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Uncomfortable User Experience

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5 Editor’s Letter 28 Law and Technology Has The Innovation Cup Run Dry? What to Do About Google? By Moshe Y. Vardi Whether it is acting as a conduit, an editor, or an advisor, the search 7 From the President engine should put user interests first. Freedom and the Social Contract By James Grimmelmann By Vinton G. Cerf 31 Historical Reflections 8 Letters to the Editor Software and Souls; For Privacy and Security, Programs and Packages Use Public Keys Everywhere How can historians tell stories about software without focusing 10 BLOG@CACM solely on the code itself? Big Data Is ‘Buzzword du Jour;’ By Thomas Haigh CS Academics ‘Have the Best Job’ 13 Michael Stonebraker analyzes 35 The Profession of IT the different varieties of Big Data, 13 Magnetic Diversion The Other Side of Language while Judy Robertson for Electronic Switches The conversation for action gives considers the rewards of ‘Chameleon processors’ could a framework for completing teaching computer science. function as programmable logic professional actions effectively. or nonvolatile memory. By Peter J. Denning 43 Calendar By Chris Edwards 38 Viewpoint 107 Careers 16 Software-Defined Networking Research and Practice: Novel architecture allows The Curious Case of ‘Small’ programmers to quickly reconfigure Researchers-Practitioners Last Byte network resource usage. Seeking a more efficient combination By Keith Kirkpatrick of the best elements of the research 110 Puzzled Answers and practice communities in Solutions and Sources 20 Ephemeral Data small organizations. By Peter Winkler Privacy issues can evaporate when By Željko Obrenovi´c embarrassing content does likewise. 112 Q&A By Esther Shein 41 Interview Big Challenge An Interview with Hadi Partovi Jeff Dean and Sanjay Ghemawat 24 Remembering Douglas Engelbart The Code.org founder discusses talk about scalability. By Laura DiDio his first program, inspirations, By Leah Hoffmann and “seizing the day.” By Lawrence Snyder

Association for Computing Machinery Advancing Computing as a Science & Profession h by Joan Chang Joan p h by Photogra

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Practice Contributed Articles Review Articles

54 66 84

46 The Balancing Act of Choosing 66 Uncomfortable User Experience 84 Verifying Autonomous Systems Nonblocking Features How to create and resolve Exploring autonomous systems Design requirements discomfort for a thrilling and and the agents that control them. of nonblocking systems. memorable experience. By Michael Fisher, Louise Dennis, By Maged M. Michael By Steve Benford, Chris Greenhalgh, and Matt Webster Gabriella Giannachi, Brendan Walker, 54 20 Obstacles to Scalability Joe Marshall, and Tom Rodden s Watch out for these pitfalls that Research Highlights can prevent Web application scaling. 74 Computing with Real Numbers, By Sean Hull from Archimedes to Turing 96 Technical Perspective o ci ate s Ass and Beyond Progress in Visual Categorization 59 An Overview of Non-Uniform How to test the usefulness By Pietro Perona Memory Access of computation for A n d r ij B ory ta/ NUMA becomes more common understanding and predicting 97 Visual Object Detection with because memory controllers continuous phenomena. Deformable Part Models get close to execution units By Mark Braverman By Pedro Felzenszwalb, Ross Girshick, on microprocessors. David McAllester, and Deva Ramanan By Christoph Lameter on by A l ici a K ub is i on by trat

Articles’ development led by queue.acm.org s d ; Illu Downar arry

About the Cover: on by B i on by trat While art and cinema have long been known for exploring ways to make the viewer feel anxious or frightened, this month’s cover story (p. 66) focuses on the benefits of designing

s i llu c k. om; Photo to computer games, apps, amusement rides, and other online experiences with the deliberate purpose of making the user feel uncomfortable. Cover photo illustration by Barry

Image from Shutter s Image Downard.

september 2013 | vol. 56 | no. 9 | communications of the acm 3 communications of the acm Trusted insights for computing’s leading professionals.

