Chapter 3 - Perceiving Objects and Recognizing Patterns

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17 Feb 2011
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Memory & Cognition Chapter 3 Perceiving Objects & Recognizing Patterns
Perception Interpreting sensory input meaningfully. Subdivided into:
1.Visual perception
2.Auditory perception
3.Olfactory perception
4.Haptic perception (touch)
5.Gustatory perception (taste)
James Gibson: you immediately acquire specific information about an object upon
inspection, including its location, shape, texture, size, name, and its function.
Classical Approach to Perception
An objects is a distal stimulus
Receive information of distal stimuli through sensory systems; the reception is the
proximal stimulus
The interpretation of the proximal stimulus is the percept
Size Constancy The phenomenon that ones perception of an object remains constant even
as the retinal image of the object changes size (an object moving closer or further from the
observer)
Pattern Recognition Recognition of a particular object, event, etc., as belong to a class of
objects, events, etc.
Gestalt Approaches to Perception
Form Perception: segregation of the whole display into objects (figure) and the
background (ground), eg. Reversible figures optical illusions. Figure is seen as
having a definite shape and is better remembered than the ground which is seen as
shapeless, less formed, and farther away in space
Subjective Contours: aka. Illusory contours; complex displays are subject to a
simplifying interpretation without the perceiver being aware of it (the non-existent
triangle)
Perception isnt entirely determined by the stimulus display; requires perceivers
active participation Perceivers follow certain laws/principles of organization in
coming to interpretations
First assert that the whole, or Gestalt, is not the same as the sum of its parts;
recognize objects as a whole instead of identifying its individual features
Gestalt Principles of Perceptual Organization
1.Principle of Proximity (nearness)
oGroup together objects that are closer to each other
2.Principle of Similarity
oGroup together objects with similar elements
3.Principle of Good Continuation
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oGroup together objects whose contours form a continuous straight or
curved line
4.Principle of Closure
oWhen observing subjective contours, we fill in the blank (non-
existent triangle)
5.Principle of Common Fate
oElements that move together will be groups together
oExtends beyond grouping by movement (eg. Grouping by luminance
change)
The Law of Pragnanz: most Gestalt principles are subsumed under this law;
tendency to select the organization that yields the simplest and most stable shape or
form out of all the possible ways of interpreting a display
oFormalized into a new theory called minimal model theory
Gestalt approach drawbacks:
oDont know how these principles are translated into cognitive or
physiological processes
oWithout further specification, the law of Pragnanz is seen as circular
(Why do we see a figure? Because its the simplest, most stable figure.
How do we know a figure is the simplest, most stable figure? Because we
so readily see it.)
Bottom-Up Processes
Data-driven; perceiver starts with bits of information from the environment that is
combined to form a percept
Lower-level processing, uninfluenced by expectations or previous learning
Involve automatic, reflexive processing that occurs even when the perceiver is
passively regarding the information (Posner &Raichle, 1994)
Common problem = cant explain how viewers make meaning of stimuli they
receive
oContext/Expectation Effects: the context in which a pattern or object
appears sets up certain expectations in the perceiver as to what objects
will occur
Three types:
1.Template Matching (UPC code model)
oTemplates: previously stores patterns; stencil
oEvery stimulus encountered and want to derive meaning from is
compared to a previously stored pattern/template
oIf a number of templates match or come close, engage in further
processing to sort out which template is most appropriate
oModel implies that somewhere in our knowledge base weve stored
millions of different templates, one for every distinct object or pattern
we can recognize
oDrawbacks…
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