Cognitive Neuroscience

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Cognitive Neuroscience

• Recognizing Objects The Computational Problems

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The problem

• The visual system needs to be general enough so
  as to allow us to recognize objects under
  variable conditionsachieve object constancy
• Yet specific enough to allow us to detect
  differences between objects, and exemplars of
  objects

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Object constancy

• We can recognize objects across changes in
• Illumination
• Size
• Occlusion
• Viewing position
• These changes create very different signals at
  the retina, the brain must be able to determine
  their constancy despite these differences

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How do we do this? Evidence from cognitive
psychology

• (1) Independence of visual feature dimensions
• (2) Vision is non-veridical not simply
  stimulus-driven but also knowledge- driven

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1-Independence of color and shape Illusory
conjunctions
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• 5 T S N 8

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1-Independence of color and form Feature and
conjunction search (Treisman and colleagues)
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Features?

• Visual search methods can be used to reveal the
  features that are independently processed by the
  visual system

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2-Knowledge-driven perception

• Data (stimulus) driven (bottomup)
• Knowledge driven (top-down)

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2-Knowledge-driven perception Illusory contours
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2-Knowledge driven perception Grouping (Gestalt)
principles
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2-Knowledge driven perception Grouping
(Gestalt) principles
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Features principles grouping of features

• Illusory conjunctions within vs. across groups

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Features principles grouping of features

• Illusory conjunctions within vs. across groups

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Structural descriptions

• How/what is information stored that will support
  general and specific object recognition across a
  wide range of viewing conditions?
• Templates?
• Structural descriptions?
• Extremely difficult problem, receiving
  considerable research attention.

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Predictions for breakdown?
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AgnosiaJGE (Leek Rapp, 199)

• 74 year-old male
• Masters degree, high-school business teacher
• Left CVA affecting left occipito-parietal region
  and a small right occipital infarct
• Auditory comprehension and spoken production
  excellent

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rack of trays mule bowl cabinet
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Picture Naming

• Accuracy 75 (349/464) correct
• Errors
• Visualsemantic 45 (sheep -gt cow)
• Semantic 26 (shoe -gt sweater)
• Visual 17 (baseball bat -gt cigarette)
• Circumlocutions 10 (helicopter -gt flies about,
  flying ambulance)
• Dont Know 1

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Where is the breakdown?
Naming?
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A naming problem?

• Naming from other modalities of input
• Tactile
• -50 objects to name from tactile presentation
  with eyes closed (including 21 items previously
  named incorrectly with visual input)
• -results 96 correct (100 correct on subset)
• To definition
• -asked to provide a definition of 42 objects
  misnamed from vision
• -results 98 correct

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Where is the breakdown?
Knowledge of The visual attributes of objects?
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Knowledge of visual attributes?

• Drawing from memory
• -36 objects he had previously misnamed
• -results 92 correct (inclusion of object parts
  and spatial configuration)
• Verbal definitions
• -asked to define 42 objects previously misnamed
• -results 100 correct, including info about
  shape and appearance

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Knowledge of visual attributes?

• Verbal definitions
• -asked to define 42 objects previously misnamed
• -results 100 correct, including info about
  shape and appearance
• Shoe made of leather, opens up, may be laced,
  has a heel, maybe a two inch heel and a sole.
  You wear them on your feet
• Chair four legs, various kinds, folding chairs,
  Used for sitting. Have upholstery, has a back
  made of wood, has a back

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Knowledge of visual attributes?

• Color, size and function matching to auditory
  stimuli (e.g.,color is an apple or a
  pineapple the color of a strawberry? size Is
  a harp or a football the size of a toaster?
  function Does a pen or a stapler have a similar
  function a a typewriter?
• auditory
• Function 100
• Size 100
• Color 100

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Knowledge of visual attributes?

• Color, size and function matching
• auditory visual
• Function 100 76
• Size 100 65
• Color 100 57

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Where is the breakdown?
Can he see forms, edges, surfaces?
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Perception?

• Copying
• -asked to copy 30 objects previously misnamed
• -results 100 correct, including info about
  shape and appearance
• Overlapping figures
• -100 (35/35) altho only
• named 27/35 correctly

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Where is the breakdown?
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Visual object recognition?

• Object Decision

Results 80 (normal Ss 94)
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Matching across orientation?
Results 71 correct (control Ss 97)
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Where is the breakdown? Working hypothesis
in constructing Or manipulating 3-D
representations of object shapes