Perception and Representation
Perception is fundamental to interact with computers. If you want to design computer systems, then it is important to understand how theories of perception can influence interface design. Two essential but opposing theories are the constructivist and the ecological approaches. With the emergence of multimedia and virtual reality, however, the notion of the interface as a screen is beginning to change. Other perceptual modalities of sound and touch are being incorporated into the newly emerging technologies.
There are several theories that have attempted to explain the way we see and they can be categorized into two classes: constructivist and ecological approaches.
Constructivist theories believe that the process of seeing is an active or in which our view of the world is constructed both from information in the environment and from previously stored knowledge. Ecological theorists believe that perception involves the process of "picking up" information from the environment and does not require any processes of construction or elaboration.
Graphical representation at the interface
The visual system could then use the same processes that it uses when perceiving objects in the environment. Following are described and compared the main methods that have been used to represent information at the interface. These are classified in terms of the various kinds of graphical modeling techniques used to represent three-dimensional objects and scenes, and the various forms of graphical coding used to represent different types of system information t the interface. The focus is on the efficacy of the different representational forms.
Graphical modeling and three-dimensional representation
Graphical models, developed for use with a conventional computer display, have to be represented on a two-dimensional surface. To make the objects appear as three-dimensional, monocular depth are used. Below a list:
Size: The larger of two identical objects appear to be closer than the smaller one.
Interposition: If one object partially obscures a second object then the blocked object is perceived to be behind and beyond the blocking object.
Contrast, clarity, and brightness: Sharper and more distinct objects appear to be nearer, and duller objects appear to be further away.
Shadow: It can provide some cues to the relative position of objects.
Texture: As the apparent distance increases, the texture of a detailed surface becomes less grainy.
In addition to using graphical models to represent three-dimensional objects and scenes, graphical representation can be used as a form of coding at the interface. Abstract system processes, data objects, and other features of the interface can be represented by different forms of graphical coding. These can consist of arbitrary mappings, where there is no relation, other than an established convention (for example, the use of red in warning signals in western cultures to represent danger) between the represented object and the representing form. Below a comparison of the various coding methods:
Alphanumerics: High versatile. Meaning can be self-evident.
Shapes: Very effective if code matches object or operation represented
Color: Attractive and efficient but excessive use can easily make the interface confusing
Object size: Can take up considerable space.
Brightness: Can be fatiguing, especially if screen contrast is poor.
Blink: Good for getting the attention but should be suppressible afterward.
Reverse video: Effective for making video stand out.
Underlining: Useful but can reduce text legibility.
Color coding provides many opportunities for coding and structuring information at the interface as well as making it pleasant and enjoyable to look at. However, excessive use of color can result in color pollution, particularly when highly saturated colors, such as a "full" red and a "deep" blue are used. This can result difficult to interpret and confusing interfaces.
Perception is an active process
There are two main theories of perception: the constructivist approach and the ecological approach
The main methods that have been used to represent information at the interface are graphical modeling and graphical coding.
Graphical coding can provide a powerful way of displaying quantitative data.
Color is most useful for identification task and as a form of redundant coding.