Univ Access Inf Soc (2011) 10:81–100 DOI 10.1007/s10209-010-0189-5

REVIEW PAPER

Game accessibility: a survey

Bei Yuan • Eelke Folmer • Frederick C. Harris Jr.

Published online: 25 June 2010 Springer-Verlag 2010

Abstract Over the last three decades, video games have 1 Introduction evolved from a pastime into a force of change that is transforming the way people perceive, learn about, and Over the past decades, video games have become a interact with the world around them. In addition to enter- mainstream form of entertainment, currently eclipsing tainment, games are increasingly used for other purposes Hollywood’s box office sales [105]. According to the NPD such as education or health. Despite this increased interest, Group, currently more than 100 million consoles are a significant number of people encounter barriers when present in US households [62], and an estimated 63% of the playing games due to a disability. Accessibility problems US population play video games, with 51% of players may include the following: (1) not being able to receive playing games on at least a weekly basis [20]. An expla- feedback; (2) not being able to determine in-game nation for this popularity could be that games provide responses; (3) not being able to provide input using con- something that other forms of entertainment, such as ventional input devices. This paper surveys the current books, music, and movies, cannot provide, i.e., interaction. state-of-the-art in research and practice in the accessibility Games are also increasingly used for other purposes of video games and points out relevant areas for future than entertainment. Educators are discovering the cognitive research. A generalized game interaction model shows how potential of games in the classroom [29, 45, 46, 84], and a disability affects ones ability to play games. Estimates are games have also been used for health [87], religion [88] provided on the total number of people in the United States and politics [66]. whose ability to play games is affected by a disability. A Despite the increased level of interest in games, a large large number of accessible games are surveyed for differ- group of people find themselves excluded from playing ent types of impairments, across several game genres, from video games because of a disability [4, 6, 33]. which a number of high- and low-level accessibility strat- Software technology is often difficult to access for players egies are distilled for game developers to inform their with disabilities. In the past decades, considerable research design. efforts have been spent investigating how software can be made accessible. As a result, many operating systems have Keywords Game accessibility Á Disability Á Strategy Á accessibility features built in, such as screen readers or Impairment support for keyboard shortcuts. As new technologies emerged, such as the Internet in the 1990s, accessibility research efforts were directed to exploring how the world & B. Yuan ( ) Á E. Folmer Á F. C. Harris Jr. wide web and related technologies, such as email, could be Department of Computer Science and Engineering, University of Nevada, Reno, NV 89557, USA made accessible, which has lead to the definition of the W3C e-mail: [email protected] Web Content Accessibility Guidelines (WCAG) [98]. These E. Folmer guidelines provide guidance on how to create web content e-mail: [email protected] that accommodates users with different types of impair- F. C. Harris Jr. ments. These guidelines have successfully contributed to e-mail: [email protected] making the Internet more accessible. 123 82 Univ Access Inf Soc (2011) 10:81–100

As the popularity of games increases, making games different strategies that have been identified and points out accessible becomes more important. Still, little research areas for future research. Section 5 concludes the paper. has been conducted in this area. In certain circumstances, such as when games are used in the classroom for educa- tional purposes, there may be a legal obligation to make 2 Disabilities and games them accessible, as Section 508 of the Rehabilitation Act [93] states that schools and universities that rely on federal Before introducing the game interaction model, this section funding must make their electronic and information tech- provides background information on disabilities and video nologies accessible. games, as well as a consistent reference terminology. Games are fundamentally different from software, as their primary use is for entertainment. There have been two 2.1 Video games attempts at composing a set of game accessibility guide- lines similar to the W3C web content guidelines [99]. The Video games come in different genres and more than 20 Independent Game Developers Association (IGDA) Spe- genres have been identified [21, 43, 103]. Due to a general cial Interest Group (SIG) on Game Accessibility [42] lack of commonly agreed-upon genres or criteria for the published a white paper [41] in 2004 that proposes 19 definition of game genres, the classification of games is not accessibility guidelines derived from a survey of 20 always consistent, therefore, certain games may fit into accessible games. The majority (16) of these games include multiple categories. This survey takes into account the games for the visually impaired and a few (4) support following eight seminal game genres: motor or hearing impaired. The Norwegian Medialt orga- nization published a set of 34 game accessibility guidelines 1. First-person Shooter (FPS) games are action games [89] on their Web site, based on the 19 IGDA game played from a first-person perspective that involves accessibility SIG guidelines as well as their own set of shooting enemies with a range of different weapons. guidelines. One of the problems with guidelines is that they Popular examples include Doom, Quake, and Halo. often assume an absolute validity, but in practice are only 2. Strategy games are combat games involving resource applicable in specific contexts [25, 97]. For example, management and strategy. Players must build and ‘‘provide subtitles’’ [41] is not applicable to a game without manage units that can be used to harvest resources or audio dialogs. ‘‘Allow for variable game speed’’ [89]isnot attack enemies. Some of these games are played in applicable to turn-based games such as chess. Another real-time (RTS) while others are turn-based (TBS). problem with guidelines is that they do not provide an Strategy games are played from a top-down perspec- explanation of what accessibility problem the guideline is tive. Popular examples include Command and Con- supposed to solve, making it difficult for a game developer quer, Warcraft, and Civilization. to understand when and why the guideline can be applied. 3. Sports games simulate the playing of traditional sports The existing game accessibility guidelines were published such as tennis, football or soccer. Examples include in 2004 and were based on a limited number of accessible Madden and FIFA Soccer. games for a small number of game genres. Since then, 4. Role-playing Games (RPG) involves playing a char- numerous accessible games have been developed for game acter that goes on quests and grows more powerful genres with more complex interaction models, as well as along the way. Examples include Neverwinter Nights for game genres not included in the guidelines. and World of Warcraft (WoW). This paper provides a comprehensive survey of the 5. Puzzle games test problem solving skills such as logic, current state-of-the-art of research and practice in game strategy, pattern recognition, and sequence/word com- accessibility. The goals of this survey are: (1) to identify pletion. Examples include Tetris and Bejewelled. how a disability affects a player’s ability to play video 6. Racing games emulate driving a car on a race track games; (2) to identify the strategies for making games such as Burnout Revenge, Project Gotham Racing, and accessible; and (3) to identify areas for future research. Super Mario Karts. The remainder of this paper is organized as follows: Sect. 7. Dance/Rhythm games emulate the playing of or 2 introduces a generic interaction model for games, which is dancing to music through custom controllers such as used to illustrate how a disability affects the ability to play Guitar Hero and Dance Dance Revolution. games. Estimates are provided for the number of people in 8. Adventure games are characterized by investigation, the US who cannot play games due to a disability. Section 3 exploration, puzzle-solving, interaction with game provides an overview of existing accessible games and characters, and a focus on narrative rather than sensi- analyzes the different strategies used in making them motor challenges. Popular adventure games include accessible. Section 4 summarizes and discusses the Myst and the Sam and Max series. 123 Univ Access Inf Soc (2011) 10:81–100 83

