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Pattern Recognition. Pattern - complex composition of sensory stimuli that the human observer may recognize as being a member of a class of objects Issue - what cognitive mechanisms need to be inferred to describe this process of recognition?. Bridge with Signal Detection.

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pattern recognition
Pattern Recognition

Pattern - complex composition of sensory stimuli that the human observer may recognize as being a member of a class of objects

Issue - what cognitive mechanisms need to be inferred to describe this process of recognition?

bridge with signal detection
Bridge with Signal Detection
  • Detection of sensory stimuli - data driven
  • Perception of Patterns - conceptually driven
  • work from the bottom (identifying stuff in the world) to the top (thinking)
necessary terms and concepts of pattern recognition
Necessary Terms and Concepts of Pattern Recognition
  • Serial and Parallel Processing
    • Serial or sequential processing means we process information one step at a time, where one process must be finished before the next can be started.
    • Parallel processing means we can process several tasks at one time
necessary terms and concepts of pattern recognition4
Necessary Terms and Concepts of Pattern Recognition
  • Bottom-up and Top-down processing
    • Bottom-up processing is similar to inductive reasoning. Basic data are combined into more complex forms.
    • Top-down processing is similar to deductive reasoning. Higher levels of processing affect lower level tasks.
      • The following gives examples of how we perceive visual patterns and how positioning or additional information affects our perception.
theories of perception
Theories of Perception

1. Gestalt

(Canonic Processing)2. Bottom-Up vs. Top Down

3. Template matching

4. Feature Analysis

Prototype Theory

Form Perception

gestalt theory
Gestalt Theory
  • Gestalt theorists are among the earliest to look at the problem of pattern recognition.
  • They postulate that we perceive stimuli as a whole pattern. That is, that individual parts have no meaning independent of the whole but combine to revel an identifiable pattern.
  • Gestalt theorists developed 5 rules of perception to explain their ideas...
gestalt laws
Gestalt Laws

1. Law of Proximity:

  • Elements that are closer together will be perceived as a coherent object.
  • On the top, there appears to be three horizontal rows, while on the bottom, the grouping appears to be columns
gestalt laws10
Gestalt Laws
  • Law of Similarity:
    • Elements that look similar will be perceived as part of the same form.
    • There seems to be a triangle in the square.
gestalt laws11
Gestalt Laws
  • Law of Closure:
    • Humans tend to enclose a space by completing a contour and ignoring gaps in the figure
gestalt laws12
Gestalt Laws
  • Law of Prananz:
    • A stimulus will be organized into as good a figure as possible (symmetrical, simple, and regular)
    • The figure appears to the eye as a square overlapping triangle, not a combination of several complicated shapes.
summary of gestalt
Summary of Gestalt
  • Modern conclusion is that some level of “natural organization” of patterns is tied to the perceptual history of the subject
    • a function of the perceiver rather than the stimulus
canonic processing
Canonic Processing
  • Extension of Gestalt
  • the first images of an object that comes to mind when thinking of that particular form.
  • perspectives fluctuate with culture and time.
    • person from Los Angeles asked to think of a house might recall a one story, 3 bedroom stucco structure; a person living in a poverty-stricken Third world country might imagine a small hut made of tree branches held together with mud
canonic processing19
Canonic Processing
  • Through common experience with objects, we develop memories of the most representational view (and gives most amount of info)
  • Studying this helps to understand form perception, prototype formation, economy of thinking, “visual shorthand”
top down vs bottom up processing
Top-down vs. bottom up processing
  • Bottom-up processing consists of mental operations influenced by the physical properties of the stimulus.
  • Top-down processing consists of mental operations influenced by the results of processes already completed.
  • Reading the following requires both kinds of processing:
reminder
Reminder...
  • Problem - perception requires that information in the environment must be matched to internal information about the environment; however, the environmental information is subject to substantial variation. How do we recognize things in the face of this variability?
template matching
Template Matching
  • Template - internal constrict that, when matched by sensory stimuli, leads to the recognition of an object
  • Assumption: a retinal image of an object is faithfully transmitted to the brain and that an attempt is made to compare it directly to various stored patterns
  • details are vague
template matching25
Template Matching
  • compare stimulus to large number of literal copies (templates) that are stored in memory to find match against all templates
    • works well with computers (check-sorting machines)
    • does not work well with humans -- too inflexible
      • does not account for similarities among objects
      • what is the effect of context?
prototype model
Prototype Model
  • more flexible version of template model - the match does not have to be exact
    • match against “prototypical A”
  • advantages
    • manageable number of representations in memory can account for how people classify similar objects into a common category
  • disadvantages
    • lack of explicit information about how stimuli are compared to prototypes
feature analysis model
Feature Analysis Model
  • Assumption: stimuli consist of combinations of elementary features; (e.g for the alphabet, features may include horizontal lines, vertical lines, diagonals, and curves)
    • make discriminations based on a small number of characteristics of stimuli
    • distinctive feature components stored in memory [a mini-template model??]
feature analysis model28
Feature Analysis Model
  • What is a feature?
    • A feature is a distinctive attribute or characteristic of a stimulus.

e.g., 'T' has 2 features: ' - ' & '|'

(E. Gibson, 1969)

feature analysis model31
Feature Analysis Model
  • Psychological Evidence: Gibson (1969)
  • decide whether or not two letters are different

• takes longer to respond to P & R versus G & M

  • P & R share many critical features
feature analysis model32
Feature Analysis Model
  • Neurological Evidence: Hubel & Wiesel (1962)
    • microelectrodes in cats’ brains (visual cortex)
    • some neurons respond only to horizontal lines, others to diagonals...
    • similar evidence in monkeys (Maunsell & Newsome, 1987)
  • certain feature detectors are “wired” and help us identify features and simple patterns
neisser example
Neisser example
  • - Look for the “X”

O O P O P O P O P

P O P P O P P P O

O O P P O X P O P

O O P O P O P O P

P O P P O P P P O

neisser example34
Neisser example
  • Look for the “X”

N N Z N Z N Z N Z

Z N Z Z N Z Z N N

N N N Z N X N Z N

N N Z N Z N Z N Z

Z N Z Z N Z Z N N

feature analysis
Feature Analysis
  • advantages
    • economical to store features in memory
    • experimental evidence consistent with features
  • disadvantages
    • lack of applicability to a wide range of stimuli
    • analysis of stimuli does not always begin with features
    • treats all features as equivalent
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