The RAD: Making Racing Games Equivalently Accessible to People Who Are Blind

Brian A. Smith Shree K. Nayar Columbia University New York, NY, USA {brian, nayar}@cs.columbia.edu

ABSTRACT We introduce the racing auditory display (RAD), an audio- based user interface that allows players who are blind to play the same types of racing games that sighted players can play with an efficiency and sense of control that are similar to what sighted players have. The RAD works with a standard pair of headphones and comprises two novel sonification techniques: the sound slider for understanding a car’s speed and trajectory on a racetrack and the turn indicator system for alerting players of the direction, sharpness, length, and timing of upcoming turns. In a user study with 15 participants (3 blind; the rest blindfolded and analyzed separately), we found that players preferred the RAD’s interface over that of Mach 1, a popular blind-accessible racing game. We also found that the RAD Figure 1. Study participant P8 — who is congenitally blind — playing allows an avid gamer who is blind to race as well on a complex our racing game prototype using the racing auditory display (RAD). The racetrack as casual sighted players can, without a significant RAD outputs spatialized sound and works with a standard pair of head- difference between lap times or driving paths. phones. Using the RAD, players who are blind can play the same types of racing games that sighted players can play with an efficiency and sense ACM Classification Keywords of control that are similar to what sighted players have. Our supplemen- tal video shows P8 using the RAD with the RAD’s audio included. H.5.m. Information Interfaces and Presentation (e.g. HCI): Miscellaneous the ramp leads to a separate, less handsome entrance to the Author Keywords library or, even worse, to a different building altogether: a Accessibility; accessible games; audio games; sonification. smaller, adjacent library that only has the digest versions of books from the main library. These facilities would clearly not INTRODUCTION be fair for people using wheelchairs. Accessibility alone is not enough to make the world a fair place for people with disabilities. Even with assistive technologies, This situation, however, is similar to what video games are if people with disabilities cannot experience the world in the like for people who are blind. Most blind-accessible games same manner as anyone else [32, 41], or even as productively today are either loaded with competing sources of information as anyone else [16], the world will not yet be fair — or as we that players must sift through [4, 15, 29, 42], slowing down will say, equivalently accessible. the efficiency of play, or are very simplified versions of games that sighted players would play [2,6, 19, 20, 21, 27, 44], to Imagine a wheelchair ramp leading to an entrance of a public the extent that the player may be doing nothing more than library. Technically, the ramp would make the library acces- following orders from the game [2, 19, 20, 27, 44]. These sible to people using wheelchairs. But if that ramp makes games are technically accessible to players who are blind, but such a circuitous route on its way up that only people who they are far from the same game that sighted players would need it would ever want to use it, the ramp would not make play, and so are not equivalently accessible. accessing the library efficient or fair [41]. Worse, suppose that The reason is that when making an existing type of game blind- Permission to make digital or hard copies of all or part of this work for personal or accessible, there is a fundamental conflict between preserving classroom use is granted without fee provided that copies are not made or distributed the game’s complexity and the game’s pace. Preserving the for profit or commercial advantage and that copies bear this notice and the full citation former allows players to have the same sense of control that on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, sighted players have when playing existing games, while pre- to post on servers or to redistribute to lists, requires prior specific permission and/or a serving the latter keeps the action continuous and in real-time. fee. Request permissions from [email protected]. CHI 2018, April 21–26, 2018, Montréal, QC, Canada Figure2 illustrates this tradeoff, with the sense of control © 2018 ACM. ISBN 978-1-4503-5620-6/18/04. . . $15.00 that the game affords to the player on the vertical axis and DOI: http://dx.doi.org/10.1145/3173574.3174090 1 sonification techniques: the sound slider for understanding a Our Goal: car’s speed and trajectory on a racetrack and the turn indicator Intention- Equivalently system for alerting players of the direction, sharpness, length, Preserving Accessible and timing of upcoming turns. Figure1 shows a participant Games Games who is congenitally blind playing a racing game with the RAD. Feels Authentic We conducted two user studies to investigate whether the RAD Efficiency- allows players who are blind to play racing games at the same Preserving pace and with the same level of control as sighted players can. Games In the first study, we found that players preferred to play a racing game using the RAD over that of Mach 1 [6], a popular Intention / Sense of Control blind-accessible racing game. In the second study, we found Feels Contrived Tedious Efficient that the RAD makes it possible for a gamer who is blind to Efficiency of Play race as well on a complex racetrack as casual sighted players Figure 2. The intention–efficiency tradeoff. When designing blind- do. When that gamer raced using the RAD, there was no accessible games, game designers must choose between sacrificing each significant difference between his lap times or driving paths game’s complexity — and by extension the player’s intention or sense compared to those of casual players racing with sight. of control within the game — and the game’s efficiency of play. More- over, sophisticated actions such as cutting corners in racing games are INTENTION AND ITS ROLE IN RACING GAMES difficult to incorporate even in intention-preserving games, so many do Here, we introduce the concept of intention to describe what not feel fully authentic to play compared to what sighted players would play. Our goal is to overcome this tradeoff to help racing games become we mean by sense of control more precisely, and will illustrate equivalently accessible to people who are blind. how this concept applies to racing games. This concept can be used to examine whether a game gives players a high sense of control and, if not, how it can be changed to do so. the game’s efficiency (pace) on the horizontal axis. For a Intention is the process of “allowing and encouraging players game to be equivalently accessible to people who are blind, it to do things [within games] intentionally” [7,8,9]. More should offer both, as the green dot at the top-right of the figure specifically, it is the process of “making an implementable indicates. In practice, however, designers must sacrifice one plan of one’s own creation in response to the current situation of the two, causing existing blind-accessible games to fall into in the game world and one’s understanding of the game play two distinct groups: what we call efficiency-preserving games options” [7,8,9]. By breaking this definition down into parts, and intention-preserving games. we can see that for a game to support intention, it must help the player perform the following three activities: Efficiency-preserving games, indicated by the blue dashed cir- cle in Figure2, are ones that sacrifice the sense of control that 1. Understand the current situation in the game. they afford players to keep their gameplay moving at a contin- 2. Understand what game play options are currently available. uous pace. These include games such as Blind Hero [44], Rock 3. Make an implementable plan of their own creation. Vibe [2], and Blindfold Racer [27]. They are often simplified versions of games that sighted players would play and often These activities are analogous to the three components of boil down the gameplay to a simple test of reaction speed. In Yuan et al.’s game interaction model [45]. When we say that Blind Hero and Rock Vibe, for example, players do not get to a game affords players a high sense of control, we mean that prepare for upcoming beats like sighted players would when the game supports intention, which more precisely means that playing Guitar Hero or Rock Band, which these games were the game supports the player in performing each of the three based on. Rather, players are tasked with pressing buttons as activities listed above. For a blind-accessible video game to equivalently accessible soon as they feel corresponding vibration cues. be to people who are blind, it must support these three elements of intention without sacrificing Intention-preserving games, indicated by the red dashed circle the game’s pace — overcoming the tradeoff in Figure2 — and in Figure2, are ones that sacrifice their efficiency of play to without simplifying the gameplay. maintain more of their complexity and, by extension, give play- ers a greater sense of control. These include Terraformers [42] To support the first activity, racing games must help players and Blindfold Color Crush [29]. They are often cumbersome understand all aspects of their current situation that are rele- to play because they force players to navigate menus and vant to racing: their vehicle’s position and orientation on the racetrack, a general sense of its current speed, the nature of process many audio cues just to understand what the current any upcoming turns, etc. The game does not need to help situation in the game is at any given time. Moreover, although players understand aspects of the current situation that are not they preserve much of their complexity and sense of control, relevant to racing, such as their vehicle’s paint color or even they cannot preserve it all: complex actions such as cutting corners and performing head shots remain out of reach. its precise speed in mph/kph. (In fact, many games such as the Grand Theft Auto series and most of the Mario Kart series In this paper, we present the racing auditory display (RAD), do not show players their vehicle’s speed.) To support the an audio-based user interface with the goal of overcoming this third activity, racing games should make it possible for play- tradeoff to help racing games become equivalently accessible ers to form strategies such as cutting corners or positioning to people who are blind. The RAD comprises two novel themselves to better handle an upcoming turn.

2 RELATED WORK section are limited in Blindfold Racer compared to racing Our work builds on two areas of research: work on develop- games that sighted players would play. ing audio navigation systems and work on developing blind- In Blindfold Racer, it is not possible for the player to anticipate accessible racing games and driver assistance systems. upcoming turns, accelerate and decelerate in an analog manner, or perform higher level strategies such as cutting corners. In Audio Navigation Systems fact, the developer explains that there is no concept of vehicle Audio navigation systems help people who are blind navigate physics, that tracks are modeled using a simplified geometry on foot from one place to another in the real world. They that requires straightaways to be in the same direction and all consist of a GPS tracker, a computing device, and a pair turns to be less than 90° [26], and that car steering is simplified of headphones. Perhaps the most archetypal examples are so that the car will move in that straightaway direction when audioGPS [17] and SWAN [43] (short for System for Wear- the mobile device is tilted to the center position [28]. able Audio Navigation), which both guide users from their current location to their destination via a sequence of way- Mach 1 (PC, 2003) points that they must reach along the way. The user must Mach 1 [6] is an audio-based racing game published on PC by follow a sound known as an acoustic beacon to travel from Jim Kitchen eleven years before Blindfold Racer was released. waypoint to waypoint until they reach their destination. The player’s goal is similar that from Blindfold Racer, but in Mach 1 there are no obstacles present on the track. Players Most research in this area has focused on how to perfect these accelerate, decelerate, and steer using a USB steering wheel or types of systems, such as discovering which type of sounds are controller joystick, and they can press a button to have a voice easier to localize and follow [35] or how large each waypoint’s speak their current lateral position on the track: a number “capture radius” should be [39, 40]. These systems, however, from 1 to 100 where 1 represents the track’s left edge, 100 the are unsuitable for racing games for two reasons. First, they as- right edge, and 50 the center. The player should tap the button sume that the user is walking and has the flexibility to stop and repeatedly to monitor their lateral position continuously. rotate to center the acoustic beacon in front of them. Second, using these systems amounts to simply following orders, while As the player approaches an upcoming turn, the game will video games should afford players a high sense of control over loop a predetermined sound effect in the left or right stereo what they are doing. audio channel depending on the direction of the turn. The sound effect starts playing quietly but grows louder as the player approaches the beginning of the turn. The game will Blind-Accessible Racing Games play a thumping sound as the player reaches the turn, and the A number of driving systems and racing games currently em- process will repeat to signify the end of the turn: a random ploy mechanisms to assist drivers and players who are blind. looping sound effect growing louder followed by a thump. Here, we will survey three blind-accessible video games and a blind driver assistance system, each employing a different Unlike Blindfold Racer, Mach 1 allows players to anticipate user interface for driving a car on a virtual track. upcoming turns and accelerate and decelerate in an analog manner. Still, players do not have full freedom to “read the Blindfold Racer (iOS, 2014) road” since it is difficult to determine from the increasing Blindfold Racer [27] is an audio racing game developed on volume effect exactly when a turn will begin and the game iOS by Marty Schultz as part of his series of blind-accessible only alerts players of a single upcoming turn or straightaway at smartphone games. In Blindfold Racer, players steer by rotat- a time. As with Blindfold Racer, there is no concept of vehicle ing their mobile device left and right as they would a steering physics, tracks are modeled using a simplified geometry (so wheel. The goal is to drive to the end of a track without hitting there is no concept of cutting corners), and car steering is fences on the track’s sides. The player can also adjust their simplified so that the car will move in a straightaway direction speed to three fixed values by swiping up or down on their whenever the player lets go of the steering. device’s touchscreen. The game outputs sound in stereo and Top Speed Series (PC, 2004) pans a music track between the left and right channels as a The Top Speed [11] series is a series of racing games released means of displaying the car’s lateral position on the track. It will play exclusively in the left channel if the player’s car is on PC by a team of four developers. The goal for players is Blindfold Racer Mach 1 adjacent to the left side of the track and vice-versa. the same as in and : to reach the end of the track as quickly as possible without hitting the sides. Treasure and animals are indicated using repeating audio sam- Top Speed 2 and 3 support multiplayer races, though the cars ples that grow louder as the player approaches them. The cannot collide with each other or interact with each other in player should try to center the sounds of treasure between the any way. Players steer with a joystick controller as in Mach 1. left and right channels to collect the treasure, and they should Like Blindfold Racer, a sound is panned between the left and keep the sounds of animals panned to the left or right to avoid hitting the animals. right channels as a means of displaying the player’s lateral position on the track. In the Top Speed series, however, that With respect to Figure2, we would classify Blindfold Racer as sound is the sound of the player’s car’s engine. A speech clip an efficiency-preserving game. While Blindfold Racer moves saying a phrase such as “easy left” or “hard right” will play at a pace that is just as fast as racing games with graphics, the when the player enters a turn. These phrases describe the three elements of player intention as described in the previous direction and sharpness of the turn, and the player must react