Virtual worlds such as Second Life [1] have gained repetitive behavior. Dyslexia and attention deficit increasing popularity in recent years and allow their users disorder are also common cognitive impairments. to explore vast user generated environments using a game like third person interface. Though virtual worlds are often 2.3 Game interaction model confused with games, they lack the typical elements most commonly found in games—such as: enemies to beat, Because an impairment may affect a player’s ability to play levels to attain, a story line, goals to achieve, and the games to different extents, a generic interaction model for possibility for a character to die [3]. Virtual worlds allow games is defined, allowing to identify exactly what kind of their users to create content and because of this high degree barrier a player with an impairment faces. This model was of customization, they have been used in various contexts derived by analyzing how a player interacts with a game for and for various purposes that go beyond pure entertain- a number of different game genres and finding commonal- ment, such as education [72], business [70] and social ities between the steps that are performed when playing a interaction [36]. Games and virtual worlds are significantly game. As an example of the performed analysis and in order different. For example, the lack of combat in virtual worlds to illustrate how the model was derived, Table 1 shows the removes the need for users to respond fast as their avatar interaction of a player with three different game genres cannot die, which may lead to using different strategies (FPS, puzzle and racing) broken down into different steps. than games to make virtual worlds accessible to users with The game interaction model consists of three steps: disabilities [27]. Because of these significant differences, virtual worlds are not included in this survey. Accessibility 1. Receive stimuli: Games provide stimuli in three of virtual worlds is addressed in [9, 27, 67, 90, 102]. different forms: visual, auditory, and haptic. Depend- ing on the type of game, stimuli can be further divided into two categories: 2.2 Classification of impairments (a) Primary stimuli must be perceivable by the To refer to players with impairments, this survey uses the player in order to play the game. Almost all classification of impairments as defined by the World games use visuals as primary stimuli. For exam- Health Organization’s (WHO) manual: International ple, in an FPS game, visuals are used as a primary Classification of Impairments, Disabilities and Handicaps stimuli and without visual feedback the game (ICIDH). This classification is in accordance with the cannot be played. Though sound and haptic writing guidelines [10] for technology and people with feedback may be provided, this typically does disabilities: not provide sufficient information to be able to play the game. For example, the player may hear • Visual impairment is the consequence of a certain or feel the presence of an enemy, but may not be degree of vision loss such as low vision/partially able to determine the enemy’s location. Though a sightness, legal blindness, complete blindness. Color game typically has only one primary stimuli, blindness is considered a visual impairment. some games such as dance/music games rely • Hearing impairment refers to complete or partial loss of upon music to such an extent that visuals and the ability to hear from one or both ears. The level of audio are both primary stimuli. impairment can be mild to profound. Deafness refers to (b) Secondary stimuli is provided as a supplement to the complete loss of ability to hear from one or both a primary stimulus. Being able to play a game ears. does not depend upon being able to perceive a • Motor impairment is a loss or limitation of function in secondary stimuli. In an FPS without sound or muscle control or movement or a limitation in mobility. haptic feedback, the player can still play the Common causes include arthritis, paralysis, cerebral game to a large extent, but may suffer from a palsy, or repetitive strain injury. Motor impairment may reduced gaming experience. also include difficulties in speech control and the need to use input devices other than a mouse or keyboard. 2. Determine response: Based on the specific set of • Cognitive impairment is a mental and psychological stimuli that the game provides, the player must disorder ranging from mental retardation developed cognitively determine which in-game response(s) to during childhood to Alzheimer’s or senility as a result provide from the set of available game actions. These of aging. People with autism, Down syndrome or other actions are specific to the game and are typically mental retardation are also included. Their main defined by the game’s genre. For example, an FPS may characteristics are impairments in social interaction, allow the player to navigate his character, whereas an impairments in communication, restricted interests and RTS game may allow the player to group units 123 84 Univ Access Inf Soc (2011) 10:81–100

Table 1 Game interactions for different game genres FPS (Quake) Puzzle (Tetris) Racing (NFS) Player

An enemy is visible on the A falling block is visible. A road and an opponent’s car 1. Receive stimuli screen. Gunfire and Music can be heard are visible. The sound of the explosions can be heard car’s engine is heard. The controller provides haptic feedback The player decides to fire his The player decides to change The player decides to overtake 2. Determine response gun at the enemy the block’s orientation and the opponent by steering to position and then drops the the right and speeding up block The player presses a button on The player presses the arrow The player tilts the wheel of his 3. Provide input his controller to fire his gun keys to move and rotate the controller to the right and block and the space bar to presses the gas pedal with his drop it feet The enemy is killed, the status A line is cleared, and a new The opponent is overtaken; an Repeat steps 1,2,3 of the game changes, and a block appears empty road is visible new enemy may appear

together. The player either chooses a combination of be provided. The subsequent steps rely on each other. For one or more actions or may decide to not provide an example, if a user cannot receive stimuli, this will impair action at all. their ability to successfully determine what response to 3. Provide input: After deciding which in-game provide. The steps are repeated until the player wins, loses response(s) to provide, the player must physically or quits the game. The steps are illustrated by a message issue the chosen action(s) through the input device sequence diagram and a state machine in Figs. 1 and 2. used to interact with the game. Typically games require the player to actuate a physical device such as 2.4 Playing a game with an impairment keyboard, mouse, controller or a steering wheel. Some games may allow voice commands. Input devices can Using the interaction model from the previous section, it is be categorized into two different groups: possible to analyze precisely how an impairment affects each one of the steps defined in the model: • Discrete input: A device that measures discrete input, such as an on-off switch. A keyboard and the buttons • Visually impaired players may be unable to perceive on controllers are examples of this type of input. primary stimuli. Without this feedback, it is impossible • Analog input: A device that measures continuous to determine what in-game response and what physical input, such as a mouse or a thumbstick on a input to provide, though these players are cognitively controller. Because the amount of interaction and physically able to perform such tasks. required to control an analog input device is significantly higher than that of a discrete device, precise motor skills are required. Discrete input devices are relatively easy to control if the number is inputs is small. However, as the number of inputs increases (such as on a keyboard with dozens of keys) or when multiple inputs need to be provided simultaneously, it becomes increasingly difficult for the player to provide input efficiently. Control- lers typically provide a combination of analog and discrete inputs. Most game controllers have two analog inputs (thumbsticks) and a number of discrete inputs (buttons or triggers).

