With apologies to this app's developer for a harsh critique of what's obviously meant to be a throwaway novelty app, here is the simplest example I've seen of mistakes made when using gestures in an iPhone app.
RPS Gestures (iTunes link) is a "gesture-based version of the classic" Rock Paper Scissors, a.k.a. Rochambeau. This version of the game lets you play paper by swiping, rock by tapping, and scissors by pinching.
Here is the interface. Can you spot a problem?
What's novel about this app compared to the 100's of other RPS apps (yes, there are that many) is that you have to make your play using gestures -- slide for paper, tap for rock, pinch for scissors. But that's the only way to do it. If you mistakenly tap on the nice big icon for paper you don't get paper, you get rock. This reviewer sums it up eloquently:
As any good UX'er should do, I confirmed this issue with a totally (im)precise 1-minute usability study. I found that 100% of users shown this game for the first time, without having read the app store description, tapped on the icons rather than doing the gestures (sample-size = 1).
Some lessons here, about this issue and others with the app:
- Don't give misleading cues. (Don't make the icons look so darn tappable; put the descriptions in a list or something and make the words "slide," "tap," and "pinch" more prominent.)
- Don't make gestures the only way to perform actions. Many users just won't know to use them or will have difficulty. An exception is a creative novelty app like this, which is all about gestures. That's fine as long as you pay attention to these other details.
- Give good feedback and if you're going to ask people to do the extra work of gestures, give them some sort of reward or eye candy that makes it fun. This app could give animated feedback of the gestures as you're doing them. Instead it doesn't show you any feedback until you complete a gesture.
- Give people plenty of space to do the gestures. It's hard to do a pinch inside that blue square, which is what it looks you have to do (even though the app actually lets you do the gesture over the whole screen).
- Make sure your gesture recognition is rock-solid (pardon the pun). I sometimes get paper in this app when I try for scissors.
Okay, enough harshing on this poor app.
Via Google I also stumbled upon this fascinating site by independent game developer David Lovelace: RPS-101. It's a 101-gesture version of RPS -- "The most terrifyingly complex game ever." I look forward to the iPhone version!