3 Figure 2. Overview of sound slider.Figure 2. Overview of sound slider. Figure 2. Overview of sound slider.Figure 2. Overview of sound slider. Figure 2. Overview of sound slider. Figure 2. Overview of sound slider. Figure 3. Four driving scenarios.Figure 3. Four driving scenarios. the sound of the car’s enginethe right sound in offront the of car’s their engine face. Theright in front of their face. The Figure 3. Four driving scenarios.Figure 3. Four driving scenarios. car’sthe sound sound will of the move car’s toward enginecar’sthe the soundright sound left in or will offront the the move right of car’s their toward as engine the face. car the Theright left in or front theFigure right of 3. their Four as drivingthe face. car scenarios. The Figure 3. Four driving scenarios. thebecomes sound of the more car’s at engine risk of rightthe hittingbecomes soundin front the of of track’s the more their car’s face. at left engine risk orThe of right right hitting edges, in front the of track’s their face. left orThe right edges, car’s sound will move towardcar’s the sound left or will the move right toward as the car the left or the right as the car > > car’srespectively. sound will move When toward they thecar’s steer,respectively. left sound or they the will right control move When as the toward the car they car’s the steer, soundleft or they the right control as the the car car’s sound lCL lCL becomesbecomes more at morerisk of at hitting riskbecomes theof hitting track’sbecomes more left the at or track’s morerisk right of edges, at lefthitting risk or theof right hitting track’s edges, left the or track’s right edges, left or right edges, directly, so if they hear the car’sdirectly, sound so move if they far hear toward the car’s the left, sound move far towardSlider the left, Display> Value = >Slider> Display, > Value(1)= > >, (1) respectively.Figurerespectively. 2. Overview When they of When sound steer, slider. theyrespectively. theyFigure steer, controlrespectively. 2. Overview they theWhen car’s control they of When sound sound steer, the slider. they car’s they steer, control sound they the car’s control sound the car’s soundlCL lCL+ lCRCL lCL lCL+ lCRCL directly,theydirectly, so will if they want so hear if to they the steer car’s hear right sounddirectly, thethey tocar’s movedirectly, bring so will ifsound far they want thetoward so hear move ifsound to they the steer far left,car’shear back toward right sound the toward tocar’sthe move bring left, sound far thetowardSlider move sound the Display far left, back toward Value towardSlider the= left,> Display>Slider, Value Display=(1) Value>Slider=>> Display, >, Value(1)=(1)> >, (1) Figure 2. Overview of soundFigure slider. 2.Figure Overview 2. Overview of sound of slider. soundFigure slider. 2. Overview of sound slider. lCL+ lCR lCL+ lCRlCL+ lCR lCL+ lCR theythe willthey center. want will to want steer right to steer tothey bring rightthe will thethey center. to want sound bring will to back want steer the toward sound right to steer to back bring right toward the to sound bring backwhere the toward sound zerorepresents back toward the leftmostwhere zero position represents on the the slider leftmost and position on the slider and the center. the center. Figure 3. Four driving scenarios.Figure 3. Four driving scenarios. If thethe player center. is in a turn andIf thethe not player center. turning is nearly in a turn as sharplyandwhere not zero turning representsonewhere nearly represents the zero as leftmost sharply therepresentswhere rightmost position zero therepresents onone position leftmostthewhere represents slider the on zero andposition leftmost the therepresents slider. rightmost position on There the the onslider position are leftmostthe aslider and on andposition the slider. on There the slider are a and the sound of theIf the car’s player engine is inthe right a sound turn in and front of not theIf of the turning car’s their player engine face. nearly is in The right as a turn sharply in and front not of turningone their represents face. nearlyfew The the as sharplyspecial rightmost cases, positionone however, represents on the slider.few in the which specialrightmost There the are cases, systemposition a however, setson the the slider. in slider which There the are system a sets the slider as theyIf the need player to, perhaps is in a turn becauseas and theyIf the they not need player turning are to, going perhaps is nearly inFigure too a turn because fast, as 3.Four sharplyand the theydriving not turning are scenarios.Figure goingone nearly represents 3.Figure too Four fast, as driving 3.Four sharply the the scenarios. drivingrightmost scenarios.Figureone position represents 3. Four on driving the the slider. scenarios. rightmost There position are a on the slider. There are a the sound of the car’scar’sthe engine sound soundthe right willas of sound theysound the move in car’s frontneed of slider towardthe to, engine of car’s perhapscar’s their willthe engineright emit soundface. soundleft because inaor The tireright will frontas of the they theyscreechingsound the move in right ofarecar’s frontneed their slider goingastoward to, engine of the face. sound perhaps their will too car the The fast, right emit face.adapted left because the inaor The tire front the from they screechingfew right of [ are4 special their] goingas the face. sound cases,value too car The fast, however, adapted to the something in from whichfew [ different.4 special the] system cases,value If sets both however, to the something trajectories slider in which different. thehit systemthe track’s If sets both the trajectories slider hit the track’s becomes more at riskas theyof hitting needbecomes the to, track’s perhaps more left at because risk oras right theyof hitting they edges,need are the to, going track’s perhaps too left becausevalue fast, or right to the something they edges, arefew different. going special too If cases, bothvalue fast, trajectories to however,the something hitfew in different. the which special track’s the If cases, both system trajectories however, sets the hit in slider the which track’s the system sets the slider car’s sound will movecar’s toward soundcar’ssound the will soundfrom left slider move or the will the will same toward move right emitcar’s position a astoward thetire thesound screeching left ascarsound the or the willfrom the left car’s slider sound move right or the engine the will adapted same astoward right emit the position sound. from a car as thetire the [ screeching4 left This] ascar or the acts the car’s sound toright engine adapted asleft the sound. from caredge [4 (which This] acts means to > thatleft the edge player (which is driving means> toward that the the player is driving toward the from thesound same slider position will as emitthe car’sfrom a tire engine the screechingsound same sound. slider position This sound will acts as emitthe adapted to car’s a tire engineleft from screeching edge [sound.4] (which This soundvalue means acts adapted to that something theleft from playerw edge [ different.4 is] (which drivingvalue means Iftoward both to that somethingthe trajectories the playerw different. is hit driving the track’s Iftoward both the trajectories hit the track’s becomes more at riskrespectively.becomes of hittingbecomes more Whenthewarn track’s at more risk they the ofleftplayer at steer, hittingriskrespectively. orbecomes right thattheyof thehitting theyedges, control track’s more must Whenthewarn the track’sleft at slow risk they car’sthe or downright ofleftplayer steer, sound hitting or edges, by right thatthey hitting the theyedges, control track’s the must brake the left slow car’s or downright soundleft edges, by edge) hitting or the the brake player’slCL carleft is edge) currently or the off player’s the tracklCL car on is the currently off the track on the directly, so ifwarn they hearthefrom player the the car’s thatdirectly, same soundthey position must so move if slowwarn they as far down hearthe towardfrom player car’s bythe the hitting thecar’s enginethat same left, soundtheythe position sound.brake must move slow This as farleft down the toward acts edge) car’s bySlider to hitting the or engine the left, Display theleft player’s> sound.brake edge Value car (which This isleft= currently acts edge)> meansSlider to off or> the thatthe Display, left player’s track the> edge playeron Value car the(1) (which is is= currently driving> means off> toward thatthe, track the the playeron the(1) is driving toward the respectively. Whenrespectively. they steer,respectively. theyor When letting control they When go the steer,ofrespectively. they car’s the they accelerator steer, sound control theyor When letting tocontrol the properly they car’s go the steer,of sound car’scomplete the they accelerator sound control theleft turn. to the side, properly car’s systemleft sound complete will side,lCL set system the the sliderleft turn. will valuel side,CL set+ to system thellCLCR zero.left slider will Likewise, side,lCL set value system the in sliderto zero. will valuelCL set Likewise,+ to thellCLCR zero. slider Likewise, in value in to zero. Likewise, in they will wantor to letting steerwarn go right ofthe thethey player to accelerator bring will that wantthe they toor sound properly to letting must steerwarn back go slow complete right ofthe toward the down player to accelerator bringthe by turn.thatR hitting the they to sound properly the mustbrake back slow complete toward down theleft by turn.R edge) hitting or the the brake player’s carleft is edge) currently or the off player’s the track car on is the currently off the track on the directly, so if they heardirectly, the car’sdirectly, so sound if they so move hear if they thefar hear towardcar’sdirectly, the sound thecar’s soleft, move sound ifL they far move hear toward thefar thetowardcar’s left,Slider sound the left, moveDisplayL the far case Value toward ofSlider the=the track’s> left,case DisplaySlider right> of the Display, edge, Value track’sthe the= case Value system right(1)> ofSlider the= will edge,the> track’s> set case Display, the the right> of systemslider the, edge, Value track’s(1) will the= system set right(1)> the will edge, slider> set, the the systemslider (1) will set the slider the center. or lettingthe go center. of the acceleratoror letting to properly go of complete the accelerator the turn. to properlylCLleft+ complete side,lCR system the turn. willlCL set+ l theCRlCLleft slider+ side,lCR value system to zero. willlCL set Likewise,+ l theCR slider in value to zero. Likewise, in they will want to steerthey right willthey to want bring will to wantthe steer sound to right steer backthey to right bring will toward to wantthe bring sound to the steer back sound right toward back to bring towardwhere the soundvalue zero to represents back one. value towardthe the to case leftmostone.where of thevalue zero position track’s to represents one. right onvalue the edge,the the slider to case leftmostone. the and of system the position track’s will set right on the the edge, slider slider the and system will set the slider the center. the center.theComputing center. the Sliderthe Value center.Computing the Slider Value one represents the rightmostone position represents on the the slider. rightmost There positionare a on the slider. There are a If the player isComputing in a turn and theIf the not Slider player turning Value is nearlyComputing in awhere turn as sharply and thezero not Slider represents turning Valuewhere nearly theFrom leftmost zerowhere Raw as sharplyrepresents Position zero positionFromvalue represents to Raw Relativethe on to Positionleftmostthe one.wherethe RisksliderFrom leftmost tozero position Raw and Relative represents Position positionFrom onvalue Risk the to Raw Relativethe slider on to Positionleftmostthe one. and Riskslider to position and Relative on Risk the slider and as they need to,Figure perhaps2 illustrates becauseas how they they our need sound are to,Figure going slider perhaps2 tooillustrates system fast,because computes the how they our the sound arefew going special slider too system cases, fast, computes however, the the infew which special the cases, system however, sets the inslider which the system sets the slider If the player is in aIf turn the and playerIf the notFigure isplayer turning in a2 is turnillustrates nearly in and aIf turn as the not how sharply and player turning our notFigure sound is turning nearly inone a2 slider turnillustrates representsasnearly sharply andsystem as not how sharplythe computes turning rightmost ourone soundThe representsnearly the algorithmone position slider representsas sharplytheThe system ondescribed rightmost thealgorithm the slider. computes above rightmostone position There described representsThe represents the algorithm positionare on a the abovea new theThe slider. ondescribed approachrightmost representsthe algorithm There slider. above for positionare There describeda represents newa are approachon a the abovea new slider. approachfor represents There for are a newa approach for sound slider willslider emit valueComputing a tire to display screechingsound the to slider Slider the sound player. willslider Value adaptedemit GivenvalueComputing a tire to fromtheC display screeching car’s [4 the] current to Slider the soundvalue player. Value adaptedto Given something fromtheC car’s [different.4From] current Rawvalue If both Position to trajectoriessomething to Relative different. hitFrom the Risk track’s Raw If both Position trajectories to Relative hit the Risk track’s as they need to, perhapsas they becauseas need theyslider theyto, need perhaps are value to, going perhaps because toas too display they fast,because they need to the are theslider theyto, going player. perhaps arefew value too going special Given fast,because to too display thecases, the fast, they car’s however, to the arefew the currentletting going special player. infew which players too specialcases, Given fast,letting the know however, thecases, systemthe players where car’s however, sets infew they current which knowletting the special are inslider situatedthe where which players cases, systemletting the theyon know however, a systemsets racetrack. are players where the situated sets inslider they which know the are on slider situatedthe where a racetrack. system theyon a sets racetrack. are the situated slider on a racetrack. from the sameposition, positionFigure orientation, as the2 fromillustrates car’s and the engine speed same howposition, on sound. position our theFigurerace sound orientation,This as track, the2 slider actsillustrates it car’s tocomputes and system engine speed howleft computes on sound. edge our theUnlikerace sound (which This thethe track, slider actsstereo means it tocomputesThe systempan that algorithmvaluesleft the computes in edge playerUnlikeBlindfold described (which the is the driving Racer stereo means above,TheMach pan toward that represents algorithmvalues 1, theand the in playerBlindfold describeda new is driving approachRacer(a) above, Mach toward for represents 1, and the a new(b) approach(a) for (c) (b) (d) (c) (d) sound slider will emitsound a tire sliderscreechingsoundthe willposition,slider trajectoriesslider emit sound will a orientation, value tire adaptedemit that screechingsound theato tire display from car sliderscreeching and would [4 soundthe speed] to willposition, trajectories follow theslider adaptedemit soundonvalue player. the if a orientation, value the tire adaptedtorace thatfromsomethingplayer Given screeching theto track, [4 display from] car was the andit would [different. car’scomputes4 soundvalue speed] to follow the current adaptedto onvalue player. Ifsomething the if both the to race fromUnlike trajectoriessomething playerGiven track, [different.4] wasthe the itstereo different. car’scomputeshitvalue If the both current pan track’sto trajectoriesIfsomething values bothUnlike trajectories in Blindfold different. hit the thestereo track’s hit If Racer the both pan track’s, trajectoriesMach values 1, in andBlindfold hit the track’s Racer, Mach 1, and warn the playerthe that trajectoriesthey mustwarn slow that the downplayer the car bythe that hitting would trajectoriestheyleft the followmust edge brakeslow (which thatif the down the meansleft player car byleft edge) hittingthe would that edge wasTopleft or the (which theSpeed follow edge player brake player’sseries, (which meansletting if is the driving car the thatmeansleft player players soundisleft currently theedge) towardthe that edge slider’swas player knowTop or the the (which theSpeed off display is player where player’s thedrivingseries, means trackletting value is they driving toward car the on is that are players soundisnot thesituated currently the toward the slider’s player know the on off display is where a thedriving racetrack. track value they toward on is arenot the situated the on a racetrack. from the same positionfrom as thefrom car’ssameto steerthe engine positionposition, same fully sound. position to as the orientation, thefrom left This car’s as or the acts fully engine car’ssame andto to steer the sound.enginespeed positionposition, right. fully on sound.This to It as the modelsthe orientation, the acts race left This car’s to orthese track, acts fully engine and to it to computes thea sound.speed direct right. on This reflection It the modelsthe acts raceTop toof these track, the Speed car’s it computesseries,a lateral directd the position reflection soundthe onTop of slider’s the the Speed track. car’s displayseries, lateral valued the position sound is onnot slider’s the track. display value is not or letting go of the acceleratoror lettingto properly go of complete the acceleratorleft the edge) turn. to or> properly the player’sleftleft complete side, edge) car systemleft is theor currently edge) the willturn. player’s orUnlike set> the off the player’s theleft slider cartheleft track side, isstereo value currently edge) car on system pan is the to or currently zero. values the off will player’s the Likewise,Unlike set in offtrack theBlindfold the slider carthe on intrack isstereo the value currently Racer onFigure pan the to, Mach zero. values off 3. the Likewise, 1, in Four trackandBlindfold on car in the poses RacerFigure, andMach their3. 1, Four and corresponding car poses and sound their slider corresponding values. sound slider values. warn the player that theywarn must thewarn player slowtrajectories theto down steerthatthe player theytrajectoriesbyas fullythat circular hitting must to theywarn the slow arcs.the must thatthe left brake down We player theslow ortrajectories will fullyto carby down steerdenotethatthe hitting would to theytrajectoriesbyasthe fully them circular thehitting right.mustfollow to brakeas theCL slow arcs.the It thatifand left models brake the down We the or player will fully carbyRather, these denote hitting would to was the it them isthe right.followa brakeas directfunctionCL It ifand models reflection the of the playerRather, these car’s of was relative the it is car’sa risk directfunction lateral ofhitting reflection of position the car’s of on relative the the car’s track. risk lateral of hitting position on the track. > > left side, system willtheleftset case> theside, ofleft slider the system side, track’s value system willthe right to setTop zero. will edge, thethe Speed Likewise,left sliderset case> the theside, ofseries, system value slider the system in track’s to the will value zero. willsound setthe right to Likewise, the setTop zero. slider’s edge, sliderthe Speed Likewise, slider the in displayseries, system valueThough in tovalue the will zero. sound setthe is Likewise, thenot car’s slider’s slider lateral in displayThough position value the is isnot car’s the same lateral between position (a) is and the (b) same and between (a) and (b) and or letting go of the acceleratoror lettingor go lettingtoCR properlyoftrajectories, respectively. theto go steer accelerator of complete the fully as Theacceleratoror circular to radiiletting to the the properly turn.of arcs.left thego toCR properlyoftrajectories arcsor, respectively.complete We the fullyto are will steer accelerator modeled tocomplete denote the fully as Theturn. circular right. as to radii to them thebeing the properly It turn.of arcs.left asmodels theCL arcsorthecomplete Weand fully arethese track’s will modeled to denote theleftRather, turn.or right. as right them being it It edgesis asmodels aCL iffunctionthe theand thesetrack’s player of left wantedRather, the or rightcar’s to. it edges This relativeis a iffunction the risk player of of hittingwanted the car’s to. This relative risk of hitting > > the case of the track’svaluethe right to case one. edge,the of case the the track’s of systema the direct righttrack’s willvalue reflection edge, setthe rightto the case the one. edge, slider of system of the the the track’s system will car’sa direct set right lateral will the reflection edge, slider set position the the sliderbetween system of on the the will car’s (c) track. set and lateral the (d),slider position thebetween corresponding on the (c) track. and sound (d), the slider corresponding values are soundvery dif- slider values are very dif- directlyCR, respectively. proportional to The the radiicar’sdirectlyCR currentof, the respectively. proportional arcs speed, are where modeled to The the the radiicar’s ascurrentof beingdistinction> the arcs speed, is arethe what where modeled track’s makes the the left as sound being ordistinction> right slider edges intuitive isthe what if track’s makes for the players player the left sound or wanted right slider edges intuitive to. This if for the players player wanted to. This Computing the Slidertrajectories Value Computing as circular the arcs.Slidertrajectories Wevalue Value will(a) to one.denote as circular themvalue arcs. as CL to Wevalueand one. will(a) to one.denoteRather, them itvalueis as a(b)CL tofunctionand one. ofRather, the car’s it relativeis a(b) functionferent. risk of of Thishitting the car’s is because relativeferent. the risk left of Thishitting and is right because trajectories’ the left lengthsand right — trajectories’ and lengths — and constantdirectly> of proportionality proportional torepresentsconstant thedirectly car’s> how of current proportionality proportional sharply speed, the car torepresentsFrom where the Rawto car’s understandthe how Position current sharplydistinction even to speed, Relative the with car theFrom whereisRisk complex what Rawto understandthe makes vehiclePosition the physics,distinction even tosound Relative with steering slider the isRisk complex what intuitive makes vehicle for the players physics, sound steering slider intuitive for players Figure 2 illustratesturns.CR how Through, respectively. our soundFigure manual slider2 tuning,illustrates The systemturns. radii we foundCR how Throughofcomputes, the respectively. our the arcs sound valuemanual the are of slider modeled tuning, the The system radii webehaviors, as found ofcomputesbeing the the arcs and value the track arethe of modeled track’s geometries the leftbehaviors, as that being or areright present and edges trackthe in if track’s geometriesmodern the player left that or wantedtherefore areright present edges to. the inThis if modern relative the player risks wantedtherefore of hitting to. the This the relative left and risks right of hitting sides of the the left track and right sides of the track Computing the SliderComputing Value Computing theconstant Slider the Value Sliderof proportionalityComputing Value Figure theconstant represents Slider 2.From RAD’s Value of Raw proportionality how Position sound sharplyThe slider. toFigureFrom Relativethe algorithm represents car Raw(a) 2.From RiskSampleRAD’s Position described Rawto how understand Position sound carto sharply Relativeabove poseThe slider. toFrom represents evenRelativethewith algorithm Risk car Raw(a) with the RiskSample Positionacar’s thedescribed newto complex understandapproach trajecto- carto Relativeabove pose vehicle for represents evenwith Risk physics, with the acar’s the new steering complex approachtrajecto- vehicle for physics, steering slider value toconstant displaydirectly in to our the prototypeslider proportional player. value racing Given toconstant to game display the thedirectly to car’s car’sin be to our very currentthe prototypecurrent proportional close player. to speed, racing 1.6. Givenletting to game where theracing the players to car’s car’s be the games. very current know current close Recalldistinction where tospeed, that 1.6.letting thethey other whereis areracing what players games situated the games.makes used know on Recall theverydistinction awhere sound racetrack.simplified that thethey slider other is are what intuitive games situated— makes are used for veryon thevery players a sound racetrack.simplified different slider in intuitive each— are pair for very players of different cases. in each pair of cases. Figure 2 illustrates howFigure our2 soundFigureillustratesturns. slider2 illustrates how system Through our how computes soundFigure manual our slider2 soundillustrates theries tuning, systemturns. slider if theThe how we system computes Through player algorithm found our computes sound was the manualthe described sliderto value thesteerriesThe tuning, system ofmodels if above algorithmfully the theThe we computesfor playerrepresents left algorithm found vehicle describedbehaviors, or rightwas the the handling a described newto value drawn.above steerand approachThe and of trackmodelsrepresents abovetrack algorithmfully the (b) geometriesdesigns. for Overheadfor representsleft vehicle a describedbehaviors, or new right handlingapproach athat view new drawn.above are and approach and forpresent trackrepresents track (b) geometriesdesigns. for Overhead in modern a new approach that view are forpresent in modern position, orientation,It is veryconstant and important speedposition, of on proportionalityto set the orientation, this raceIt valuetrack, is veryconstant to represents andit be important computes as speedFigure accurately of on proportionalityto how 2. set theOverview assharply this raceUnlike value track, of sound the to represents it bestereo car computes slider. as accurately panto how values understand assharplyUnlike in Blindfold eventhe stereo car with Racer panthe, Machto complex values understand 1, in and vehicleBlindfold even physics, with Racer the, steeringMach complex 1, and vehicle physics, steering slider value to displayslider to the valueslider player.possible. toconstant value display Given to in display to the our the car’sslider prototype player. to currentthe value player. Givenpossible. racing toconstant display the Givenletting game car’s in to the toour players currentthebe car’s prototype player. very current know close Givenletting racing where to 1.6. the playerslettinggame they car’s are to players currentracing know be situated very games.where know close onletting they awhere Recallto racetrack. 1.6. are players they that situated the areracing know other situated on agames.where games racetrack. on they a used Recall racetrack. are very that situated simplified the other on a games racetrack. used very simplified the trajectories thatturns. the car Throughthe would trajectories follow manualof if correspondingthat tuning, theturns. the player car we Through would was found rendered follow manualtheof value if correspondingFigure tuning, spatializedthe of player the3 illustrates we was found (3D)behaviors,rendered the the benefitsoundscape. value and ofFigure spatialized using of track the3 ourillustrates RAD’s geometries approach (3D)behaviors, thesound over benefitsoundscape. that the are and of using present track our RAD’s geometries approach in modern sound over that the are present in modern position, orientation,position, and speedposition, orientation, onIt the is orientation, race very and track, important speedposition, andit computes on speed to theorientation, set race onIt this the track,is racevalue veryUnlike andit track, computesimportant to speedtheFigure be it stereo ascomputes on 2. accurately to the Overview panthe set raceUnlikeTop values this track, ofSpeed as valueUnlike soundthe in itBlindfold stereoseries, computes slider. to themodels be pan stereo the as Racer values accuratelyfor sound panthe vehicle, MachUnlike inTopvalues slider’sBlindfold Speed1 ashandling, the in and displayBlindfold stereoseries, Racermodels and pan value, the trackMachRacer values for sound is designs.vehicle,not 1Mach, in and slider’sBlindfold 1handling, and display Racer and value, trackMach is designs.not 1, and to steer fullyNext, to the theconstant left system or fullyto in computes steer our to prototypethe fully right. thesliderNext, to respective the Itracing theconstant models isleft asystem or gamespeaker points fully these in computes toour at to be which emitting prototypethe verya right. theslider direct close respectivecar’s theItracing modelstoreflection is car’slateral 1.6. a gamespeaker points these positionengine of to atracing the be which emitting on verynoise car’s games.a the direct close track. lateral whosecar’s the Recall toreflection The car’slateral position1.6. lateral car’s that positionengine lateral the of on positionracing the other the positionon noise car’s track.games. the games track. lateral whose used Recall The position lateralvery car’s that simplified lateral the on position other the position track. games used very simplified the trajectories thatthe trajectoriescarthe would trajectoriespossible. follow that the if that car thethe would player trajectoriescar followwould was possible. follow if that thetheFigure the playerTop> if 2. car the Overview Speed would wasplayerseries, ofsound follow wasthe theslider.Top if sound thethe Speed playerTop> slider’sseries, Speed was display theseries, soundthe value theTop slider’s sound is Speednot slider’s displayseries, display value the sound is valuenot slider’s is not display value is not trajectories asthe circular trajectoriesIt is arcs. very intersecttrajectories We important will the denote track’s asin tothe circular set the trajectories themedges,It this soundscape is as arcs.then valueveryCL intersect computes Weand important to will be thetracks theas denote track’sRather, accuratelyin to setthe theis themedges, theitthis ratio soundscape isas same then as valueaCL function of computes inFigureand the to Figuresmodels be trajectories’ tracks of3 theasillustrates3Rather, the(a) accuratelyfor car’sand vehicletheis theit(b), ratio the relative is lengths. same butashandling benefita function of due inFigure risk the Figures tomodels of andIn theof using trajectories’ of3 thishitting naturetrackillustrates3 the(a) forFigure our car’sanddesigns. vehicle approach 3. (b), theFour relativeedge lengths. buthandling benefit driving over due (whichrisk to of thescenarios. andIn theof using thishitting naturetrack means our designs. approachedge that over the (which the player means is driving that the toward player the is left driving toward the left to steer fully to the> leftto steer or fullyto fully steer to to the fully the right. left to the or It> modelsfully leftto steer or> to fully these the fully right. to> to the the Ita right. models leftdirect or It modelsreflectionfully these> to these the ofa right.> the direct car’s Ita modelsreflection direct lateral reflection these position of the car’s of ona the direct the lateral car’s track. reflection positionlateral position of on the the car’s ontrack. the lateral track. position on the track. respectiveNext,possible. the arc lengthssystemlCL computes>andthecase,respectivel soundCRNext, thefrompossible. the of respectivethe arc the the player lengthssystem car’s car’s> position will engine pointslCL computes>and hearthecase, rightatlCR track’s which theof thefrom in the front car’srespective left tracks the player or of car’s engine>car’s in righttheir these position will points lateral face.edges figures right hearthe Theat position if track’s theinwhich the theof player frontthe player car’s left ontracks has the of or wanted enginecar’s anin righttheir track. these equal lateral edges to. facefigures Theright risk This of position ifcar’s thein the player frontlateral player on has the of position wanted an their track. equal to. face The risk This of car’s lateral position trajectories as circularCRtrajectories, respectively. arcs.trajectories We as will circular The denote as radii circular arcs. themCR of thetrajectories, We respectively. as arcs. arcsCL will We areand denoteas modeledwill> circular The denote themRather, radii> as as arcs. thembeing ofCL it the Weisand as arcsaCL will function areand denoteRather, modeled>hitting of themRather, the it the> asis car’s as track’s beingaCL functionit relativeFigure isand left a function and of3 risk rightillustratesRather, the ofhitting edgescar’sof hitting the it the intherelative is car’s Figure track’sa benefit function relativeFigure risk3 left(a) of butof and using of3 risk hittingnot rightillustrates theFigure ourof edgescar’s hitting approach 3.edge), intherelativeFour Figure benefit driving over or risk3(a) of theifscenarios. butof using the hittingnot player’sour approachedge), car over or is theif currently the player’s off the car track is currently on the off the track on the > > >to these points of intersection.> car’stolCL these soundand points willlCR represent of move intersection. toward thedistinction thelCL leftand is orlCR what therepresentis right makes the as same the the thedistinction sound carin Figures slider is what intuitive3Figure(a)is makes and the 3. forFour same(b), the players driving sound but in scenarios.due Figures slider to theintuitive3(a) nature and for (b), players but due to the nature CR, respectively.directly TheCR radii, respectively. proportionalCR of the, respectively.the arcsNext, trajectories The are to themodeled radiithedirectly The car’s systemCR of intersect radii the, as current respectively. proportional arcsbeing ofcomputesbut the thethe are speed,the arcs track’s soundslightly modeledNext, trajectories Thethe are to where ofedges, track’sthe modeled radiirespectivetheto the as car’s thesystem being of car’s thenintersect left theleft. as current enginecomputes orpoints arcsbeing computes right Thebut thethe are speed, rightatin track’s edgesslightlyratio track’s modeled Figurethewhichthe in where ifrepresents frontedges, track’s left3respective the(b): to as ortheof being playerin thencar’s right leftthat their left. figurecomputes orpointsthe wantedlateral edges face. right The player’sthe the Theat ifpositionin edgesplayer to.ratio track’s theFigurewhich This player should relativeifrepresents left3 on the(b):the or steer wantedplayer incar’s right that track.risk to figure the wantedlateral edges to. of leftThe player’s theThis ifposition car’s playerto. the This lateral player should relative on the steerposition wanted track.risk to the to. of leftThe This car’s lateral position constant of proportionalitydistances the carconstant would represents travelthe ofbecomes sound beforehow proportionality>distances of sharply hitting the more the> car’s an car theat edge engine wouldrisk represents car were of righttravel hitting theto in beforehow> frontunderstand the sharplyhitting of track’s their> an even face.the left edgeof car with orThe the were right the tracks the complexedges,to understand in these vehicle figures even physics,of with the the theplayer tracks steering complex inhas these an vehicleleft equal figures side, physics, risk the of system player steering has will anleft equal set side, the risk sliderof system value will to set zero. the slider Likewise, value in to zero. Likewise, in directly proportionaldirectly to thedirectly car’sproportionalplayerrespective current proportionalthe to steer trajectories tospeed, fully arc thedirectly tolengths car’s to where the intersect the left current car’sproportionall theorCLhittingplayercar’s right,respective theand current speed,the tosound respectively. track’sdistinctionl either steerCR trajectories tospeed, wherefrom willfully arc edges, the edge tomovelengths theiscar’s thewhere the what thenofintersect car’s left toward currentthelmakes computestheorCLhittingdistinction positiontrack. right, theandand the speed, the respectively. track’s woulddistinctionl eitherleftCR sound the is whereorfrom otherwise what edges, theslideredgeis the makesrightthewhat theintuitive thenof soon car’sthe as same themakes computes hit thedistinction position track. sound the forand carin track’sthe players Figures would slider sound the isright otherwise what intuitive slider3 edge.(a)is makes and theintuitive Likewise, soon for same(b), the players hit sound thefor but in track’s playersdue Figures slider torightintuitive the3 edge.(a) nature and Likewise, for> (b), players but due to the nature turns. Through manual tuning,turns. we Throughcar’s foundrespectively. sound> the manual will value move> When> tuning, of toward the they> we the steer, found leftbehaviors, or they> thethe car’svalueright control and> lateral>as oftrack thehitting the thecar position> geometries car’s the soundbehaviors, is track’s the thatthe same left car’s are andin and Figures presentlateral track righthitting position3 geometries(c) in edges modernthe and istrack’s (d), in the Figure that same left arethe in3 and(a) Figures present case but right not3(c) inof edges modernl andCL the (d), in track’s Figurethe3 right(a) case but edge, not of the the track’s system right will edge, set the the slider system will set the slider constant of proportionalityconstantconstant represents of proportionalityto theserespective of how proportionality points sharply arcconstant represents of lengths intersection.becomes the represents car ofbecomes howl proportionalityCLto more theserespectiveand sharplyto atl howCL morerisk understandl pointsCRand ofsharply the atfrom hitting arc representslriskCR of car lengths even the intersection. theofrepresent hitting car’strack’s car withto howlCL understand positionthe left the theand sharply complexto orl track’sCL understand rightlCRand even theedges,from left vehiclelofCR car with or the even the rightrepresent physics, the tracks car’s with complexto edges, understand positionthe in steering the these complex vehicle figures even vehicle physics,of with the the physics, the player tracks steering complex inhas steering these an vehicle equal figures physics, risk the of player steering has an equal risk of constant in ourFinally, prototype the system racingconstant sets game the in sliderdirectly, to ourFinally, be value prototype very so tothe close if the systemthey racingfollowing to hear 1.6. sets game the the quan- car’s slider toracing be sound value verybut games. todue move close the to Recall following the tofarin 1.6.difference toward Figure that quan- the the3racing in(b): other left,the in cars’but games games. that due headings figure toused Recall thein very difference thewith Figure that player simplified respect theSlider3 in(b): other should theto Display in cars’ games that> steer headings figure Value used to the very thewith= left player> simplified respect> should to , steer to(1) the left turns. Through manualturns. tuning,turns. Throughdistances we Through found manual the the manual tuning, car valueturns. would tuning,respectively. we ofFigure Through the travelfoundrespectively.distances we 2. Overview before the found manual Whenbehaviors, value thehitting> they the of When tuning, sound carof value steer,and the anwould slider. they>edge theywe oftrack the travelsteer,found control werebehaviors, geometries theybefore the thebehaviors, value car’s control and hitting> that sound oftrack arehitting theand the an presentgeometries> edgecar’s track the werebehaviors, sound geometries track’sin modern the that left are and that and present track arerighthitting presentgeometries in edges modern the track’sin in modern Figure thatvalue left are3 and(a) present to but rightl one.CL not in+ edges modernlCRCL in Figurevalue3(a) to but one. not It is very importanttity, whichto to these we set call thisIt points the is value verytime-to-impact of importantto intersection.tity, be as which ratioto accurately to these we: setlCL call this points theand as valuetime-to-impactlCR of to intersection.modelsrepresent be asthefor ratio accurately tracks’, vehiclethe: lCL theand handlingand as player wouldlCR ismodels moreand otherwiserepresent track atthe forrisk tracks’, designs.soonvehicle the of hitting thehitand handling playerthe the would track’s left is edge moreand otherwise right track at riskl edge.CL designs. soon of hitting Likewise, hit the the track’s left edge right edge. Likewise, constant in our prototypeconstant racingconstant in our gameplayer prototype in to our to be steerprototype very racingconstant fully close gamedirectly, racing to tothey the 1.6.in to our gameleft so willplayer be if prototype orvery they want toracing right, to be hear close steer to very games.respectively.the racing steer to fullycar’s close 1.6. right Recallgamesound to to the 1.6. to move toracing that leftbring be farthe orvery games.racing thetoward right, other close sound gamesthe games.respectively. Recall to left,in back 1.6. usedFigure that Recall toward the very3racing that other(b): simplified the in games games. otherthatSlider figure used games Recall Displayin very the usedFigure that Value playersimplified the verySlider=3 other(b): should simplified> Display in games that> steer, figure Valueused to the very the= left(1) playersimplified> > should, steer to(1) the left distancesFigure 2. Overview the car would of soundIfFiguredirectly, travel the slider.distances 2. Overview playerbefore so if they thehitting of ishearsound car in anwould the slider. aedge car’sIf turn travel the were sound and playerbefore the move not hitting far is turning toward in an aedge the turn left,nearly were and the as not sharply turningl nearlyCL+ lCR as sharply It is very importantpossible.It to is set very thisIt is important value very importantto be to assetpossible. accurately thisIt to is set valuethey very thisthe will as importantto center.value be want as tomodels to accurately be steerto asset rightfor accurately this vehicle toas value bring handling asto themodels be sound asmodels andfor accurately back vehicle track towardthe for designs. vehiclecar’s handling as lateral handlingmodels and position track andforwhere designs. vehicle track isthe the zero designs. car’s samehandling represents lateral in Figures and position thetrack leftmost3(c) designs. is and the position (d), samelCL in on+ FigureslCR the slider3(c) and and (d), player to steer fully tothey the left willplayer or want right, to steer to respectively. steer fully rightFigure to the to3 leftbringillustrates or the right, sound the respectively.and benefit back wouldFigure toward of otherwise using3 illustrates our soon approach the hitand benefit the over would track’s the of otherwise using rightFrom our edge. soon approach Likewise, Lateral hit the over track’s Position the rightFrom edge. to Relative Likewise, Lateral Risk Position to Relative Risk possible. possible.possible.Finally, the systempossible. setsthe center. theasFinally, slider they value need the system to theto, following setsperhaps theas slider they quan- because value need tobut theto, they due following perhaps to are the difference going quan- becauseFigure too in 3.but the fast,Four they duecars’ driving tothe headingsare the scenarios. difference going with too respect in the fast, cars’ to the headings with respect to Next, the system computesNext, the respective theIf system thethe points player center. computesFigure at is which in3 theillustrates a turn respective andcar’s theFigure not benefit lateralpoints turning3Figureillustrates positionofat usingwhich nearly3 illustratesthe ouron the as thecar’s approach benefit sharplycar’swhere track. the lateralFigure benefit oflateral zero over The using position3 representsillustrates car’stheone positionof our usingwhere represents lateral approach is the ourtheon thezero leftmost positionthecar’s sameapproach benefit therepresents over track. lateral rightmost in position the of Figures over The using position theon car’sthe position our leftmostthe3(c) lateral sliderapproach is and the on andposition (d), position the same over slider. in theon Figures There the slider are3(c) a and and (d), tity, whichthe sound we call of the thetime-to-impact car’ssoundtity, engine which slider right ratio we inwill call: front the emit ofistime-to-impact theirsound the a tire same face. slider screeching The in ratioFiguresthe will: tracks’,3 emit(a) soundisone and the the a represents player (b),tire same adapted but screechingfew in is the due more Figures specialrightmostthe from to tracks’,at the cases,risk3 position(a)[ naturesound4 of] and the however, hitting on player (b),adapted theThe butslider. the in is duewhich left more algorithmThere from edge to atthe theare risk system a[ nature4 of] described hitting sets theThe the slider left algorithmabove edge represents described a new above approach represents for a new approach for Next, the systemthe computesNext, trajectories theNext, the system intersectrespective theFinally, system computes the points thethe track’s computesNext, system trajectories the at edges,If respective which the theas sets the theysystem player then theintersectrespective needFinally, slider computespoints iscar’s computes in to, the a value lateralturnatpoints perhapsthe track’swhich the systemand to the positionat the not edges, becauserespective which following setsturningcar’s thenon the they the nearly sliderlateral computespoints quan-car’s track. are as value going positionlateralat sharply Thewhich the tobutFigure too car’s position the on due fast, following 3. thelateral to Four thecar’s track.onthe driving positionthe difference lateral quan- The track. scenarios.Figure car’sone position The in represents 3. lateralbut the Fourcar’s on duecars’ driving positionthelateral to theheadings track.the scenarios. rightmost position difference The with car’s position respect in lateral the cars’on to position the headings slider. There with are respect a to car’s> sound> will moveIf the toward player> the is left in> aor turn theof right and the not tracksas the turning carin these nearly figures asoffew sharplythe the special player tracks cases, has in these however, an equal figures in risk which the of the player system has sets an the equal slider risk of the trajectories intersectrespectivethethe trajectories the soundthe track’s arc trajectorieslengths of edges,the intersecttity, car’sl whichCL thenthe intersect engine theandrespective sound computes wethe track’slCR call righttrajectories theas offrom theysound track’stheedges, arc in thefromtime-to-impact car’s frontneed lengthsthe slider then edges, intersect car’stity, to, engine oftheis perhapscomputes their willl which theCL positionthen same right theemit sameand face. computes ratiobecause we track’sl ina theCR position The incall tire: front Figuresfrom they screeching theedges, thefrom ofistime-to-impact are the their the as then3going(a) car’s the same face.theis sound computesand too the position same car’s The infast, (b), same adapted Figures ratio thethe but the positionengine in: tracks’, due from Figures3(a) tois [4 sound.and the] the the as3(a) nature (b),player same the andvalue but This car’sfew in (b),is due to Figuresmore specialsomethingthe but acts engineto tracks’,at due the3 cases,riskto(a) nature to different. ofsound. and the the however, hitting nature (b),playerletting butIf Thisthe inboth is due whichleft more players trajectoriesacts toedge atthe the riskto system nature knowof hit hitting thesetsletting track’s wherethe the slider left players theyedge are know situated where on they a racetrack. are situated on a racetrack. becomes more>sound at risk slideras> theyof will hitting need emit the ato, tire track’s perhaps screeching> lefthitting because or sound> right the adapted they edges, track’s are from goingleft [4] and too righthittingvalue fast, edges to the the something intrack’s Figure different. left3(a) and but If right both not edgestrajectories in Figure hit the3 track’s(a) but not to thesecar’s> points sound> of will intersection. movecar’s>to toward thesesoundlCL> the> points willandfrom left movelCR> or the of the intersection.represent same towardof right the position> tracksas the the the leftlCL ascar in> or thetheseand the car’sofl rightfiguresCR the enginerepresent tracksasof the the the sound. player carin tracks the these This has in figures these an acts equalof to figures the the riskplayer tracks theleft of hasplayer edgein these an (which equalhas figures an risk meansequal the of> riskplayer that of the has player an equal is driving risk of toward the respective arc lengthsrespectivelCL andrespective arclCR lengthsfrom arcrespectively. lengthsthelCL car’sandrespectivelCL positionlfromCR Whenandfrom thewarnsound arclCR they same lengthsthefrom sliderthe steer, position car’s theplayerl will theyCL position as car’sand emitthe control car’sthat positionl aCR tire engine thefromwarn they screeching car’s sound. the must the sound car’s This soundplayer slow position acts adapted to down thatleft from they by edge [4 hitting] must (whichvalue meansslow the to thatbrake down something the playerw byl different.CL hittingis drivingUnlike Iftoward the both the brake the trajectories stereo pan hitUnlike the values track’s the in stereoBlindfold pan Racer values, Mach in Blindfold 1, and Racer, Mach 1, and becomes more> at riskbecomes> of hitting more the>warn track’s at risk the>> ofleftplayerhitting hitting or> right that the the they edges, track’s track’s must>in left left Figureslowhitting and or> downright right3hitting the(b): edges, track’sby edges inhittingthe that intrack’s left figure Figure the andin brakethe left right Figurehitting3 player(a) and edges but right3 the(b): should notleft intrack’s edges in edge)Figure that steer in left figure or to Figure3(a) andthe the the but player’sleft right3 player(a) not edges but car should not in isFigure currently steer to3(a) the off but left the not track on the to these points ofdistances intersection.to these theto points these carlCL would ofpointsand intersection.directly, travellCR ofdistances intersection.represent beforeto so ifthesewarn theylCL hitting the pointsthe heartheand carfromlplayer anCL wouldthelCR ofedgetheand car’sthat intersection.represent same travel werelCR soundthey positionrepresent thebeforemust move the slowlCL hitting as far down the theand toward ancar’s bylCR edge hitting the enginerepresent left, were the sound.brake the the Thisleft acts edge)Slider to or the Displayleft player’s> edge Value car (which is= currently> means off> thatthe, track the playeron the(1) is driving toward the respectively. Whenrespectively. they steer, theyor Whenor letting control letting they go the steer,of car’sgo the they accelerator of sound the controland acceleratoror to the would lettingproperly car’s otherwise sound completego to of properly soon the the hitand acceleratorleft turn. the side,would complete track’s system otherwiseleft right will side,tolCL edge. the set properly soon system the turn. Likewise, slider hit willthe valuelCL complete track’s set+ to thellCLCRthe zero. right slider Likewise,Top edge. the value Speed turn. Likewise, in to zero.series, Likewise,the theTop in sound Speed slider’sseries, display the sound value slider’s is not display value is not distances the car wouldplayerdistances travel to steerdistances before the fully car hitting thewouldtothey the car leftan travel would willplayer edge ordistances want beforeright, travel weretoor steer to letting respectively. hittingthe before steerthewarn fully cargo right anofhittingthe wouldtoin the edge theplayer toFigure accelerator bringleftan travel were edgethat or3(b): the thebeforeright,they were to sound in properly thatrespectively. must hittingthein back figure Figure slow complete an towardin the edgedown3 Figure(b): player the were by in turn.R3 thathitting(b): should the figure in thethat steerin thebrake figure Figure to player the the left3(b): should playerleft in edge) that steershould figure or to steer the the left player’s to player the left carshould is currently steer to the off left the track on the directly, so if they heardirectly, the car’s so sound if they move hear thefarand towardcar’s would sound the otherwise left, moveLthe farand soon car’s toward would hit lateraland the the otherwise would track’s left, positionSlider otherwise right soonDisplay is theedge.thethe hitandsoon same casecar’s Valuethe Likewise, would oftrack’s hit lateralinSlider the= the Figuresthe track’sotherwise> righttrack’s case position Display right3 edge.> of(c) right the soon, edge, Valueandis Likewise, track’s theedge. hit (d), the= same the system Likewise, right(1)> track’s ina will Figuresedge, direct> right set, the the3 edge.