Lesson 2.5
Errors and User-Control
Human error is the result of any action whose consequences are not what was intended by the
person performing the action.
• slips and lapses and mistakes according to how they occur.
• Slips and lapses are found in skilled behavior – execution of procedures that the user has already
learned.
• A slip is a failure of execution or control
- A good mental picture for this is that you’ve developed a mental groove from executing
the same sequence of actions repeatedly, and this groove tends to capture other sequences
that start the same way.
• A lapse is a failure of memory
- A loss of intention lapse happens when you start executing a procedure and forget your
goal in the interim.
• A mistake is an error made in planning or rule application.
MODE ERROR
• states in which the same action has different meanings.
- Mode errors are generally slips, an error in the execution of a learned procedure, caused
by failing to correctly evaluate the state of the interface.
COMMON FEATURES OF HUMAN ERROR
→ Inattention - associated with insufficient attention to the execution of the procedure, or omission
or distraction of attention at a key moment.
→ high similarity to the correct behavior
AVOIDING CAPTURE AND DESCRIPTION SLIPS
→ applying the converse of the Consistency heuristic - different things should look and act
different, so that it will be harder to make description errors between them.
→ Avoid actions with very similar descriptions, like long rows of identical buttons.
→ well-separated from frequently-used commands.
AVOIDING MODE ERRORS
→ Eliminating the modes
→ spring-loaded or temporary modes - user has to do something active to stay in the alternate
mode
→ designing action sets so that no two modes share any actions.
AVOIDING LAPSES
→ keep procedures short
→ put more obvious structure on the procedure, a technique called dialog closure
→ Action sequences should be designed with a beginning, a middle, and an end
OTHER RULES FOR ERROR PREVENTION
• allow users to select rather type - reduces the user’s memory load
• information needed by a task should be visible or otherwise accessible in the interface for that
task
• Protect users’ work
• Confirmation dialogs can substantially reduce the efficiency of the interface
