Objects by zhangsshaohui123

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									 Cognitive Neuroscience



Recognizing Objects: The
 Computational Problems
             The problem:
• The visual system needs to be general
  enough so as to allow us to recognize
  objects under variable conditions—achieve
  object constancy
• Yet specific enough to allow us to detect
  differences between objects, and exemplars
  of objects
             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
  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
1-Independence of color and shape:
      Illusory conjunctions
5 T S N 8
1-Independence of color and form:
 Feature and conjunction search
     (Treisman and colleagues)
                Features?
• Visual search methods can be used to reveal
  the features that are independently
  processed by the visual system
      2-Knowledge-driven perception

• Data (stimulus) driven (bottom–up)
                +
• Knowledge driven (top-down)
2-Knowledge-driven perception: Illusory
              contours
2-Knowledge driven perception: Grouping
         (Gestalt) principles
2-Knowledge driven perception:
Grouping (Gestalt) principles
 Features + principles   grouping of features

Illusory conjunctions
   within vs. across
   groups:
 Features + principles   grouping of features

Illusory conjunctions
   within vs. across
   groups:




      22%                    15%
        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.
Predictions for breakdown?
                 Agnosia
          JGE (Leek & Rapp, 199*)
• 74 year-old male
• Master’s degree, high-school business
  teacher
• Left CVA affecting left occipito-parietal
  region and a small right occipital infarct

• Auditory comprehension and spoken
  production excellent
rack of trays



mule



bowl




cabinet
                   Picture Naming

Accuracy:    75% (349/464) correct

Errors:
Visual+semantic:    45%   (sheep -> cow)
Semantic            26%   (shoe -> sweater)
Visual              17%   (baseball bat -> cigarette)
Circumlocutions     10%   (helicopter -> flies about, flying
                          ambulance)
Don’t Know          1%
Where is the breakdown?




                          Naming?
                     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
Where is the breakdown?




                          Knowledge of
                          The visual attributes of objects?
                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
                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
                 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%
                Knowledge of visual attributes?


Color, size and function matching

                   auditory         visual

Function:          100%             76%

Size:              100%             65%

Color:             100%             57%
Where is the breakdown?   Can he see forms, edges,
                          surfaces?
                               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
Where is the breakdown?




                          ?
                  Visual object recognition?


Object Decision




      Results: 80% (normal Ss: 94%)
Matching across orientation?



                   Results: 71% correct
                   (control Ss: 97%)
Where is the breakdown?
Working hypothesis: in constructing
Or manipulating 3-D representations
of object shapes

								
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