On Symmetry, Illusory Contours and Visual Perception - PowerPoint PPT Presentation

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On Symmetry, Illusory Contours and Visual Perception

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... Illusory Contours and Visual Perception. Introduction to ... Visual Illusions. Neglect ' ... Do Neglect patients perceive the illusions? A new diagnosis tool ... – PowerPoint PPT presentation

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Title: On Symmetry, Illusory Contours and Visual Perception


1
On Symmetry, Illusory Contours and Visual
Perception
  • Introduction to Computational and Biological
    Vision 2007

2
Symmetryinvariance under a specified group of
transformations
  • Widely present in nature
  • Most animals have bilateral symmetry
  • Its detection seems to be fundamental to survival
  • Its detection is pre-attentive

3
Illusory Contours
Modal shape completion occurs when the borders
are perceived, despite of being inexistent in the
visual stimulus, as being above the stimulus by a
brightness enhancement of the completed shape.
4
Visual Illusions
5
Neglect
Neglect is a neurological condition under which
patients with unilateral (often right) parietal
lesion fail to consciously perceive stimulus
shown in the contra-lateral (left) visual field.
- Driver Mattingley, 1998.
6
Symptoms
  • fail to detect objects on the contralateral side
    (opposite) to their injury
  • fail to notice or hear people standing in their
    left side
  • eat just what is in the right side of his plate
  • shave just the right side of his face
  • hold his head slightly inclined to the right
  • claim that his left limbs are somebody elses
  • read just the second part of a word

7
Diagnosis
8
Experiment OneWhat do you see?
9
Experiment TwoLine Bisection
  • Vuilleumier and Landis, 1997
  • Driver, Baylis and Rafal 1992

10
Experiment ThreeThe Symmetry-Completion effect
Neglect patients tend to copy/draw just half of a
symmetrical object, although they dont report
seeing just one half of it. Is it an indication
that this symmetrical completion takes place?
11
Conclusions/Future Research
  • Do Neglect patients perceive the illusions?
  • A new diagnosis tool
  • Is Contour Completion really pre-attentive?
  • Better understanding of perceptive processes
  • Symmetry detection x contour completion
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