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doi:10.1145/2500889 and sociality. We draw on our experi- How to create and resolve discomfort for ence creating and studying interactive performances and amusement park a thrilling and memorable experience. rides to explore how discomfort can address the following questions: by Steve Benford, Chris Greenhalgh, ˲˲ What are the potential benefits of Gabriella Giannachi, Brendan Walker, uncomfortable interaction?; Joe Marshall, and Tom Rodden ˲˲ What forms can such interaction take?; ˲˲ How can discomfort be created?; ˲˲ How can it be embedded in an experience?; and Uncomfortable ˲˲ What ethical challenges must be addressed?

Benefits User Uncomfortable interaction causes a degree of suffering to the user, men- tally through suspense, fear, and anxiety or even physically through Experience movement, exertion, and pain. While suffering is not the goal of a cultural experience, discomfort is often employed in a transitory way to realize three key benefits: Entertainment. Discomfort can arouse and excite and so entertain us. Amusement park rides employ The increasing use of computers in games, rides, extreme acceleration, sudden drops, performances, installations, and other cultural and inversions to create the visceral sensation of thrill, while games and experiences is shifting the focus of user-experience films (rides, too) employ an uncom- design from the traditional usability goals of fortable feeling of suspense through anticipation of dangers to come. Dis- learnability, performance, and minimizing errors comfort may increase the subjective to new ones, like fostering emotional and aesthetic intensity and memorability of such engagement.17 This switch inspires unconventional an experience, heightening a participant’s sense of flow, or the psychologi- approaches that turn traditional interaction design cal state of deep focus associated with on its head, as in, say, celebrating the role of immersive activities like computer ambiguity rather than clarity11 and transforming games.5 4 system limitations into opportunities. Here, we key insights integrate perspectives from human-computer T he deliberate use of discomfort in interaction (HCI) and performance studies to explore interaction design can help produce a more entertaining, enlightening, the deliberate engineering of discomfort as a way to socially bonding cultural experience. create intense, memorable interactions and engage Designers can employ combinations d Downar arry of visceral and cultural discomfort challenging themes. by distorting control and social relationships.

Uncomfortable interaction—managed carefully B i on by trat Embedding discomfort into an overall and ethically—may become an important tool for user experience must be done with care and reflect ethical considerations. designers, promoting entertainment, enlightenment, s Illu Photo

