Models and Theories in Human-Computer Interaction/Norman’s Affordances
The term affordance was originally proposed by psychologist James J. Gibson in 1977. Don Norman applied the concept in the context of Human Computer Interaction in 1988, refers to “the perceived and actual properties of the things, primarily those fundamental properties that determine just how the thing could possible be used”. He believed that affordances, along with constraints and mappings, can provide strong visual clues to help users know intuitively how things operate. He took a pair of scissors as an example in his book “The Design of Everyday Things” to illustrate the concept: the hole-shape structures are affordances imply that you can put fingers into; the constraints of holes’ sizes limit the fingers that can be possibly used; and the mappings between fingers/holes and their movements and the possible results hint the set of operations.
Principles of design for understandability and usability
In addition to making things visible, Norman pointed out that providing a good conceptual model/mental model is also required to facilitate the understandability and usability of a design, especially for a complex product. Norman defined mental models as “our conceptual models of the way objects work, events take place, or people behave, result from our tendency to form explanations of things”. Therefore, he strongly believed that good mental models can help users to predict the outcomes of their actions and handle the unexpected occurrences when operating a product.
Norman uses the term affordance to describe the number of potential uses an object inherently has – intended or not (e.g. a glass pane for looking through or for breaking) – and how keeping these uses in mind can lend to proper design of said object. According to Norman, users of well-designed objects should be able to form a conceptual model – that is, be able to imagine how it is used and/or the potential outcome of its use – from simply looking at it. A dial on an oven should have indications as to the temperature at each slight rotation as well as to what part of the oven the temperatures refer to. Is it to the main heating unit itself or potentially to one of two or four stove-top burners?
To ease the ability to form a conceptual model for the use of an object Norman says that visibility is important. As he notes in his book The Design of Everyday Things, “Visibility indicates the mapping between intended actions and actual operations.” Rely on learning-by-doing represents poor design. Users should be able to mentally map what they perceive to be its usage and how it is used as close as possible with its actual use and actual effect for that object to be considered well designed.