Perception

• Perception


  The primary process by which we obtain knowledge about the world we live in, involving taking in of information through the senses and processing it to make sense of what we see, hear, smell, taste and touch
• William James: 'The world of an infant is "Blooming, buzzing and confusion"'
• Perception


  • Selective
  • Constructive
  • Interpretative
• Sensation


  Occurs at the level of sensory receptors
• Perception


  A cognitive activity involving complex mechanisms in the brain and influenced by higher mental processes such as memories, motivations and expectations
• Perceptual systems


  • Visual
  • Auditory
  • Haptic
  • Savor
  • Basic orientational
• Visual perceptual system


  • Localization - Separating and organizing objects into groups
  • Figure-ground organization - Distinguishing the figure from the background
• The Gestalt psychologists proposed principles of organization that govern how people "combine" sensations into meaningful wholes
• Gestalt principles of grouping

  • Proximity - Objects near each other tend to be seen as a unit
  • Similarity - Objects similar to each other tend to be seen as part of the same pattern
  • Good Continuation - Objects arranged in a line or curve tend to be seen as a unit
  • Closure - We tend to perceive incomplete figures as complete
  • Common Fate - Objects moving in the same direction tend to be seen as a unit
• Depth perception


  The ability to know how far an object is from us
• Monocular depth cues


  • Relative size
  • Superimposition
  • Relative height
  • Linear perspective
  • Motion parallax
• Binocular depth cues


  • Parallax
  • Disparity
  • Convergence
• Direct perception


  An alternative to inferring distance based on depth cues, where people look at information on the ground itself, such as texture gradient
• Types of retinal changes in motion perception

  • Whole field image movement
  • Movement of a portion of the image
  • Retinal change when following a moving target
  • Retinal change from head/body movement
  • Movement in the third dimension
• Apparent motion


  When things seem to move due to quick flashes of images, like in movies
• Apparent motion


  • Things seem to move because of quick flashes of images
  • Like in movies, each picture is a bit different from the one before it
  • When shown quickly, it looks like things are moving smoothly
• Stroboscopic motion


  Movement of a big thing makes a small thing nearby seem like it's moving too
• Stroboscopic motion


  • The moon looking like it's moving through clouds, even though it's not really moving
  • Feeling like your train is moving when another train moves
• Induced motion


  The movement of a big thing makes a small thing nearby seem like it's moving too
• Object recognition


  Quickly knowing what something is by its features
• Theoretical approaches to pattern recognition

  • Template theory
  • Prototype theory
  • Feature theory
• Template theory


  • We have templates (miniature copies) of previously learned patterns held in long-term memory
  • Recognizing new stimuli as belonging to a loose defined category is difficult
• Prototype theory


  • Members of a particular category share certain key visual attributes
  • Prototypical features are stored in memory
• Feature theory


  • Visual pattern consists of a set of specific features or attributes
  • Features are extracted from the present stimulus and compared with a bank of features stored in memory
  • Underemphasizes the roles of context and expectations
• Marr's computational theory


  • Seeing requires a sequence of representations, each one derived from its predecessor by an appropriate set of processes
  • The task of visual processing is to create a description of the object viewed from the presenting image
• Marr's approach to visual processing

  1. Starts with the retinal image

  2. Early stages identify basic features like lines and angles

  3. Later stages match the description of the object to shape descriptions stored in memory
• Recognizing natural objects


  • Rely on intuitive features like distinct parts and attributes
  • Shape is the most crucial aspect
  • Researchers aim to express intuitive features as a smaller set of basic primitives like cylinders, cones, blocks, and wedges
• Bottom-up recognition


  Process driven solely by the visual input and builds upward to an interpretation
• Top-down recognition


  Process driven by stored knowledge and expectations to help resolve ambiguities in the sensory input
• Context effects in recognition

  Top-down processes set up perceptual expectations that influence what is perceived
• Context effects in recognition

  • Recognizing a familiar face in less than 250 milliseconds
  • Being visually alert to vehicles when waiting to cross the street
• Perceptual sets


  Predispositions or readiness to perceive particular features of a stimulus
• Factors that may influence perceptual sets

  • Motivation
  • Expectations
  • Emotion
  • Experience
  • Culture
  • Individual differences
• Perceptual constancies


  • Size constancy
  • Lightness constancy
  • Color constancy
  • Shape constancy
  • Location constancy
• Size constancy


  An object's size remains relatively constant no matter how far it is from us
• Lightness constancy


  An object appears equally light regardless of how much light it reflects
• Color constancy


  An object looks roughly the same color regardless of the light source illuminating it
• Shape constancy


  The perceived shape of an object remains constant even though its retinal image changes

  
• Location constancy


  The positions of fixed objects appear to remain constant despite changing images on the retina
• The constancies make the tasks of localization and recognition easier