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Enlightenment. Discomfort can terfaces have also experimented with frame our engagement with challeng- discomfort; for example, users of “The ing themes, provoking us to reflect Meatbook” (2007) interacted with the on our feelings and responses. Artis- system by manipulating raw meat;14 tic works that confront challenging exertion games involving intense or themes may employ discomfort to es- Designers may stressful physical interaction (such as tablish an appropriate tone, demand prefer materials punching, kicking, and hanging from personal commitment, avoid trivial- ceiling bars);18 “I Seek the Nerves Un- ization, and promote empathy and that are rough, der Your Skin” requiring participants respect. Religious and spiritual prac- tight, prickly, to increase their running pace to hear tices may involve abstinence, fasting, a frantic punk poem;15 and “Mediated and asceticism. sweaty, or Body” transgressing conventional so- Sociality. Confronting discomfort otherwise cial norms by requiring participants can prompt social bonding through to stroke a performer’s body in public shared rites of passage, as in, say, a physically view to explore an interactive sound- child’s “first” roller coaster ride8 or scape.13 adolescent boys watching horror films unpleasant. Even this brief dip into the arts and together.12 The same principle is in entertainment reflects how routinely effect in team-development activities discomfort is employed in all man- involving physically demanding tasks. ner of cultural experiences. In order to ground a more in-depth exploration of Examples the phenomenon consider the follow- The arts, especially the performing ing examples: arts, involve a longstanding tradition “Breathless.” This prototype of discomfort. In the 1930s, German amusement park ride, created as part poet and playwright Bertold Brecht of the Horizon Centre for Digital Econ- proclaimed theater should contain omy Research Day in the Park project, some level of verfremdung (alien- focuses on entertainment in the main- ation), causing unease or discomfort stream setting of an amusement park by encouraging the audience to look as part of a long-term exploration of at something or someone from an- future ride technologies. An early other’s point of view.3 The latter part prototype in which a conventional of the 20th century saw numerous per- bucking-bronco ride was controlled formances that pushed the boundar- through a chest-strap breathing moni- ies of discomfort, including Marina tor highlighted the potential of using Abramovi´c’s “Rhythm O” (1974) breathing to control rides, especially where the audience was encouraged by requiring riders to simultaneously to apply a gun, bullet, pocket knife, battle the ride and their own physi- axe, and matches to a performer’s cal response, focusing them inward body and Vito Acconci’s “Project for on their own feelings.16 “Breathless” Pier 17” (1971) where the audience extended this approach in 2011 by was invited to a late-night meeting on upping the discomfort level through a derelict pier to hear Acconci confess respiration sensors embedded into a secret. Since the 1990s, the Cypriot- a Wi-Fi-enabled gas mask to control Australian performance artist Ste- a powered swing while requiring the larc has created a series of works in rider to breathe in harmony with the which audience members are invited swing’s resonant frequency to make it to observe his suspended body being go higher. moved and controlled by machinery This control mechanism was em- and, in one memorable case, remotely bedded in an overall ride experience controlled through electric stimuli.21 through a design inspired by Frago- While artists may intend to push nard’s painting “The Swing” (1767), the boundaries, discomfort is also an erotic scene involving three peo- found in mainstream entertainment, ple: a woman on a swing, a voyeur in from the visceral thrills and scares of the bushes watching the woman’s ex- an amusement park ride to the sus- posed legs, and a bishop controlling pense of computer games, with the the swing through a pull rope (see Fig- latter including even commodity elec- ure 1). This scene was mapped onto a tric-shock game controllers.9 HCI re- ride structure in which a participant searchers and designers of tangible in- would move among three distinct

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roles: voyeur, rider, and controller. Figure 1. Rider on the Swing, with human controller in background, in “Breathless.” Upon arrival, participants would join a queue, to be fitted with a gas mask when reaching the front. They were then taken to a specific location where they would be the voyeur watching a floodlit rider swinging before them. Next, they mounted the swing as the new rider and subsequently took the role of controller. Each ride began with the controller’s breathing driving the swing but transferring swing control over to the rider halfway through. “Ulrike and Eamon Compliant.” In contrast, in an example from the arts, the British artists Blast Theory are re- nowned for their mobile and interactive performances, several of which have been studied within the HCI con- text.2 “Ulrike and Eamon Compliant,” created for the 2009 Venice Biennale, addresses the theme of terrorism, in- viting participants to enter the minds of one of two notorious international terrorists, Ulrike Meinhof and Eamon Collins. The work takes the form of a solo city walk where participants receive a series of automated phone calls guiding their direction while nar- rating episodes from the lives of either Ulrike or Eamon, detailing the events Figure 2. Complying with an instruction in “Ulrike and Eamon Compliant.” leading to their terrorist acts, their subsequent arrests, and ultimately their deaths. The instructions are de- signed to establish a sense of constant surveillance and increasing compliance through such tactics as requiring participants to perform physical ges- tures (such as stopping in the middle of a bridge and touching their heads) (see Figure 2) or taking off their sun- glasses and sitting on a bench. They are twice asked to confirm they wish to proceed. Participants are eventually guided to a deserted alleyway leading to a canal (or similar landmark in other cities) where they are asked to make one final commitment to continu- ing the journey. If yes (nearly all do), they are guided to a waiting performer who leads them to an interview room with two chairs and a mirror to be interviewed by a second performer who asks their personal views on terrorism, leading to the question, “Could you imagine a situation in which your community is being attacked, with people killing your neighbors and friends at random, and where you

