Designing Gestural Interfaces

THE ERGONOMICS OF MOTION

Authors Michael Nielsen, Moritz Störring, Thomas B. Moeslund, and Erik Granum, in their 2003 paper "A Procedure for Developing Intuitive and Ergonomic Gesture Interfaces for Man-Machine Interaction,"^[22] have compiled a list of ergonomic principles to be aware of when considering motions:

• Avoid "outer positions," those that cause hyperextension or extreme stretches.

• Avoid repetition.

• Relax muscles.

• Utilize relaxed, neutral positions.

• Avoid staying in a static position.

• Avoid internal and external force on joints.

These principles serve designers well when selecting gestures to make interactive.

Since fingers and hands play such an important role in interactive gestures, especially for touchscreens, let's take a close look at them.

FINGERS AND HANDS

Adult fingers typically have a diameter of 16 mm to 20 mm (0.6 inches to 0.8 inches).^[23] Children's and teens' fingers may be smaller, whereas disabled, elderly, or obese people may have misshapen or larger fingers.

For pushing buttons or touching screens, usually the pad of the finger is used instead of the tip. Fingertips are narrow, only 8–10 mm (0.3–0.4 inches) wide. Because of this small surface area, humans usually push buttons at an acute angle using the pad of the finger, not straight on using the tip of the finger. Finger pads are wider than fingertips, but narrower than the full finger, typically 10–14 mm (0.4–0.55 inches).

Fingernails are a blessing and a curse. Long fingernails, although unlikely to scratch a ...