In universal design, perceived affordance-that is, the implicit understanding of how to interact with an object-actually coincides with the user's ability to execute the action.
This scene is funny and believable: The mouse has no visual affordance that it is a pointing device. However, as soon as we are shown how the movements of the mouse and the cursor are related, understanding is instantaneous.
For example, the three-dimensional sculpting of a button control is static visual hinting because it provides manual affordance for pushing (see Figure 19-3).
The basic shape, behavior, and visual affordance (see Chapter 13) of controls should be driving factors in developing the visual style, and purely aesthetic considerations should not interfere with the meaning of the interface or a user’s ability to interact with it.
If, when we push it, it causes a trapdoor to open beneath us and we fall into it, it turns out that it wasn’t a doorbell, but that doesn’t change its affordance as one.
Touch screens should also avoid idioms that involve dragging; single-tap idioms are easier to control and more obvious (when given proper affordance) to novice users.
If the control is rectangular (or sometimes oval) and appears raised (due to its shadow on the right and bottom and highlight on the top and left), it has the visual affordance of an imperative.
What’s missing from an unadorned, virtual manual affordance is any idea of what function it performs.
The use of shading and highlights suggest dimensionality, which gives these buttons affordance or clickability.
