Visual search

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The more distractors there are, the longer it takes to find the letter B in the array
The more distractors there are, the longer it takes to find the letter B in the array
Feature search: The red X is a color singleton, the O is a shape singleton. Both can be found efficiently.
Feature search: The red X is a color singleton, the O is a shape singleton. Both can be found efficiently.
Conjunction Search: Find the orange square
Conjunction Search: Find the orange square

In theory of cognition, visual search is a type of perceptual task requiring attention. Visual search involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distracters). Visual search can take place either with or without eye movements. Common examples include trying to locate a certain brand of cereal at the grocery store or a friend in a crowd (e.g. Where's Waldo?). The scientific study of visual search typically makes use of simple, well-defined search items such as oriented bars or colored letters.

The efficiency of visual search depends on the number and type of distracters that may be present. Search tends to be more efficient when the target is very different from the distracters. The number of targets and distractors in a given visual array is called the display size. The display size effect is the degree to which task performance (Reaction time and/or accuracy) depends on the display size. The magnitude of the display size effect can vary greatly, from effectively zero (e.g., in searches for a red target among green distracters, called a feature search) to a large effect (e.g., in searches for a red X among green Xs and red Os, called a conjunction search). Search tasks with a small display size effect are referred to as "efficient;" search tasks showing a large display size effect are termed "inefficient."

Contents

Types of search

Feature search

Feature Search is the process of searching for targets defined by a unique visual feature, such as color, size, orientation or shape. Feature searches are typically efficient. For instance, an O is rapidly found among Xs, and a red target is rapidly found if all the distracters are black (see illustrations).

Conjunction search

Conjunction Search occurs when a target stimulus is defined not by any single visual feature, but by a combination of two or more features. An example is search for an orange square among blue squares and orange triangles (see illustration): neither the single feature "orange" nor the feature "square" is sufficient in isolation to uniquely specify the search target.

Conjunction searches are typically inefficient, with the time to complete the search task increasing linearly with the number of distractors. This behavior is as if the subject were forced to examine each item in the search array one at a time before deciding whether or not it was the search target, leading to the term "serial search".

Theories of visual search

See also

References

  • Wolfe, J M (1998). Visual Search. In H. Pashler (Ed.), Attention, East Sussex, UK: Psychology Press. Fulltext
  • Theeuwes, J. (1992). Perceptual selectivity for color and form. Perception & Psychophysics, 51, 599-606. Fulltext
  • Treisman, A., & Gelade, G., 1980. A feature integration theory of attention. Cognitive Psychology, 12, 97-136.
  • Verghese, P. (2001). Visual search and attention: A signal detection theory approach. Neuron, 31, 523-535(13).
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