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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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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
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.
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.
Classification of Illusions • Luminance and contrast • Motion • Geometric or angle illusions • 3D interpretation: size constancy and impossible figures • Cognitive gestalt effects • Color
Geometric/angle illusions • Poggendorf • Hering
3-D Interpretation • Muller-Lyer • Ponzo • Ames Room • Moon Illusion
Theories of Illusions • Size constancy • S=k(RxD) • Applying size constancy • Gregory’s theory • Ponzo • Muller-Lyer • Moon Illusion
Demonstrations • http://www.michaelbach.de/ot/ • Muller Lyer • Impossible figures
Theories of Illusions • Conflicting cue theory • Illusion depend on the surrounding information • Importance of frames of reference
Müller-Lyer stimuli Howe C. Q., Purves D. PNAS 2005;102:1234-1239 ©2005 by National Academy of Sciences
Moon Illusion • Elevated versus horizontal moon • Apparent distance theory • Sky surrounding the moon
Ambiguous & Impossible Figures • Points of view • Conflicting perception of object • http://sites.sinauer.com/wolfe3e/home/startF.htm
Ambiguous & Impossible Figures • Create your own impossible figure
Ames Room • Do in lab
Final Exam • 50 Multiple choice questions • Cumulative
Final Exam • Review Exams 1 and 2 • Problem Sets 1 and 2
New Material • Prism Adaptation • Determine where first pointing should be • Determine the amount of after affect • How to use prism for treating visual neglect
Visual Attention • Types of attention • Characteristics of visual neglect
Visual Illusions • Types of illusions • Theories of illusions
Final Exam • Lab material