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Figure 3. Final interview in “Ulrike and Eamon Compliant.” reject the actions of terrorists; and Design culturally resonant devices. Cultural associations extend to the form of the interface itself. In addi- tion to visceral discomfort, gas masks may invoke chilling associations with, or even memories of, warfare and civil unrest. Such resonance may be culturally and contextually specific, as in, say, the contrasting associations of a gas mask in a war museum compared to a fetish-themed nightclub. Control. HCI guidelines have long maintained that the locus of control should remain with the user;20 that is, it is generally good when people control the interface rather than the interface controls them. Experience designers can therefore generate discomfort by distorting this relation- ship: Surrender control to the machine. Part of the thrill of a ride involves giving up control to a machine, being strapped in and unable to dismount. Interactive experience opens up the might have to fight?” As they are led Encourage strenuous physicality. possibility of partial or unreliable from the interview room, they are in- The second tactic is to drive interac- control; for example, the “Bronco- vited to pause behind a (one-way) mir- tion through unusually strenuous matic” invoking the powerful feeling ror to briefly watch the next partici- physical activity. Roller coasters and of simultaneously battling to control pant being interviewed (see Figure 3). other thrill rides place physical stress a ride and one’s own body while ulti- on the body through high g-forces, mately losing control of both; Uncomfortable Interaction inversions, rolls, and drops, while “I Surrender control to others. Theat- These scenarios reflect how uncom- Seek the Nerves” and other exertion rical performances typically involve fortable interaction can be in prac- experiences generate intense feelings surrendering control to performers, tice, identifying four primary forms through exertion or stressful posi- possibly engendering uncomfortable of discomfort, each leading to a set of tions (such as hanging from ceiling feelings of disempowerment. This design tactics: bars);18 and surrender is a familiar tactic in many Visceral. In light of the growing Cause pain. The most extreme tac- everyday conventional performances, interest in physically embodied in- tic is to cause pain, as through, say, as in, say, a comedian singling out teraction,7 we first consider visceral electric-shock game controllers. An ef- an audience member; for example, discomfort, referring to the aspects of fective tactic here is to deliver “acute” “Ulrike and Eamon Compliant” de- our personal experience relating most pain (in the sense of transitory rather mands deep compliance with detailed directly to physical sensation, from than especially strong) as opposed instructions, while “Breathless” in- the unpleasant sensation of materials to “chronic” pain while not causing volves surrendering control to anoth- to demanding stressful or strenuous physical damage. er participant; and movement to causing pain. They re- Cultural. A contrasting form of Require participants take greater flect three tactics for creating visceral discomfort invokes dark cultural control. Discomfort can be found in discomfort: associations: assuming greater control of others, Design unpleasant wearables and Confront challenging themes and as it may invoke feelings of power, tangibles. Devices can be uncomfort- difficult decisions. The cultural accept- responsibility, capriciousness, and able to touch, hold, and wear. The gas ability of material considered adult, mischief. Thus, “Breathless” requires mask from “Breathless” has a striking difficult, or vulgar provides a signifi- participants to control others, as well physicality—hot, sweaty, and claustro- cant (and shifting) boundary for dis- as being controlled by others, while phobic, with an overpowering rubbery comfort. Interactive works increase Blast Theory’s performance “Uncle smell—while the tactile sensations of discomfort by requiring users to take Roy All Around You” invites online “The Meatbook” evoke disgust. De- difficult moral decisions directly, participants to control pedestrians on signers may prefer materials that are rather than being left to observe; for the streets of a remote city.1 rough, tight, prickly, sweaty, or other- example, “Ulrike and Eamon Compli- Intimacy. Computers are increas- wise physically unpleasant; ant” invited participants to defend or ingly employed to maintain social

