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

4. Vision: Outline EYE Anatomy Retina Receptive Field Edge Detection Color vision

5. Eye Anatomy We study this in the lab

6. transparent mediumair (cornea, aqueous humor, pupil, lens, vitreous humor) lens iris diaphragm retina filma focal point Similarity btw eye & camera known since 1600’s Eye anatomy: Functions

7. 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) Eye Anatomy: Abnormalities

8. Near-Sightedness nearby things are on focus

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

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

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

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

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

15. 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

16. Each strip is uniform, Strips look lighter on the left Edge detection

17. : Center-surround receptive fields & Edge Detection Neither excitatory nor inhibitory parts of RF are stimulated Both excitatory & inhibitory parts of RF are stimulated, canceling each other

18. : Center-surround receptive fields & Edge Detection Inhibitory part of RF is stimulated: reduced firing A A Part of Inhibitory area of RF is not being stimulated: above baseline firing B B

19. Edge detection

20. Hermann Grid + - + Inhibition (-) Excitation (+) + -

21. Tri-chromatic theory –Blue, red, & green “color” receptors –But some colors don’t mix! Peak sensitivities of the three cones Opponent process theory Red vs. Green; Blue vs. Yellow - Negative afterimage - But there is no ‘yellow’ receptor! COLOR VISION (-) BLUE (-) GREEN (+) RED (+) YELLOW

23. 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 No ‘green’ cones

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

25. Visual Paths

26. LGN thalamic organization Magnocellular –M ganglion cells –large receptive fields –motion detection –locating stimulus in space –dorsal cortical stream –parietal lobe Parvocellular –P ganglion cells –small receptive fields –Object identity –Color recognition –ventral cortical stream –temporal lobe Concentric receptive fields (center surround)

27. VISUAL PATHWAY Retinal Field: representation of visual field in the retina (reversed: right/left, up/down) Visual Field: outside world you see

28. Right homonymous most common Can also get upper and lower deficits and scotoma Visual Path: Lesions & Deficits Quadrantanopia Homonymous Hemianopia Bitemporal

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

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

31. Visual Cortex V1: primary visual cortex

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

33. Primary visual cortex (V1) Orientation selective cells are organized in a topographic map in V1

34. How does orientation selectivity in V1 emerges? LGN cells with concentric receptive field provide input to simple cells in V1

35. 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

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

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

38. Ventral & Dorsal Paths & how

39. Ventral & Dorsal Paths

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

41. R.V. has bilateral parietal lobe damage ventral lesion (patient DF): - Agnosia - Normal grip dorsal lesion (patient RV): - Normal recognition - poor grip Independence of Dorsal and Ventral paths: Neurpsychological evidence

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

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

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

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

46. Area MT: motion perception

48. 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 (next week)

49. Spare slides Spatial frequency

51. Neurons respond to specific spatial frequencies ‘Blurry’ As nearsighted

53. 3-D vision Retinal disparity Stereograms

54. http://www.ritsumei.ac.jp/%7Eakitaoka/index-e.html