(c) systemslider reflection and Likewise,(1) will(d), setof thea sliderdirectthe car’s reflection lateral position of the car’s on the lateral track. position on the track. player to steer fullyFinally, toplayer the the left toplayer system steeror right, to fully sets steer respectively.the to the fully the center. sliderFinally, left toplayer the orvalue right,the left to to system steeroror therespectively. right, letting followingfully sets respectively. to thego the of slider quan- left the orvalueaccelerator right,but to therespectively. due tofollowing to properly the difference quan- complete in thebut the cars’ due turn. to headings thel differenceCLleft+ with side,lCR respect insystem the tocars’ willlCL headings set+ l theCR slider with value respect to to zero. Likewise, in they will want to steerthey right will to want bringComputing to the steer sound rightthe car’s back to the bring lateral toward Slider the position soundComputingthe Value car’s back is thethe lateral toward same car’s the position lateralin Figureswhere Slider position isvalue zero the3the Value(c) torepresents same car’s andis one. the (d),value lateralin same Figuresthe the to caseposition in leftmostone. Figures3 of(c) the andis position thetrack’s3(c) (d), same and right onRather, (d), in the Figures edge, slider the it3 and(c) system is and afunction (d), will setRather, the slider of the it is car’s a function relative of risk the of car’s hitting relative risk of hitting tity, whichthe center. we call the time-to-impactthetity, center. whichComputing ratio we call: the the Slidertime-to-impact Value ratiothe: tracks’, the playerone is more representsthe at tracks’, risk the of therightmost hitting player the positionis left more edge aton risk the slider. of hitting There the are left a edge Finally, the system setsFinally, the sliderFinally, the system value the to systemsetsIf the the the following player sets sliderFinally, the valueis slider quan-Computing intheFigure a to systemvalue turn the following andbut to setsthe2 the dueillustrates not Slider the following to turning slider quan- the Value difference value nearlyquan- howFigurebut towherethe as dueRAD in sharply following thebut to2 zero cars’the dueillustrates computes represents difference to headings quan- the differencewhere thein howwithFrom the thebut leftmost zero respectRawsound cars’ dueRAD in represents the Position to headings positionFrom tocars’ the slidercomputesvalue difference to Raw headings Relativetheon with to value Positionleftmostthe one. respect Risksliderinwith the the to position respectsound toandcars’ Relative headings to on slider Risk the slider with value respect and to tity, which we call thetity,time-to-impact whichtity, we which call ratio we theas call: theytime-to-impact the needtity,time-to-impact which to,Figure perhaps ratio2 weillustrates call: because ratiothe the how: tracks’,time-to-impact they our sound theare playergoing slider ratiothe too system is: tracks’, more fast,the computes atthe tracks’, the risk player ofthe thefew hitting is player special more thethe is atcases, left tracks’, more risk edge however, of at the riskhitting player of in hittingthe which is left more the edgethe at left system risk edgethe of sets hitting track’s the slider the left edge or rightthe track’s sides if left the or player right wanted sides if to. the This player wanted to. This If the player is in aIf turn the and player notFigure is turning in a2 turnillustrates nearly and as not how sharply turning our sound nearlyone slider representsas sharply system the computes rightmostoneThe represents the algorithm position theThe ondescribed rightmost thealgorithm slider. above position There described represents are on a the abovea new slider. approach represents There for are a newa approach for sound slider willslider emitto valueComputing a display tire to display screeching the to Slider the thesound player. Value player. adaptedto Given display fromtheC Given car’s [4] current to the thevalue car’s player. to something current Given different.From position, theRaw If both Position car’s trajectories current to Relative hit the position, Risk track’s as they need to, perhapsas they because needslider theyto, perhaps are value going because to too display fast, they to the are the going player.few too special Given fast, thecases, the car’s however,few currentletting special in which players cases,letting the know however, system players where sets in they which know the are slider situatedthe where systemdistinction theyon a sets racetrack. are the situated slider is what on a makes racetrack.distinction the sound is what slider makes intuitive the sound for players slider intuitive for players from the sameposition, positionorientation,Figure orientation, as the2 illustrates car’s and engineand speed how speedon sound. our theorientation,race sound This on track, slider actsthe it tocomputes race system and track,left computes speed edgeUnlike RAD (whichon the the thestereocomputes meansThe race pan that algorithmvalues track, the thein playerBlindfold described RAD is driving Racer computes above, Mach toward represents 1, and the the a new approach(a) for (b) (c) (d) sound slider will emitsound a tire sliderscreechingthe willposition, trajectoriesslider emit sound a orientation, value tire adapted that screeching theto display from car and would [4 sound speed] to follow the adapted onvalue player. the if the to race fromsomethingplayer Given track, [4] was the it different. car’scomputesvalue current to Ifsomething bothUnlike trajectories different. the stereo hit If the both pan track’s trajectories valuesto in understandBlindfold hit the track’s Racer even, Mach withto 1, understand and the complex even vehicle with the physics, complex steering vehicle physics, steering warn the playerthe that trajectoriesthey must slow that down the car by hitting wouldleft the follow edge brake (which if the meansleft playerleft edge)the that edge wasTop or the (which theSpeed player player’sseries, meansletting is driving car the that players soundis currently the toward slider’s player know the off display is where thedriving track value they toward on is arenot the situated the on a racetrack. from the same positionfrom as the car’ssameto steer engine positiontrajectoriesposition, fully sound. to as the orientation, the left This car’s that or acts fully engine the and to to the sound.speedcartrajectories right. would on This It the models acts race follow to that these track, the if it computes thea car direct player would reflectionthe was followTop of theto Speed car’ssteer ifseries, the lateral playerd the position sound was on slider’s the to track. steer display value is not or letting go of the accelerator to properly completeleft the edge) turn. or> the player’sleftleft side, edge) car system is or currently the will player’sUnlike set off the the slider carthe track isstereo value currently on pan the to zero. valuesbehaviors, off the Likewise, in trackBlindfold on in and the Racer trackFigure, Machbehaviors, geometries 3. 1, Four and car and posesthat track are and geometries present their corresponding in modern that are sound present slider in values. modern warn the player that theywarn must the player slowtrajectoriesto down steerthatthe theytrajectoriesbyas fully circular hitting must to the slow arcs.the that left brake down We the or will fully carby denote hitting would to the them the right.follow brakeas CL It ifand models the playerRather, these was it isa directfunction reflection of the car’s of relative the car’s risk lateral of hitting position on the track. > fully to the left or fullyfullyleft to side,the to the right. system left will Itthe or modelsleftset casefully> theside, of slider to the system these the track’s value right. will trajectoriesthe right to setTop zero. edge, Itthe Speed models Likewise, slider theseries, system value these in to the will zero. sound settrajectories Likewise, the slider’s slider in displayThough value the is not car’s lateral position is the same between (a) and (b) and or letting go of the acceleratoror letting go toCR properlyoftrajectories, respectively. theto steer accelerator complete fully as The circular to radii to the the properly turn.of arcs.left the arcsorcomplete We fully are will modeled to denote the turn. right. as them being It asmodels>CLtheand thesetrack’s> leftRather, or right it edges is> a iffunction the player> ofracing wanted the car’s to. games. This relative risk ofracing hitting games. > the case of the track’svaluethe right to case one. edge, of the the track’s systema direct right will reflection edge, set the the slider system of the will car’s set lateral the slider positionbetween on the (c) track. and (d), the corresponding sound slider values are very dif- directlyCRas, respectively. proportional circular to arcs The the radiicar’s which currentofas the we circular arcs speed, denote are where modeled arcs theas whichCL as beingdistinctionand> weCR denoteis,the what respectively. track’s makes as the leftCL sound orand right sliderCR edges intuitive, respectively. if for the players player wanted to. This Computing the Slidertrajectories Value as circular arcs. Wevalue will(a) to one.denote themvalue as CL toand one. Rather, it is a(b) function of the car’s relativeferent. risk of Thishitting is because the left and right trajectories’ lengths — and constantdirectlyThe> ofradii proportionality proportional of the torepresents arcs the arecar’sThe how modeled currentradii sharply of speed, the theas car beingFromarcs where Rawto aredirectly understandthe Position modeleddistinction evenproportional to Relative with as thebeing isRisk complex what directly makes vehicle theFigure physics, proportional sound steering3 sliderillustrates intuitive for theFigure players benefit3 illustrates of updating the the benefit auditory of updating display the auditory display Figure 2 illustratesturns.CR how Through, respectively. our sound manual slider tuning, The system radii we found ofcomputes the the arcs value the are of modeled theThe algorithmbehaviors, as being described and tracktheabove track’s geometries represents left that or areright a presentnew edges approach in if modern the for player wantedtherefore to. the This relative risks of hitting the left and right sides of the track Computing the SliderComputing Value theconstant Slider Value of proportionalityFigure represents 2.From RAD’s Raw how Position sound sharply slider. toFrom Relativethe car Raw(a) RiskSample Positionto understand carto Relative pose evenwith Risk with thecar’s theusing complex trajecto- our vehicle trajectory-based physics,using steering our approach trajectory-based over the car’s approach lateral over po- the car’s lateral po- slider value toconstant displaytodirectly in the to our the car’s prototype proportional player. current racing Given to game speed, the theto to car’s car’s the be very where current car’s current close current theto speed, 1.6. constantletting where speed,racing players the games.of where knowproportionality Recalldistinction where the that constant thethey other is are what games situated ofmakes used proportionality on thevery a sound racetrack.simplified slider intuitive— are for very players different in each pair of cases. Figure 2 illustrates howFigure our2 soundillustratesturns. slider how system Through our computes sound manual slider theries tuning, system if theThe we computes player algorithm found was the the describedto value steerThe ofmodels above algorithmfully the for representsleft vehicle describedbehaviors, or right handling a new drawn.above and approach and trackrepresents track (b) geometriesdesigns. for Overhead a new approach that view are forpresent in modern position, orientation,It is veryconstant and important speed of on proportionalityto set the this race value track, to represents it be computes as accurately how assharplyUnlike the stereo car panto values understand in Blindfold even with Racersition the, Mach complex alone. 1, and vehicle The physics, car’ssition steering lateral alone. position The car’s is the lateral same position between is the same between slider value to displayslider to the value player.possible. toconstant displayrepresents Given in to the our the car’s prototype player. how current sharply Given racingrepresents theletting game the car’s to car players current be turns.how very know close sharply Throughletting where to 1.6. players they the manual are carracing know situated turns. games.where tuning, on Through they a Recall racetrack. are that situated manualthe other on a games racetrack.tuning, used very simplified the trajectories thatturns. the car Through would follow manualof if corresponding tuning, the player we was found rendered the valueFigure spatialized of the3 illustrates (3D)behaviors, the benefitsoundscape. and of using track our RAD’s geometries approach sound over that the are present in modern position, orientation,position, and speed orientation, onIt the is race very and track, important speed it computes on to the set race this track, value it computes to be as accuratelythe Top Speed as series,models the for sound vehicle slider’s handling displayFigures and value track is3 designs.(a)not and (b)Figures and between3(a) and Figures (b) and3(c) between and (d), Figures but 3(c) and (d), but to steer fullyNext, to thewe theconstant left system found or fully in computes our tothe prototypethe value right. theslider respective Itracingwe of models isUnlike athe found gamespeaker points these constantthe to at stereo the be which emitting very value panin closeUnlike valuescar’s ourthe of to the car’slateralin 1.6. theprototypeBlindfold stereo positionengineconstant panracing Racervalues on noise racing games. the, inMach track.in whoseBlindfold our Recall 1 The, andprototype lateral car’s that Racer lateral the position, otherMach position racing games 1, and used very simplified the trajectories thatthe trajectoriescar wouldpossible. follow that the if car the would player follow was if thethe playerTop> Speed was series,a directthe theTop sound reflection Speed slider’sseries, of the display the car’s sound value lateral slider’s is positionnot display on the value track. is not trajectories asthe circular trajectoriesIt is arcs. very intersect We important will the denote track’sin to set the themedges, this soundscape as then valueCL computesand to be tracks theasRather, accurately theis theit ratio is same as a function of inFigure the Figuresmodels trajectories’ of3 illustrates3 the(a) for car’sand vehicle (b), the relative lengths. buthandling benefitthe due risk to of player’s andIn theof using thishitting naturetrack our designs. relative approachedge overthe risks (which the player’s of hitting means relative the that track’s risksthe player of left hitting and is driving right the track’s toward left the and left right to steer fully to the> leftto steer or fully fully to to thegame the right. left to or It modelsfullybe very> to these the close right.> game Ita to models direct 1.6. to reflectionbe these very of closea the direct car’s to reflection1.6. lateral position of the car’s on the lateral track. position on the track. respectivepossible. arc lengths lCL>andcase,lCR from the the player car’s> position will hearthe track’s theof the car’s left tracks or enginecar’s in right these lateral edges figures right position if thein the player front player on has the ofsides wanted an their track. equal is to. face The risk very This of car’s different lateral positionsides between is very each different pair. In between Figure each3(b), pair. for In Figure 3(b), for trajectories as circularFigureCRtrajectories, respectively. arcs. 2. Overview We as willNext, circular The of denote sound radiithe arcs. system them ofslider. the We as arcs computesCL will areand denote modeled> the themRather, respective> as as beingCL it isand points a function atRather, whichhitting of the it the is car’s track’s a function relativeFigure left and of3 risk rightillustrates the of edgescar’s hitting intherelative Figure benefit risk3(a) of butof using hittingnot our approachedge), over or theif the player’s car is currently off the track on the > > to these points of intersection. lCL and lCR represent thedistinction is whatis makes the same the sound in Figures slider intuitive3(a) and for (b), players but due to the nature CR, respectively.directly TheCR radii, respectively. proportional of theFigurethe arcsNext,Next, trajectories The are2. to Overview themodeled radiithe RAD car’s system of intersect the asfinds current of arcsbeing computes soundbut the arethe speed, track’s slightly modeledNext, slider. pointsthe where edges, track’s respectiveRAD to as at the being then which left left.finds computes orpoints right The the the atin edgesratio track’s trajectories Figurethewhichpoints ifrepresents left3 the(b): at or playerincar’swhich right that intersect figurethe wantedlateral edges theplayer’s the ifposition playerto.trajectories the This player should relative onexample, the steer wanted track.risk tointersect the to. of leftThethe This car’s player lateral isexample, positionmuch more the player at risk is of much hitting more the attrack’s risk of hitting the track’s distances the car would travel before> hitting> an edge were theto understand evenof with the the tracks complex in these vehicle figures physics, the player steering has anleft equal side, risk of system will set the slider value to zero. Likewise, in directly proportionalconstantdirectly to the of car’sproportional proportionalityrespective currentthe trajectories tospeed, arc the represents lengths car’s where intersect currentl thehowCLhitting theand sharply speed, track’sdistinctionl eitherCR wherethefrom edges, edge car theis the what thenof car’s themakes computesdistinction position track.and the would sound the is otherwise what slideris makes theintuitive soon same the hit sound the for in track’s players Figures slider right intuitive3 edge.(a) and Likewise, for (b), players but due to the nature playerthe to steer track’s fully to theedges, left or right, thenthe respectively. it> track’s computes> edges,behaviors, the then respective itand computes trackhitting arc geometries the lengths the track’s respectivethat left are and presentright right arc in edges side modern lengths thanin Figure they3(a) areright but in not sideFigure than3(a) they due are to in the Figure sharp3 left(a) turn due to the sharp left turn constant of proportionalityturns.constant Through represents ofFigure proportionalityto manual these> how2. pointsOverview tuning, sharply represents> of we intersection. the of foundsound car how> the slider.> sharplyvaluetolCL understand> ofand the thel>CR car evenrepresent withto understandthe the the car’s complex lateral even vehicle positionof with the physics, the tracks is thecomplex> same in steering these in vehicle Figures figures physics,3(c) the and player steering (d),> hasthe an equal case risk of of the track’s right edge, the system will set the slider Finally,respective the system setsarc the lengths slider valuelCL and to thelCR followingfrom quan- theracing car’sbut position games. dueFigure to Recall the difference 3. that Four the driving in other the cars’ games scenarios. headings used very with simplified respect to turns. Through manualconstantturns. tuning, in Through our prototypedistances welCL found manualand racingthe the tuning, car valuelCR game would we offrom to the travelfound be veryl the beforeCL thebehaviors, close value car’sand hitting> to 1.6.ofl positionCRand the an> edge trackfrom werebehaviors, geometries to the the these car’s and thatin points. track Figurearehitting position presentgeometries3 the(b):lCL track’sin in to modern that that these left figure arein and present points. the Figure right player in edges modern3 shouldl(b),CL in Figure steerandvalue to the3in(a) the to Figure playerbut left one. not 3 should(b), and be the aware player of this. should be aware of this. the sound of the car’s enginetity, right whichtoin these we front call points the oftime-to-impact their of intersection. face. ratio The: lCL and lCRmodelsrepresentthe for tracks’, vehiclethe the handling player is moreand track at risk designs. of hitting the left edge constant in our prototypeIt isconstant very racing important in our game prototype to be set> very this racing close value game to to 1.6. be to be as very accuratelyracing close> games. to as 1.6. Recallracing that the games. other games Recalland would used that the very otherwise other simplified gamesFigure soon used hit 3. the very Four track’s simplified driving right edge. scenarios. Likewise, playeranddistances tolCR steer therepresent fully car towould theIf left travel the theand or right,playerbefore distanceslCR respectively. hittingrepresent is in the an aedge car turn thewere would and distances the not travelin turning Figure the before car3(b): nearly would in that figureas travel sharply the player before should steer to the left car’sIt is sound very important willpossible. moveIt to is set towardvery this important value the to left be toor asset accuratelythe this right value as to bethe as carmodels accurately for vehicle as handlingmodels andfor vehicle trackthe designs. car’s handling lateral and position track designs. isAs the another same in Figures example,3(c)As and the another(d), car’s heading example, in Figurethe car’s3(c) heading puts the in Figure 3(c) puts the the sound of the car’splayer engine to steer right fullyto in the front left or of right, their respectively. face.Figure The3 illustrates theand benefit would of otherwise using our soon approach hit the over track’s the rightFrom edge. Likewise, Lateral Position to Relative Risk becomespossible. more at riskpossible. of hittingFinally, thehitting track’s the ansystem left edge setsor rightwere theas slider they edges,hitting the value playerneed an to theto, edge to following perhaps steer were fully quan- the because to player thebut left they dueto steeror to are the right, differencefully going to toothe in the fast, left cars’ or the headings right, with respect to Figure 2. Overview of soundNext, slider. the system computes the respective pointsFigure at which3 illustratescar’s theFigure benefit lateral3 illustrates positionof usingthe ouron the thecar’s approach benefit track. lateral of over The using positionFigure car’sthe> ourcar lateral3. approach is Four themore position same driving over at in the risk Figures scenarios. of3 hitting(c)car and more (d), the at track’s risk of left hitting edge the than track’s its right left edge than its right respectively.car’s When sound they will steer, movetity, they which toward control we call the the the car’stime-to-impact leftsound orsound the slider right ratio will: as emit theis the acar tire same screeching in Figuresthe tracks’,3(a) sound and the player (b), adapted but is due more from to at the risk[ nature4 of] hittingThe the left algorithm edge described above represents a new approach for Next, the systemthe soundthe computesNext, trajectories of the the the system intersectrespective car’srespectively.Finally, computes engine the points the track’s system the right at edges, respective whichFinally, sets in then the frontrespectively. slider computespoints RADcar’s of value lateralat their setswhich the toposition face.the the Finally, following sound Thecar’s on the lateral quan-RAD slider track. position Thesets valuebut car’s the on due thetolateral tosound thetrack. the position difference The sliderlCL car’sedge, in value lateral the while cars’ positionto headings the its heading withedge, respect in whileFigure to its3(d) heading does the in Figure opposite.3(d) The does the opposite. The > > of the tracksSlider in Display these figures Value the= player has an equal, risk of (1) directly,the trajectories sobecomes if they intersectrespective hearthe more trajectories the track’s arccar’s at lengths risk sound edges,following intersecttity, ofl whichCL movethen hitting theand computes we track’s far quantity,lCR call thetowardfrom theedges, the track’sfromtime-to-impact the the which thenfollowing car’s theleft,is computesleft the position same we sameor ratio callright quantity, the position in: Figures the edges,istime-to-impact the aswhich3(a) same the and car’swe in (b), Figures callthe but engine tracks’,ratio due the3(a) to:time-to-impact sound.and the the nature (b),player> but This is> due more acts to ratioat the riskto nature: of hittingletting the left players edge know where they are situated on a racetrack. car’s sound> will> move toward> > the> left> or the right as thehitting car the track’s left and right edgeslCL in+ FigurelplayerCR3(a) but should not be awareplayer> of should this as be well. aware The of sound this as slider’s well. The sound slider’s theyrespective will wantrespectively. arc lengths toto steer theserespectivelCL right pointsand When arcl toCR of bringlengths intersection.from they the thelCL steer, car’s soundandlCL positionl theyCR backandfromwarnl controlCR toward therepresent theof car’s the player the positiontracks the car’s inthat these sound theyof figures the must tracks the playerslow in these hasdown figures an equal by the hitting riskplayer of has the an brakeequal risk of UnlikelCL the stereo pan values in Blindfold Racer, Mach 1, and becomesdistances more the car at> wouldrisk of travel> hitting before the hitting> track’s an> edgehitting left were or the the right track’s edges,in left Figurehitting and right3 the(b): track’s edges in that in left figure Figure and the right3 player(a)Slider edges but should not in Displaytrajectory-based Figure steer to3(a) the Value but left not= approachtrajectory-based communicates, approach(1) these communicates risks. these risks. theto center. these pointsdirectly, of intersection.to so these if they pointslCL hear ofand intersection. thelCR car’srepresent soundlCL theand movelCR represent far towardwhere the Figure theand zero left, would 3. represents Four otherwise driving the soonleftmost scenarios. hit the track’s position right on edge. the Likewise, slider and >> > respectively.player to steer When fully to they the left steer, or right, they respectively.or control lettingin Figure thego of3 car’s(b): the in sound that acceleratorin figure Figure the3(b): player to in properly that should figure steer the complete to player the left should the steer turn. to the left thelCLlCLTop+ lCR Speed series, the sound slider’s display value is not the sound of the car’s enginedistances rightthey the car in will would frontdistances want travel of beforethe to theircar steer hitting would face. right an travel The edge to before were bring hittingthe the an sound edge were backone the represents towardthe car’s> lateral the rightmost position is position the sameSlider> on inthe Figures Display slider.3(c) There Value and (d), are= a , (1) Ifplayer the player to steerdirectly, is fully in toplayer a sothe turn ifleft tothey and steeror right, not hear fully respectively. turning to the the car’s left nearly or sound right, as respectively. movesharplyand far would toward otherwise theandleft, soonl wouldCL hit the otherwise track’s right soon edge. hit the Likewise,lCL track’s rightOvercoming edge. Likewise, the>a Intention–Efficiency directOvercoming> reflection the of TradeoffIntention–Efficiency the car’s lateral position Tradeoff on the track. car’s sound will move towardthe the center. leftFinally, or the the system right sets as the the slider car valueSlider toComputing the Display followingthe car’s quan- theValue lateralfew SliderSlider special= positionbutthe Valuedue Displaycases, car’s is to the the lateral same however,difference. Value position in Figures in in= the iswhich the3 cars’(1)(c) same and the headings (d), insystem Figures. with sets respect3(c) the and slider to(1) (d), lCL+ lCR quickly by steering the appropriate amount. Asas with they needBlindfoldthey to, perhapstity, will which want because we to call steer the theytime-to-impact right are going to bring ratio too: fast, thethe sound back towardthe> tracks’, the> playerwhere is more zero at> represents risk of> hittingWe the the argue left leftmost edge that positiontheRather, soundWe on argue it slider’s theis a sliderthat function trajectory-based the and sound of the slider’s car’s approach relative trajectory-based risk of hitting approach becomes more at risksound ofFinally, hitting slider the thesystem will track’s emit setsFinally, thea tire left slider the screeching orsystem value right to sets the edges,sound the following slider adapted value quan-Figure to from the following [but42] dueillustrates to quan-value the difference to howl somethingbutCL dueRAD in+ the tolCR cars’the computes different. difference headings If inwith the bothl theCL respectsound cars’ trajectories+ l headingsCR to slider withhit value the respect track’s to the center.time-to-impact ratio time-to-impact ratio one represents> the rightmost positionthe on the track’s slider. left There or right are a sides if the player wanted to. This Racer and Mach 1, there is norespectively. concept When of vehicle theyfromtity, steer, thewhich same physics,If we they the call position player the controltity, which as is the the we in car’s callcar’s a turn enginethe: sound and sound. not This turning acts: the to nearly tracks’,leftas the edge playersharplythe (which is tracks’, more meansat thewhere risk player of that hitting zero isw the more therepresents player at left risk edge is of driving hittingto the computingleftmost the toward left edge the position its displayedto on computing the valueslider allowsandits displayed RAD to value overcome allows RAD to overcome to display to the player. Givenfew the special car’slCL cases, current however, position, in which thedistinction system setsis what the makesslider the sound slider intuitive for players tracks are modeled using a simplifieddirectly, so geometry, if they hearwarn the and car’s the car playeras soundIf they steer- the that move playerneed they farmustto, is towardperhaps in slow a turn down the because andleft, by hitting not they turningorientation, the are brake going nearly and tooSliderleft as speedfast, edge) sharply Display the or on> the the player’sValue raceone represents= track, car> is currently RAD> the computes, rightmost offthe the intention–efficiency track position the(1) on the on thethe slider. intention–efficiency tradeoff There are that a plagues tradeoff other that blind- plagues other blind- left side, systemlCL willvalue set the tolCL slider something+ valuelCLCR to different. zero. Likewise, If both in trajectoriesto understand hit eventhe track’s with the complex vehicle physics, steering they will want to steeror right letting to gosoundas bring of they the slider the accelerator need sound will to, emit perhaps backto properly a tire toward because screeching complete they the sound are turn.R going adapted too fast,from the [4] few special cases, however,accessible in which racing the gamesystemaccessible interfaces sets the racing slider (Figure game1). interfaces The reason (Figure is 1). The reason is ing is simplified so that the car will move in a straightaway L Slidertrajectories Display Value thatthe theSlider case= car> of Display wouldthe track’s> followwleft Value right edge ifedge,= the (which>(2) the player system> means wasw will to that set steer the the slider(2) playerbehaviors, is driving and toward track the geometries that are present in modern the center. fromsound the slider same will position emit a as tire the screeching car’s engine sound sound. adapted This from actslCL [4 to]+ lCRvalue to somethinglCL+ lCR different.that this If approach both trajectories distillsthat this hit many the approach track’s pieces distills of information many pieces — the of information — the fullywhere to zerothe left representsvalue or fully to one. to the the leftmost right.left Itedge) position models or the onthese player’sthe trajectories slider car and is currentlyracing off games. the track on the direction when the player lets go of the steering. warnfrom the the player same positionthat they as must the car’sslow engine down by sound. hitting This the acts brake to left edge> (which> meanscar’s that lateral the player position is drivingcar’s on the lateral toward track, position its the heading on the with track, respect its heading to with respect to Computing the Slider Value asone circular represents arcs the which rightmost we denote positionleft as side,CL on systemandthe slider.CR will, respectively. There set the are slider a value to zero. Likewise, in If the player is in a turn andor notwarn letting turning the go player ofnearly the thatThe accelerator as they sharply sound must slider’s toslow properly down leftmostThe by complete sound hitting andFrom slider’s rightmostthe the Raw brake turn. leftmostPosition positions toleft and Relative edge) are rightmost repre- Risk or the positions player’sthe track’s, car are is repre- currently its speed,Figure offthe the the3 track’s,illustrates track’s track onits width, the speed, benefit whether the of track’s updating the track width, the is whether auditory the display track is as they need to, perhapsFigure because2 illustrates they how are goingour sound too slider fast, system the computesThefew radii special the of the cases, arcs however, are modeled in whichthe as case being the of systemdirectly the track’s sets proportional the right slider edge, the system will set the slider Sucu and Folmer’s Haptic Steering Interface or letting go of thesented accelerator by zeroC to properly and onesented complete respectively. byThe zero the algorithm and turn. There one described arerespectively.left a few side, above special system represents There will are aabout set new a few the approach to slider special immediately forvalueusing toabout zero. turn, our totrajectory-basedLikewise, and immediately more in — into turn, approach a single and more measure over — the into car’s a single lateral measure po- sound slider will emit aslider tirescreeching value to display sound to the adapted player. from Given [4] the car’stovalue currentthe car’s to something currentletting speed, different.players where know Ifvalue boththe where constant trajectoriesto they one. are of situated proportionality hit the on track’s a racetrack. position, orientation, and speed oncases, the race however, track, it computesin whichcases, the however, system in sets which the sliderthe case system value of the sets to track’s the sliderthat right is edge, value no less the to relevant systemsitionthat will toalone. is the set no process the lessThe slider relevant car’s of racing lateral to the than position process all of is ofthat the racing same than between all of that Sucu and Folmer’s haptic steeringfrom the interface same position [34 as] the is car’s a driver engine sound. This acts to representsleft edge (which howUnlike sharply means the stereo the that car pan the turns. values player Through in isBlindfold driving manual Racer toward, tuning,Mach the 1, and the trajectoriesComputing that the the car Slider wouldsomething Value follow if different. the playersomething was If both trajectories different. hitIf both thevalue track’s trajectories to one. left hit theinformation track’s left put together.Figuresinformation3(a) and put (b) together. and between Figures 3(c) and (d), but assistance system publishedwarn as a the response player that tothey the must National slow down by hitting the brake weleft found edge) the orthe the valueTop player’s ofSpeed the carseries, constant isFrom currently the sound Raw in our Position slider’soff prototype the display track to Relativeracing on value the isRisknot to steer fullyFigureComputing to the2 illustrates left theor fully Slider how to theValue our right. sound It models slider these system computesa direct reflection the of the car’s laterald position on the track. the player’s relative risks of hitting the track’s left and right or letting go of the accelerator to properly complete the turn. gameleft> side, to be system very close will set to 1.6. the sliderFromThe valuealgorithm Raw Positionto zero. described toLikewise, Relative above in Risk represents a new approach for Federation of the Blind’s Blind Driver Challengetrajectories [slider22Figure as], circular value an2 illustrates arcs. to display We how will to denote our the sound player. them slider as GivenCL systemand the computes car’sRather, current it the is a function of the car’s relative risk of hitting sides is very different between each pair. In Figure 3(b), for > the case of the track’s right edge,Theletting the algorithm system players willdescribed know5 set thewhere above slider they represents are5 situated a new on approach a racetrack. for initiative to make it possible for people who are blindCR, respectively. toposition,slider drive The value a orientation, radii to of display theand arcs to speedare the modeled player. on theNext, as Given race being RAD track, the finds car’s itthe computes track’s thecurrent points left or at right whichlettingUnlike edgesthe players the if trajectories stereo the know player pan where wanted valuesintersect they to. in Blindfold This are situatedexample, Racer on the, aMach racetrack. player 1, is and much more at risk of hitting the track’s directly proportional to the car’s current speed, wherevalue the to one.distinction is what makes the sound slider intuitive for players theposition, trajectories orientation, that the and car speed would on thethe follow race track’s track,if the edges, it player computes then was it computesUnlikethe Top the the Speedrespective stereoseries, pan arc values the lengths sound in Blindfold slider’sright Racer display side, thanMach value they 1, isand arenot in Figure 3(a) due to the sharp left turn car by themselves. The driver steersComputing with the a Slider steering Valueconstant wheel of proportionality and represents how(a) sharply> the car > to understand even with the complex vehicle physics,> steering tothe steer trajectories fully to the that left the or car fully would to thel followCLFrom right.and Raw ifl It theCRPosition models playerfrom theseto the was Relative car’s positionthea Risk directTop(b) Speed toreflection theseseries, points. of the the sound car’slCL slider’s lateralin positionFigure display3 value(b), on the and is not track. the player should be aware of this. has rumble motors (in this case,Figure PlayStation2 illustrates Move howturns. our controllers) sound Through slider manual system tuning, computes we found the the value of the behaviors,> and track geometries that are present in modern trajectoriesto steer fully as to circular the left arcs. or fully We towill theThe denote right. algorithm> them It models as describedCL theseand aboveaRather, represents direct reflection it is a newa function approachof the car’sof for the lateral car’s position relative riskon the of track. hitting slider value to displayconstant to the inplayer.> our prototype Given racing theFigure car’s game current to 3. be The very close RAD’sand tolCR 1.6. soundrepresentracing slider.>the games. (a) distances RecallSample that the car the car other pose would games showing travel used very before what simplified As another example, the car’s heading in Figure 3(c) puts the attached to the back of their hands. It is veryCR importanttrajectories, respectively. to set as this circular The value radii arcs. to be of We as the accurately will arcsletting denote are as modeled players themmodels as know asCL being forand where vehicle they handlingRather,the are track’s situatedand it is track left a function or ondesigns. right a racetrack. of edges the car’sif the relative player wantedrisk ofhitting to. This position, orientation, and speed> on the race track,the it computes car’s trajectorieshitting would an edge be were if the the player player to were steer tofully steer to the fully left leftor right, or car more at risk of hitting the track’s left edge than its right possible. directlyCR, respectively. proportional The to radii the of car’s the arcscurrentUnlike are modeledspeed, the stereo where as pan being the values inthedistinctionBlindfold track’s leftRacer is what or, rightMach makes edges 1 the, and sound if the sliderplayer intuitive wantedfor to. players This the trajectories that the car would follow if thefully player right. was (b)respectively. Overhead view Finally,Figure of3 correspondingillustrates RAD sets the the benefit sound rendered of using slider our spatialized value approach to the over the edge, while its heading in Figure 3(d) does the opposite. The At each time step, the system computes the locationconstant ofdirectly what of proportional proportionality to the represents car’s currentthe howTop speed, Speed sharply whereseries, the the car the sounddistinctionto understandslider’s is display what even makes value with the is not complexsound slider vehicle intuitive physics, for players steering to steer fully to the leftNext, or fully the system to the computes right. Itthe models(3D) respective soundscape. these pointsfollowing at The which RAD’s quantity,car’s sound lateral which slider position we is call a onspeaker the thetime-to-impact track. emitting The car’s the lateral ratio car’s: position player should be aware of this as well. The sound slider’s Sucu and Folmer call a target point, which isthe the trajectories pointturns.constant intersect on Through of the proportionality track’s manual edges,> tuning, then represents computes wea found direct how the the reflectionsharply valueis the the of same of car the the in car’s Figurestobehaviors, lateral understand3(a) and position and (b), even track but on with due the geometries the to track. thecomplex nature that vehicle are present physics, in steering modern trajectories as circular arcs. We will denote> themengine> as CL noiseand whoseRather, lateral it positionis a function in the of soundscape thebehaviors, car’s relative tracks and track risk the geometriesof ratio hitting of thattrajectory-based are present in modern approach communicates these risks. the median of the track a fixed> distance aheadrespective of theconstant driver’s arcturns. lengths Through in ourlCL prototypeand manuallCR from racing tuning, the car’s game we position found to be very the value closeof the of to tracks the1.6. in theseracing figures games. the player Recall has that an equal the other risk of games used very simplified the> trajectories’> lengths. Thehitting ratio the represents track’s left and the right player’s> edges inrelative Figure 3 risk(a) but not CR, respectively. Theto radii these of pointsIt theconstant is arcs very of intersection. are in importantour modeled prototypelCL to as setand being racing thislCR valuerepresent gamethe to to track’s be thevery as accurately left close or to right 1.6. as edgesracingmodels if the games. player for vehicle Recall wanted handling that to. the This other andtrack games designs. used very simplified current position. If the car’s current heading points too far of hitting either edge of the track.in Figure In3(b): this in case, that figure the the playerlCL player will should hear steer the to the left Overcoming the Intention–Efficiency Tradeoff directly proportionaldistances to the car’s thepossible.It car is current verywould important travel speed, before where to hitting set the this anedge valuedistinction were to be the as accuratelyisSlider what makesDisplay as the Value soundmodels= slider> for vehicle intuitive>. handling for players and(1) track designs. possible. car’s engine right in front ofand their would face otherwise but slightlyFigure soon hitl toCL3 theillustrates the+ track’slCR left. right the edge. benefit Likewise, of usingWe our argue approach that the over sound the slider’s trajectory-based approach away from the target point’s direction,constant of the proportionality systemplayer will to represents steer vibrate fully to how the left sharply or right, the respectively. car to understand even with the complexFigure 3 vehicleillustrates physics, the benefit steering of using our approach over the Next, the system computes the respectivebehaviors, points andthe at track car’s which lateral geometries positioncar’s that is lateral the are same present position in Figures in on modern3 the(c)track. and (d), Theto computing car’s lateral its position displayed value allows RAD to overcome the left or right rumble motors.turns. The analogy Through manual is thatFinally, tuning, of the a rumbleNext, system we found the setssystem the the slider value computes value of to the the the following respective quan- pointsbut at due which to the differencecar’s in lateral the cars’ position headings on with the respect track. toThe car’s lateral position the trajectories intersect the track’s edges,racing then games. computes Recall that the the otheris the games same> used in Figuresvery simplified3(a) and (b),the but intention–efficiency due to the nature tradeoff that plagues other blind- constant in our prototypetity, whichracing wethe game call trajectories the to betime-to-impact very intersect close> ratio to the 1.6.: track’s> edges, then computesthe tracks’, the the playeris the is more samelCL at risk in Figures of hitting3 the(a) left and edge (b), but due to the nature strip on the side of a highway:It is if very the important vibration to isset felt thisrespective valueon the to be arc as lengths accuratelylCL>and as lCR>modelsfrom the for car’s vehicleSlider position Display handling Value andof track= the tracks designs. in thesew figures(2) the playeraccessible has an racingequal risk game of interfaces (Figure 1). The reason is respective arc lengthsFigurelCL3 andshowslCR> thefrom specific the> car’s soundposition sliderofhitting configuration the tracks> the track’s in> these left that figures and we right the player edgesthat inhas this Figure an approach equal3(a) risk but distills of not many pieces of information — the right the player should steer topossible. the left and vice-versa.to these points of intersection. lCL> and lCR> represent the lCL+ lCR propose for blind-accessibleFigure 3 illustrates racing the benefit games.hitting of using the The our track’s approach slider’s left and over track right the edgescar’s in Figure lateral3(a) position but not on the track, its heading with respect to distancesto these the points car ofwould intersection. travel beforelCL hittingand lCR an edgerepresent were the the in Figure 3(b): in that figure the player should steer to the left Next, the system computes the respective points at which car’s lateral position on the track.in Figure The3 car’s(b): in lateral that figure position the player should steer to the left Although the authors state that making a racing gameplayerdistances with to steer the car fullyis would to a the virtual travel left orbefore horizontalright,The hitting respectively. sound anslider’s edgebar wereof leftmost width the andwandplaced rightmost would a otherwise positions distance soonared repre- hitin the track’sthe righttrack’s, edge. itsLikewise, speed, the track’s width, whether the track is the trajectories intersect the track’splayer edges, to steer then fully computes to the left the or right,sentedis respectively.the by same zero in and Figures one respectively.3(a) andandthe would (b),car’s There but lateral otherwise due are position ato few soonthe special naturehit is the the same track’sabout in right Figures to edge. immediately3(c) Likewise, and (d), turn, and more — into a single measure this system is promising future work, we feel that> its current> front of the player’s face in the soundscape.the car’s lateralIn our position prototype is the same in Figures 3(c) and (d), Finally, the system sets the slider valuecases,of tothe the however, tracks following in inthese which quan- figures the systemthebut player due sets to hasthe the difference an slider equal value risk in the ofto cars’that headings is no with less relevant respect to to the process of racing than all of that respective arc lengths lCL andFinally,lCR from the systemthe car’s sets position the slider value to the following quan- but due to the difference in the cars’ headings with respect to goal as a driver assistance system runs contrary to supportingtity,> which we> callracing the time-to-impact game, somethingwhitting ratiois 65: the m different. track’s and leftd If andis both 12 right trajectoriesthe m. edges tracks’, The in Figurespeaker hit the the player3 track’s(a) emits is but more left not at riskinformation of hitting the put left together. edge to these points of intersection.tity,lCL whichand welCR callrepresent the time-to-impact the ratio: the tracks’, the player is more at risk of hitting the left edge intention. When drivers use thisdistances system, the car they would must travel follow before hitting its an edgethe were sound the of thein Figureplayer’s3(b): car’s in that engine figure the and player slides should left steer and to theright left player to steer fully to the left or right, respectively. and would otherwise soon hit the track’s right edge. Likewise, orders as soon as those orders are felt and nothing more. Our along the bar asthe the car’s sound lateral slider position updates is the same its in value. Figures 3(c) and (d), 5 interface, by contrast, is designedFinally, to the support system setsintention. the slider value to the following quan- but due to the difference in the cars’ headings with respect to tity, which we call the time-to-impact ratio: We explained the tracks’, concept the playerof the is sound more atslider risk of hitting to our the studies’ left edge participants as follows. We asked them to imagine being THE RACING AUDITORY DISPLAY (RAD) behind the car that they were controlling, so they could hear In this section we introduce the racing auditory display (RAD), the sound of the car’s engine right in front of their face. The a user interface whose goal is to help racing games become car’s sound will move left or right as the car becomes more equivalently accessible to people who are blind. The RAD was at risk of hitting the track’s left or right edges, respectively. designed with the principle that it should not just tell players When they steer, they control the car’s sound directly, so if what to do but rather give them enough relevant information they hear the car’s sound move far toward the left, they will to form a plan of action themselves. want to steer right to bring the sound back toward the center. The RAD comprises two novel sonification techniques: the If the player is in a turn and not turning nearly as sharply sound slider and the turn indicator system. The sound slider as they need to, perhaps because they are going too fast, the helps the player understand their car’s speed and trajectory on sound slider will emit a tire screeching sound adapted from [5] a racetrack while the turn indicator system alerts players of from the same position as the car’s engine sound. This acts to the direction, sharpness, length, and timing of upcoming turns warn the player that they must slow down by hitting the brake well in advance of the actual turns. Together, the techniques or letting go of the accelerator to properly complete the turn. allow players to understand aspects about the race and perform a wide variety of actions that are not possible to understand Computing the Slider Value and perform in current blind-accessible racing games. Figure3 illustrates how the RAD computes the sound slider value to display to the player. Given the car’s current position, The RAD’s Sound Slider orientation, and speed on the race track, the RAD computes The RAD’s sound slider is a novel mechanism for displaying the trajectories that the car would follow if the player was to a value within a range using spatialized (3D) sound. It is anal- steer fully to the left or right. It models these trajectories as > > ogous to a traditional user interface slider, where the slider’s circular arcs which we denote as CL and CR, respectively. The track is a line segment in the 3D soundscape and the slider’s radii of the arcs are modeled as being directly proportional to handle is replaced with a virtual speaker (sound emitter). The the car’s current speed, where the constant of proportionality position of the speaker on the virtual track represents the represents how sharply the car turns. Through manual tuning, slider’s displayed value, where one end of the track represents we found its value in our prototype game to be roughly 1.6. the slider’s minimum value, the other its maximum value, and positions in between intermediate values. The slider’s value is Next, the RAD finds the points at which the trajectories in- tersect the track’s edges, then it computes the respective arc for display only: the speaker cannot be manually manipulated > > by the user like a traditional user interface slider’s handle can. lengths lCL and lCR from the car’s position to these points.

