in her map can give her a hint asto where to find a Pacman. Therefore, a Pacman has tobe careful as her physical interaction with the real world(i.e., movement) can be digitally reflected in the virtualworld, and be made used of by a Ghost. Novelty is againseen in such an intimate relationship between interactionin the physical world and its effect in the fantasy virtualworld. Neither physical distance nor mobility could re-strict each player from seeing this real-time effect as allplayers, including the Ghosts, can see an update of thevirtual map in real time.

Collection of special cookies Pacman collects a specialcookie by touching real Bluetooth-embedded objectsplaced in different parts of the game area. In Fig. 10, asequence of pictures shows a Pacman collecting a spe-cial cookie. When the Pacman is within range of theBluetooth object (a distance of about 10 m), commu-nication takes place between the wearable computerand the Bluetooth device. The wearable computer sendsthe unique address of the Bluetooth device to the ser-ver. Upon receiving it, the server will then decide if theplayer is eligible to collect the special cookie that isassociated with the physical Bluetooth object. If theplayer is not eligible (e.g., she has already collected itpreviously), she will not be alerted to the object.Otherwise, an alert message will be shown in theplayer’s HMD display.

The player has to hunt for the Bluetooth-embeddedobject in the surrounding physical area upon receivingthe alert message, thus, adding elements of fun andadventure to the game play. Having found the object,the collection is done simply by physically holding theobject in her hands. Once haptic data is collected bythe touch sensor, the Bluetooth device embedded in theobject will send an alert message to the wearable com-puter, which will in turn be relayed to the server.

Fig. 6 First-person view of human Pacman

Fig. 7 Bluetooth-embedded object

Fig. 8 Close collaboration between Pacman and her Helper

Fig. 9 Pacman collecting cookies

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The server performs a legitimacy check on the play-er’s action and then proceeds to update its database aswell as informing the wearable computer. The collectionof the special cookie exemplifies a natural tangibleinteraction involving physically interacting with thisobject through human touch. Pacman is able to hold areal object naturally in her hands as should be in real-lifetreasure finding. Such a tangible action provides theplayer with a sense of touch in the fantasy domain of thegame play. The collected special cookie will be kept in avirtual inventory list. As seen in the figure, collection isshown by an addition of an icon to the inventory listafter the special cookie has been collected. Pacman neednot lug the physical object with her as she has collectedthe special cookie virtually.

Collaboration between players There is an essentialelement of collaboration in the game play between aPacman or Ghost with her Helper, and between anyallied Pacman.

(I) Pacman or Ghost and Helper collaboration. TheHelper is in a good position to assist her partner as shehas a complete view of Pac-World all of the time,including the positions of all players and special cookies.Furthermore, as Helpers within the same team arephysically close, they are able to collaborate betweenthemselves and work out a strategy to achieve the team’sgoal. The advantage of this setup is that social interac-tion and collaboration is significant between Helpers, aswell as between the Helper and her partner.

(ii) Pacman and Pacman collaboration. Pacmanplayers collaborate through the transferring of specialcookies between them. However, so as not to disad-vantage Ghosts, Pacmen are only allowed the transfervia Bluetooth. This enforces a proximity requirement forthis exchange. For example, Pacman A can initiate arequest for the list of unused special cookies that Pac-man B has. Upon approval, A can request the transfer of

a special cookie from B, subjected to approval by B.Transfer of the special cookie is important as a Pacmanmay not be able to comb the whole game area for thespecial cookie. Strategy and team work could beimplemented, with coordination from the Helpers, todistribute special cookies between the Pacmen.

Use of special cookies All special cookies can only beused once. When a Pacman consumes a special cookie,she will see an alert message in her HMD, informing herof the 1 min Ghost-devouring power she has acquired. Inreal time, a label describing her acquired power will alsobe placed on top of her Pacman avatar in the VR mode.This serves to inform allHelpers, including those from theGhost team, of her ability. This is illustrated in Fig. 11.

Devouring enemy players To devour a Pacman, aGhost must physically touch Pacman’s shoulders (seeFig. 12) to trigger the touch sensor located there. Thesame applies when a Pacman with Ghost-devouringcapability devours a Ghost. When a Pacman or Ghostis devoured, she loses one life point of her two lifepoints. Devouring involves tangible physical touchcontact between two players. As close proximity is in-volved, other forms of human interaction come intoplay. The act of devouring makes the game more tan-gible and fun by involving more types of naturalphysical movement. When a Pacman player is the prey,her agility determines the ‘‘life-and-death’’ of her vir-tual Pacman role. Hence, not only is tangibilitybrought to play in this fantasy world, but also otherhuman perceptions and instincts. Thus, this computergame provides the benefits of natural wide-area freebodily movements as part of humanistic interactionbetween each person.