After successfully performing these three steps, the internal state of the game may change and new stimuli may Fig. 1 Interaction sequence diagram 123 Univ Access Inf Soc (2011) 10:81–100 85

the game interaction model. Sensory impairments such as vision and auditory impairments affect the first step, cog- nitive impairments affect the second step and motor impairments affect the third step of the game interaction model. The inability to perform a step in the model has a detrimental effect on the ability to successfully perform each subsequent step. For example, someone who is visually impaired cannot perceive visually stimuli, and consequently cannot perform step 2 or 3. However, if non-visual stimuli are provided, users will be able to perform steps 2 and 3, as is evident from games for users who are visually impaired that are identified in this survey (see Sect. 3.2.1). The same argumentation can be held for users with cognitive impairments and motor impairments, who are able to suc- cessfully perform the other steps of the model as long as the game provides some accommodation for the step they are unable to perform. For example, a player with a cognitive Fig. 2 Interaction finite state machine impairment may find it difficult to use a regular controller, not because this player is physically unable to use the controller, but because this player may find it difficult to • Hearing impaired players may be unable to perceive determine what in-game action to provide or which button secondary stimuli. Because audio is typically used as a on the controller this action corresponds to. Conversely, a secondary stimuli, the player with an auditory impair- player with a motor impairment may be physically unable to ment may still be able to play games, but players may use the controller despite being able to reason what in-game experience a reduced gaming experience and may miss action to provide based on the feedback provided. out on spoken dialog in cut-scenes and ambient sounds This strict separation of impairments to particular steps like approaching footsteps. There are some games that in the model further indicates that, for these impairments, rely on both audio and visuals as primary stimuli, such fundamentally different solution strategies must be as dance/rhythm games. In such cases, the auditory explored to make a game accessible. impaired player may be unable to perform steps 2 and 3 of the model. 2.5 Game accessibility statistics • Cognitive impaired players are primarily affected in their ability to cognitively determine an in-game ‘‘How many people cannot play video games because of a response. A learning disability, for example, may make disability?’’ is a key question to investigate because, to the it difficult for the player to learn how to play a game authors’ knowledge, such data has not been determined in and understand what in-game response options the any study and could lead to more awareness. International game provides. Limited cognitive reasoning skills may disability statistics can be found at the United Nations prevent a cognitively impaired player from determining Statistics on Human Functioning and Disability [16]. what in-game response to provide based on the However, it is not recommended to combine statistics from feedback provided. different countries or regions, given the many differences • Motor impaired players are limited in their ability to in survey design, definitions, concepts and methods. As a provide input physically. A quadriplegic player may be result, only the statistics for the US are presented, because unable to use a regular controller or a mouse and it is the largest gaming market in the world and also has keyboard, and often has to rely upon specific input detailed data available on people with disabilities. devices with limited input capabilities. Consequently, According to the census of 2002 [92], about 51.2 million these players may have a hard time providing specific people had some level of disability, and 32.5 million of types of input, because they may find it difficult to them are severely disabled. The interaction model of the position a game object precisely, or activate multiple previous section reveals that an impairment limits one’s input devices simultaneously, especially when these ability to play games to different extents. Players with inputs need to be provided within a certain amount of severe vision impairments typically find themselves time. excluded from playing games, whereas individuals with The above analysis reveals that each type of impairment severe auditory impairment can still play games, but typi- primarily affects the ability to perform one particular step in cally suffer from a reduced gaming experience. The 123 86 Univ Access Inf Soc (2011) 10:81–100 barriers to playing games may also differ within a partic- census data, it was first analyzed whether it affects the ular type of impairment. A severe vision impairment such ability to play games and then, if that is the case, the type as blindness restricts the ability to perceive visual feed- of barrier was categorized (critical/non-critical) based on back, completely excluding someone from playing games, the above analysis of how a disability affects the ability to whereas a minor vision impairment such as colorblindness play games. Because audio is typically used as secondary often leads only to minor problems while playing games. It stimuli in games, a severe hearing impairment was iden- is important to distinguish the different types of barriers tified as a non-critical barrier, and a non-severe hearing individuals with disabilities face when trying to play impairment is not identified as a barrier. To select motor computer games. Consequently, two different types of impaired players who are unable to provide primary input, barriers are defined: the task ‘‘difficulty grasping objects’’ was selected from the 2002 census data. Unfortunately, this task is missing for the • Critical: A player with a disability is unable to play the data for children age 5–14 and instead the related physical game. tasks were selected such as difficulty eating. These two • Non-critical: The game is playable, but the player with numbers are listed in parentheses. a disability may suffer from a reduced gaming In Table 2, the total number of people in the US esti- experience. mated to have their ability to play games affected by a Table 2 has been constructed by analyzing the data disability is 32,213,000 (*11% of US population). This collected for the 2002 census [92]. The number under each can be further detailed into 6,267,000 individuals (*2%) age group on the first row indicates the total surveyed who are unable to play a game at all, and 25,946,000 population for that group. The 2002 census provides a individuals (*9%) who are able to play games but with a detailed breakdown of each type of impairment into more reduced gaming experience. The number of people who specific impairments. For example, motor impairments are want to play games but find themselves excluded from broken down into specific physical tasks that cannot be playing games is likely to be smaller than the numbers that performed (difficulty walking, difficulty grasping objects, were found, simply because not everybody plays games. etc.). Sensory disabilities are subdivided into severe and According to the NPD Group, 63% of the US population non-severe categories, allowing to distinguish players who plays video games [62]. This report is based on online are blind or deaf from those with less severe vision or survey responses from 5,039 members of NPDs consumer auditory impairments. For each impairment subtype in the panel, but no detailed break down into different age

Table 2 Selected disability measures (number in thousands) Disability level from census Barrier type Age 0–14 Age 15–24 Age 25–64 Age [ 64 All age (60,605) (39,453) (149,031) (282,831) (33,742)

Motor impaired: difficulty grasping objects Severe Critical (147) 130 310 331 918 Not severe Non-critical (433) 382 283 2,647 3,745 Visually impaired: difficulty seeing words/letters Severe Critical 42 210 762 951 1,965 Not severe Non-critical 147 383 2,987 2,852 6,369 Hearing impaired: difficulty hearing conversation Severe Non-critical 39 155 418 506 1,118 Hearing or cognitive impaired: difficulty with speech Severe Non-critical 135 123 313 156 727 Cognitive impaired: cognitive limitations Learning disability Non-critical 1,082 1,217 2,036 154 4,489 Mental retardation Critical 226 339 827 55 1,447 Alzheimer, senility, dementia Critical N/A 30 648 1,259 1,937 Other mental or emotional Non-critical 256 483 2,140 352 3,231 Totals All disabilities Critical 415 709 2,547 2,596 6,267 All disabilities Non-critical 2,092 2,743 8,177 6,667 25,946 All disabilities All barrier 2,507 3,452 10,724 9,263 32,213

