Database Reference
In-Depth Information
According to
Information Theory
, vision is the sense that has the largest
bandwidth: 100 Mb/s [30]. Audition only has around 100 b/s. In that respect,
the visual canal is the best suited to carrying information to the brain.
According to Ware [30], there are two main
psychological theories
that explain
how vision can be used effectively to perceive features and shapes. At the low
level,
Preattentive processing
theory [23] explains what visual features can be
effectively processed. At a higher cognitive level, the
Gestalt
theory [9] describes
some principles used by our brain to understand an image.
Preattentive processing theory
explains that some visual features can be per-
ceived very rapidly and accurately by our low-level visual system. For example,
when looking at the group of blue circles in Figure 2, it takes no time and no
effort to see the red circle in the middle. It would be as easy and fast to see that
there is no red circle, or to evaluate the relative quantity of red and blue cir-
cles. Color is one type of feature that canbeprocessedpreattentively,butonly
for some tasks and within some limits. For example, if there were more than
seven colors used in Figure 2, answering the question could not be done with
preattentive processing and would require sequential scanning, a much longer
process.
Fig. 2.
Example of preattentively processed task: finding if there is a red circle among
the blue circles
There is a long list of visual features that can be preattentively processed for
some tasks, including line orientation, line length or width, closure, curvature,
color and many more. Information visualization relies on this theory to choose
the visual encoding used to display data to allow the most interesting visual
queries to be done preattentively.
Gestalt theory
explains important principles followed by the visual system
when it tries to understand an image. According to Ware [30], it is based on the
following principles:
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