4 Overcoming the Intention–Efficiency Tradeoff We argue that the RAD’s trajectory-based approach to com- puting its sound slider’s displayed value allows it to over- come the intention–efficiency tradeoff that plagues other blind- accessible racing game interfaces (Figure2). The reason is that this approach distills many pieces of infor- (a) (b) (c) (d) mation — the car’s lateral position on the track, its heading Figure 4. Four car poses and their corresponding sound slider values. with respect to the track’s, its speed, the track’s width, whether Though the car’s lateral position is the same between (a) and (b) and the track is about to immediately turn, and more — into a between (c) and (d), the corresponding sound slider values are very dif- single measure that we hope is as relevant to the process of ferent. This is because the left and right trajectories’ lengths — and racing as all of that information put together. Moreover, it does therefore the relative risks of hitting the left and right sides of the track so in a way that gives players the freedom to decide how risky — are very different in each pair of cases. they would like to race: whether they should cut corners by > > being close to hitting the track’s inside edge or stay closer to lCL and lCR represent the distances the car would travel before the track’s center. Sucu and Folmer’s haptic driving interface, hitting an edge were the player to steer fully to the left or right, by comparison, eliminates intention by simply telling players respectively. Finally, the RAD sets the sound slider value to which way they should steer at any given time. the following quantity, which we call the time-to-impact ratio: We liken this process of distilling the many pieces of informa- tion to that of dimensionality reduction in machine learning > and statistics. Dimensionality reduction is important in these lCL Slider Display Value = > >. (1) fields because it boosts classification speed and removes re- lCL + lCR dundancies in the representations of features. In the RAD’s sound slider’s case, the process reduces the amount of infor- The sound slider’s leftmost and rightmost positions are rep- mation that must be conveyed to the player while preserving resented by zero and one respectively. The system will set its meaning and relevancy. the slider value to something different than the time-to-impact ratio in two cases. The first case is when both trajectories hit the track’s left edge — which means that the player is driving toward the left edge — or when the player’s car is currently The RAD’s Turn Indicator System off the track on the left side. The second is the analogous case The RAD’s turn indicator system uses spatialized (3D) sound for the track’s right edge. In these cases, the system will set cues to alert players of the direction, sharpness, and timing of the slider value to zero and one, respectively. upcoming turns and the length of in-progress turns. It works by playing a series of four beeps that trigger when the player’s From Lateral Position to Relative Risk car crosses four corresponding and equally spaced distance The algorithm described above represents a new approach for markers placed ahead of the turn. The last beep is a continuous letting players know where they are situated on a racetrack. sound that begins playing just as the turn begins and continues Unlike the stereo pan values in Blindfold Racer, Mach 1, and sounding until the player completes the turn. Left and right the Top Speed series, the sound slider’s display value is not turns are indicated by beeps emitted from the left and right a direct reflection of the car’s lateral position on the track. ends of the sound slider’s track, respectively. Overlapping Rather, it is a function of the car’s relative risk of hitting turns are indicated by overlapping sets of beeps. the track’s left or right sides if the player wanted to. This distinction is what makes the sound slider intuitive even with By using four beeps to indicate turns, the player is given the complex vehicle physics, steering behaviors, and track enough time to recognize the beeps’ rhythm and anticipate the timing of the last beep, which marks the beginning of the turn. geometries that are present in modern racing games. The player can then time their steering accordingly, cutting Figure4 illustrates the benefit of updating the auditory display the corner if they wish by starting to steer a little before the using our trajectory-based approach over the car’s lateral po- last beep begins sounding. The distance markers triggering sition alone. The car’s lateral position is the same between the four beeps are spaced 20 m apart, giving the player 1.7 s Figures4(a) and (b) and between Figures4(c) and (d), but of advance notice of the turn when they are driving at the the player’s relative risks of hitting the track’s left and right maximum speed of 35 m/s (approximately 75 mph). sides is very different between each pair. In Figure4(b), for The beep sounds themselves are modified recordings of a example, the player is much more at risk of hitting the track’s distant engine hum, adapted from [10]. Low pitched beeps right side than they are in Figure4(a) due to the sharp left turn indicate soft turns, moderately pitched beeps indicate moderate in Figure4(b), and the player should be aware of this. turns, and high-pitched beeps indicate sharp turns. We defined As another example, the car’s heading in Figure4(c) puts the soft turns as those which turn less than 0.3° per meter of track car more at risk of hitting the track’s left edge than its right and sharp turns as those which turn more than 1° per meter of edge, while its heading in Figure4(d) does the opposite. The track. When a turn changes sharpness partway through, as in player should be aware of this as well. The sound slider’s Turns 7a and 7b in Figure6, the system treats each part as a trajectory-based approach communicates these risks. separate turn and alerts the player accordingly.