123 Univ Access Inf Soc (2011) 10:81–100 87 categories is provided. Since video games were invented in or a mouse and keyboard, and they have to revert to the early 1970s and became mainstream only in the 1980s alternative input devices specifically designed to accom- and 1990s, it is a common understanding that elderly play modate their abilities. fewer video games than younger generations since many of them did not grow up with video games. Also, age is 3.1.1 Alternative input devices strongly correlated to the likelihood of disability. As shown in Table 2, less than 4% of people under age 15 are A number of input devices have been developed that allow impaired, and over 27% of senior citizens (persons motor impaired players to interact with games, such as 65 years old and older) have an impairment. Due to a lack switch inputs [68], brain wave controllers [59], head of detailed statistics on how many people of different ages trackers [58], eye controllers [81], mouth controllers [51] play games, no estimate for the total number of players or one-handed controllers (See Fig. 3 for some examples). who are unable to play a game is formulated here. Nev- Software solutions exist, such as a vocal joystick [38, 40], ertheless, while the percentage of senior game players is that enables the player to control a cursor using voice relatively low, one should keep in mind that current gamers commands. This technique has been successfully used to are getting older and accessibility problems might emerge control games as well, such as Tetris [82], either using in the near future as they age. speech or non-speech techniques. Alternative input devices are typically constrained with regard to the amount and types of input that can be pro- 3 Overview of accessible games and strategies used vided when compared with conventional game input devices. A game that allows voice control will accept only This section surveys existing accessible games for each of one voice command at the same time, whereas a regular the disability categories defined in Sect. 2.2 for a number of controller allows one to provide a combination of inputs. different game genres. Section 2.4 revealed that each type A one-handed controller typically provides only one analog of impairment corresponds with one step in the interaction input, whereas a regular controller has two analog thumb model, which gave rise to the conjecture that fundamentally stick inputs. Playing a game with a one-handed controller different solution strategies may be required to make these that requires two analog inputs often leads to problems. For games accessible. By analyzing the strategies used in each example, a first-person shooter may use one analog input game, this section seeks to find evidence to support this for moving and another one for controlling the camera. conjecture. Information regarding to the accessible games Typically these controls are used simultaneously, which is have been gathered from technology Web sites, online and not possible with a one-handed controller. An eye con- paper-based journals, academic databases, academic insti- troller or brain wave controller may not allow for precisely tution Web sites and related conference Web sites. controlling a cursor on the screen with the same precision as a non-disabled player with a mouse or a thumbstick. 3.1 Games for motor impaired players A switch is an assistive technology device that replaces the use of a mouse, keyboard, controller or joystick which Motor impaired players often find it difficult or impossible severely motor impaired players may find difficult to use. to use conventional game input devices such as controllers Switches can be operated by any body part that is able to

Fig. 3 Controllers for players with motor impairments 123 88 Univ Access Inf Soc (2011) 10:81–100 produce consistent and voluntary movement, and different • Strange Attractors [100] is a one-switch puzzle game. types of switches can be identified based upon the type of Holding the switch activates the spaceships gravity action required to use them (sip and puff, pull, push, or drive, allowing the player to sling and bounce himself squeeze). Individuals with severe motor impairments may through a field of planets toward the exit. The gameplay sometimes be able to use only one switch, whereas indi- is built around switch input and is completely original. viduals with less severe motor impairments may be able to • Mini Golf [85] is a remake of a two-dimensional golf use multiple switches. A mouth controller, like the quad game. It uses a two-step scanning mechanism that controller [51] used by players with quadriplegia, offers a allows the player to first select a direction where the number of different switch inputs such as a sip and puff. ball needs to go and then select the amount of impulse Binary input is the smallest amount of interaction that can to give the ball. After these two variables are set, the be provided with a switch, because holding down the ball is hit. If the ball does not end up in the hole, the switch for a certain amount of time may be impossible for a two-step scanning process is repeated. sip and puff device or painful for someone with arthritis. • Branston and the Lost Machine [24] is a one-switch Switch players who have good cognitive skills, includ- adventure game. The game uses a context-sensitive ing the ability to time their input, distinguish between scan mechanism that changes the action bound to the choices, or understand the results of a particular choice, can switch input to allow for a larger amount of actions to provide more complex input (at a slower rate) through a be provided. For instance, when moving through the mechanism called scanning [80]. Scanning folds a set of world, holding down the key will move the character in interaction options into a chain and iterates over each link, its facing direction, and tapping the button will change allowing the player to select that interaction option. For the direction the character is facing. If the character is example, Microsoft Windows XP has a built-in, on-screen standing in front of a door however, tapping the key keyboard with support for scanning, allowing the player to will make the character move into the building. input 40 different keys through a switch device. Input • Jet Boarder [11] is a racing game. During the race, the through a scanning mechanism inherently slows down the player will always accelerate and will continuously rate of input because it may take time before the right input steer left. Holding the switch will steer the player to the is selected, depending on how many input options are right. attached to each chain. A number of different scanning • Frogger [83] is remake of the classic 1981 Sega game mechanisms [86] have been developed that aggregate Frogger. To allow for one-switch access, the amount of several different input options and offer multi-step selec- interaction in this game has been reduced. In the tion as a mechanism to access each aggregated option. For original version of the game it is possible to move the example, to select a point in a 2-D grid, one can use a two frog left and right, as well as jump forward or step row-column scanning mechanism. backward. In this version, the frog can move only forward and backward using a scan mechanism. 3.1.2 Selected games • Sudoku Access [61] uses a three step column/row scanning mechanism to allow a player to play the game Alternative input devices are constrained with regard to of Sudoku using one-switch input. The game also the amount and type of input that can be provided. As a allows for control using voice input. result, motor impaired players who use such devices are • Gordon’s Trigger Finger [39] is a modification of the constrained to playing games that take into account the multi-player version of the popular FPS Half-Life 2. limited amount of input the player can provide. Though This modification puts the player on top of a bot which some games exist with limited input options, alternative automates navigation as well as aiming, allowing the strategies can be elaborated for making games accessible player to control the gun using one-switch input. A to players with motor impairments. This section therefore player can play against other bots or against other focuses on games that can be played with the smallest players. amount of input, e.g., one-switch games. The one-switch web site (http://www.oneswitch.org.uk) is a non-profit 3.1.3 Strategies identified Web site dedicated to such games, and it lists about 70 arcade-style one-switch games, all of which can be All the games use scan-accessible menus that allow the downloaded for free. A number of games have been player to configure or start the game. In addition, a com- selected that cover all game genres, as well as all the bination of strategies is used to make the game accessible: different strategies used to make the game switch acces- sible. Figure 4 shows screenshots of some of the games • Reduction: Part of the original interaction is completely discussed. removed. For example, in the one-switch Frogger the 123 Univ Access Inf Soc (2011) 10:81–100 89

