visual search

Topics: Attention, Feature integration theory, Anne Treisman Pages: 7 (2144 words) Published: September 27, 2014
Visual Perception and Pop-out effect
Simphiwe Ngwenya(NGWSIM006)
According to the Feature Theory the sensory system breaks down the stimuli it receives into various features by using different processes to process the incoming information. The Feature Integration Theory was born from this theory. The Feature Integration Theory analyses and proposes different paradigms on how people are able to identify targets among distractors after or during processing of incoming information. Findings suggest that it takes less time to identify the target if it is among dissimilar distractors. Keywords: Feature Integration Theory, serial processing, parallel processing, visual search, pop-out effect Introduction:

Visual information is being constantly presented to people and processed in various manners. People are able to identify a target either by its individual features or by the combination of all the known features, this phenomenon is known as Visual Search. Numerous researchers have developed a number of theories on how people are able to identify targets amongst distractors. However the most communal theory is the one developed by Treisman and Gelade(1980), this theory is known as the Feature Integration Theory. According to Treisman as cited in Muller and Krummenacher(2006) visual search in the Feature Integration theory(FIT) occurs in two stages namely pre-attentive stage and attentive stage. During the pre-attentive stage the basic features are analysed such as size, colour and orientation etc. across the entire field, this process happens rapidly as there is no focus on items individually since processing during the pre-attentive stage occurs in parallel. The above mentioned authors go on to mention that during pre-attentive processing there are spatiotopically organized feature maps that hold the site for each feature. During the attentive stage a focused search is applied and features are processed serially. After the pre-attentive stages in order to ensure that all features are processed, features are combined and processed serially with the use of focal attention. Treisman and Gelande(1980) explain that focal attention is like a “glue” that integrates the parallel processed features into one object. They believe that without focal attention features that are being processed during the pre-attentive stage will not be relatable to each other. Features are not randomly combined but rather by top-down processing. In 1980 during the development of the Feature Integration Theory Treisman and Gelade suggested numerous paradigms in order to test all aspects of the theory. The most common paradigm is the one of visual search. This paradigm allows a target to be defined either by its individual features or by the combination of all the features. The individual features are obtained in parallel with no attention restrictions and the search should not be affected by the number of distracters present. In dissimilarity an assumption is made that focal attention is needed for the combination of features therefor target is only found after a serial search is conducted from a number of distractors. Pop-out effect refers to identification of a target in a number of distractors, basically recognizing the feature that makes the target different from its distractors therefor making it pop-out. According to Treisman(1986) during pre-attentive stage processing occurs automatically in a visual field therefor a target that is different from its distractors should pop-out. Treisman conducted a study to investigate visual search in 1986 and found that the time it takes to identify a target in an array of distractors with similar properties is not affected by the amount of distractors on the array whereas when the target is identified by a conjunction of features the time increases linearly with the amount of distractors. She justifies the results by stating that it is like when participants need to identify a target by a...

References: M"uller, H., & Krummenacher, J. (2006). Visual search and selective attention. Visual Cognition, 14(4-8), 389--410.
M"uller, H., & Krummenacher, J. (2006). Visual search and selective attention. Visual Cognition, 14(4-8), 389--410.
Neisser, U. (1963). Decision-time without reaction-time: Experiments in visual scanning. The American Journal Of Psychology, 376--385.
Terre Blanche, M., Durrheim, K., & Painter, D. (2006). Research in practice (1st ed.). Cape Town: UCT Press.
Treisman, A., & Gelade, G. (1980). A feature-integration theory of attention. Cognitive Psychology, 12(1), 97--136.
Treisman, A. (1986). Features and objects in visual processing. Scientific American, 255(5), 114--125.
Table : Descriptive stats of reaction time (in ms-1)
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