On This Page: Legibility and Clutter Graphics for Perceptual Layers
The concept of perceptual layers refers to a graphic scheme in which several classes (layers) of data are superimposed while retaining their different demands on the users' attention. This allows less important or less urgent data to be presented as context without detracting from the users' focus on the data that are more critical for the immediate decisions. The metaphor of transparent layers captures the sense of looking through or past other classes of data to see the one of immediate interest. Perceptual layers should not be confused with the layers of data in graphics software, which the designer may or may not choose to make perceptually distinct.
If legibility were the only
consideration, the designer should probably give all text and symbols
the same weight and luminance contrast. There is a second consideration,
however, clutter. If all of the text and symbols in a complex graphic
have high luminance contrast it can be hard to find the relevant information
among the context information. Good perceptual
layering can greatly increase the amount of information that can be
displayed by imposing perceptual order on the graphic elements.
There are several graphic manipulations that can be used to establish perceptual layers. The most common are brightness contrast, line weight, symbol size, and blinking and flashing. Of these only brightness contrast is directly affected by color assignments, but color design issues such as legibility and discrimination interact with the others.
Designing with Luminance Contrast
Color Discrimination and Identification
Blinking, Flashing, and Temporal Response