Fig. 4 One-switch games

option to make the frog go left or right has been make it one-switch accessible may significantly alter the removed, and the player can move only up or down. gameplay. For example, in Frogger, by removing the option • Automation: Part of the original interaction is auto- to go left or right, the gameplay changes from being able to mated. For example, firing the gun in Gordon’s Trigger positioning the frog in two dimensions to more of a timing- Finger is done automatically. based challenge game that requires carefully timing when to • Scanning: Several games use scanning mechanism. move the frog back or forward. By automating the navigation Two different forms can be distinguished. A context- and aiming in Gordon’s Trigger Finger, the gameplay has sensitive (CS) scanning mechanism changes depending fundamentally changed from an FPS to a ‘‘rail shooter’’ on the state of the game. In Branston and the Lost where the player feels he is tied on a rail like a roller coaster. Machine, the switch action changes depending on When making games accessible to the motor impaired, it whether the character stands in front of an object such is important to understand how the gameplay must change as a door. A context-agnostic (CA) scanning mecha- to avoid creating a game that is not fun or challenging to nism is the same throughout the game. Multistep play. To avoid any changes in the gameplay, it is important scanning mechanisms are used in Sudoku Access, to preserve the original input options as much as possible. which uses a three-step row-column-number selection, Sudoku Access and Mini Golf are examples of one-switch and in Mini Golf with a two-step scanning mechanism games that offer the same number of input options as the to determine the direction and magnitude. Most of the non-accessible versions. They have been implemented games that use scanning are not time sensitive, with the using a scanning mechanism. One of the disadvantages of exception of Frogger, which only has two different using a scanning mechanism is that it slows down the input actions to be scanned over. rate, but this is not a major problem for these games because they are not time sensitive. For time-sensitive Table 3 shows the strategies used in each game. With the games such as Frogger, having the player interact through a exception of Strange Attractors, most games use one or a scan mechanism with many inputs may be too slow and combination of strategies. Games can further be distin- frustrating, and as a solution some of the input options have guished by whether or not they are binary, one-switch com- been removed to keep the game fun to play. patible. Applying particular strategies to an existing game to

Table 3 Strategies used to Name of the game Genre Modification Binary one switch Reduction Automation Scanning make games one-switch accessible Strange attractors Puzzle No No – – – Sudoku access Puzzle Yes Yes No No CA Jet boarder Racing Yes No Yes Yes No Mini golf Sports Yes Yes No No CA Frogger Arcade Yes Yes Yes No CA Branston Adventure Yes No No Yes CS Gordon’s trigger finger FPS Yes Yes Yes Yes No

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3.2 Games for visually impaired players player uses keyboard for basic control, including the spacebar for stats reporting and instructions and arrow Visually impaired players may find it difficult or impossi- keys for navigation. ble to receive feedback from games because visuals are • AudioBattleShip [75] is a turn-based strategy game that typically used as a primary stimulus. Features, such as was initially designed to be used for cognitive devel- high-contrast color schemes accommodating color blind- opment purposes with blind children. A wacom tablet is ness, scalable fonts or the ability to zoom in, are recom- used as an input device. A grid system is built over the mended by accessibility guidelines for software and the tablet in order to represent the matrix of the battlefield web [98] and can be found in a number of commercial and some additional help buttons for triggering actions. games. For example, many games allow increasing the font Audio cues are provided to inform about a specific size. A number of puzzle games allow using different color spatial location on the board or the occurrence of schemes when a player is colorblind [77], and many FPS certain actions such as the sound of a bomb dropping and RTS games allow for customizing the colors of the over certain cells in the battle grid. Though the wacom units of the enemy. Individuals with severe visually tablet does not provide haptic feedback, because it is a impairments, however, do not benefit from such features constrained input device it allows for better mental and specific strategies are used to make games accessible to mapping of the battlefield. them. • GMA Tank Commander [32] is an audio-only version of the classic game Tank Commander. The type of enemy is indicated using audio cues and its location 3.2.1 Selected games through surround sound. The player controls their tank using the keyboard. Many games have been developed for the blind [28, 73]. • Speed Sonic Across the Span [64] is a platform game. An extensive list can be found on the web site Audio cues are used to indicate objects and obstacles. (http://www.audiogames.net). A number of games have The sound is consecutive with the platform panning to been selected that cover a broad range of game genres, as the right-left throughout the game. Players control their well as all the different strategies that are used to make the characters using a controller. game accessible to blind gamers. • Metris [44] is a musical version of Tetris that works • Mach 1 Car Racing [48] is a remake of the classic with a screen reader. Audio cues such as tone and beats racing game Pole Position. Audio cues, such as the determine what input the player must provide. echo of the player’s engine, are used to indicate which • Finger Dance [55], AudiOdyssey [30] and Blind Hero direction to turn. The game uses self-voicing with an [106] are dance/rhythm games. Blind Hero and Finger adjustable rate of speech. Players control their car using Dance are modifications of Guitar Hero [37] and Dance the arrow keys. Dance Revolution (DDR), respectively. Music games • Shades of Doom [31], AudioQuake [4], Terra formers provide visual feedback based on the music that is [101] are FPS games. These three games use different played, indicating which inputs to provide on specific accessibility strategies. Shades of Doom uses audio input devices such as a dance mat or a guitar controller. cues such as footsteps to help find the way through the Finger Dance changes the original game play of the levels. A navigation tool provides synthetic speech DDR game significantly, because it replaces the about the player’s surrounding. AudioQuake uses original music with audio cues that indicate which ‘‘earcons’’ which are structured sounds that obey keys the player must provide. Blind Hero adopts a musical conventions [8]. These alert the player to an different strategy by using a glove that provides tactile object or event. Terraformers uses a sound compass feedback on which inputs the player must provide, where different tones are used to indicate the direction preserving the original music. AudiOdyssey caters to the player is pointing. It also offers a sound radar that sighted as well as visually impaired players and uses can be used to identify what is in front of the player. By audio cues to indicate to the player when to provide using a ‘‘ping’’, it is possible to tell how far objects are input with a motion sensitive Wii-mote controller. in front of the character. Using a key on the keyboard, it is also possible to tell what type of object is in front of the character, using a voice playback system. All games 3.2.2 Strategies identified use stereo sound to convey spatial information. These games have the same controls as regular FPS games. The menus in all games are accessible through speech • The Last Crusade [18] is a role-playing RPG game that except for Metris, which requires a screen reader. The uses self voicing to read out the events of the game. The overall strategy used to make games accessible to severely

