Visual Cortex

Question 1

describe why certain tracts cross at the optic chiasm

Answer 1

nasal retinal tracts decussates, temporal do not

ganglion cells in temporal retina express Eph B1 and optic chiasm cells express Eph B2, and those two signals repel each other

nasal retina ganglion cells dont express Eph B1, so there is no repulsion

Question 2

optic radiation

Answer 2

projections from lateral geniculate

2 routes

above calcarine sulcus- upper retinal quadrants and lower visual field

below calcarine sulcus (meyers loop) - lower retinal quadrants, upper visual field

Question 3

point to point projection

Answer 3

there is point to point projection from retina thru the lateral geniculate and to the visual cortex

on the retina, the image is inverted top to bottom and left to right

Question 4

monocular blindness

Answer 4

disease or damage of one of the eyeballs or of the optic nerve and loss of the visual field

Question 5

anopsias

Answer 5

large field deficits

Question 6

bitemporal hemianopsia

Answer 6

loss of info from temporal visual fields

Question 7

homonomous hemianopsia

Answer 7

loss of vision in half of a visual field, same visual field in each eye is lost

Question 8

ocular dominance columns

Answer 8

arrangements of vertical columns w/ cells receiving input from a small piece of retina in one eye adjacent to cells receiving input from that same piece of retina in the other eye

hypercolumn- left and right ocular dominance columns together

Question 9

BLOBS

Answer 9

cells interspersed among the columns that process color info w/o orientation specificity

Question 10

laminar organization in V1

Answer 10

LGN input goes to layer 4, which projects to 2/3, then down to 5/6

layers 2/3 project to visual association layers

Question 11

development of topographic organization in V1

Answer 11

ephrins and eph gradients guide inputs from LGN to v1

Question 12

abnormal ocular dominance

Answer 12

if one eye is neglected, thinner ocular dominance columns result

critical period where there is plasticity to develop cells that have duel input from both eyes

can result in cortical blindness

Question 13

strabismus

Answer 13

misalignment of the two eyes

causes more “individualy driven” cells in the cortex rather than cells that receive input from both eyes

esotropia- cross eyed
exotropia- divergent strabismus

Question 14

amblyopia

Answer 14

“lazy eye”- brain ignores input from eye

Question 15

both chemical cues (ephs/ephrins) and coordinated electrical activity is required for ocular dominance columns

Answer 15

ok

Question 16

orientation columns

Answer 16

cells are arranged in vertical orientation columns where all cells respond to the same orientation at varying sensitivities

Question 17

as you go higher in the visual system, there is a greater degree of convergence of visual info. at each level, there is a greater capacity for extracting info

Answer 17

ok

Question 18

simple cortical neurons

Answer 18

respond to stimuli of specific orientations

Question 19

complex cortical neurons

Answer 19

receive info from multiple simple neurons, respond to orientation and on/off stimuli

respond to orientation and shape of a stimuli

Question 20

hypercomplex cortical neurons

Answer 20

receive info on location, orientation, and direction of a stimulus

Question 21

parallel processing

Answer 21

the simulataneous processing of motion, depth, and color in the visual system

Question 22

akinetopsia

Answer 22

motion blindness

Question 23

how is motion detected?

Answer 23

image movement- change in position on the retina

eye movement- if our eye/head moves and the position on the retina stays in the same place

medial temporal area involved

Question 24

stereopsis

Answer 24

when cues from both eyes are used for depth perception- used only at short distances, beyond which monocular cues are used

compared to fixation point, medial retinal projection = far away, lateral retinal projection = close

Question 25

monocular cues

Answer 25

previous familiarity relative size interpostion linear perspectives shadows and illumination motion parallax

Question 26

characteristics of color vision

Answer 26

constancy perception- hue- proportion to which each cone is stimulated brightness- total amount of stimulation of all the cone types saturation- how much all cone types are stimulated to the same degree gradation

Question 27

color opponent cells

Answer 27

either single or double opponent cells double are excited by one color in the middle and inhibited by another in the surround

Question 28

feature maps/master maps

Answer 28

generate an image of object in stages, making note of its characteristics (color, edge, texture, and depth) then generate a master map from feature maps, going from one location to another

Question 29

binding problem

Answer 29

how the brain determines which features group together into which objects one way- familarity

Question 30

aperceptive agnosia

Answer 30

inability to pull out and recognize the image of an object from the background