Fig. 11 HMD display and the corresponding VR mode view

Fig. 12 Ghost catching a Pacman

Fig. 10 Sequence of pictures showing the collection of a specialcookie

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Ending the game The game ends when either teammeets its goal or when a time limit of 15 min (chosenarbitrarily) has been reached.

4 User study

To gain useful feedback from the end user, we conductedan experimental user study survey on the human Pac-man system. Our aim is to find out from the actual users,their experience of the positive and negative aspects,interaction, and level of enjoyment in playing the humanPacman game. In these tests, the focus had been placedon the different novel experiences offered by the game.Our study involved 23 subjects between the age of 21and 33, of which eight were females and 15 were males.Amongst these people, 39% indicated their level ofexpertise in computers as advanced, 43% as intermedi-ate, and the rest as beginners.

The experiment setup consisted of four parts. First,the subject was asked to play traditional arcade Pacmangames on a desktop computer for 5 min. Then, a 3-minhuman Pacman video was shown to give him or her abetter understanding of the game. This was followed bya 15-min trial where the subject tried the roles of Pac-man, Ghost, and Pacman’s Helper for 5-min each,alongside other subjects taking a different role. An ex-pert user acted as the Ghost’s Helper. Finally, the sub-ject had to fill in a questionnaire and provide commentson the system.

Questions and aims Table 2 shows the list of questionsthat were asked in the survey. Following each question isthe reason for asking this question in the user study.Except for questions (I), (iv), (xi), and (xvi), multiplechoices are given for all other questions.

Figure 13 gives the user study results of all of themultiple-choice questions listed earlier. The options foreach question and the percentage of users who choseeach option are given in the figures.

4.1 Discussion

In this section, the response to the multiple-choicequestions will be discussed. All of the data have beenanalyzed using statistical methods. However, due to lackof space, only the data obtained from (I), (iv), and (xi)will be analyzed in detail in this paper. Insights providedby users’ comments from question (xvi) are also used inthe analysis.

Questions (i), (x), (xii), and (xiii) examine how wellreceived human Pacman is by its users, and how itcompares with respect to other types of games in termsof user preference. As seen from the respective findingsgiven in Fig. 13, most of the users are enthusiastic abouthuman Pacman. However, it is noted that, when com-pared with the traditional ‘‘Catch Me’’ game, 34.8% ofthe users gave a neutral stand in their preference. Results

from (I) gives an average rating of 5.85 (with a varianceof 1.46) indicating that human Pacman is much morefavored than normal Pacman in terms of entertainmentvalue. Statistical analysis with a t-test confirms the sig-nificance of our inference (p=6.72·10)7).

The element of physicality may have been the pushingfactor for the preference shown towards human Pacmanover arcade Pacman and conventional computer games.However, this is not so much of a benefit over the tra-ditional ‘‘Catch Me’’ game (which, by itself, is a gamethat involves a high level of physical participation). Anumber of users commented that they liked the idea of‘‘physical involvement’’ and ‘‘physical movement’’ inhuman Pacman. Some said that such movement is a goodform of exercise. Note that 60.9% of the users still preferhuman Pacman over the traditional ‘‘Catch Me’’ game.This indicates that the element of physical involvement inhuman Pacman is not its sole attraction. The immersiveexperience in the role-playing of Pacman could be an-other element that users enjoyed over arcade Pacman andconventional computer games. Findings from question(iv) gives the average level of excitement rated by thesubjects to be 6.0 (with a variance of 0.182) for the first-person experience in Pac-World and 3.33 (with a varianceof 0.97) for the third-person experience in arcade Pac-man, indicating a higher level of excitement in the former.A non-parametric two-conditionWilcoxon statistical testconfirms the significant difference in the feeling ofexcitement by the players at a level of p=4.88·10)4.

As reflected by many users, the backpack holding thewearable computer system is bulky and heavy, and theHMD is cumbersome to wear. As seen from the resultsobtained for question (ii), 73.9% of the users found thewearable computer to be uncomfortable. This could bethe deterring factor for 77% of those who indicated thatthey liked playing human Pacman, but would refrainfrom playing it frequently. The absence of equipmentweighing down the user could also make the traditional‘‘Catch Me’’ game more attractive as one is unencum-bered physically.