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Table 4 Blind-accessible Name of game Genre Modification Feedback Input games and strategies used Mach 1 car racing Racing Yes Audio cues Keyboard Shades of doom FPS Yes Audio cues, speech Keyboard Audio quake FPS Yes Sonification, speech Keyboard Terraformers FPS No Sonification, speech Keyboard The last crusade RPG No Speech Keyboard AudioBattleShip RTS Yes Audio cues Tablet GMA tank commander Arcade Yes Audio cues Keyboard Speed sonic across the span Platform No Audio cues Controller Metris Puzzle Yes Sonification Keyboard AudiOdyssey Music No Audio cues Wiimote Blind Hero Music Yes Haptic Guitar controller Finger dance Music Yes Audio cues Keyboard visually impaired players is to replace visual feedback with provide haptic feedback [74]. Blind Hero provides haptic a form of feedback that the player is still able to perceive, feedback through a custom glove because this is a music such as auditory or haptic. Only one game (Blind Hero) game and audio cues may interfere too much [106] with provides haptic feedback, while audio feedback is used in the music. With the exception of AudioOdyssey, all of all the other games. A number of different strategies for the games are modifications or remakes of existing turning visuals into audio have been identified: games. • Replace visuals with audio. 3.3 Games for hearing impaired players • Speech can be provided either by a screen reader when text is available or using self voicing. Audio plays an important role in most games. Sound and • Audio cues use real world sounds such as the sound music can add an extra dimension to the gaming experi- of wind or footsteps to provide information or hints ence. Few games use audio [96] as a primary stimulus, but to the player. the gaming experience for hearing impaired players may be • Sonification uses non-speech audio to convey significantly reduced when games fail to provide alterna- information using changes in pitch, amplitude or tive forms of output. Though many games support subtitles tempo [5]. A number of specific sonification [14], audio cues such as the sound of footsteps may indi- techniques can be used: cate important events to a player, especially in an FPS game. • Auditory Icons: sound effects indicate different objects or actions. 3.3.1 Selected games • Ear Cons: one or more tones are used as a language to indicate different objects or actions. A number of games offer additional features that aid • Sonar: a sonar-like mechanism conveys spatial hearing impaired players: information on the locations of objects. • XIII [91] is an FPS based on a comic book series that • Replace visuals with haptic. When audio is difficult to transcribes sounds in a comic-like style (see Fig. 5 for a provide such as with music games, haptic feedback may screenshot). be considered. • The Sims [54] is a strategic life-simulation computer • Enhance visuals. Players with low vision can be game that offers visual clues to indicate when audio is supported by modifying visual stimuli using high- being heard. For example, a radio will display little contrast color schemes, color schemes for color blind music notes coming out of it when playing. players, scalable fonts, zoom options or the ability to • Doom3 [CC] [47] and Torque CC [104] are third-party customize the color of enemy units. modifications to an existing game and game engine that Table 4 provides an overview of the games that were describe sound effects and music as captions. For surveyed, the accessibility mechanisms used, as well as example, gunfire can be indicated by the text (Gunfire). the input devices the player uses to play the game. Most Spatial sound is indicated using a sound radar that surveyed games use regular input devices such as a displays a dot on a radar indicating the location of the keyboard or controller. Some input devices are able to source of the sound. Different sources can be

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Fig. 5 Games for hearing impaired players

distinguished through color coding. Torque CC can be • Sound Radar is used to indicate the source of the used with any game using the 3D Torque engine. audio on a radar and is often used in conjunction • Zork: Grand Inquisitor [52], Half-Life 2 [95] and Sin with closed captioning. Episodes [71] are the only three commercial games that • Signing provides in-game characters that commu- feature closed captioning. nicate with the player using sign language. To • Smile [2] and Copycat [7] are educational games effectively use sign language, game characters need targeted to deaf children. Smile has in-game characters to be able to express different hand gestures. that are able to perform hand gestures allowing for sign Table 5 lists an overview of all games, the genre to language communication. which they belong and which accessibility strategies are used.

3.3.2 Strategies identified 3.4 Games for cognitive impaired players

The overall strategy used in making games accessible to According to the game interaction model presented earlier hearing impaired players is converting audio into visuals. in this paper, players with a cognitive impairment may find The following types of visualizations have been identified it difficult to determine which in-game response to provide. to indicate the type, source and location of the audio: Because cognitive impairments are complex and variable • Replace Audio with Text: [53], the barriers that individuals with cognitive impair- ments may face when playing games vary significantly. • Subtitles are captions for in-game speech, such as Studies [13] of individuals with cognitive impairments and dialog between different characters. Portraits of the children with Down Syndrome [23] reveal that they do play character speaking can be used to indicate the source or subtitles can be prefixed with the name of the character speaking. • Closed Captioning captions for speech, sound Table 5 Strategies used to make games accessible to hearing effects, and music. Color coding or codes (soldier:) impaired players can be used to indicate the source of the sound. The Name of game Genre Modification Text Non-text location of the audio can be indicated either through XIII FPS No – Transcribing a code (south:), or the position of the caption on the The Sims Simulation No – Visual cues screen. Non-speech sounds can be captioned Doom 3 FPS Yes CC Sound radar (Explosion) or transcribed (Bang). Torque CC Any 3D game Yes CC Sound radar • Replace Audio with Non-text: Zork:GI Adventure No CC – Halflife 2 FPS No CC – • Visual cues such as displaying notes, can indicate Sin episodes FPS No CC – that a device is making sound. The way sound is being transcribed in XIII is a blend of using text and Smile Virtual world No CC – visual cues. CopyCat Adventure No CC –

123 Univ Access Inf Soc (2011) 10:81–100 93 video games. No specific details are provided in these controls such as the arrow key and spacebar are used to studies on what games are played, only that simplicity of move an avatar or interact with other players. the game is a key factor in their specific use. • Shared Interfaces to Develop Effective Social Skills (SIDES) [69] is a four-player puzzle game designed to 3.4.1 Selected games help adolescents with Aspergers Syndrome practice effective group work skills. Players interact with the In the performed survey of games, only two games were game using a tabletop touch screen. found that specifically accommodate cognitive disabilities. • Ilbo [50] is a game specifically developed for players with learning impairments. The game was designed 3.4.2 Strategies identified around a new form of providing input. Players interact with this game while sitting on a chair. This chair has Though only a small number of games accommodate the limited input options as players navigate their character needs of individuals with cognitive impairments, some through a 3D maze using their weight. To prevent the strategies are provided based on the similarities identified player from perceiving too much feedback, the inter- between these games: action with the game is paused periodically. • Reduce time constraints: none of the games are time A recent development in games research is the notion of sensitive, so there is no pressure for the player to make serious games, which are not developed for entertainment a decision within a certain amount of time. The Ilbo purposes but for other purposes, such as education, reha- game pauses the game frequently, so as not to bilitation, or health. A number of serious games (see overwhelm the player. Fig. 6) for individuals with cognitive impairments are • Reducing the amount of stimuli: all of the rehabilitation included in the analysis: games provide small amounts of visual stimuli. The number of game objects on screen is limited, and all the • Coucou Cache` [78, 79] is a puzzle game specifically information required to play the game is available on developed for autistic children. The game is character- screen. ized by simplicity in order to not perturb autistic • Reduce input: similar to the strategies used for to children who are often sensitive to complex environ- make games accessible to motor impaired players, ments. Players interact with the game using a touch almost all games for cognitive impaired players offer screen. limited but intuitive controls, such as using a touch • Flexibility Learning on the Web (FLOW) [63] is a web- screen. Reducing the amount of input can be achieved based multi-player puzzle game that is designed for with techniques such as removing input or automating children with autism. The goal of this game is to input. enhance social interaction and cognitive flexibility by having children cooperate with each other to solve Table 6 lists an overview of each game, the genre to problems and thereby successfully complete games and which it belongs and which accessibility strategies are activities. Players interact using a keyboard and simple used.

