object and scene perception

• The stimulus on the retina is ambiguous


  Where a 1D image can be ambiguous, and 2D images can be ambiguous in that multiple stimuli can give rise to the same 2D retinal image
• Objects can be partially occluded or blurred

  An object can be partially occluded or blurred, making it difficult to recognise the main object
• Objects look different in different poses and from different view-points 


  Machines find it hard to recognise objects when they appear in unexpected angles
• Structuralism


  Sensations combine to from perceptions - conscious awareness is the sum elementary sensations, and contains nothing that was already present there
• Sensations


  elementary processes occur in response to stimulation
• Perceptions


  Conscious awareness of objects and scenes
• Gestaltism


  Claims that conscious awareness is more than the sum of the elementary sensations
• Apparent motion


  Conscious precept of motion was developed and not there in elementary sensations - physical stimulus doesn't actually move
• Illusory contours

  • Seen in places where there are no physical contours
• Grouping


  Process by which parts of an image are perceptually bound together to form a whole
• Segregation


  Process by which parts of a scene are perceptually separated to form separate wholes
• Gestalt principles

  5 principles in where the more of them apply, the more likely that components of an image will be grouped together to form a perceptual whole
• Good continuation


  Aligned or nearly aligned contours are grouped together to form a single object
• Pragnanz


  Groupings occur to make the resultant figure as simple as possible
• Similarity


  The more similar objects are, the more likely they will be grouped together
• Proximity


  The closer objects are, the more likely they are to be grouped together
• Common fate


  Things that are moving the same way are grouped together
• Common region


  Elements are within the same region of space tend to be grouped together
• Uniform connectedness


  Connected regions with the same visual characteristics tend to be grouped together
• Segregation


  Can't just group contents of an object together in a whole, because then it can't be separated from the background
• Figural properties

  • In the front of the rets of the image
  • At the bottom of the image
  • Convex
  • Recognisable
• Convexity

  • Peterson & Salvagia (2008): if you see a single border, you may see a convex region as a figure
  • But if multiple convex regions in the same colour are seen, these may be seen more than the figure
• Gist perception


  Scenes are flashed rapidly in front of the observer, making it unclear as to what they are viewing, but they can still get an overall jist of it
• Fei-Fei et al

  • Investigated minimum scene exposure needed to perceive a scene's jist
  • Found that the longer a stimulus was displayed for, the more detailed and accurate the observer's description would be