5 9 7b 11 15 8 13 7a 17 10 14 18 16 12 6 2 4 19 5b 20 1 3 5a Figure 6. Circuit diagram for the racetrack used in user studies. This track is difficult and much more complex than ones in previous blind- accessible games, featuring a wide variety of turns. Figure 5. Racing game prototype implemented in Unity.

the RAD in that racing game. Our prototype, shown in Fig- In addition to playing the beeps, the system announces each ure5, is an extension of TurnTheGameOn’s Racing Game upcoming turn’s number, where Turn 1 is the track’s first turn, Template [23]. It features full 3D graphics and uses realistic Turn 2 the second, and so on. The number is announced at vehicle physics from the Edy’s Vehicle Physics package [13]. the same time as the first beep, and the goal is to help players learn the track over time as sighted players do. Our game is played with a Sony DUALSHOCK 4 (PlayStation 4 controller) [31] and a standard pair of headphones. The Supported Actions controls are mapped similarly to other PlayStation 4 racing The RAD’s sound slider and turn indicator system work to- games: the left analog stick controls steering, R2 (the right gether to support the following actions: analog trigger) is gas/acceleration, L2 (the left analog trigger) Understand the car’s current speed: The sound slider’s car is brake and reverse, and R1 (the right shoulder button) is the engine sound will increase in pitch as the engine revs up, handbrake. In case of a crash, participants could press the giving the player a general sense of the car’s current speed. Triangle button to reset their car to the center of the track. Align the car with the track’s heading: If the player’s car To generate spatialized (3D) sound, we enabled the sim- is not aligned with the track’s heading, the car engine sound ple demo spatializer provided by Unity’s Audio Spatializer will begin moving left or right on the sound slider. The SDK [38]. The spatializer applies a direct head-related transfer player can align their car with the track’s heading by steer- function (HRTF) that is based on a data set generated from a ing until the engine sound stops moving. KEMAR dummy-head [14]. Learn the track’s layout: The turn indicator’s turn number announcements help the player remember specific turns and sequences of turns. The Racetrack Profile upcoming turns: The direction, sharpness, timing, Figure6 shows the track that we used for our user studies. and length of upcoming turns are indicated by the turn The track was developed internally at Unity [36] and is much indicator beeps’ left vs. right location in the soundscape, more complex than ones in previous blind-accessible games. the beeps’ pitch, the beeps’ rhythm, and the fourth beep’s It features a wide variety of turns: soft, moderate, and sharp duration, respectively. turns; a long straightaway; a series of hairpin turns (Turns Cut corners: By steering into a turn just before the turn indi- 9–11) that require players to slow down; a 270° turn (Turn cator’s fourth beep, the player can cut corners. The player 16); several short kinks in the track (Turns 8, 13, 14, & 17); can maintain an inside position during the turn by steering several series of esses (Turns 1–5 & 19–20); long and gradual such that the engine sound moves toward the inside of the turns (Turns 5b & 7a); and turns that vary in sharpness as they turn on the sound slider (and away from the slider’s center). progress (Turns 5, 7 & 17). The track is 3,641 m long, 19 m Choose an early or late apex: By steering into a turn just be- wide, and has 20 turns in total. fore or after the turn indicator’s fourth beep, the player can choose between taking an earlier apex or a later apex [25]. STUDY 1: THE RAD VS. OTHER INTERFACES Position the car for an optimal turning path: By steering We performed a study with both blind users and sighted users the car in a way that moves the engine sound to a desired wearing blindfolds to compare the RAD with Mach 1’s inter- position on the sound slider ahead of a turn, the player can face [6] and Sucu and Folmer’s haptic steering interface [34]. position the car for a more optimal driving path. These interfaces represent a broad range of design alternatives. Know when braking is needed to complete a turn: The sound slider emits a tire screeching sound when the player Our study had three goals. First, we wanted to determine how is going too fast in a turn to turn sharply enough. well the average person would perform with each of these user interfaces with a short amount of training. Second, we RACING GAME PROTOTYPE wanted to see how users would rank the three interfaces by As a proof of concept, we developed a racing game using order of preference. Third, we wanted to observe how well the Unity game engine (version 5.4.2) [37] and implemented each interface helped players anticipate upcoming turns.

