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Physiology of visionIII.

Learning objectives 100-101.

Prof. Gyula Sáry

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Hypercolumn in the primary visual cortex

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From the LGB to layer IV. of V1

Layer IV. C simple receptive fields, Ø ~ 1º

Below and above layer IV. C: orientation sensitivity

Layers I.-III. and V.-VI.: orientation sensitivity

Columnar organisation (RFs on the same spot of the visual field)

orientation columns

dominance columns

CO „blobs”

„hypercolumns”

Organisation of V1

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Rubin (1915) Esher (1898-1972)

6Twilight Pink Floyd: The Division Bells

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Cortical visual areas

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object perceived object

processing

movement, direction

details, form

Visual stimuli are processed by different cortical areas

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colour

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Primary visual cortex

parietal pathway

“Where?”

temporal pathway

“What?” Inferotemporal cortex

Parietal cortex

motor

memory

Extrastriate pathway

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Experimental setup

fixációs pont

stimulus

(Wurtz után)

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Responses of a single IT cells

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The ice-cube model

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face specific cell “hand” cell

inferotemporal cell inferotemporal cell

Face and hand

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Spatial vision

1. monocular spatial keys:

lens accommodation

size differences

overlapping, shadows

color fading

motion parallaxis

perspectivity

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Colors far away seem to be washed out

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The visual cliff experiment (Gibson)

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corresponding retina locations

non corresponding (disparate)retina locations

Binocular depth perception

Horopter circle

> 12’-16 ‘

Optical axis

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in V1 and in V2:

binocular neurons with RF on the horopter

binocular neurons with RFoutside or inside of the horopter circle

Fixation pointFusion region

Double image

Double image

Further away

closer

Stereo vision

Béla Julesz (1959)

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What determines a color?

hue: which color ? (200-400)

saturation: how much neutral grey is added ? (20-25)

intensity: how intensive (bright) it is ? (500-700)

Color constancy

How many colors can we distinguish?

Colors ad names

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rodsshort

medium

long

The trichromatic theory of color vision:

Short, medum, long wave sensitive cones (Helmholtz, Young, Maxwell)

middle

long short

perceived image

as seen with rodsmiddle

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Red green

yellowblue

center

center

periphery

periphery

The color contrast theory (Mach and Hering)

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broad band opponent

colors

double

opponent

colors

brightness brightness

and color

color

contrast

wavelength sensitive receptive fields

trichromats: protanomaly (men, 1.6%)deuteranomaly (men, 4.4%)tritanomaly (autosom. dom. 0.0001%)

dichromats: protanopydeuteranopytritanopy (autosom., rec.)

cone monochromacy (autosom., rec.)rod monochromacy (achromatopsy, autosom., rec.)

photophoby, bad resolution, no colours

rod problems: hemeralopy

Ishihara plates for testing colour vision

Color vision anomalies:

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