The action cycle
The action cycle is a model of human actions. The cycle consists of two phases, the execution phase and the evaluation phase, each of which is seperated in stages.
To achieve usability one should bridge the gulf of execution, meaning aid the user in selecting actions and evaluate the outcome.
The cycle begins with the user forming a goal, the state that is to be achieved.
The execution phase begins with that goal being translated into an intention to act so as to achieve the goal.
Next this intention is translated into an action sequence
- Finally this sequence it physically executed
The evalutation phase begins with our perception of the world
The perception is interpreted according to our expectations
and finally evaluated against our intention and goal
When presented with a new object you form a conceptual model of how it operates and behaves. This model is constructed largely from its visible structure, also called its system image, and perceived functionality.
When the designer fails to communicate the conceptual model of the object, through the system image, the user forms a faulty conceptual model.
Affordance is the perceived possible uses of an object. A chair affords sitting on, standing on, carrying around. A window affords seeing thorough or breaking.
An object supposed to be pressed should thus be presented as something that affords pressing, f.ex. as a button.
A product which makes good use of affordances requires no labels or explanations, the user knows, without thinking, what to do with it.
Constraints are the operating limitations. A coin slot affords inserting things into but constrains those things to objects with certain shapes, coins.
Mapping refers to how well controls map to the results in the world. One example is how the arrow keys are arranged on a keyboard. On most keyboards the arrow keys are placed so that the button signifying left is on the left side of the others, while the button signifying up or forward is above the others, and so on.