Fig. 6 Games accessible to cognitive impaired

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Table 6 Strategies used to Name of game Genre Modification Reduce input Reduce stimuli Reduce time make games accessible to cognitive impaired players Ilbo FPS No Yes Yes Yes Coucou Cache` – No Yes Yes Yes FLOW – No Yes Yes Yes SIDES Puzzle No Yes Yes Yes

3.5 Universally accessible games 4.1 Accessibility strategies

In this survey of games a small number of identified games In the definition of the game interaction model, it was incorporated the ‘‘design for all’’ paradigm. Most of the identified that each type of impairment corresponds to one accessible games that were surveyed accommodate the needs step in the game interaction model (see Sect. 2.3). Table 7 of players with one particular impairment. A few games summarizes the strategies that have been harvested from implement a multi-modal approach where multiple interfaces each accessible game for each type of impairment based on are designed for different impairments. Universal design does the interaction model. This information led to the not indicate that all impairments are supported, but rather that assumption that fundamentally different solutions strate- multiple types of impairments are supported. These games gies may need to be explored to make games accessible to are listed here (see Fig. 7) for informative purposes because different impairments. Based on the strategies that have the strategies used in these universally accessible games are been harvested from the different games this conjecture can the ones already identified in the previous subsections. be confirmed to some extent. Sensory impairments correspond to the first step of the • UA Chess [34] and Universal Tic-Tac-Toe [65] are board interaction model and the strategies used to make games games supporting access by vision- and motor- impaired accessible to individuals with these impairments are sub- players using scanning, voice input and synthetic speech. stantially different from those used for motor and cognitive • Access Invaders [35] is a remake of the classic game of impairments. Although motor and cognitive impairments Space Invaders. It offers one-switch control using affect different steps in the game interaction model, there is scanning, as well as larger amounts of input, allowing some overlap in their identified strategies. For example, access to motor impaired players. Synthetic speech, reducing the amount of input is a strategy used in games for audio cues and the ability to increase the size of game both motor impaired and cognitive impaired players. Their objects allow access to visually impaired players. difference concerns the low-level strategies. Scanning is not identified in the games for the cognitive impaired, but it is used in one-switch games to allow for providing larger amounts of input for the motor impaired. A possible 4 Discussion and research issues explanation may be that a scanning mechanism typically increases the cognitive load, whereas accessibility strate- This survey identifies a number of issues that are discussed gies for cognitive impaired aim to reduce the cognitive in this section. load.

Fig. 7 Games designed for all

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Table 7 Accessibility Interaction model High-level strategies Low-level strategies strategies summary Receive stimuli Enhance stimuli visual High contrast color schemes (visual and hearing) Increase font size Color blind color schemes Zoom options Replace stimuli Audio ? visual Text (subtitles, closed captioning) Non-text (visual cues, sound radar, signing) Visual ? audio Speech (screenreader, self voicing) Audio cues Sonification (earcons, sonar, auditory icons) Visual ? haptic Haptic cues

Determine response Reduce stimuli Visual Limit number of game objects (cognitive) Simplify storyline Reduce time constraints Increase response time Slow down game Reduce input Remove input Automate input

Provide input (motor) Reduce input Scanning Remove input Automate input Replace input Voice/brain control

The strategies identified in this survey represent design advice on how to make a accessible game that purely relies knowledge at a higher level of abstraction than existing game upon haptic feedback. Using the proposed game interaction accessibility guidelines, and are targeted to offer a more model, a developer could analyze that someone with ana- usable format. The game interaction model points out exactly phia would not be able to perform the first step—receive what types of barriers a player with an impairment faces, stimuli. The high-level strategy ‘‘replace stimuli’’ points out whereas game accessibility guidelines [41, 89] do not iden- that visual or audio feedback could be used to make the tify the accessibility problem that the guideline solves. There game accessible. In the future, when more accessible games are many similarities between the low-level strategies iden- may have been developed for new game genres, new low- tified here and the two sets of game accessibility guidelines. level strategies may be identified that complete the model. Some accessibility guidelines, such as ‘‘use sound radar’’ [89] or ‘‘provide subtitles’’ [41], are part of the low-level 4.2 Tradeoffs strategy ‘‘replace audio with text based visualization’’. Though each one of the low-level strategies has been iden- Two different approaches can be used toward developing tified a number of times in the surveyed games, they are accessible games: neither complete nor exhaustive. The games included in the 1. An existing game is made accessible using one of the survey cover only a limited number of genres and the low- strategies in Table 7. The majority of the games level strategies for players with cognitive impairments have surveyed in this paper are modified games. been harvested from a very small number of games. 2. A game is specifically developed to accommodate a More confidence can be attributed to the high-level particular disability. In the survey two examples of strategies, because they are derived from the game inter- such games were found: Strange Attractors and action model, as well as from the numerous low-level AudiOdyssey are two accessible games not based on strategies at the implementation level. The high-level previously existing game. strategies may also be used to explore and develop new solutions for which guidelines fail to provide advice. For Both approaches have their advantages and disadvan- example, someone with the rare condition of anaphia is tages. It may be more resource-intensive to create a game unable to feel touch. Existing guidelines do not provide any from scratch than it is to modify an existing game. By

