The Figure 1.0 below schematically depicts the two information processing stages, "preattentive (or "ambient) and "attentive.' (or focal).
Visual information is detected by the most elementary parts of the nervous system, the eyes, ears, etc. in the preattentive stage. At this point, the visual input is coarsely processed for raw sensory attributes such as color, shape, size, and location in the visual field. Meaning is not attached to an object, so Mr. Z 's information processing system might register a blob of blue (coat) or white (hat) in the visual field, but would not yet interpret the blob as a person. In fact, he would not be consciously aware that it was there.
This preattentive stage has four important properties:
-It is automatic and occurs without volition, At we are unaware that we are doing it.
-Information remains in sensory memory for only a small fraction of a second. If not penetrating the attention filter, it is then permanently lost.
-It only analyzes as far as basic properties of color, size, location, etc. The meaning of the blue blob is unknown
-It has a very large capacity. It can process the entire visual field simultaneously
This last property is critical, because the vast quantity of information is too large for subsequent processing stages to handle. There needs to be a mechanism for selecting an information subset for more detailed analysis.
This mechanism is called ''attention" and is sometimes depicted as a spotlight that focuses processing on a selected part of the visual field - it defines an area of 3-D space for detailed examination. Attention is usually viewed as a filter the cyclist uses to focus his or her limited mental resources to important parts of the visual field and to exclude extraneous parts.
To see how this all works in practice, imagine a cyclist moving through the environment.
- Some sensory information (a blob of blue) registers in the peripheral field, where acuity is low.
- Something is there, but the cyclist doesn't know what it is.
- Next. the cyclist involuntarily moves his eyes and the attentional spotlight toward the object for further processing. In doing so, the cyclist causes the object's image to fall on the fovea, the area of the retina with the highest resolution. Once in focus with attention the blob becomes a well-defined shape.