70 communications of the acm | september 2013 | vol. 56 | no. 9 contributed articles relationships, giving rise to various elegant way to embed uncomfortable social tactics for creating discomfort: interaction into an experience: Isolate people. Isolating a partici- Exposition. The first act addresses pant from friends and family is a com- the initial framing of the experience mon tactic, leaving them alone in an to set an appropriate expectation. In unfamiliar environment. Isolation is A variety of risks “Ulrike and Eamon Compliant” the not only disturbing but naturally fo- must be considered, exposition takes the form of an initial cuses people inward on their own feel- briefing that explains the work, while ings. Both “Ulrike and Eamon Com- from physical the branding and ratings of rides sup- pliant” and “Breathless” exploited danger and injury port judgment of what is appropriate; this tactic, with the former requiring Rising action. Anticipation of dis- solo exploration of Venice and the lat- to emotional comfort increases as the experience ter using gas masks to anonymize par- trauma to social proper begins and suspense builds; ticipants, reduce their ability to com- for example, a roller coaster gradually municate, and focus them on their embarrassment. rises up a ramp toward the first drop; own breathing; Climax. Anticipation is now trans- Establish intimacy with strangers. formed into experience. Two impor- In contrast, intimate encounters with tant principles guide the design of strangers can be especially uncom- this moment: First, it must be transi- fortable. The one-to-one interview in tory, or relatively brief compared to “Ulrike and Eamon Compliant” is a the exposition and rising action, with challenge, while the “Mediated Body” effects that pass quickly. Thus, elec- required participants to physically tric-shock game controllers deliver touch a stranger’s body; and brief shocks after long periods of sus- Employ surveillance and voyeurism. pense, while the initial drop on a roll- This final tactic emphasizes the sense er coaster takes seconds compared to of vulnerability inherent in surveil- perhaps an hour of queuing and wait- lance by unseen observers, as implied ing. Lingering feelings of nausea are a by the instructions in “Ulrike and different matter, and it is unlikely that Eamon Complaint.” There is also dis- anyone would deliberately design a comfort in watching others, as in, say, ride to deliver such discomfort; the helplessness a viewer would feel Falling action. Discomfort is fol- watching loved ones on a dramatic lowed by a moment of release or ca- roller coaster ride. The reverse is the tharsis that may be associated with illicit thrill of voyeurism exploited feelings of intense pleasure, even eu- by “Ulrike and Eamon Compliant” phoria. The designer might seek to ex- when participants are invited to look tend such feelings for a while by, say, through a one-way mirror. adding gentle curves to the end of a ride; and Embedding Discomfort Dénouement. The final act address- in the Experience es the importance of reflection, letting Having identified tactics for creating participants assimilate the discom- uncomfortable interactions, recall fort, share it with others through sto- that our intention is to employ them rytelling, deliver new insight, or sim- in the longer-term pursuit of enter- ply enjoy the bragging rights of having tainment, enlightenment, and social- survived, supported by a photo and, ity. Discomfort is not our overall goal but rather a transitory point on a jour- Figure 4. Freytag’s pyramid. ney. Again, an experience designer can turn to the field of performance studies for assistance. The European Climax th th Renaissance of the 14 –17 centuries Falling action saw development of the classic five- act performance structure consisting

of exposition, rising action, climax, Rising action falling action, and dénouement, as visualized in Gustav Freytag’s pyra- Exposition Dénouement mid (see Figure 4) based on Aristotle’s earlier three-act structure.10 The pyramid gives an experience designer an