Despite not being a normal day-to-day experience,collection of virtual cookies by walking through them isdeemed to be intuitive by 87% of the users (as seen inFig. 13(iii)). The rest found the experience to beacceptable, though not intuitive. Findings for question(v) show that 78.3% found that the use of virtualcookies enhances the game, whereas 17.4% feel that thecookies are acceptable as virtual objects, but it fail toenhance the game.

A shift in alignment of virtual cookies from its sup-posed absolute position in real space (caused by sensingdrifts), mentioned by some users, could be the reasonwhy virtual cookies seem lacking to some users in beingrealistic and, thus, its inability to enhance the game. Asthe views of virtual cookies are calculated with respect tothe user’s location, any discrepancies in her exact posi-tion may lead to the ‘‘shifting’’ of the absolute positionof the virtual cookies in real space. Since the system usesa DRM-III module and the dead-reckoning method to

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Table

2Questionsin

theuserstudy

Question

Reasonforasking

I.How

doyourankhumanPacm

ancomparedwiththenorm

alPacm

angamein

term

sofentertainmentvalue?

Please

rate

between1(norm

alPacm

anmore

entertaining)to

7(humanPacm

anmore

entertaining).

Astheidea

ofhumanPacm

anoriginatesfrom

thepreviousarcadePacm

an,the

fundamentalconceptofgameplayissimilar.Thequestionaim

sto

findoutifany

valuehasbeenadded

totheold

Pacm

angamein

thenew

system

ii.How

comfortable

doyoufeel

when

youare

usinghumanPacm

ansystem

?Thewearable

computersystem

isstillrather

bulkyandheavycomparedto

mobile

devices

such

asphones,GameBoys,andPDAs.Wewantto

findoutif,andby

how

much,itaffects

thelevel

ofcomfort

oftheuserwhen

userdonsit

iii.How

intuitivedoyouthinkitisto

collectcookiesbyphysicallywalking

throughthem

?In

everydaylife,collectionofanitem

isseldom,ifever,madebywalkingthroughit.

Weseek

tounderstandiftheuserfindsitintuitiveto

collectvirtualcookiesbywalking

throughthem

,just

asitisdonein

theoriginalPacm

angame

iv.Please

rate,from

1(lowest)

to7(highest),thelevel

ofexcitementofplaying

asaPacm

anin

Pac-World(first-personexperience),in

comparisonwiththearcade

Pacm

anthatyoucanplayusingjoystick/keyboard

(third-personexperience)?

Wewantto

findoutiftheim

mersiveexperience

ofhumanPacm

anmakes

thegame

more

exciting.ArcadePacm

anisusedasthebaselineforcomparisonasitis

fundamentallysimilarin

gameplay

v.Whatdoyouthinkofdisplaying‘‘cookies’’asvirtualobjectsaugmentedinside

therealworld?

From

thisquestion,wewantto

findouthow

realistic

istheexperience

ofcollecting

virtualcookiesusingAR

vi.Does

thephysicalcollectionofarealobject

(specialcookies)

enhance

the

gamingexperiences?

Thecollectionofspecialcookiesisatangible

interactionwithaphysicalobject

that

translatesinto

adigitalmeaning(i.e.,update

ofPacm

an’sinventory

list).Wewant

tofindoutifsuch

graspable

interactionenhancesthegamefortheuser

vii.How

doyoufeel

aboutthecollaborationofthePacm

anandtheHelper

inthehumanPacm

angame?

TheHelper

role

isadded

tobringin

anelem

entofcollaborativeexperience

betweenthe

humanplayers.However,itmakes

thegamemore

sophisticated.Thequestionaim

sto

findoutifsuch

collaborationmakes

thegamemore

exciting,ordoes

itmakes

thegame

overly

complex

viii.Does

theVR

modegiveyouagoodidea

aboutthegameenvironment?

Itisim

portantfortheHelper

tounderstandthesituationher

partner

isin

soasto

dispense

theappropriate

advice.

Theabilityto

comprehendthegameenvironment

from

theVR

mode(‘‘G

odsview’’)isessentialin

helpingher

accessthesituation.

Thus,wewantedto

seeifthisisconfirm

edin

theuser’sopinion

ix.Whatdoyouthinkofthe‘‘capturing’’eventim

plementedin

oursystem

(touchingthePacm

anbytheGhost)?

The‘‘capturing’’eventisareflectionofthenaturalistic

andphysicalapproach

human

Pacm

antooktowardstangible

interaction.Weseek

tofindoutifuserenjoyed

thisfeature

x.Did

youlikeplayingthehumanPacm

angame?

