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Visual Illusions

Visual Illusions. Illusions of Form Perception. Perceptual not conceptual Can diminish with repeated exposures Not retinal Not caused by eye movements. Why Study Illusions. Patient may ask Migraine Head trauma Charles Bonnet Syndrome Helpful for understanding perception.

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Visual Illusions

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  1. Visual Illusions

  2. Illusions of Form Perception • Perceptual not conceptual • Can diminish with repeated exposures • Not retinal • Not caused by eye movements

  3. Why Study Illusions • Patient may ask • Migraine • Head trauma • Charles Bonnet Syndrome • Helpful for understanding perception

  4. Charles Bonnet Syndrome • Yacoub and Ferruci (Optometry 2011) • Visual hallucinations occurring in individuals with sensory vision but intact cognitive ability. • No evidence of psychiatric or neurological abnormalities that account of the illusion.

  5. Charles Bonnet Syndrome • Tends to occur in elderly patients with vision loss. • Patient aware that hallucination is not real • Simple type: light or shapes • Complex type: Faces, animals, plants or trees, etc.

  6. Classification of Illusions • Luminance and contrast • Motion • Geometric or angle illusions • 3D interpretation: size constancy and impossible figures • Cognitive gestalt effects • Color

  7. Geometric/angle illusions • Poggendorf • Hering

  8. Poggendorf

  9. Hering

  10. 3-D Interpretation • Muller-Lyer • Ponzo • Ames Room • Moon Illusion

  11. Theories of Illusions • Size constancy • S=k(RxD) • Applying size constancy • Gregory’s theory • Ponzo • Muller-Lyer • Moon Illusion

  12. Demonstrations • http://www.michaelbach.de/ot/ • Muller Lyer • Impossible figures

  13. Theories of Illusions • Conflicting cue theory • Illusion depend on the surrounding information • Importance of frames of reference

  14. Müller-Lyer stimuli Howe C. Q., Purves D. PNAS 2005;102:1234-1239 ©2005 by National Academy of Sciences

  15. Moon Illusion • Elevated versus horizontal moon • Apparent distance theory • Sky surrounding the moon

  16. Ambiguous & Impossible Figures • Points of view • Conflicting perception of object • http://sites.sinauer.com/wolfe3e/home/startF.htm

  17. Ambiguous & Impossible Figures • Create your own impossible figure

  18. Ames Room • Do in lab

  19. Final Exam • 50 Multiple choice questions • Cumulative

  20. Final Exam • Review Exams 1 and 2 • Problem Sets 1 and 2

  21. New Material • Prism Adaptation • Determine where first pointing should be • Determine the amount of after affect • How to use prism for treating visual neglect

  22. Visual Attention • Types of attention • Characteristics of visual neglect

  23. Visual Illusions • Types of illusions • Theories of illusions

  24. Final Exam • Lab material

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