6 Study 1 Participants — to help the participants relate the interfaces’ feedback with Our study included fifteen participants. Three of them — P4, easily understandable shapes. We told participants to play P8, and P11 — were blind their entire lives and the rest were with each interface until they understood how they worked. sighted but blindfolded. Seven were age 16–25 and the rest We followed the three trials with a survey asking participants were age 26–35; four were female and the rest were male. Our to rank the three interfaces from their most to least favorite, study was approved by our institution’s Institutional Review rate how well each interface helped them anticipate upcoming Board, and parents were present with minors. turns on a 20-point Likert scale in which higher values were We recruited P4, P8, and P11 through Helen Keller Services better, and offer feedback justifying their ratings. Participants’ for the Blind. P4 had no prior experience with racing games, feedback was extensive. To analyze it, we first transcribed it while P8 and P11 had played just one audio racing game each in full, then — via a series of repeated readings — wrote topic years prior: Top Speed and Blindfold Racer, respectively. P8, labels for each piece describing what it was talking about. We however, described himself as a gamer and had played other then tallied positive and negative opinions for each identified types of audio games before, namely an RPG [12] and a first- topic. We report these numbers along with the quotes that person shooter [18]. Six of the twelve sighted participants had were most descriptive and representative of overall opinions. at least a moderate amount of experience playing video games, and the rest had very little experience. Of those with moderate Study 1 Results: Participants Who Are Blind experience, three would describe themselves as gamers. User Interface Ranking We should note that participants who are sighted but blind- P4 ranked the user interfaces from best to worst as Mach 1’s folded are generally not suitable proxies for participants who interface, the RAD, and Sucu and Folmer’s interface, in that are blind. Silverman et al. [30] found, for example, that sighted order. Both P8 and P11 ranked them as the RAD, Sucu and but blindfolded participants can be biased by the initial chal- Folmer’s interface, and Mach 1’s interface, in that order. lenge of becoming blind, therefore judging the capability of Awareness of Upcoming Turns people who are blind as much less than it actually is. As a On a 20-point Likert scale in which higher values are better, result, and as is good practice [24], we will present the results P4 rated their ability to anticipate upcoming turns using the from these two groups of participants separately. RAD, Sucu and Folmer’s interface, and Mach 1’s interface Study 1 Procedure as 8, 11, and 15, respectively. P8’s ratings were 18, 11, and In the study, participants raced using each of the three user 7, respectively, while P11’s were 5, 10, and 12, respectively. interfaces in a counterbalanced order while we observed them. The difference is sharp between P8 and the others. Both P4 Participants controlled their car using a Sony DUALSHOCK and P11 had very little experience playing video games while 4 (PlayStation 4 controller) [31] and wore a pair of Amazon- P8 considers himself a gamer. Although P11 rated the RAD Basics on-ear headphones [3]. All sighted participants wore lowest and Mach 1’s interface highest on this scale, she ranked blindfolds and could not see us loading the track, nor could the RAD as the best of the three interfaces overall and Mach they see what they were doing in the games. We told the partic- 1’s interface the worst of the three. ipants that our team developed all three of the user interfaces. Driving Performance in Our Prototype Game Each session lasted approximately two hours. Of the participants who are blind, only P8 was able to complete For both the haptic steering interface and the RAD, we had a full lap, and he did so with each of the three user interfaces. participants play our prototype racing game in which we im- P8, the only self-described gamer among the three, completed plemented both. For Mach 1’s interface, however, we had our track (Figure6) with zero major collisions on his first try participants play Mach 1 itself. We did this because Mach 1 with both Sucu and Folmer’s interface and the RAD. uses simplified models rather than realistic designs for its Neither P4 nor P11 could complete a full lap using any of the tracks and steering system, and its user interface was designed user interfaces, though all three participants completed our with the simplified models in mind. Since we loaded Mach 1 square and figure eight training tracks using both the RAD and into a level before the study began, the participants were not Sucu and Folmer’s interface. Recall that there were no training aware that they were playing a previously published game. tracks for Mach 1. We should note that our track (Figure6) Like other modern game controllers, the DUALSHOCK 4’s resembles what one would find in a real video game and is rumble motors are different in size, with the left motor being very challenging compared to ones in existing blind-accessible significantly larger than the right motor. Since the haptic steer- racing games. Sucu and Folmer, for example, tested a basic ing interface requires identical rumble motors for the user’s left oval and still found many crashes [33, 34]. and right hands, however, we replaced our DUALSHOCK 4’s Qualitative Feedback: Mach 1’s Interface left motor with one identical to the right motor. We clamped P4 rated Mach 1’s user interface as his favorite because it was the motors’ vibration intensity to 50% of its normal maximum to make it easier for players to distinguish between the motors. the only one to explicitly read out the car’s lateral position and because he felt that he “had [more] time to think and react” We began each user interface trial by training each participant to its cues compared to the other interfaces. This is likely with hands-on instruction for 15–20 minutes on how to use because Mach 1 does not provide continuous feedback about the interface. We created two training tracks in our prototype the car’s positioning as the other interfaces do; rather, it reads — a square track with rounded corners and a figure eight track the information whenever a particular button is pressed.

