One-handed games on iPhone: designing for motor accessibility

Anthony, Kim and Findlater took an unusual route into the question: they analysed 187 videos, posted to YouTube by people with physical disabilities, of themselves using ordinary phones and tablets. The videos showed people succeeding, often with adaptations of their own, such as using a knuckle, a stylus or another part of the body, and resting a hand on the screen edge for stability. Touchscreens were frequently described as empowering. They also showed the recurring problems: accidental touches, targets too small to hit, and gestures that were hard to perform.

A controlled lab study by Findlater and colleagues put numbers on it. They compared a touchscreen with a mouse for 32 people, 16 with upper-body motor impairments. The touchscreen was faster overall, but only participants without impairments made fewer errors on it. Participants with motor impairments made three times as many tapping errors on the touchscreen as with the mouse, and spurious touches were common. The authors updated the recommended minimum touch target for these users to at least 18 millimetres, which is considerably larger than most phone buttons.

Sources1Source 1Anthony, L., Kim, Y., & Findlater, L. (2013). Analyzing user-generated YouTube videos to understand touchscreen use by people with motor impairments. In Proceedings of the SIGCHI Conference on Human Factors in Computing Systems (pp. 1223–1232). ACM.2Source 2Findlater, L., Moffatt, K., Froehlich, J. E., Malu, M., & Zhang, J. (2017). Comparing touchscreen and mouse input performance by people with and without upper body motor impairments. In Proceedings of the 2017 CHI Conference on Human Factors in Computing Systems (pp. 6056–6061). ACM.

Even without any impairment, one-handed use changes the rules. Parhi, Karlson and Bederson studied thumb use on small touchscreens and found that targets of about 9.2 millimetres for single taps, and 7.6 millimetres for sequences of taps, were large enough to avoid hurting speed or accuracy. Smaller than that, and errors climbed. Reach matters as much as size: on a large phone, the far top corner is the hardest place to tap with the thumb of the hand that holds it, which is exactly where many games put their pause and settings buttons.

Trewin, Swart and Pettick studied smartphones with people with dexterity impairments and found them useful and usable, though tablets offered real advantages, such as larger targets and a steadier surface. They also noticed something awkward: some of the accessibility features themselves demanded so much dexterity to set up and use that many participants could not use them. Accessibility that is hard to switch on is not much accessibility.

Sources3Source 3Parhi, P., Karlson, A. K., & Bederson, B. B. (2006). Target size study for one-handed thumb use on small touchscreen devices. In Proceedings of the 8th Conference on Human-Computer Interaction with Mobile Devices and Services (pp. 203–210). ACM.4Source 4Trewin, S., Swart, C., & Pettick, D. (2013). Physical accessibility of touchscreen smartphones. In Proceedings of the 15th International ACM SIGACCESS Conference on Computers and Accessibility (pp. 1–8). ACM.

Kim and colleagues built a coding scheme for motor accessibility and applied it to 72 iPad games. Porter and Kientz, surveying players with disabilities and people in the games industry, found that incompatibility with assistive technology was a common barrier and that developers often lacked practical guidance. Put together, the common problems are easy to list: time limits and reaction tests, multi-finger gestures with no alternative, precise dragging, small buttons at the screen edges, and punishing penalties for a single mis-tap.

Time is the one designers most often overlook. A tremor, spasticity or fatigue all make fast, precise movement harder, and a countdown turns that into failure. A move limit is a different kind of constraint: it asks you to think, and it does not care how long your hand takes to get there. We wrote about why this also makes a game calmer in what actually makes a puzzle game relaxing.

• Targets well above the platform minimum, with space between them.
• Important controls within reach of the thumb, not only in the top corners.
• Every gesture achievable with one finger, and no gesture that must be fast.
• An undo that is easy to reach and forgives a mis-tap without penalty.
• No timers on ordinary play, and no reflex tests hidden in menus.

Sources5Source 5Kim, Y., Sutreja, N., Froehlich, J., & Findlater, L. (2013). Surveying the accessibility of touchscreen games for persons with motor impairments: A preliminary analysis. In Proceedings of the 15th International ACM SIGACCESS Conference on Computers and Accessibility (pp. 1–2). ACM.6Source 6Porter, J. R., & Kientz, J. A. (2013). An empirical study of issues and barriers to mainstream video game accessibility. In Proceedings of the 15th International ACM SIGACCESS Conference on Computers and Accessibility (pp. 1–8). ACM.

Most accessibility writing focuses on getting input right. Just as important is what happens when input goes wrong, because for some players it will go wrong often. A game that treats every stray touch as a committed move is quietly hostile to anyone with a tremor. A game that makes the last move easy to take back is kind to everyone. The web’s accessibility guidance makes a related point about pointer gestures: anything that can be done with a complex gesture should also be possible with a simple one.

This is where OutBrick sits. Bricks move with one finger, and a slide is a short, single movement rather than a precise drag to a spot. There is no clock anywhere. The first undo on every board is free, so one mis-slide never has to cost a board, and a board left with no move reshuffles itself for free. On Apple Watch the Digital Crown works as well as touch. None of that makes the game accessible to everyone, and a sliding puzzle still asks for a directed gesture. If a control is hard to reach, the accessibility page asks for your device and the screen, because that detail is what lets us fix it.

It is worth remembering how many people this covers. Designers sometimes talk about situational impairments: the parent with a child on one arm, the commuter holding a rail, the player with a cast on their wrist for six weeks. None of them would describe themselves as disabled, and all of them benefit from exactly the same choices. Designing for the player with a permanent tremor produces a game the whole carriage can play one-handed.

Apple’s motor accessibility settings are under Settings, Accessibility, Touch, and several suit games well. They are worth trying one at a time, because each changes how every app responds to your fingers. For games in particular, check whether the game still behaves when these are on; a good game should not notice. Watch players have their own set of options too, and we cover the small-screen case in puzzle games for Apple Watch.

• Reachability brings the top of the screen down within reach of your thumb with a swipe down on the bottom edge.
• Touch Accommodations can ignore repeated touches, require a touch to be held briefly before it counts, or use where your finger first or last landed.
• AssistiveTouch puts a floating menu on screen that can replace multi-finger gestures and hardware buttons.
• Back Tap turns a double or triple tap on the back of the phone into a shortcut.
• Voice Control and Switch Control offer ways to operate the phone without touch at all, though fast-paced games rarely work well with them.