Designing Gestural Interfaces

DESIGNING TOUCH TARGETS

Since 1954, when it was proposed by psychologist Paul Fitts,^[25] Fitts' Law (pronounced "Fittzez Law") has guided computer scientists, engineers, and interaction, interface, and industrial designers when creating products, especially software. Fitts' Law simply states that the time it takes for a user to reach a target by pointing with a finger or with a device such as a mouse is proportional to the distance to the object divided by the size of the object. Thus, a large target that is close to the user is easier to point to than a smaller one farther away.

This law still holds true for interactive gestures, perhaps even more so. Touchscreen and other visual targets need to be designed in such a way so that important controls are close to the user to minimize reaching across the interface. Equally important is that the objects being manipulated (e.g., buttons, dials, etc.) are large enough for an average human fingertip to touch.

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Fitts' Law and Screen Edges

One corollary to Fitts' Law isn't as true for gestural interfaces. With traditional input devices such as a mouse or trackball, it makes good sense to place targets such as menu items on the edges of the screens so that the hit target becomes huge because the user cannot overshoot the target; the cursor stops at the edge of the screen. With gestural interfaces, this is rarely true. With touchscreens, users are seldom dragging their fingers across the screen as they do with a ...