Cognitive psych, Perception

• Perception


  The acquisition and processing of sensory information in order to see, hear or feel objects in the world
• Sensation


  Physiological process where sensory organs absorb energy from physical stimuli in the environment and convert them into neural impulses
• Perception


  Psychological process where sensory information is organised, interpreted and consciously experienced - translated into something meaningful
• We don't perceive the world exactly as our eyes see it
• Our brain tries to make sense of what we see
• We add our own interpretations to what we perceive
• Complex novel scenes can be interpreted in as little as 100ms
• Perception


  • Rapid process that seems automatic
  • Almost always accurate yet computationally complex
  • Numerous processes transform and interpret sensory information
• Distal Object


  The stimulus in the environment (the thing!)
• Informational Medium


  Sound wave, light reflection, tactile info
• Proximal Stimulation


  When sound waves or light reflection comes into contact with sensory receptors
• Perceptual Object


  The thing that is perceived
• Perception involves going beyond the patterns of light and dark created on our retina
• Mental percept


  Internal representation of the stimulus
• Percept serves as the basis for subsequent identification processes
• Visual illusions


  • We might not meaningfully grasp what we sense
  • Our minds take available sensory information and manipulate that information to create mental representations of objects, properties of objects and spatial relationships
  • Sometimes we perceive something that's not there
  • Sometimes we don't perceive something that is there
  • Sometimes we perceive something that's not there
  • Or we perceive movement or contrast in unusual ways
• Visual illusions


  • Rotating Snakes Illusion
  • Café Wall Illusion
  • How this floor was made
• The precise cause of visual illusions is not well understood
• Inverse projection problem


  A particular image on the retina can be created by many different objects
• People easily understand that part of an object that is covered continues to exist - they use knowledge to perceive
• Viewpoint invariance


  Objects look different from different viewpoints
• Illusions, viewpoint invariance & stimulus ambiguity help us to understand the complexity of perception
• Artists, animators and architects understand the fundamental principles of perception
• Visual system


  • Iris controls light entering eye
  • Image brought into focus on retina by changing shape of lens (accommodation)
  • Radiant energy (light) transmitted to a neural form (transduction)
• Photoreceptors


  • Cones - sensitive to colour, located in the fovea, dominate vision in well-lit environments
  • Rods - sensitive to light and dark, located in periphery, specialised for vision in dim light
• The blind spot has no photoreceptors
• Visual pathways


  • "What" pathway - Ventral Stream
  • "Where" pathway - Dorsal Stream
• Gestalt Principles


  Fundamental principles/laws of perceptual organization that describe how we make sense of what we see
• Gestalt Principles of Perceptual Organisation


  • Law of Prägnanz
  • Proximity
  • Similarity
  • Continuity
  • Figure-ground
  • Closure
  • Symmetry
• Law of Prägnanz


  We tend to perceive visual array in a way that most simply organizes the elements into a stable and coherent form
• Law of Proximity


  Objects near each other will be perceived as a unit
• Law of Similarity


  Objects similar to each other will be perceived as a unit
• Law of Continuity


  Perceive smoothly flowing or continuous forms, not disrupted or discontinuous forms
• Law of Closure


  We tend to perceptually close up/complete objects that are not complete - by creating illusory contours
• Figure-ground


  Some elements - figures - seem prominent, and others recede into the background (ground)
• Symmetry


  Symmetrical areas tend to be seen as figures against asymmetrical backgrounds
• Our visual perception is determined by specific organising principles
• The principles are described but not fully explained
• The role of experience is considered minor compared to perceptual principles
• Modern psychologists have pointed out that the laws could be created by experience