Lec 8- Visual search - Lecture 8- Visual Search Notes from...

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Lecture 8- Visual Search Notes from page 129-133 of Eysenck and Keane, 2000 ‘Cognitive Psychology’ Visual search One of the main ways we use focused visual attention in our everyday lives is in visual search. An attempt to study the processes involved has been made by using visual search tasks. The participants are presented with a visual simply containing a variable number of items (the set or display size). A target (e.g., red G) is presented on half the trials, and the task is to decide as rapidly as possible whether the target is presence in the display. Feature integration theory The most influential approach to visual search is the feature integration theory put forward by TREISMAN (1988), She drew a distinction between the features of objects (e.g. colour, size, lines of particular orientation) and the objects themselves. Here theory based on this distinction includes the following assumptions: · There is a rapid initial parallel process in which the visual features of objects in the environment are processed together; this is not dependent of attention/. · There is then a serial process in which features are combined to form objects. · The serial process is slower than the initial parallel process, especially when the set size is large. · Features can be combined by focused attending to the location of the object, in which case focused attention provides the ‘glue’ forming unitary objects from the available features. · Feature combination can be influenced by stored knowledge. In the absence of focused attention or relevant stored knowledge, features from different objects will be combined randomly, producing ‘ILLUSORY CONJUNCTIONS’. TREISMAN & GELADE (1980) had previously obtained support for this theory. Their particpants searched for a target in a visual display having a set or display size of between 1 and 30 items. The target was either an object ( a green letter T), or consisted of a single feature (a blue letter or an S). When the target was a green letter T, all the non-targets shard one feature with the target (i.e. they were either the brown letter T or the green letter X). The prediction was that focused attention would not be needed to detect the object target (because it was defined by a combination of features), but would not be required to detect single-feature targets. The findings were as predicted. Set or display size had a large effect on detection speed when the target was defined by a combination or CONJUNCTION OF FEATURES (i.e. a green letter T), presumably because focused attention was required. However, there was very little effect of display size when the target was defined by a single feature (i.e. a blue letter or an S). According to feature integration theory, lack of focused attention can produce illusory
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This note was uploaded on 05/04/2008 for the course PSYCH 2006 taught by Professor Newellf during the Winter '06 term at Trinity College Dublin.

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Lec 8- Visual search - Lecture 8- Visual Search Notes from...

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