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Vision

Vision. “El ojo que ves no es ojo porque tu lo veas, es ojo porque te ve ” Antonio Machado “The eye you see is not an eye due to you seeing it, It’s an eye because it sees you”. Vision: Outline. Light Eye Visual Path Visual Cortex. UV rays. Wave frequency. Wave

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Vision

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  1. Vision “El ojo que ves no es ojo porque tu lo veas, es ojo porque te ve” Antonio Machado “The eye you see is not an eye due to you seeing it, It’s an eye because it sees you”

  2. Vision: Outline • Light • Eye • Visual Path • Visual Cortex

  3. UV rays Wave frequency Wave amplitude Purity of the wave Perceptual Dimensions of Light

  4. The Eye Cornea Pupil/Iris Lens Retina Cones Rods Fovea Optic disc (blindspot) 4

  5. Similarity btw eye & camera known since 1600’s Eye anatomy: Functions transparent medium air (cornea, aqueous humor, pupil, lens, vitreous humor) lens lens iris diaphragm retina film a focal point a focal point

  6. Eye Anatomy: Abnormalities Near-sightedness (Myopia ): image falls too short of retina (eyeball too long) newborns Far-sightedness: focal point of light falls beyond retina (Eyeball is too short) Lasik Changes the shape of the cornea (Laser-Assisted In Situ Keratomileusis)

  7. Near-Sightedness nearby things are on focus

  8. Cataracts • Reduced illumination, acuity, and color saturation • Deposits in the lens • Common in older adults

  9. Eye Anatomy: Retina Red eye in photos due to dilated pupils Retina of diabetic patient • fovea: center of the retina, high concentration of cones • optic disk (blindspot) & direct view of arteries (clinical importance) • photorreceptors: cones (color vision) and rods

  10. Concentration of Cones & Rods in Retina Visual Acuity Eye Anatomy: Retina

  11. Eye Anatomy: Retina

  12. One Cones --> one ganglion cell high acuity (fovea) Many Rods --> ganglion cells. High sensitivity (periphery) (e.g, night vision)

  13. Eye Anatomy: Optic disc (blindspot) Lateral visual field Medial Retina The eye is a device 'designed' to see, but the ‘blindspot’ reveals it is not perfect

  14. Receptive field (RF) • is that portion of the visual field (outside world) in which the presentation of visual stimuli will produce an alteration in the firing rate of a particular neuron

  15. Peak sensitivities of the three cones Tri-chromatic theory • Blue, red, & green “color” receptors COLOR VISION

  16. No ‘green’ cones Test for Deuteranopia: Name number: (‘5’ or ‘2’) If you see a 2: Red/Green Color blindness (male) Most people who are color blind can see colors

  17. Vision: Outline • Light • Eye • Visual Path & its deficits • Visual cortex

  18. Visual Paths

  19. Hemianopia – objects are bisected with ½ obscured experiencing the obscured part as “blank” or “void” Scotoma: A small blindspot in the visual field caused by a small lesion, usually in the occipital lobe

  20. Vision: Outline • Light • Eye • Visual Path & its deficits • Visual cortex • V1: Orientation sensitive • Ventral Pathway • Dorsal Pathway

  21. Visual Cortex V1: primary visual cortex

  22. V1 cells respond to lines of particular orientations of particular widths. Primary visual cortex (V1)

  23. Vision: Outline • Light • Eye • Visual Path & its deficits • Visual cortex • Orientation sensitive • Ventral Pathway • Area MT (motion), Object Recognition, Area V4 (color) • synesthesia • Dorsal Pathway • Spatial Attention • Hemispatial Neglect

  24. Cortical Connections of Visual areas • Complex & with multiple connections • Over-simplified version: dorsal & ventral paths

  25. Ventral & Dorsal Paths ¼ of the brain is involved in visual processing, more than for all other senses

  26. & how Ventral & Dorsal Paths

  27. Ventral & Dorsal Paths

  28. Ventral Path: Object recognition Lesion of ventral pathway Agnosia fMRI: Object recognition

  29. Ventral Pathway (V4): Color perception Cerebral Achromatopsia: bilateral damage to V4 Color is more important of ‘what’ than for ‘where’ Synesthesia

  30. Ventral Path: Objects vs. Faces Are faces very difficult objects or special ones (i.e., specific process)

  31. Cars-Objects Birds-Objects Car Experts Fusiform Gyrus Bird Experts Gauthier et al., 2000 Fusiform Gyrus Neuroimaging of face, bird and car experts Fusiform Gyrus “Face Experts”

  32. Fusiform Gyrus Fusiform Gyrus Children with autism as face “novices” Faces Control Group Autism Group Hypoactivation of fusiform face area Schultz, et al. 2000

  33. Area MT: motion perception

  34. In sum, different parts of the visual cortex are specialized in the processing of specific features • For example, • movement, • color. • Objects • Faces • Location Binding problem: If the brain processes features separately, how does it bind those features into a single conscious representation: Answer: Attention

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