2 perception

• Perceptual organisation


  Deciding which parts of a scene belong together
• Challenge in perception: deciding which information from the environment should go together or belong to other distinct objects
• Challenges in perception


  • Many objects in visual environment overlap and are overlapped by other objects
  • Recognising the same object across different viewing angles/distances/orientations
  • An object with the same label can come in various different visual properties like colors, size, shape
  • Figure-ground segregation: determining which part of the visual field is the figure (distinct form, main thing of focus) and ground (no distinct form)
• Pattern recognition


  Recognition occurs when there are specific critical features in the pattern
• Template theory


  • Templates are whole precepts stored in long-term memory
  • Matching occurs when the precept in long-term memory (template) matches the stimulus
• Feature theory


  • Pattern recognition occurs when there are specific critical features in the pattern
• Feature theory examples


  • A contains 2 straight lines and a connected cross-bar
  • Looking for Z in different conditions of straight vs rounded letters
• Global processing precedes specific processing


  Recognising general, broad structures before specific features
• Object superiority effect


  Features are easier to process when part of meaningful objects
• Word superiority effect


  Letters are easier to identify in real words than in nonwords
• Object recognition


  Recognising objects via their components (geons) which make up all objects
• Object recognition model


  • Biederman's Recognition-By-Components (RBC) model
  • Geons: 36 basic shapes, components that make up all objects
  • Viewpoint independent recognition
• Object recognition involves both representations ultimately
• Stages of object recognition

  1. Using neuropsychological evidence from disorders of object recognition (visual agnosia)

  2. Agnosia: loss of ability to interpret sensory stimuli leading to inability to recognize visual objects despite information reaching the visual cortex

  3. Differentiating two kinds of agnosia using "draw what you see" tasks

  4. Apperceptive agnosia: deficits in perceptual processing
• Types of agnosia


  • Apperceptive agnosia
  • Associative agnosia
• Edge grouping by collinearity

  Edges of objects derived, form and shape discrimination
• Feature binding into shapes

  Identified object features combined to form shapes, integrate visual info
• View normalisation


  Viewpoint independent representation of object
• Structural description


  Access stored knowledge about structural description of objects
• Semantic system


  Access stored knowledge relevant to object
• Face recognition involves 2 fixations to recognise face, focusing on eyes and nose
• In a European study population, there is more focus on European eyes compared to Asian eyes
• Faces are processed differently than objects, being more holistic and combining information across the whole object
• The part-whole effect states that memory of a part of a face is more accurate when presented in a whole face than in isolation
• Prosopagnosia is face blindness where individuals can recognize objects but not faces
• Object and face recognition are linked to separate systems and brain areas, with the fusiform face area being damaged in prosopagnosia
• The Muller-Lyer illusion explains visual illusions in two systems, dorsal pathway for action and ventral pathway for perception
• Inattentional blindness is the failure to perceive the appearance of an unexpected object
• Change blindness is the failure to detect a visual stimulus after it has moved or changed
• Subliminal perception involves perceiving objects without being consciously aware of them, such as in masked priming
• Blindsight is an oxymoron term referring to the ability to respond to stimuli presented in an unconscious manner