Lecture 2 - Theories of Perception

• Cartesian skepticism


  Descartes' view that the only thing we can be certain about is that we are thinking
• Naive realism


  The view that our senses provide us with direct awareness of objects as they truly exist
• Passive theories of perception

  • We take in sensory information with little interpretation or processing
  • Bottom-up processes: all information comes from the stimulus - perception begins with the automatic analysis of basic sensory information and builds up to more complex perceptions

  
• Active theories of perception


  • Support constructivism
  • Bruner effect of expectation and familiarity on perception
  • Top-down processes
• Descartes' quote: "I think, therefore I am"
• Neisser's beliefs about visual perception under 'naive realism'


  1. Visual experiences mirror the external stimulus

  2. Visual experience starts and ends with the onset/offset of external stimulus

  3. Visual experiences are based on passive copies of the outside world
• Selfridges' 'pandemonium model'


  Theoretical framework of visual letter recognition

  Suggests cognition involves a chaotic interplay of numerous processes

  Higher level 'demons' select more relevant info for processing

  Strictly bottom-up processing
• Passive perception


  Distal stimulus (at a distance) → Proximal stimulus
• Fodor's modularity of the mind hypothesis


  Sensory encoding → 5 senses each have their input modules which analyse different features → then processed for interpretation

  Bottom-up

  
• Quinn, Burke, Rush (1993) - used behavioural markers with 3 month old infants to show they group by colour
• Old look (Gestalt)

  Bottom-up, stimulus driven, passive
• New look (Bruner)


  Top-down, knowledge driven, active (not just soaking in information)
• Bruner & Postman (1949) - knowledge of the world influences our perception


  Incongruent stimulus (red spade) is less accurately recognised than normal cards
• Familiarity influences perception


  Common letters are better reported than uncommon ones

  Harder to describe patterns when they are unfamiliar
• Difference between perceptual and interpretive operations
• Epstein & Rock (1960) - recency or expectancy as an overriding factor in determining perception


  Perception more influenced by recency in this experiment
• Minksy's frame theory of perception


  Role of expectancy

  Active top-down approach, actively generate expectations about what will occur next based on our knowledge of the world

  Both visual and auditory
• Stevens and Halle's analysis by synthesis


  Preliminary analysis into important auditory features

  Generated a hypothesis of what is expected to happen next based on rules of language

  Compare with what actually happens (synthesis)

  Predicting is key
• Bruner's perceptual readiness


  Value and familiarity of the coin influenced the size estimation
• Simplicity & likelihood

  Two squares overlapping is easiest to describe, but also may be more likely based on knowledge of the world
• What are Hochberg's 2 principles?

  Minimum principle: 'perceive whatever object or scene would most simply/economically fit the sensory pattern'

  
  

  Likelihood principle: 'perceive whatever object would be based on past experience and current context '
• Necker cube: where you look influences your interpretation of the stimulus - top down influences on perception
• Crude-fine distinction (Global and local processing)

  Faster reactions when classifying global, bigger letters

  When small letter matches large letter, they are faster at saying the small letter

  Shows global preference

  Global processing applies a filter and provides a more detailed representation of the image
• Summary: 'Old view' - passive, bottom up approach vs Alternative: interaction hypothesis generation - active! (process of comparison, further processing, Analysis by synthesis - prediction is key)
• What are Gestalt's Laws of perceptual organisation

  1. similarity (colour, shape, size)
  2. proximity
  3. symmetry