7 Both P8 and P11 found Mach 1’s interface to be the worst of Most Favorite In Between Least Favorite the three, with P11 saying that it was “the hardest” and “hard to use properly.” P8 said that while “it had pretty much [all Mach 1 of the game elements that] [he] would expect from a racing game,” it was “very difficult [to use because] there are so many Sucu and Folmer things going on” at the same time, including many “sounds that are not relevant.” He also said that it “was difficult [ . . . ] The RAD knowing when you are in the turn and when you are out of the turn” because the steadily increasing sound effect volume that 0 2 4 6 8 10 12 14 it employs to indicate the beginnings of turns was not precise. Count Qualitative Feedback: Haptic Steering Interface Figure 7. Participants’ user interface rankings. The dot patterns indi- cate rankings from participants who are blind. Most disliked Mach 1’s P4 considered Sucu and Folmer’s haptic steering interface to interface, and eight of fifteen preferred the RAD’s the most. be the worst of the three “mainly due to not being able to see upcoming turns.” P8 and P11 ranked the haptic steering interface in between their most and least favorite, with P11 without the dot patterns. Six sighted participants chose the saying that she “did not get to think about how to attack the RAD as their preferred interface, five chose the haptic steering turn[s]” and that “[using] it would have been easier if there was interface, and one chose Mach 1’s interface. Ten out of twelve a warning in advance, when you should start turning.” Still, sighted participants liked Mach 1’s interface the least. P11 felt that while the lateral positioning feedback “wasn’t exact[ly precise], it was to the point that I [...] could kind of Awareness of Upcoming Turns tell if the car wasn’t in the center.” An ANOVA showed that the user interface has a significant P8 said that the vibrations “didn’t give much [of an] indication main effect on the sighted participants’ awareness of upcom- of how sharp [each] turn was,” preventing him from making ing turns (F2,22 = 4.83, p = 0.02). Pairwise mean comparison strategies such as, “I shouldn’t turn too much here to avoid showed that the only significant difference was between the colliding with the [inside] wall.” He felt that “the experience RAD and Mach 1’s interface (p < 0.05). The mean (std. dev) would be better, perhaps, by “mak[ing] the game controller ratings for this metric for the RAD, the haptic steering inter- vibrate more or less” in intensity depending on the sharpness of face, and Mach 1’s interface are 13.0 (4.9), 8.8 (6.5), and 6.8 the turn. Sucu and Folmer, however, found users’ performance (5.5), respectively. This suggests that the RAD does a better with continuous vibration feedback to be worse than with job communicating the nature of upcoming turns for sighted binary (on/off) feedback [33, 34]. players than Mach 1’s sound effects of increasing volume.

Qualitative Feedback: Racing Auditory Display (RAD) Driving Performance in Our Prototype Game P4 ranked the RAD in between his most and least favorite, Ten out of twelve sighted participants were able to complete saying “it is definitely better than the vibration method” (Sucu the track in Figure6, five of which after crashing and resetting and Folmer’s interface) but that he “still had a hard time” themselves many times. Their performance seemed to de- because it was “confusing to parse between the two types of pend on their prior experience with video games: participants sounds” (the sound slider and the turn indicator system). Both tended to perform well with both interfaces or poorly with P8 and P11 considered the RAD to be their favorite interface, both interfaces. All seven sighted participants with at least with P8 saying that it was “very, very logically built up [ . . . ] moderate video game experience completed the track, two because it gave [him] an indication of how sharp the turns of whom after crashing many times. By contrast, only three were [and] for how long [he was] in [each] turn.” of the five participants with limited video game experience P8 felt that distinguishing between soft, moderate, and sharp completed the track, all of whom after crashing many times. turns “worked very well with the tonality of the sound.” P11, These results suggest that both the RAD and the haptic steering on the other hand, said that while she “got the concept, it interface make it possible for gamers to play racing games was [ . . . ] harder to put the concept into use,” finding the without sight, but neither can make a non-gamer proficient at RAD “difficult to [learn] but very entertaining” to play with. playing racing games. She remarked that with the RAD “the feeling of the game is fast-paced,” adding, “Yes, you have the time [to plan], but Qualitative Feedback: Mach 1’s Interface sometimes you might not be able to [pull it off].” P8 said that Of the three interfaces, sighted participants liked Mach 1’s he liked how the RAD did not “constantly sa[y] ‘Do this, do the least in general. Though many mentioned that “it was that,”’ and followed up by saying, “After the training was done, relatively easier to understand [their] horizontal location with I had the possibility of doing whatever I wanted to.” These [this interface’s spoken] numeric value[s]” (P2) than with last two comments suggest that the RAD supports intention. the other interfaces’ feedback, four lamented that “having numbers read to [them] took extra brain power [to process, Study 1 Results: Sighted but Blindfolded Participants making] it much more difficult for [them] to move forward User Interface Ranking quickly” (P5). All said that it “took [them] a while to sort out Figure7 shows how participants ranked each interface from all the sounds that were going on” (P15) and that there was most to least favorite. Sighted participants’ rankings are those “too much auditory information for too long a period” (P9).

8 Ten felt that determining the position and length of turns was Sighted “very difficult” (P2) and that they could not determine the turns’ sharpness at all because “the sound leading up to the The RAD thump which indicates [when] turn[s begin and end were] more confusing and disorienting than anything” (P13). A Sucu and Folmer different set of ten felt that a “[big] difficulty was to determine the difference between the probe number [(lateral position)] 90 100 110 120 130 140 and the speed of the vehicle” (P10). Mean Lap Time (s) Figure 8. Mean lap times of P8 — a gamer who is blind — using Qualitative Feedback: Haptic Steering Interface Sucu and Folmer’s haptic steering interface [34], P8 using the RAD, and Ten sighted participants felt that this interface’s vibrations sighted players using vision. The error bars indicate standard deviations. With the RAD, P8 races significantly better than he does using the haptic were “easier to [learn and] focus on [compared to] the [other steering interface and comparably to casual players racing with sight. interfaces’] multiple sounds” (P10), but five felt that “turning and preparing for turns was completely out of [their] control” (P5) because “the only interaction [they] had was immediately the three interfaces, and that with the RAD he “could actually responding to the vibrations” (P5), “conforming to the rumble visualize the car and its location.” indicators” (P14), or as P13 put it, “just [ . . . ] bouncing around from wall to wall trying to stay in the center.” P5 added that STUDY 2: FIELD TEST WITH GAMER WHO IS BLIND she “had no idea when a turn was coming up, how sharp or Our second study tests whether the RAD makes it possible for long it would be, [or] whether or not it was actually a turn a player who is blind to race better than Sucu and Folmer’s [she] was dealing with or simply trying to straighten [her]self haptic steering interface does, and whether their racing perfor- out on a straightaway after a turn.” mance can match that of a sighted player’s. Some liked how “the rumble [being] binary [made it] really clear [to know] when you are ‘good’ or ‘bad”’ (P13) but six Study 2 Procedure bemoaned the resulting lack of intention (though not using In this study, we had participant P8 from our first study — that word). Three mentioned that they would prefer having our only participant that is both blind and considers himself a differing levels of vibration so they could tell “exactly how gamer — drive thirteen laps around the racetrack in Figure6 far [ . . . ] from the middle of the road” (P6) they are or “how using Sucu and Folmer’s haptic steering interface and fourteen sharp the turn was” (P1, P3). As mentioned earlier, however, laps using the RAD. We recorded his lap times, full driving Sucu and Folmer found that users crashed much more with paths, and gameplay video of him racing as he played. The such a system than with binary vibration feedback [33, 34]. car starts at the beginning of the long straightaway in Figure6 so that it can reach full speed by the start of the first lap. Our Qualitative Feedback: Racing Auditory Display (RAD) supplemental video shows P8’s third lap ever on this track. Eight sighted participants felt that the RAD’s turn indicator We then had eight sighted players (three female, five male) system made them “well aware of the upcoming turns with drive one to three laps around the track using sight as we their position and sharpness” (P3). Two of them, however, recorded their lap times and driving paths. We used just one to mentioned that the system was “sometimes confusing when three laps here because we found in a pilot study that sighted [turns were] very short. . . ” — in which case the fourth turn players’ lap times did not improve over the course of driving indicator beep would be very short — “. . . and/or followed 14 laps. The same was true for P8: his average lap time for his immediately by another turn” (P1) — in which case the RAD first three laps was 0.3 s faster than for his last three. would output multiple overlapping sets of beeps. Four participants found the RAD difficult to use while two Study 2 Results found it very natural. In particular, eight participants found it Figure8 compares lap times for the three conditions: P8 difficult to distinguish between the sound slider’s engine sound using the haptic steering interface, P8 using the RAD, and and the turn indicators, with P5 mentioning that “as a full- sighted players using vision. The mean (std. dev) lap times are sighted person [she is] not used to using every single sound 128.2 s (8.2 s), 117.0 s (3.7 s), and 111.7 s (3.5 s), respectively. as an informational cue and usually do[es]n’t pay attention to An ANOVA showed that the user interface has a significant such noises as engine volume.” P2 and P5 sometimes found the main effect on the mean lap times (F2,32 = 23.38, p < 0.0001). RAD’s sound slider “difficult to understand” (P2, P5) because Pairwise mean comparison showed that the differences were “the location of the engine sound (left vs. right vs. middle) significant between every pair of interfaces (p < 0.01) except [can] change incredibly fast” as they enter sharp turns. the RAD vs. sighted players using vision. This suggests that the RAD allowed P8 to race significantly better than the haptic Seven participants mentioned that they were “almost always steering interface did — saving an average of 11.2 s per lap — aware of which side of the track [they are] on” (P3) when and comparably to that of players using sight. Only one of the using the RAD, with P3 adding, “[ . . . ] compared to both sighted players, however, described themselves as a gamer. [of] the other methods where I was quite clueless.” Seven participants felt that the RAD made them “fe[el] the most like Figure9 compares typical driving paths from P8 using the [they were] racing” (P13) compared to the other interfaces. P9 haptic steering interface and the RAD, respectively. The haptic found the RAD “fun and definitely the most immersive” of steering interface causes P8 to oscillate around the track’s

9 The RAD Furthermore, the RAD can be used in place of AudioGPS [17] and SWAN [43] for pedestrian navigation tasks. AudioGPS Sucu and Folmer and SWAN tell users know which way to walk, but the RAD can tell users how wide the path or bridge is, how much “wig- gle room” they have, and whether they are in the middle or toward one side, helping them avoid oncoming foot traffic.