123 96 Univ Access Inf Soc (2011) 10:81–100 modifying an existing game, a developer does not have to limited number of game genres. Popular game genres [20] worry about parts of the game that are expensive to create such as strategy, sports and role playing games are not yet such as the graphics and sounds, or worry about whether available to those groups. Unlike hearing impaired players, the game will be fun, because the gameplay is taken from severe motor impaired and visually impaired players typi- an existing game. However, by applying certain accessi- cally face critical barriers preventing them from playing the bility strategies, the original gameplay may be significantly game. However, one popular game genre, FPS, has many altered. For example, a one-switch racing game does not accessible games for almost every type of impairment [4, allow the player to brake or speed up because certain input 31, 39, 47, 101]. What makes FPS games different from options may have been removed to allow for one-switch other game genres is that many FPS game engines are input. Converting feedback from one modality into another available as open source. Some FPS developers allow for modality often leads to loss of information. For example, making modifications to their games through a software the resolution and detail of stimuli received from a visual development kit [94]. Being able to reuse an existing game modality is much larger than what can be perceived engine or modify an existing game may significantly through audio or haptic modalities. Audio games often reduce the cost of developing an accessible game. If other reduce the amount of feedback provided when compared game genres would allow for such modifications, this may with the original game so as not to overwhelm the player. open up the opportunity for third party developers or Players must determine what in-game response to provide researchers to develop accessible versions of games for based on a smaller amount of information. such game genres. Consequently, such accessible games These tradeoffs may significantly alter the original may allow for the identification of new low-level strategies, gameplay, and a developer may end up creating a game that as well as serve as examples on how to make a particular is not fun to play. An additional concern with regard to game genre accessible to game developers. multiplayer games is the notion that games must be fair [12]. Cognitive impairments: Cognitive impairments are A player with an impairment who is playing against a player complex and variable. The research challenges of under- with a different impairment or without an impairment standing them and understanding how to combat or com- should not have an advantage nor a disadvantage. A one- pensate for their effects are profound [53]. Only five games switch FPS [39] that automates moving and aiming may were identified that accommodate players with cognitive give a motor impaired player a significant advantage over impairments. Though studies [13, 23] indicate that indi- players that have to perform these tasks themselves. When viduals with cognitive impairments play games, little is modifying an existing game, the original gameplay must be known about what type of games are being played or what preserved as much as possible, but because gameplay and level of barriers are faced. The increasing interest in using interaction are typically closely intertwined, it is often games as educational or rehabilitation tools and using HCI challenging to do so, especially for games for players with technology in the treatment of cognitive impairments [56, motor impairments. Few games, such as UA Chess, Uni- 57] may help to explore exactly how game interfaces can versal Tic-Tac-Toe and Sudoku Access, manage to succeed be made accessible to individuals with different types of in making the game accessible while preserving the amount cognitive impairments. Though strategies related to cog- of input options the player has available. Because their nitive impaired players are included in this survey, they original counterparts, Chess, Tic-Tac-Toe and Sudoku are have been extracted from a small number of games and not time-sensitive games, a scanning mechanism can be game genres, which warrants further investigation. applied, whereas most other games involve combat and Metrics: ‘‘You can’t control what you can’t measure’’ require the player to respond quickly. The scanning mech- [15] is a well-known statement in Software Engineering, anism may be too slow for the player to be able to respond which applies to game accessibility as well. How can a fast, and tradeoffs are required when parts of the input are game’s accessibility be measured? Similar to usability removed or automated. When developing a new accessible evaluation, a heuristics-based approach [60] can be used, in game, such tradeoffs do not have to be made because a game which a number of experts identify which accessibility is developed from within the constraints imposed by an guidelines have been implemented. The low-level strate- impairment (bottom–up), whereas when a game is modified, gies proposed in this survey could be used for this purpose, gameplay often has to be compromised to meet the con- however, a number of problems arise: straints imposed by the impairment (top–down). 1. The different low-level strategies accommodate 4.3 Directions for research impairments to different extents. For example, closed captioning is a better solution than subtitles to Game genres: As discussed in Sect. 3, severe motor and accommodate hearing impaired players. For one- visually impaired players can only play games within a switch games, a scanning mechanism that preserves

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all input is preferred over one that automates input or the perception that the number of gamers who would reduces it because such modification may significantly benefit from accessible games is relatively small. This change gameplay. survey identified that 6.2 million individuals in the US 2. The application of low-level strategies is context- cannot play games because of a disability. It is estimated sensitive. For instance, the game of chess may not have that a game must sell more than half a million copies to dialog or sound, and a strategy such as closed captions be profitable [49]. Though the provided estimate is likely cannot be applied. However, this strategy can be to include a large number of individuals with no interest applied to other types of games such as an FPS, but it in playing games, this number is large enough for game does not imply that a chess game lacking closed developers to consider investing in accessible games, captions is less accessible than an FPS with closed especially when players with disabilities outside of the US captions because it depends on the game genre. are considered. 3. A game that supports multiple impairments is likely to The nature of game development is very competitive, be more accessible than a game that supports only one and the number of games that are profitable is relatively impairment. However, the level of accessibility low [17, 19]. As the game industry continues on a path depends on the degree to which a particular impair- toward longer development times and increasing develop- ment is supported. A game that offers all types of ment costs [26], game developers may explore new ways to interaction, ranging from regular input to one-switch sell more games. Making games accessible could help control, can be considered to be more accessible than a selling more games; however, without exactly under- game that offers subtitles and a high contrast color standing the amount of effort required for implementing scheme. the various accessibility strategies, game developers may be hesitant to invest in game accessibility. Measuring the accessibility of a game is complicated This survey did not collect data on the implementation because of these factors. One possible solution would be to effort of developing accessible games. In sources used for develop accessibility ratings for games similar to the this survey the amount of implementation effort is rarely Entertainment Software Rating Board [22] ratings. This reported. A study that would analyze and report the could help players with disabilities evaluate before they implementation effort required to implement various purchase the game whether they will be able to play it. accessibility strategies would allow for game developers to Visible and tactile accessibility ratings on the boxes of the make more informed decisions on whether or not to invest games have the potential to raise awareness of the impor- in making their games accessible. tance of game accessibility. Because the application of low-level strategies is context dependent and thus relies on the game genre, an accessible reference game for each 5 Conclusions game genre could be developed. Such a reference game must be the most accessible version of that game genre for This survey paper provides an overview of the current state a particular impairment and allows for measuring the rel- of research and practice in game accessibility. ative accessibility of any game. Accessibility ratings could Through analysis of a number of player interactions with indicate the accessibility for each of the impairment cate- games from different game genres, a general game inter- gories on a certain scale where the reference game acts as action model was defined. This interaction model consists the highest rating for that genre. Certain accessible games of three distinct steps that players perform when playing we identified in this survey could already be used as ref- games: (1) receive stimuli (2) determine response and (3) erence games. provide input. This model allows for identifying how a Cost: Existing literature on game accessibility [4, 33, disability affects a player’s ability to play games: players 41] and this survey confirm that the accessibility of games with visual or hearing impairments may be unable to is lacking. This situation seems to be primarily related to receive stimuli, individuals with cognitive impairments a lack of awareness [6], as many game developers are not may be unable to determine an in-game response, and aware that players with disabilities would like to play individuals with motor impairments may be unable to their games. Potential reasons for this lack of awareness physically provide input. Further analysis reveals that dif- could be that schools for game development do not ferent impairments may affect the ability to play games to include game accessibility in their curriculum. Of the different extents. dozens of introduction-to-game-development books used Using the data from the 2002 US census, it was deter- at various game schools, only one recently published mined that, because of a disability, an estimated 2% of the book discusses game accessibility [76]. An additional US population is unable to play games at all, and 9% of the cause may be that within the game industry there may be US population can play games but suffers from a reduced

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