Friday, December 08, 2006

Visual Feedback: Why Modes Kill

Providing sensory feedback to avoid mode errors ...

"Let me set the scene. It's the comedy film "Airplane". The flight crew is violently ill and Striker, a shell-shocked, former pilot, is forced to land a jet full of passengers in dire need of medical attention. The air is heavy with fog, rain pounds on the cockpit windows. Over the static-filled radio comes the voice of ground control desperately talking Striker through the landing.

Ground Control: The radio is off. Our one hope is to build this man up, I've got to give him all the confidence I can. Turns radio on. Striker... Have you ever flown a multi-engine plane before?

Striker: No, never.

Ground Control: Thinking the radio is off. #@&*#! This is a waste of time... there's no way he can land that plane. Striker starts to tremble.

How did Ground Control make this mistake? The answer is simple. Mode error.

Don Norman defines mode errors as occurring when a user misclassifies a situation resulting in actions which are appropriate for the conception of the situation but inappropriate for the true situation. In Airplane, the action could not have been more inappropriate for the situation.

Mode errors are a ubiquitous bane: they cause us to lose our work and to kill hundreds of people. Despite the millions of dollars spent on the design of airplane cockpits, between 1988 and 1996 five fatal airline crashes were the direct result of mode errors. Many more crashes were probably indirectly caused by mode errors. What's the lesson? If a system contains modes, people will make mode errors; if we design systems that are not humane—responsive to human needs and considerate of human frailties, we can be guaranteed that people will make mistakes with sometimes cataclysmic consequences.

Luckily, there are methods for combating mode errors, generally by employing sensory feedback to indicate the current system mode to the user. Let's return to the radio in Airplane. It could have used visual feedback to indicate mode by employing a light that glows during transmission. Or, the radio could have used kinesthetic feedback by allowing the radio to transmit only while a button was pushed and held. With either of these two methods, ground control might have avoided the costly (albeit humorous) blunder."    (Continued via Humanized)    [Usability Resources]

Is Caps Lock On? - Usability, User Interface Design

Is Caps Lock On?


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