CONCLUSION, LIMITATIONS, AND FUTURE WORK This paper offers a vision of how video games can go beyond just being blind-accessible to being equivalently accessible to (a) people who are blind, allowing them to play with a similar sense of control (intention) and efficiency as sighted players can. To this end, we introduce the racing auditory display (RAD) to help racing games become equivalently accessible to people who are blind. It comprises two novel sonification techniques: the sound slider for understanding a car’s speed and trajectory on a racetrack and the turn indicator system for alerting players of the direction, sharpness, length, and timing (b) (c) (d) of upcoming turns. Figure 9. Sample driving paths of P8 — a gamer who is blind — using Through a pair of empirical studies, we found that players the RAD and using Sucu and Folmer’s haptic steering interface [34]. We preferred the RAD’s interface over that of Mach 1, a popular compare the paths for (a) the entire circuit, (b) an ess turn, (c) a near- blind-accessible racing game, and at times “felt like [they] had straight section, and (d) a hairpin turn. P8 oscillates constantly with the as much information as if [they] could see the track” (P1). We haptic steering interface but drives more smoothly when using the RAD. He is also able to cut the corners in (b) using the RAD. Our supplemental demonstrated that the RAD makes it possible for a gamer who video shows P8’s third lap with the RAD’s audio included. is blind to race comparably to casual players using sight. Still, there are several limitations to our studies and to the RAD. center line for the entire lap, which is this interface’s usual First, our study included just four self-described gamers and behavior since it works by vibrating the player’s controller three people who are blind, so our results cannot be assumed to when their heading is too far away from that of a center target apply to everyone from these groups. A more thorough follow- point [34]. By contrast, P8 drives in a much smoother path up study targeting gamers who are blind would be needed for using the RAD. In Figure9(b), for example, we see that P8 this. Second, the RAD relies on 3D sound spatialization. Not carves a nearly straight path through Turns 19 and 20 (which everyone can hear spatialized sounds correctly with off-the- form an ess turn sequence) when using the RAD but follows shelf head-related transfer functions (HRTFs). Future games the track’s center line when using the haptic steering interface. could allow players to load an HRTF from a profile so they can hear spatialized sound clearly in many different games. The mean (std. dev) driving path lengths are 3,639 m (74 m), 3,557 m (40 m), and 3,469 m (71 m) for the three respective Last, the RAD is not as effective with non-gamers and does conditions: P8 using the haptic steering interface, P8 using the not teach them “video game literacy” such as how video game RAD, and sighted players using vision. An ANOVA showed vehicle handling works, nor is it effective at helping players that the user interface has a significant main effect on the driv- recover from crashes or from driving off the track. A future version of the RAD could include a Mach 1-style probing ing path length (F2,32 = 19.21, p < 0.0001). Pairwise mean comparison showed that the differences were significant be- feature for helping players learn the game mechanics and tween every pair of interfaces (p < 0.05 for the haptic steering recover from crashes. We also think it would be feasible to interface vs. the RAD and p < 0.01 otherwise). This shows that extend the RAD to incorporate other racing game elements P8 can perform shorter laps with the RAD than with the haptic such as opponent vehicles, boosts, item pickups, and shortcuts. steering interface (mainly by reducing oscillations), though We hope that just as user interface toolkits provide tools such not quite as short as laps made by players driving with sight. as scrollbars, sliders, menus, and radio buttons that “just work” when software is published, game engines will one day include HUMAN–COMPUTER INTERACTION (HCI) IMPLICATIONS building blocks such as walls and track pieces that will “just Though games especially benefit from intention, our work work” with user interfaces such as the RAD or AudioGPS [17] has broader implications within HCI. First, our definition of when games are published to make all games blind-friendly. a sound slider is generic: a virtual speaker that indicates a value within a range by its position on a 3D line segment in ACKNOWLEDGMENTS the soundscape. For blind users, sound sliders can substitute We would like to thank Russell Martello and Gus Chalkias at for traditional UI sliders; brightness, temperature, or pressure Helen Keller Services for the Blind (HKSB) for help recruiting gauges; progress bars; and any other display that displays a participants, Daniel Sims for help conducting user studies and value within a range. They can also help users perform steering preparing figures, Sean Pagaduan and Janet Kayfetz for help tasks in the classical sense [1] by representing a tunnel’s width. writing, and the CHI reviewers for valuable suggestions.

10 REFERENCES 15. GMA Games. 2005. Shades of Doom Version 1.2. (2005). 1. Johnny Accot and Shumin Zhai. 1997. Beyond Fitts’ Retrieved September 16, 2017 from Law: Models for Trajectory-based HCI Tasks. In Proc. http://www.gmagames.com/sod.html. ACM SIGCHI Conf. Hum. Fact. in Comput. Sys. (CHI 16. Terri Hedgpeth, John A Black Jr., and Sethuraman 1997). ACM Press, New York, NY, USA, 295–302. DOI: http://dx.doi.org/10.1145/258549.258760 Panchanathan. 2006. A Demonstration of the iCARE Portable Reader. In Proc. 8th Int. ACM SIGACCESS Conf. 2. Troy Allman, Rupinder K. Dhillon, Molly A.E. Landau, Comput. Access. (ASSETS 2006). ACM Press, New York, and Sri H. Kurniawan. 2009. Rock Vibe: Rock New York, USA, 279–280. DOI: Band® Computer Games for People with No or Limited http://dx.doi.org/10.1145/1168987.1169054 Vision. In Proceeding Elev. Int. ACM SIGACCESS Conf. 17. Simon Holland, David R. Morse, and Henrik Gedenryd. Comput. Access. (ASSETS 2009). ACM Press, New York, 2002. AudioGPS: Spatial audio navigation with a New York, USA, 51–58. DOI: http://dx.doi.org/10.1145/1639642.1639653 minimal attention interface. Pers. Ubiquitous Comput. 6, 4 (September 2002), 253–259. DOI: 3. Amazon.com, Inc. 2014. AmazonBasics Lightweight http://dx.doi.org/10.1007/s007790200025 On-Ear Headphones. (25 November 2014). Retrieved 18. Jeremy "Aprone" Kaldobsky. 2011. Aprone’s Accessible September 17, 2017 from http://a.co/9OFo5NC. Software and Games. (2011). Retrieved January 2, 2018 4. Matthew Tylee Atkinson and Sabahattin Gucukoglu. from http://www.kaldobsky.com/audiogames/. 2004. The AGRIP Project (AudioQuake). (2004). 19. Joy Kim and Jonathan Ricaurte. 2011. TapBeats: Retrieved September 16, 2017 from http://agrip.org.uk. Accessible and Mobile Casual Gaming. In Proc. 13th Int. 5. audible-edge. 2009. Chrysler LHS tire squeal 04 ACM SIGACCESS Conf. Comput. Access. (ASSETS 2011). (04-25-2009).wav. Audio file. (27 April 2009). Retrieved ACM Press, New York, New York, USA, 285–286. DOI: September 14, 2017 from http://dx.doi.org/10.1145/2049536.2049609 https://freesound.org/s/71739/. 20. Daniel Miller, Aaron Parecki, and Sarah A. Douglas. 6. audiogames archive. 2015. Games by Jim Kitchen. 2007. Finger Dance: A Sound Game for Blind People. In (2015). Retrieved September 16, 2017 from Proc. 9th Int. ACM SIGACCESS Conf. Comput. Access. http://www.agarchive.net/pages/devs/kitchensinc.html. (ASSETS 2007). ACM Press, New York, New York, USA, 253–254. DOI: 7. Doug Church. 1999a. Formal Abstract Design Tools. http://dx.doi.org/10.1145/1296843.1296898 Game Developer Magazine 6, 7 (August 1999), 28. 21. Tony Morelli, John Foley, and Eelke Folmer. 2010. 8. Doug Church. 1999b. Formal Abstract Design Tools. VI-Bowling: A Tactile Spatial Exergame for Individuals Gamasutra. (16 July 1999). Retrieved August 25, 2017 with Visual Impairments. In Proc. 12th Int. ACM from http://www.gamasutra.com/view/feature/131764/ SIGACCESS Conf. Comput. Access. (ASSETS 2010). formal_abstract_design_tools.php. ACM Press, New York, New York, USA, 179–186. DOI: 9. Doug Church. 2006. The Game Design Reader: A Rules http://dx.doi.org/10.1145/1878803.1878836 of Play Anthology. MIT Press, Cambridge, MA, USA, 22. National Federation of the Blind. 2013. Blind Driver Chapter Formal Abstract Design Tools, 366–381. Challenge. (2013). Retrieved September 12, 2017 from 10. CosmicD. 2007. engine_hum_new.wav. Audio file. (10 http://www.blinddriverchallenge.org. April 2007). Retrieved September 14, 2017 from 23. Stephen "TurnTheGameOn" O’Donnell. 2015. Racing https://freesound.org/s/33503/. Game Template. (2015). Retrieved January 3, 2018 from 11. Leonard de Ruijter, Pieter de Ruijter, Bram Duvigneau, https://www.turnthegameon.com/racing-game-template. and Davy Loots. 2004. Playing in the Dark: Top Speed. 24. Andrew Sears and Vicki L. Hanson. 2012. Representing (2004). Retrieved September 16, 2017 from users in accessibility research. ACM Trans. Access. http://www.playinginthedark.net/topspeed_e.php. Comput. 4, 2 (2012), 1–6. DOI: 12. Driftwood Audio Entertainment. 2010. Entombed - An http://dx.doi.org/10.1145/2141943.2141945 RPG Roguelike Game for the Blind and Visually 25. Seas. 2012. Cornering Technique. (2012). Retrieved Impaired. (2010). Retrieved January 2, 2018 from September 14, 2017 from http: http://www.blind-games.com/entombed.aspx. //www.formula1-dictionary.net/cornering_tech.html. 13. Angel "Edy" García. 2015. Edy’s Vehicle Physics. (2015). Retrieved September 15, 2017 from 26. Marty Shultz. 2013. Blindfold Racer: Creating the Track. Blog post. (3 December 2013). Retrieved September 12, http://www.edy.es/dev/vehicle-physics/. 2017 from https: 14. William G. Gardner and Keith D. Martin. 1995. HRTF //blindfoldgames.org/2013/12/03/creating-the-track/. Measurements of a KEMAR. J. Acoust. Soc. Am. 97, 6 (June 1995), 3907–3908. DOI: 27. Marty Shultz. 2014a. Blindfold Racer. (2014). Retrieved http://www.blindfoldracer.com http://dx.doi.org/10.1121/1.412407 September 16, 2017 from .

11 28. Marty Shultz. 2014b. Blindfold Racer: It’s Too Hard to 38. Unity Technologies. 2017. Audio Spatializer SDK. Control. Blog post. (10 March 2014). Retrieved (2017). Retrieved September 15, 2017 from September 12, 2017 from https://blindfoldgames.org/ https://docs.unity3d.com/2017.2/Documentation/Manual/ 2014/03/10/blindfold-racer-its-too-hard-to-control/. AudioSpatializerSDK.html. 29. Marty Shultz. 2015. Blindfold Color Crush. (2015). 39. Bruce N. Walker and Jeff. Lindsay. 2004. Auditory Retrieved September 16, 2017 from navigation performance is affected by waypoint capture https://blindfoldgames.org/user-guides/ radius. In Proc. Int. Conf. Audit. Disp. (ICAD 2004). blindfold-color-crush-user-guide/. Georgia Inst. Tech., Sydney, NSW, AU, 6–9. http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1. 30. Arielle M. Silverman, Jason D. Gwinn, and Leaf Van 1.97.9443 Boven. 2015. Stumbling in Their Shoes: Disability Simulations Reduce Judged Capabilities of Disabled 40. Bruce N. Walker and Jeffrey Lindsay. 2006. Navigation People. Soc. Psychol. Personal. Sci. 6, 4 (2015), 464–471. Performance With a Virtual Auditory Display: Effects of DOI:http://dx.doi.org/10.1177/1948550614559650 Beacon Sound, Capture Radius, and Practice. Hum. DOI: 31. Sony Interactive Entertainment. 2013. DUALSHOCK 4 Factors 48, 2 (June 2006), 265–278. Wireless Controller. (2013). Retrieved September 15, http://dx.doi.org/10.1518/001872006777724507 2017 from https://www.playstation.com/en-in/explore/ 41. WBDG Accessible Committee, Jordana L. Maisel, and accessories/dualshock-4-wireless-controller/. Molly Ranahan. 2017. Beyond Accessibility to Universal Design. (15 February 2017). Retrieved August 22, 2017 32. Edward Steinfeld and Jordana Maisel. 2012. Universal from https://www.wbdg.org/design-objectives/ Design: Creating Inclusive Environments. Wiley, accessible/beyond-accessibility-universal-design/. Hoboken, NJ, USA. 33. Burkay Sucu and Eelke Folmer. 2013. Haptic Interface 42. T Westin. 2004. Game accessibility case study: for Non-Visual Steering. In Proc. 2013 Int. Conf. Intell. Terraformers - A real-time 3d graphic game.. In Proc. User Interfaces (IUI 2013). ACM Press, New York, New Fifth Int. Conf. Disabil. Virtual Real. Assoc. Technol. York, USA, 427–434. DOI: (ICDVRAT 2004). University of Reading, Reading, UK, DOI:http://dx.doi.org/10.1.1.103.8041 http://dx.doi.org/10.1145/2449396.2449451 95–100. 34. Burkay Sucu and Eelke Folmer. 2014. The Blind Driver 43. Jeff Wilson, Bruce N. Walker, Jeffrey Lindsay, Craig Challenge: Steering using Haptic Cues. In Proc. 16th Int. Cambias, and Frank Dellaert. 2007. SWAN: System for ACM SIGACCESS Conf. Comput. Access. (ASSETS 2014). wearable audio navigation. In Proc. IEEE Int. Symp. ACM Press, New York, New York, USA, 3–10. DOI: Wearable Comput. (ISWC 2007). IEEE Press, Boston, http://dx.doi.org/10.1145/2661334.2661357 MA, USA, 91–98. DOI: http://dx.doi.org/10.1109/ISWC.2007.4373786 35. T V Tran, T Letowski, and K S Abouchacra. 2000. Evaluation of acoustic beacon characteristics for 44. Bei Yuan and Eelke Folmer. 2008. Blind Hero: Enabling navigation tasks. Ergonomics 43, 6 (2000), 807–827. Guitar Hero for the Visually Impaired. In Proc. 10th Int. DOI:http://dx.doi.org/10.1080/001401300404760 ACM SIGACCESS Conf. Comput. Access. (ASSETS 2008). ACM Press, New York, New York, USA, 169–176. DOI: 36. Unity Technologies. 2015. Car Tutorial (Unity 3.x only). http://dx.doi.org/10.1145/1414471.1414503 (5 May 2015). Retrieved September 16, 2017 from http://u3d.as/1qU. 45. Bei Yuan, Eelke Folmer, and Frederick C. Harris. 2011. Game accessibility: A survey. Univers. Access Inf. Soc. 37. Unity Technologies. 2016. Unity Download Archive. 10, 1 (2011), 81–100. DOI: (2016). Retrieved September 14, 2017 from http://dx.doi.org/10.1007/s10209-010-0189-5 https://unity3d.com/get-unity/download/archive.

12