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What's Your Idea of a Mental Model?
by Scott McDaniel
“We should create these mental model descriptions during user analysis to document users’ current understanding. Then, during a design phase, we should create the target model to show the mental model we want users adopt.”As usability and design professionals, we often use the term “mental model” loosely. Part of the problem is that there isn’t a clear English definition, though there are several serviceable academic ones (for some examples, see Johnson-Laird, Girotto, and Legrenzi’s introduction and Martina Angela Sasse’s excellent Ph.D. thesis on the subject).
Even in these works, however, mental models aren’t defined more specifically than a mental representation of something. How, then, do you tell people in other disciplines, such as managers or developers, what they are? I often use examples to convey what a mental model is. If I tell them that I recently ordered a steak at a restaurant, they might assume that I was met at the door by a host or hostess, seated, and presented with a menu. They assume these details, and others, that I never actually mentioned because they have a mental model of how restaurants operate. To illustrate the consequences of having a mismatched mental model, I describe a person who goes into a buffet restaurant and waits for someone to take their order. The person’s mental model of how that restaurant operates doesn’t match the actual situation, and he would experience confusion and frustration until he modified his original model to include buffets.
Defining mental models by example is not sufficient if we want to treat them more formally, however. All mental models have a few key characteristics:
Mental models include what a person thinks is true, not necessarily what is actually true.
Mental models are similar in structure to the thing or concept they represent.
Men
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What is Cognitive Ergonomics? found in Ergonomics Today(TM)
June 11, 2001
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Editor's Note: This is a revised version of Cognitive Ergonomics and Engineering Psychology which appeared in Ergonomics Today(TM)on June 11, 2001.
Ergonomics is sometimes described as "fitting the system to the human," meaning that through informed decisions; equipment, tools, environments and tasks can be selected and designed to fit unique human abilities and limitations. Typical examples in the "physical ergonomics" arena include designing a lifting job to occur at or near waist height, selecting a tool shape that reduces awkward postures, and reducing unnecessary tasks and movements to increase production or reduce errors and waste. "Cognitive ergonomics," on the other hand, focuses on the fit between human cognitive abilities and limitations and the machine, task, environment, etc. Example cognitive ergonomics applications include designing a software interface to be "easy to use," designing a sign so that the majority of people will understand and act in the intended manner, designing an airplane cockpit or nuclear power plant control system so that the operators will not make catastrophic errors.
Cognitive ergonomics is especially important in the design of complex, high-tech, or automated systems. A poorly designed cellular phone user-interface may not cause an accident, but it may well cause great frustration on the part of the consumer and result in a marketplace driven business failure. A poor interface design on industrial automated equipment, though, may result in decreased production and quality, or even a life threatening accident.
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Ergonomics
Why is the video recorder one of the most frustrating domestic items to operate? Why do some car seats leave you aching after a long journey? Why do some computer workstations confer eyestrain and muscle fatigue? Such human irritations and inconveniences are not inevitable ? ergonomics is an approach which puts human needs and capabilities at the focus of designing technological systems. The aim is to ensure that humans and technology work in complete harmony, with the equipment and tasks aligned to human characteristics.
Ergonomics has a wide application to everyday domestic situations, but there are even more significant implications for efficiency, productivity, safety and health in work settings. For example:
Designing equipment and systems including computers, so that they are easier to use and less likely to lead to errors in operation ?particularly important tin high stress and safety-critical operations such as control rooms.
Designing tasks and jobs so that they are effective and take account of human needs such as rest breaks and sensible shift patterns, as well as other factors such as intrinsic rewards of work itself.
Designing equipment and work arrangements to improve working posture and ease the load on the body, thus reducing instances of Repetitive Strain Injury/Work Related Upper Limb Disorder.
Information design, to make the interpretation and use of handbooks, signs, and displays easier and less error-prone.
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