Using Gestures Effectively
Gesture-based interaction is without a doubt the most exciting development in human-machine interface design of the last decade. The introduction of two-, three-, four-, and even five-finger multitouch gestures in the Mac and iOS product lines has contributed significantly to the success of both. The numbers speak for themselves. During the new iPad announcement this week, Apple mentioned the quarterly sales for iPads were higher than the collective sales of all the products offered by each of the big PC manufacturers. Consumers bought more iPads than all HP PC products combined, more than all Dell PC products combined, and more than all Acer PC products combined. People are quickly embracing the iPad, with its multitouch usability. They’re also choosing Mac laptops over Windows-based products because of the baked-in support for gestures in the Mac OS X experience.
So, how can designers take advantage of gestures to add richness to their user experience? Consider these aspects:
1. Affordance
Probably the most important aspect of usability design is affordance – the degree to which a component describes its behavior visually. Gestures are events in time. They don’t have any visual presentation at all. As a result, they have no affordance. This means the gesture can not be the only mechanism that triggers an action. They must be coupled with on-screen controls that perform the same function.
2. Ambiguity
When adding a gesture, it’s important to be aware of the system-wide gestures supported by the platform. Otherwise, there is a risk of ambiguity, where one or another or both actions occur when the gesture is triggered. Also, it’s important to have clear distinction of gesture direction. For example, it’s possible to add a “swipe up” gesture to a scrolling list view, but to do so would introduce ambiguity. Sometimes, a swipe would cause the view to scroll. Other times, a scroll action might trigger the gesture. This is a bad idea. It’s best to limit gestures to directions orthogonal (perpendicular) to scrolling. Even in that case, gestures don’t always work, since “swipe to delete” is an iOS SDK feature.
3. Relevance
When assigning a behavior to a gesture, ask yourself what feels most natural as a user. One common use of gestures is swipe left/right to navigate to the next/prev item in a collection. This feels natural, especially when the gesture is on a detail view of a single item in the collection, visible only after tapping an item in a summary list view. The context of the collection is fresh in the user’s mind, so there remains a strong desire to traverse the collection. If they must tap a “back” button to seek another item in the collection, that quickly becomes tedious. By adding next/prev buttons in the detail view and enabling swipe left/right, the collection interaction feels much more fluid and natural. Swipe up/down would not feel natural. Similarly, swipe left/right to select different tabs in a tabbed layout doesn’t feel natural.
Conclusion: Let the user decide
Designers will always push the envelope to give users new options, new interactivity metaphors they would never have asked for. Sometimes, users embrace new designs, and sometimes they prefer the familiar. In the end, the goal is to satisfy the needs of many. If the designers do their job well, users will discover gestures and decide for themselves whether or not to use them. Some users will prefer gestures. Others will prefer on-screen controls. If they don’t discover them or don’t use them after discovering them, that is not an indication of failure of the design. It is merely an expression of preference.
