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Feature integration theory

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The feature integration theory, developed by Anne Treisman and Garry Gelade since the early 1980s, posits that different kinds of attention are responsible for binding different features into consciously experienced wholes. The theory has been one of the most influential psychological models of human visual attention.

Stages

According to Treisman, in the first stage of visual processing termed the preattentive stage, several primary visual features are processed and represented with separate "feature maps" that are later integrated into "saliency maps" that can be accessed in order to direct attention to the most conspicuous areas. During this stage, the object is analyzed with details such as shape, color, orientation and movement in mind. Each of these aspects is processed in different areas of the brain. The main idea that a processed object's features are automatically separated may seem counter-intuitive because we perceive the whole object instead of seeing each separate aspect; however, this analysis happens in the perceptual process before we are even conscious of the object.

The second stage involved in perceiving an object is the focused attention stage. This stage involves integrating individual features in order to perceive the whole object, or recognize it if enough information is presented. If the object is familiar, associations are made between the object and prior knowledge in order to aid in recognition. Bálint's syndrome sufferers, who as a consequence of parietal lobe damage seem incapable of properly focusing attention, lend credence to this two-staged model of attention.

The stages of Feature Integration Theory.

It was widely speculated that the saliency map could be located in early visual cortical areas, e.g. the Primary Visual Cortex (V1), though this is controversial. Wolfe's popular Guided Search Model offers a more up to date theory of visual search but is also problematic. [1]

Treisman distinguishes between two kinds of visual search tasks, "feature search" and "conjunction search". Feature searches can be performed fast and pre-attentively for targets defined by only one primitive feature, such as color, shape, movement or orientation. Conjunction searches proceed serially for targets defined by a conjunction (two or more) of primitive features - it is much slower and requires conscious attention. She concluded from many experiments that color, orientation, and intensity are primitive features, for which feature searches may be performed.

Experiments

In order to test the statement that features are independent in the early preattentive stage, Treisman and Schmidt (1982) designed an experiment in which participants are shown a picture involving four shapes and two black numbers for one-fifth of a second. After the display, a random-dot masking field appeared on screen to eliminate “any residual perception that might remain after the stimuli were turned off” [2]. The task of participants was to report the black numbers first, followed by what colored shapes they saw at four locations.The results of this experiment verified Treisman and Schmidt's hypothesis. In 18% of trials, participants reported seeing shapes “made up of a combination of features from two different stimuli” [3], even when the stimuli had great differences. This is an illusory conjunction, an often occurring illusion people experience during visual search. While people can typically remember the presence of an object, they often forget its location or color. They occur in various situations; for example, you may identify a passing person wearing a red shirt and yellow hat and very quickly transform him or her into one wearing a yellow shirt and red hat. Feature integration theory can explain illusory conjunctions – in Treisman’s words, features are “free floating” so they may be incorrectly combined [4]. Research participant R.M., a Bálint's syndrome sufferer who is unable to focus attention on individual objects, experiences illusory conjunctions when presented with simple stimuli such as a "blue O" or a "red T." For 23% of trials, even when able to view the stimulus for as long as 10 seconds, R.M. reported seeing a "red O" or a "blue T" [5]. This finding is in accordance with feature integration theory's prediction of how one with a lack of focused attention would erroneously combine features.

The stimuli resembling a carrot, lake and tire, respectively.
The stimuli resembling a carrot, lake and tire, respectively. Treisman et al.(1986).

However, if people use their knowledge or experience to perceive an object, it is less likely to make mistakes. Treisman did another experiment to explain this phenomenon – she presented three shapes to participants and illusory conjunctions persisted. Surprisingly, when she told participants that they were being shown a carrot, lake and tire (in place of the orange triangle, blue oval, and black circle, respectively), illusory conjunctions disappeared [6]. Treisman maintained that prior-knowledge played an important role in proper perception. Normally, bottom-up processing is used for identifying novel objects; but, once we recall prior knowledge, top-down processing is used. This explains why people are good at identifying familiar objects rather than unfamiliar.

Reading

When identifying letters while reading, not only are there shapes picked up but also other features like their colors and surrounding elements. Individual letters are processed serially when spatially conjoined with another letter. The locations of each feature of a letter are not known in advance, even while the letter is in front of the reader. Since the location of the letter's features and/or the location of the letter is unknown, feature interchanges can occur if one is not attentively focused. This is known as lateral masking, which in this case, refers to a difficulty in separating a letter from the background [7].

References

  • Anne Treisman and Garry Gelade (1980). "A feature-integration theory of attention." Cognitive Psychology, Vol. 12, No. 1, pp. 97-136.
  • Anne Treisman and Hilary Schmidt (1982). "Illusory conjunctions in the perception of objects." Cognitive Psychology, Vol. 14, pp. 107-141. [8]
  • Anne Treisman (1988). "Features and objects: the fourteenth Bartlett Memorial Lecture." Quarterly Journal of Experimental Psychology, 40A, pp. 201-236.
  • Anne Treisman and Nancy Kanwisher (1998). "Perceiving visually presented objects: recognition, awareness, and modularity." Current Opinion in Neurobiology, 8, pp. 218-226.
Notes
  1. ^ Wolfe JM, Cave KR, Franzel SL. (1989) Guided search: an alternative to the feature integration model for visual search. Journal Experimental Psychological: Human Perception Performance. 1989 Aug;15(3):419-33. PMID 2527952
  2. ^ Cognitive Psychology, E. Bruce Goldstein, P 105
  3. ^ Cognitive Psychology, E. Bruce Goldstein, P 105
  4. ^ Treisman, A. Cognitive Psychology 12, 97-136 (1980)
  5. ^ Friedman-Hill et al., 1995; Robertson et al., 1997.
  6. ^ Illusory words: The roles of attention and of top–down constraints in conjoining letters to form words. By Treisman, Anne; Souther, Janet. Journal of Experimental Psychology: Human Perception and Performance, Vol 12(1), Feb 1986, 3-17.
  7. ^ Anne Treisman and Garry Gelade (1980). "A feature-integration theory of attention." Cognitive Psychology, Vol. 12, No. 1, pp. 97-136.
  8. ^ Abstract
    In perceiving objects we may synthesize conjunctions of separable features by directing attention serially to each item in turn (A. Treisman and G. Gelade, Cognitive Psychology, 1980, 12, 97-136). This feature-integration theory predicts that when attention is diverted or overloaded, features may be wrongly recombined, giving rise to "illusory conjunctions." The present paper confirms that illusory conjunctions are frequently experienced among unattended stimuli varying in color and shape, and that they occur also with size and solidity (outlined versus filled-in shapes). They are shown both in verbal recall and in simultaneous and successive matching tasks, making it unlikely that they depend on verbal labeling or on memory failure. They occur as often between stimuli differing on many features as between more similar stimuli, and spatial separation has little effect on their frequency. Each feature seems to be coded as an independent entity and to migrate, when attention is diverted, with few constraints from the other features of its source or destination.

See also

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