Havingreflectedonthegamebyansw

eringthepreviousquestions,theuserisquizzed

ontheoveralllevel

ofinterest

shehasonhumanPacm

an

xi.Please

rate,from

1(lowest)

to7(highest),thefeelingof‘‘socialinteraction’’

inbeingtheGhost,thePacm

an,andtheHelper.

Wewantto

findoutthelevel

ofsocialinteractionexperiencedbytheuserin

each

role

xii.How

doyoucompare

thisgamewithother

computergames?

AshumanPacm

anaim

sto

extendanddiffer

itselffrom

conventionalthehuman–

computerinterface

usedin

norm

alcomputergames,thisquestioninvestigateshow

well

hashumanPacm

anachieved

itsaim

xiii.How

doyoucompare

humanPacm

anwiththetraditional‘‘CatchMe’’game?

Thisquestionlooksathow

humanPacm

ancompareswithsimple,non-computer-based

games.Thetraditional‘‘CatchMe’’gameisusedasabasisforcomparisondueto

its

similarity

withthe‘‘capturing’’eventin

humanPacm

an.Wewantto

seeifaddingthe

fantasy

elem

enthasanybenefitin

theuser’senjoymentover

anorm

alcatchgame

xiv.If

thereissuch

agamein

anamusementpark,how

much

are

youwilling

topayto

playthegame?

Currently,acquiringthewhole

humanPacm

ansystem

requires

ahighoverhead,

soacommerciallyviable

versionofthesystem

could

only

besustained

bybeingbased

onapay-per-use

basis,whichisthenorm

inamusementparks.Thisquestion

investigatestheamountofrevenueper

personthesystem

could

bringin

ifim

plementedcommercially.Thequestionisasked

toseeifthereisalinkbetween

such

researchsystem

s,andpotentialcommercialuse

xv.How

often

doyouplaycomputergames?

Thisquestionfindsouthow

frequentlytheuserplaycomputergames.Thisenables

usto

findoutifher

loveforconventionalcomputergames

would

influence

her

desire

toplayhumanPacm

an

xvi.Please

giveussomecomments

onhow

wecanim

provethesystem

and

whatthecurrentdrawbacksofthesystem

are

Weseek

users’comments

onoursystem

tofurther

improveitin

areaswemayhave

neglected

78

estimate the displacement of the user, an inaccurateestimation of her stride (which varies with the individ-ual) or the wrong count for the number of steps takenwill introduce errors into the estimate. The location ofthe user thus computed is an estimate and may not re-flect her true position in the physical space. Some usershave reflected that the DRM-III module failed to senseall of the footsteps taken by the user.

Users also found the visual cue of the cookie collec-tion (i.e., cookies disappearing from the AR world whencollected) to be weak and insufficient in providing a‘‘better feel’’ of collection. A number of users suggestedusing sound, for example a ‘‘beep’’, to indicate the col-lection of each virtual cookie. A lack of realistic affor-dance of virtual cookies makes reliance on other cues, toindicate collection, more important.

Fig. 13 Graphs of the resultsfor all multiple-choice questions(not including (I), (iv), (xi), and(xvi) which, due to lack ofspace, are described in the textonly)

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On the issue of the tangible interaction element inhuman Pacman, 78.3% (as seen in Fig. 13(vi)) foundthat the graspable interaction offered by the collection ofreal objects enhances the game. The other 21.7% gave aneutral response towards having this collection as partof the game. Almost all of the users indicated in question(ix) that they liked the ‘‘capturing’’ event. Despite bothevents being naturalistic interactions with the physicalworld, users seemed to like the ‘‘capturing’’ event more.This suggests the physical human-to-human interactionin the process of ‘‘capturing’’ makes the event moreenjoyable.

In response to question (vii), 34.8% of the users didnot find that the Helper role makes the game moreexciting. In fact, 17.4% found that it makes the gametoo complex. Results obtained for question (xi) showsthat the feeling of having social interaction has ratedmeans of 5.67, 5.41, and 4.17 with variances of 0.97,1.17, and 0.88 in playing as Pacman, Ghost, and Helper,respectively. The non-parametric Wilcoxon test showsinsignificant difference in the level of social interactionbetween the Pacman and the Ghost (p=0.5), while thedifference between being the Ghost and the Helper issignificant, with p=0.0039. The Helper role is perceivedto have a lesser social interaction compared to the otherroles. As the study does not involve a trial of the role ofthe Helper in a full-scale-length game, the users may nothave been able to fully comprehend the essence of theHelper role.

