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Chapter 2

CHAPTER 2: Cognitive Notes.docx

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Western University
Psychology 2135A/B
Patrick Brown

Cognitive Chapter 2: Pattern Recognition Chapter 2: Pattern Recognition - Pattern recognition: the stage of perception during which a stimulus is identified o The study of how people identify objects in their environment Describing Patterns - How we recognize patterns… o LTM contains descriptions of many kinds of patterns o When we see or hear a pattern, we form a description of it and compare the description against the descriptions stored in our LTM o We are able to recognize the pattern if its description closely matches one of the descriptions stored in LTM o What form do these descriptions take?  (1) templates, (2) features, and (3) structural descriptions Template Theories - Patterns are not “described” - Template: an unanalyzed pattern that is matched against alternative patterns by using the degrees of overlap as a measure of similarity - Problems with this model… o 1. The comparison requires that the template in the same position and the same orientation, and be the same size as the pattern you are trying to identify o 2. There is a great variability of patterns so it would be difficult to construct a template for each letter that would produce a good match with all the different varieties of that letter. o 3. A template theory does not allow for alternative descriptions of a pattern  E.g. ambiguous figures that have more than one interpretation, such as a young lady or an old lady - How are the patterns preserved in the sensory store if they are unrecognized? o One possibility is that the patterns can be represented as unanalyzed templates, which are analyzed into their features during the pattern recognition stage - Phillips… o Presented with two identical or similar patterns and had to decide weather the two patterns were the same or different o Trial 1: they were presented in the same location (possible to use a sensory store to make a template match) o Trial 2: the second pattern was moved horizontally by the width of one cell (prohibits a template match because the two patterns were not correctly aligned) o Interstimulus interval: the amount of time between the end of stimulus and the beginning of another stimulus o Accuracy declined as the Interstimulus interval increased in trial 1  This showed that sensory store was rapidly decaying o In trial 2, subjects could not use the sensory store to make a template match, and so accuracy was not influenced by the interval separating the patterns o Result…  The use of the sensory store resulted in more accuracy when the interstimulus interval was less than 300 msec (this is how long the sensory store lasts)  Reaction times were slower for the “move” condition and were uninfluenced by the interstimulus interval Feature Theories - Feature theories: allow us to describe a pattern by listing its parts o E.g we might describe a friend as having long blond hair, a short nose, and bushy eyebrows Cognitive Chapter 2: Pattern Recognition - Gibson… o Perceptual learning occurs through the discovery of features that distinguish one pattern from another o Proposed the following criteria as a basis for selecting a set of features for uppercase letters:  1. The features should be critical ones, present in some members of the set but not in others, so as to provide a contrast  2. The identity of the features should remain unchanged under changes in brightness, size, and perspective.  3. The features should yield a unique pattern for each letter  4. The number of proposed features should be reasonably small - Hubel and Wiesel… o Recorded the action potentials of individual cells in the visual cortext o Placed microelectrodes in the visual cortex of animal and discovered that cells respond to only certain kinds of stimuli, as a line of a certain width, oriented at a correct angle, and located at the correct position in its visual field - Perceptual confusions: a measure of the frequency with which two patterns are mistakenly identified as each other - Gibson model proposed by Geyer and De Wald… o The major change in the modification was the specification of the number of features in a letter (such as two vertical lines for the letter H) rather than simply listing whether that feature was present o A comparison of the two models revealed that the feature set proposed by Geyer and De Wald was superior in predicting the confusion errors made both by adults and by 4-year-old children o Come features are more important than others in accounting for confusions o Because the straight/curved distinction is particularly important, it should be emphasized more than the others Distinctive Features - Distinctive feature: a feature present in one pattern but absent in another, aiding one’s discrimination of the two patterns - Emphasizing the distinctive features produced two benefits o First, it enabled the children to learn the distinctive features so that they could continue to differentiate letters after the distinctive features were no longer highlighted o Second, it enabled them to learn the features without making many errors during the training sessions Faces - Levin… At what level do we identify a pattern? o Some levels are very general (a person’s face), some are intermediate (an Asian face), and some are very specific (Angie Chen’s face) o Identifying faces within a category can be difficult when we emphasize features that allow us to distinguish between categories rather than within categories o We particularly have trouble distinguishing among faces of an ethnic category that is different from our own o Levin argues that this does not occur because we have more practise identifying faces in our own race o Rather, it occurs because we simply don’t try as hard to recognize people as individuals in they belong to other racial categories - Brennan… o Caricatures: an exaggeration of distinctive features to make a pattern more distinctive Cognitive Chapter 2: Pattern Recognition o They identified people faster when shown caricatures than when shown accurate line drawings. o Making distinctive features more distinctive through exaggeration facilitated recognition Structural Theories - A limitation of feature theories is that descriptions of patterns often require that we specify how the features are joined together - Structural theories: A theory that specifies how features of a pattern are joined to other features of the pattern o Emphasize the relations among the features by building on feature theories o A structural theory allows for specification of how the features fit together - Hoffman’s… o Book on visual intelligence is that people follow rules in producing descriptions of patterns o First of many rules described in his book is to always interpret a stright line in an image as straight line in three dimensions o Therefore, we perceive the long vertical line in the centre of the right pattern a in Figure 2.5 as a single line o However, it is necessary to split this line into two separate lines to form a cube because the lines belong to different surfaces Biederman’s Component Model - A briefcase is more similar to the pail than to the cup because of the relation between components—the handle is on top for both the briefcase and pail. - The advantage of being able to form many different arrangement from a few components is that we may need relatively few components to describe objects
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