Chapter 4: Perception

Modified: 2006-02-17

I. INTRODUCTION

• Perception
  • The process of recognizing, organizing and interpreting information
• Percept
  • Sensory Adaptation
    • Occurs when sensory receptors change their sensitivity to the stimulus
    • Constant stimulation leads to lower sensitivity
    • Our senses respond to change

 II. FROM SENSATION TO REPRESENTATION

• Some basic concepts
  • Distal object
  • Proximal
• Perceptual Constancies--Object remains the same even though our sensation of the object changes
  • Size constancy
  • Shape constancy
• Depth Perception--The ability to see the world in 3 dimensions and detect distance
  • Depth
    • Vision only has a 2-dimensional view
    • We must interpret the information given to perceive depth
    • We take flat images and create a three dimensional view
    • Optical illusions demonstrate that this interpretation does not always have to be correct
  • Monocular depth cues
    • Texture Gradients
    • Grain of item
    • Relative Size
    • Bigger is closer
    • Interposition
    • Closer are in front of other objects
    • Linear Perspective
    • Parallel lines converge in distance
    • Aerial Perspective
    • Images seem blurry, the farther away (clarity)
    • Motion Parallax
    • Objects get smaller at decreasing speed in distance
  • Binocular Depth cues
    • Binocular Disparity
      • Each eye views a slightly different angle of an object; Brain uses this to create a 3-d image
    • Binocular Convergence
      • Eyes turn inward as object moves towards you, brain uses this information to judge distance
• Approaches to Object and Form Perception
  • Viewer-centered representation
    • Object is stored in the perspective seen
    • Store multiple views of object as seen under various conditions
    • Viewpoint dependent process
  • Object-centered representation
    • Object is stored in a way that best represents the object
    • Viewpoint invariant process
  • Evidence supports both
    • How to reconcile?
    • Maybe both contribute to object recognition
    • Two ends of a continuum that contribute to object recognition
    • Burgund & Tarr researched this issue
  • Gestalt Approach--"The whole is more than a sum of its parts."
    • Law of Pragnanz
      • Individuals organize their experience in as simple, concise, symmetrical and complete manner as possible
    • Gestalt's Principles of Visual Perception
      • Figure-Ground
        • Organize perceptions by distinguishing between a figure and a background
      • Proximity
        • Elements tend to be grouped together according to their nearness
      • Similarity
        • Items similar in some respect tend to be grouped together
      • Continuity
        • Based on smooth continuity which is preferred to abrupt changes of direction
      • Closure
        • Items are grouped together if they tend to complete a figure
      • Symmetry
        • Prefer to perceive objects as mirror images

 III. THEORETICAL APPROACHES TO PERCEPTION

• Bottom-up theories: Direct Perception
  • Perception comes from the stimuli in the environment
  • Parts are identified, put together, and then recognition occurs
  • People actively construct perceptions using information based on expectations
• Bottom-up Approaches
  • Gibson's Direct Perception (Ecological model)
    • All the information needed to form a perception is available in the environment
    • Perception is immediate and spontaneous
    • No top down processing is necessary
    • Perception and action cannot be separated
    • Perception guides action and action generates more new perceptual information
  • Template Theories
    • Basics of template theory
      • Multiple templates are held in memory
      • To recognize the incoming stimuli, you compare to templates in memory until a match is found
    • Weakness of theory
      • Problem of imperfect matches
      • Cannot account for the flexibility of pattern recognition system
  • Prototype Theories
    • Modification of template matching (flexible templates)
    • Takes various instances of an object and abstracts out the common characteristics
    • No match is perfect; a criterion for matching is needed
    • Prototype Evidence
      • Franks & Bransford (1971)
        • Presented objects based on prototypes
        • Prototype not shown
        • Yet participants are confident they had seen prototype
        • Suggests existence of prototypes
      • Solso & McCarthy (1981)
        • Participants were shown a series of faces
        • Later, a recognition test was given with some old faces, a prototype face, and some new faces that differed in degree from prototype
        • The red arrow notes that participants were more confident they had seen the prototype than actual items they had seen
    • Research on Prototypes
      • Researchers have found that prototypical faces are found to be more attractive to participants
        • Halberstadt & Rhodes (2000)
          • Examined the impact of prototypes of dogs, wristwatches, and birds on attractiveness of the stimuli
          • Results indicate a strong relationship between averageness and attractiveness of the dogs, birds, and wristwatches
  • Feature Theories
    • Recognize objects on the basis of a small number of characteristics (features)
    • Detect specific elements and assemble them into more complex forms
    • Brain cells that respond to specific features, such as lines and angles are referred to as "feature detectors"
    • Feature Evidence
      • Hubel & Wiesel (1979) using single cell technique
      • Simple cells detect bars or edges of particular orientation in particular location
      • Complex cells detect bars or edges of particular orientation, exact location abstracted
      • Hypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular direction
  • Structural-Description Theory
    • Recognition-by-components (RBC) Theory
      • Biederman (1987)
      • Describes how 3D images are identified
      • Breaks objects down into geons
      • Objects are identified by geons and relationship between them
    • Evidence for Geons
      • Beiderman (1987) demonstrated the importance of the use of geons to recognize objects
    • Biederman & Cooper (1991)
      • Used visual priming to demonstrate the existence of geons in a picture naming task
      • Subjects were shown a series of fragmented pictures and were asked to identify the objects
• Top-Down Approaches: Constructive Perception
  • Perception is not automatic from raw stimuli
  • Processing is needed to build perception
  • Top down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another
  • Top-down Processing Evidence
    • Context effects
      • Palmer (1975) Context Effect
    • Configural-superiority effect
      • Easier to recognize objects in context than in isolation
• Synthesizing the Two Approaches
  • 1. A Computational Theory of Perception
    • Marr's Computational Theory
      • Features
        • Edges
        • Contours
        • Similarities
      • Three steps
        • 2-D primal sketch
        • 2 1/2-D sketch
        • 3-D sketch

 IV. DEFICITS IN PERCEPTION

• A. Agnosia
  • Inability to recognize and identify objects or persons despite having knowledge of the characteristics of the objects or persons
  • Shows the specialization of our perceptual systems
  • 1. Simultagnosia
    • Normal visual fields, yet act blind
    • Perceives only one stimulus at a time&emdash;single word or object
  • 2. Spatial Agnosia
    • Cannot navigate in real world easily
    • Gets lost
    • Fails to recognize landmarks
  • 3. Prosopagnosia
    • Inability to recognize faces, including one's own
    • Cannot recognize person from face
    • Knows a face is a face  
    • Can recognize individuals from voice
    • Can recognize objects
    • Can discriminate whether two faces are same or different
  • 4. Auditory Agnosia
    • Inability to recognize specific sounds