Cognitive Processes PSY 334

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Cognitive ProcessesPSY 334

• Chapter 2 Perception

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Marr

• Depth cues (texture gradient, stereopsis) where
  are edges in space?
• How are visual cues combined to form an image
  with depth?
• 2-1/2 D sketch identifies where visual features
  are in relation to observer.
• 3-D model refers to the representation of the
  objects in a scene.

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Pattern Recognition

• Classification and recognition occurs through
  processes of pattern recognition.
• Bottom-up processes feature detection
• Top-down processes -- conceptually driven
  processing

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Object Recognition

• Two stages
• Early phase shapes and objects are extracted
  from background.
• Later phase shapes and objects are categorized,
  recognized, named.

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Disruptions of Perception

• Visual agnosias impairment of ability to
  recognize objects.
• Demonstrate that shape extraction and shape
  recognition are separate processes.
• Apperceptive agnosia (lateral) problems with
  early processing (shape extraction).
• Associative agnosia (bilateral) problems with
  later processing (recognition).
• Prosopagnosia visual agnosia for faces.

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Gestalt Priniciples

• Wertheimer, Koffka, Kohler.
• Form perception segregation of a display into
  objects and background.
• Principles of perceptual organization allow us to
  see wholes (gestalts) formed of parts.
• We do not recognize objects by identifying
  individual features.

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Five Principles

• Proximity
• Similarity
• Good continuation
• Closure
• Common fate
• Elements that move together group together.
• These will be on the midterm.

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Examples

• Gestalt principles of organization
• Reversible figures
• Stuart Anstis demos
• http//psy.ucsd.edu/sanstis/SACamov.html
• http//psy.ucsd.edu/sanstis/motion.html

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Law of Pragnanz

• Of all the possible interpretations, we will
  select the one that yields the simplest or most
  stable form.
• Simple, symmetrical forms are seen more easily.
• In compound letters, the larger figure dominates
  the smaller ones.

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Visual Illusions

• Depend on experience.
• Influenced by culture.
• Illustrate normal perceptual processes.
• These are not errors but rather failures of
  perception in unusual situations.

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Visual Pattern Recognition

• Bottom-up approaches
• Template-matching
• Feature analysis
• Recognition by components

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Template-Matching

• A retinal image of an object is compared directly
  to stored patterns (templates).
• The object is recognized as the template that
  gives the best match.
• Used by computers to recognize patterns.
• Evidence shows human recognition is more flexible
  than template-matching
• Size, place, orientation, shape, blurred or
  broken (ambiguous or degraded items easily
  recognized by people.

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Feature Analysis

• Stimuli are combinations of elemental features.
• Features are recognized and combined.
• Features are like output of edge detectors.
• Features are simpler, so problems of orientation,
  size, etc., can be solved.
• Relationships among features are specified to
  define the pattern.

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Evidence for Feature Analysis

• Confusions people make more errors when letters
  presented at brief intervals contain similar
  features
• G misclassified as C (21), as O (6), as B (1),
  as 9 (1)
• When a retinal image is held constant, the parts
  of the object disappear
• Whole features disappear.
• The remaining parts form new patterns.

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Object Recognition

• Biedermans recognition-by-components
• Parts of the larger object are recognized as
  subobjects.
• Subobjects are categorized into types of geons
  geometric ions.
• The larger object is recognized as a pattern
  formed by combining geons.
• Only edges are needed to recognize geons.

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Tests of Biedermans Theory

• Object recognition should be mediated by
  recognition of object components.
• Two types of degraded figures presented for brief
  intervals
• Components (geons) missing
• Line segments missing
• At fast intervals (65-100 ms) subjects could not
  recognize components when segments were missing.

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Speech Recognition

• The physical speech signal is not broken up into
  parts that correspond to recognizable units of
  speech.
• Undiminished sound energy at word boundaries
  gaps are illusory.
• Cessation of speech energy in the middle of
  words.
• Word boundaries cannot be heard in an unfamiliar
  language.

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Phoneme Perception

• No one-to-one letter-to-sound correspondence.
• Speech is continuous phonemes are not discrete
  (separate) but run together.
• Speakers vary in how they produce the same
  phoneme.
• Coarticulation phonemes overlap.
• The sound produced depends on the sound
  immediately preceding it.

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Feature Analysis of Speech

• Features of phonemes appear to be
• Consonantal feature (consonant vs vowel).
• Voicing do vocal cords vibrate or not.
• Place of articulation where the vocal track is
  constricted (where is tongue placed).
• The phoneme heard by listeners changes as you
  vary these features.
• Sounds with similar features are confused.

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Categorical Perception

• For speech, perception does not change
  continuously but abruptly at a category boundary.
• Categorical perception failure to perceive
  gradations among stimuli within a category.
• Pairs of bs or ps sound alike despite
  differing in voice-onset times.

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Two Views of Categorical Perception

• Weak view stimuli are grouped into recognizable
  categories.
• Strong view we cannot discriminate among items
  within such a category.
• Massaro people can discriminate within category
  but have a bias to same items are the same
  despite differences.
• Category boundaries can be shifted by fatiguing
  the feature detectors.