Databases Reference
In-Depth Information
2.3
VISUAL PERCEPTION
Visual perception is the ability to transform light stimuli reaching the eyes into information that can
be recognized and processed. Perception is unavoidably selective: we can't see all there is to see. There
are of course physiological limits (both for the human species and for individuals); some argue that
there are limits to cognitive capacity. And then, there are the constraints of our locational viewpoint:
we can't see things from every angle at once. But in addition to such physical limits, we focus on
salient features and ignore details that are irrelevant to our current purposes or interests. Selectivity
thus involves omission. People may either 'filter out' data or 'seek out' data of a certain kind.
Selective attention often involves redundancy: we don't always need much data in order to
recognize something. Often, we can manage with minimal visual data, making use of what is called
'redundancy.' You may know those 'blocky' pictures of famous people in which you can just about
recognize who it is. Our schemata allow us to 'fill in gaps' because we know what should be there.
Objects, events or situations are 'sized up' in relation to our frames of reference, and these influence
how perception is structured (
Newcomb, T.
,
1952
). Selective perception is based on what seems
to 'stand out.' Much of this 'standing out' is related to our purposes, interests, expectations, past
experiences and the current demands of the situation.
The characteristics of visual perception are exploited in visual systems in general and VQSs in
particular. Indeed, they use visual representations based on visual signs (
Bertin, J.
,
1981
). Visual signs
are characterized by a high number of sensory variables: size, intensity, texture, shape, orientation,
and color. By exploiting the multi-dimensionality of visual representations, users are allowed to
perform, in a single instant, a visual selection. Other constructions, for example a linear text, do
not permit this immediate grasping since the entire set of correspondences may be reconstructed
only in the user's memory. However, visual signs need to be used in an appropriate manner to avoid
the user to derive from the visual representation incorrect information, i.e., information that is not
actually stored in the data source, as discussed in Section
2.1
above. Moreover, the visual perception
principles provide the scientific basis for the design of visual interfaces that best match the users
requirements and effectively help them to make sense out of data.