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perhaps, other souvenir objects. ics and human rights follow the 18th This structure can be extended in century German philosopher Im- various ways; for example, multiple manuel Kant and others in assign- climatic moments can be embed- ing a primary value to the individual, ded into a complex experience, as and in particular to free choice and in, say, designing climbs, drops, and An experience self-determination, possibly includ- loops into a roller coaster or twists designer might ing the right to deliberately choose and false endings into a narrative. An discomfort, subject to limitations of experience may deliver different feel- ask: Would its effect on others and assuming the ings when repeated (such as when the participants individual is competent to make such suspense gives way to the pleasure of a decision. This idea is commonly physical movement) or adapted to par- be happy in invoked in relation to an artistic or ticipants so as to provide them with a entertainment experience where fresh experience each time round; hindsight with both artist and audience could claim some roller coasters even involve con- what has occurred? a right to freely express themselves trol of individual seats. A final option through acts of creation or participa- is to reveal how discomfort was engi- tion. However, the same principles neered during the dénouement (such of individual value and autonomy as participants looking back through also disallow the arbitrary imposi- the one-way mirror in “Ulrike and tion of discomfort on another, at least Eamon Compliant”), reflecting the against that person’s will. way stage magicians sometimes reveal Such arguments do not, of course, their trickery as part of the set up for a provide blanket justification for un- further trick. comfortable interaction. Rather, designers must carefully weigh each ex- Ethics of Uncomfortable perience, focusing on specific ethical Interaction concerns, and balance any temporary Finally, deliberately introducing dis- discomfort against the longer-term comfort into an experience requires value of entertainment, enlighten- ethical consideration; the following ment, and social bonding: comments therefore address key ethi- Informed consent. The idea of in- cal challenges: formed consent is challenging for The first overarching question is to cultural experiences, especially those consider on what basis an experience involving surprise, where, by defini- designer might justify the deliberate tion, participants do not necessarily use of discomfort at all. While deon- know in advance what they signed up tological ethical systems are based on for. This surprise is further compli- an axiomatic definition of the right- cated when playing up the anticipa- ness or wrongness of actions, other tion of discomfort beyond the actual schools of ethical thought since the experience, though this would seem 19th century British philosopher Jer- preferable to experiences where ac- emy Bentham have argued a conse- tual discomfort exceeds anticipated quentialist position that assesses the discomfort. goodness of an action solely in terms Requiring written formal consent of that goodness or otherwise of its to take part in such an experience is consequences.6 Adopting this point rare; rather, consent is often achieved of view, might an experience designer through the careful framing of the justify a degree of short-term discom- experience in advertising, ticketing, fort through the longer-term benefits branding, and trust in the hosting to participants of entertainment, en- venue, all representing an unwritten lightenment, and sociality? An expe- contract with participants. Peer pres- rience designer might ask: Would the sure is another factor designers must participants be happy in hindsight consider. In recognizing the impor- with what has occurred? And given tance of social bonding, they must be what they know afterward would they aware of the possibility of personal still have chosen to take part? social pressure on participants to par- A second potential route to justi- ticipate. Some members of groups fying an uncomfortable interaction may be more hesitant than others, focuses on an individual’s right to and designers may wish to be wary of choose. Contemporary Western eth- an experience in which the leader de-

