Theories Of Visual Search :: essays research papers

Theories of Visual Search A standard theory of visual search tasks assumes that when a person searches for a target in an array of other items, memory is used in locating the target. The following analysis of three articles shows that there is both strong support for this highly respected theory and evidence that this theory may have some flaws in reasoning. In the article "Features and Objects in Visual Processing," Anne Treisman states that there are two theoretical levels of visual processing. In the first level of visual processing, certain components of visual information are processed instantly and unconsciously. A person does not have to concentrate on individual parts of the scene. This stage of processing is called the preattentive stage. During the preattentive stage, the light received by the visual receptors is translated in to the lines, curves, colors and textures of the objects. Within the brain, there are two distinct visual areas that specialize in different areas of processing. The first area processes lines, curves, color, and texture and other areas deal with movement. After this initial processing occurs, another area of the brain processes the more complex and distinct qualities of a scene. Then, all of the components of the objects in the scene are recombined into whole objects. In order to support the pr eattentive stage of visual processing, Treisman devises that parts of objects that belong to the same object share similar attributes. Attributes such as color, continuity of lines and curves that define the boundaries between objects. She uses an experiment to determine which properties of a visual stimulus make its boundaries stand out from other similar objects. The properties of an object that make it stand out are used by the visual processing system in distinguishing the object from ground. In actuality, boundaries are conspicuous between components that are distinctive in basic properties such as color, brightness and line orientation but not in the way their properties are connected or grouped. In an experiment showing evidence of this principle, subjects are shown a picture in which a region of T’s easily distinguishes itself from an area of slanted T’s but not from a region of backwards L’s that are constructed of the same geons as the T’s. This illustrates that line orientations are important features in the preattentive stage of visual processing and that the specific configurations or conjunctions of lines are not.