vision
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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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”
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Vision: Outline
• Light
• Eye
• Visual Path
• Visual Cortex
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Perceptual Dimensions of Light
Wave amplitude
Purity of the wave
Wave frequency
UV rays
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4
The Eye
• Cornea
• Pupil/Iris
• Lens
• Retina– Cones
– Rods
– Fovea
– Optic disc (blindspot)
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transparent medium air(cornea, aqueous humor, pupil,lens, vitreous humor)
lens lensiris diaphragmretina film a focal point a focal point
Similarity btw eye & camera known
since 1600’s
Eye anatomy: Functions
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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
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Near-Sightedness
nearby things are on focus
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Cataracts
• Reduced illumination, acuity, and color saturation• Deposits in the lens
• Common in older adults
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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
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Concentration ofCones & Rods
in Retina
Visual Acuity
Eye Anatomy: Retina
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Eye Anatomy: Retina
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One Cones --> one ganglion cell high acuity (fovea) Many Rods --> ganglion cells. High sensitivity (periphery)
(e.g, night vision)
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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)
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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
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Tri-chromatic theory – Blue, red, & green “color”
receptors
Peak sensitivities of the three conesCOLOR VISION
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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
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Vision: Outline
• Light
• Eye
• Visual Path & its deficits
• Visual cortex
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Visual Paths
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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”
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Vision: Outline
• Light
• Eye
• Visual Path & its deficits
• Visual cortex• V1: Orientation sensitive
– Ventral Pathway – Dorsal Pathway
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Visual Cortex
V1: primaryvisual cortex
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Primary visual cortex (V1)
• V1 cells respond to lines – of particular orientations – of particular widths.
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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
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• Complex & with multiple connections
• Over-simplified version: dorsal & ventral paths
Cortical Connections of Visual areas
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Ventral & Dorsal Paths
¼ of the brain is involved in visual processing, more than for all other senses
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Ventral & Dorsal Paths
& how
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Ventral & Dorsal Paths
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Ventral Path: Object recognition
Lesion of ventral pathwayAgnosia
fMRI: Object recognition
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Cerebral Achromatopsia: bilateral damage to V4
Color is more important of ‘what’ than for ‘where’ Synesthesia
Ventral Pathway (V4): Color perception
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Ventral Path: Objects vs. Faces
Are faces very difficult objects or special ones (i.e., specific process)
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Neuroimaging of face, bird and car experts
“Face Experts”
FusiformGyrus
FusiformGyrus
CarExperts
BirdExperts
FusiformGyrus
Gauthier et al., 2000
Cars-Objects Birds-Objects
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ControlGroup
AutismGroup
Hypoactivation of fusiform face area Schultz, et al. 2000
Faces
FusiformGyrus
FusiformGyrus
Children with autism as face “novices”
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Area MT: motion perception
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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