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termines the level of discomfort for an so as to deliver an entertaining, en- resource for design. In Proceedings of the Conference on Human Factors in Computing Systems (Fort entire group; lightening, socially bonding cultural Lauderdale, FL, Apr. 5–10). ACM Press, New York, The right to withdraw. It may be im- experience. While this idea is famil- 2003, 233–240. 12. goldstein, J. The attractions of violent entertainment. possible for participants to withdraw iar in the worlds of art and entertain- Media Psychology 1, 3 (1999), 272–282. from an experience once a key point is ment, it is unconventional in HCI. We 13. hobye1, M. and Löwgren, J. Touching a stranger: Designing for engaging experience in embodied passed, as in, say, dismounting a mov- therefore aimed to unpack the various interaction. International Journal of Design 5, 3 ing roller coaster, though such a ride ways deliberate discomfort could po- (2011), 31–48. 14. levisohn, A., Cochrane, J., Gromala, D., and Seo, J. is typically short and carefully regu- tentially be achieved, identifying four The Meatbook: Tangible and visceral interaction. In lated to minimize risk to participants. primary forms of discomfort and as- Proceedings of the First International Conference on Tangible and Embedded Interaction (Baton Rouge, LA, Consequently, it may be justifiable for sociated set of design tactics for each. Feb. 15–17). ACM Press, New York, 2007, 91–92. 15. marshall, J. and Benford, S. Using fast interaction a designer to limit opportunities for Most important, we have urged the to create intense experiences. In Proceedings of the withdrawal than would be the case embedding of such tactics within an Conference on Human Factors in Computing Systems (Vancouver, Canada, May 7–12). ACM Press, New York, in other contexts. While one might experience, along with careful consid- 2011, 1255–1265. argue an experience should be clear eration of ethical challenges. 16. marshall, J., Rowland, D., Egglestone, S., Benford, S., Walker, B., and McAuley, D. Breath control of about any point of no return, explicit Our intent is to stimulate discus- amusement rides. In Proceedings of the Conference warnings about the right to withdraw sion around the challenges of cultur- on Human Factors in Computing Systems (Vancouver, Canada, May 7–12). ACM Press, New York, 2011, 73–82. are employed to further increase sus- al applications of computers across 17. mcCarthy J. and Wright, P. Technology As Experience. pense in some rides, even in “Ulrike games, rides, performances, and MIT Press, Cambridge, MA, 2007. 18. mueller, F., Edge, D., Vetere, F., Gibbs, M., Agamanolis, and Eamon Compliant”; installations. An open question is S., Bongers, B., and Sheridan, J., Designing sports: A Privacy and anonymity. An individu- whether it has implications for other framework for exertion games. In Proceedings of the Conference on Human Factors in Computing Systems al’s right to privacy is another ethical types of computing. (Vancouver, Canada, May 7–12). ACM Press, New York, principle. However, tactics that gener- 2011, 2651–2660. 19. Schnädelbach, H., Rennick Egglestone, S., Reeves, ate discomfort by distorting intimacy, Acknowledgments S., Benford, S., Walker, B., and Wright, M. Performing especially through voyeurism, clearly This work is funded by the Research thrill: Designing telemetry systems and spectator interfaces for amusement rides. In Proceedings of the impinge personal privacy. A designer Councils UK (http://www.rcuk.ac.uk/) Conference on Human Factors in Computing Systems (Florence, Italy, Apr. 5–10). ACM Press, New York, must therefore consider whether pri- through Horizon Digital Economy Re- 2008, 1167–1176. vate actions would become visible search grant (EP/G065802/1) and by 20. Shneiderman, B. Designing the User Interface, Second Edition. Addison-Wesley Publishing Co., Reading, MA, to those outside the “performance the Engineering and Physical Sciences 1992. frame.” Breeches of privacy and ano- Research Council (http://www.epsrc. 21. Smith, M. Stelarc: The Monograph. MIT Press, nymity should be restricted largely to ac.uk/) through Dream Fellowship Cambridge, MA, 2007. those within the frame, especially in award EP/J005215/1. We also thank Steve Benford ([email protected]) is an EPSRC-funded situations involving a degree of sym- the artists of Blast Theory (http://www. Dream Fellow and a professor of collaborative computing metry (such as where observers are blasttheory.co.uk/) for their collabora- in the Mixed Reality Laboratory and Horizon at the University of Nottingham, Nottingham, U.K. themselves observed); and tion. Chris Greenhalgh ([email protected]) Managing risk. Finally, experience is a professor of computer science in the Mixed Reality designers have a clear responsibility References Laboratory and Horizon at the University of Nottingham, 1. benford, S., Crabtree, A., Reeves, S., Sheridan, J., Dix, Nottingham, U.K. to consider and manage risk. Given A., Flintham, M., and Drozd, A. The frame of the game: the breadth of the tactics we have Blurring the boundary between fiction and reality in Gabriella Giannachi ([email protected]) is a mobile experiences. In Proceedings of the Conference professor of performance and new media and Director of covered here, a variety of risks must on Human Factors in Computing Systems (Montréal, the Centre for Intermedia in the Department of English at be considered, from physical danger Canada, Apr. 24–27). ACM Press, New York, 2006, the University of Exeter, Exeter, U.K. 427–436. and injury to emotional trauma to 2. benford, S. and Giannachi, G. Performing Mixed Reality. Brendan Walker ([email protected]) is a senior research MIT Press, Cambridge, MA, 2011. fellow in Horizon at the University of Nottingham, social embarrassment. Dealing with 3. brecht, B. The modern theatre is the epic theatre. In professor of creative industries at Middlesex University, them is a practical matter requiring Brecht on Theatre, J. Willett, Ed. Methuen, London, and director of design practice at Aerial, U.K. 1993, 33–42. assessment and management within 4. Chalmers, M. and Galani, A. 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