As reflected by the response for question (viii), almostall of the users are able to comprehend the game envi-ronment from the VR mode. It is noted that more thanhalf of the users feel that more improvement still needsto be made for the VR mode. Users would like to seebetter 3D graphics and more variety of virtual objects inthe VR world. Perhaps the lack of a visually appealing3D interface compared to that found in commercialcomputer games makes the Helper role less attractive(our 3D models are non-commercial and designed in thelaboratory by students).

Based on the results from question (xiv), the averageamount that users are willing to spend to play humanPacman in amusement parks is SGD$8.15, with a vari-ance of 16.5. This is in the typical price range ofamusement rides available locally. It is noted that the17.4% who would pay less than SGD$5 to play humanPacman also indicated in question (xv) that they seldomplay computer games. Perhaps they do not enjoy playinggames and are, therefore, less willing to spend on it.

4.2 Summary of findings and future work

We believe that the findings indicate that users like theidea of human Pacman as a whole. This is seen fromtheir attitude towards playing the game, their willingnessto pay to play the game, and their preference of humanPacman over other types of games. It is promising thatthe users were positive about the physical interaction

aspects of the game, such as the first-person point-of-view and the tangible interactive elements. However, it isclear that improvements can be made to reduce the sizeand weight of the wearable computer.

On the individual elements of human Pacman, thecollection of virtual cookies is well accepted, thoughimprovements can be made to make the whole experi-ence of moving towards virtual cookies and collecting itmore realistic. Sound could be added as a cue to thecollection. More accurate and precise tracking devicescould also be developed to minimize error in locationtracking, which was a factor of disapproval from theusers.

Though both the ‘‘capturing’’ event and collection ofphysical objects add value to the game, it is found thatthe former is preferred. This could be because, duringthe ‘‘capturing’’ of Pacman, physical human-to-humaninteraction is involved, along with other forms of humaninteraction that comes into play (e.g., shrieking). Thestudy also shows that the immersive experience is valuedby users. Users like to be ‘‘physically involved’’ in thisfirst-person gaming experience. This positive reception isimportant to note, as the tangible and physical aspectsintroduced into human Pacman are one of its majorthesis.

As for the issue of having the Helper role in humanPacman, a less than enthusiastic response is obtainedfrom a large portion of users, with half of these usersfeeling that it makes the game too complex. A more in-depth study will, in future, be made on why suchsentiment is prevalent. A preliminary suggestion is thelack of a full-length trial of the game in the experimentfor the user to fully appreciate the important roleplayed by the Helper. Improvements in the aestheticalvalue of the VR mode may also make the Helper rolemore enticing.

Despite encouraging responses from the users, thehuman Pacman system is still unsuitable for commercialproduction for the following reasons:

– The cost of each set of wearable computer system isvery high as they are lab prototypes

– The bulkiness and heaviness of the prototype wear-able computer and HMD restricts the user to onlywalking, though the short response time of the systemsoftware does totally allow for quick movement, suchas running

– An accurate and sensitive positioning system is neededto enhance the realism of the game

– The robustness of the system needs improvement

5 Conclusion

The continual propagation of digital communicationand entertainment in recent years has forced manychanges in societal psyche and lifestyle, that is, how wethink, work, and play. With physical and mobile gaminggaining popularity, traditional paradigms of entertain-

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ment will irrevocably shake one from the stale televisionset inertia. We believe that human Pacman heralds theconjuration and growth of a new genre of computergame that is built on mobility, physical actions, and thereal world as a playground. Reality, in this case, isbecoming more exotic than fantasy because of the mixedreality element in the game play. On the other hand,emphasis on physical actions might even bring forth theevolvement of professional physical gaming as a com-petitive sport of the future, for example ‘‘PacmanInternational League’’.

The element of social gaming in human Pacmansymbolizes the nascence of humanity in future digitalentertainment. People are looking forwards to wideningtheir circle of friends and colleagues through socialcollaboration in game play. A new form of interactiveentertainment has evolved.

Another important area of impact is the field ofeducation. The technology presented in human Pacmancan be exported to applications in educational trainingthat stress ‘‘learn by experience’’. Students are immersedin the real site of action, and are given instructionsvisually through head-mounted displays or verballythrough speakers or earphones. This technology servesas a powerful instrument of cognition since it can en-hance both experimenting and reflective thoughtsthrough mixed reality and interactive experience.

In conclusion, we believe human Pacman is a novelsystem in the new hybrid field of physical, social, andmobile gaming that is built on ubiquitous computingand networking technology. The players are able toexperience seamless links between the real and virtualworlds and, therefore, a higher than ever level of sensorygratification is obtained.

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