chapter 7: vision

Question 1

what are the parts of the eye

Answer 1

pupils - lets light in
iris and cilliary muscles - iris controls the size of the pupil, and cilliary changes the shape of the lens
cornea - protects eyes from UVs and refracts light
lens - focuses light on the retina
retina - receives light, site of sensory transduction
optic disc - where blood vessels and ganglion cell axons leave
blind spot - region on the retina that is sightless due to lack of photoreceptors in the optic disc

Question 2

what is myopia

Answer 2

nearsightedness; difficulty seeing distant objects

Question 3

what is hyperopia

Answer 3

farsightedness, difficulty seeing close objects

Question 4

what are the 5 cell types found in the retina

Answer 4

photoreceptors (rods & cones), bipolar cells (internuerons), ganglion cells (conduct action potential out of eye), horizontal cells (contact photoreceptors and bipolar cells), amacrine cells (contact bipolar and ganglion cells)

Question 5

why are rods and cones in the back of the retina

Answer 5

1. rods and cones get recycled constantly
2. use large amounts of energy
3. helps to absorb scattered light

Question 6

how do rods and cones work

Answer 6

light particles strike the discs and captured by photopigment receptors (rods = rhodopsin, cones = photopsin)

Question 7

what do photoreceptors do in the dark

Answer 7

continually release neurotransmitters; light triggers a hyperpolarization of the cell, causing it to release less

Question 8

how is the size of the hyperpolarizing signal determined

Answer 8

brightness of light

Question 9

what are the two effects glutamate has on bipolar cells

Answer 9

off-center excitatory - turning on light hyperpolarizes the cell
on-center inhibitory - turning on light depolarizes the cell

Question 10

on-center bipolar cells excite _____ when depolarized?

Answer 10

on-center ganglion cells

Question 11

off-center bipolar cells excite _____ when depolarized?

Answer 11

off-center ganglion cells

Question 12

what is photoreceptor adaptation

Answer 12

each receptor adjusts its level of senstivitiy to match the average ambient level of light

Question 13

what is range fractionation

Answer 13

using different photoreceptors to handle different intensities

Question 14

optic nerves go to what place?

Answer 14

optic chiasm

Question 15

optic tacts goes where? (multiple places)

Answer 15

pretectum in brainstem, hypothalamus, superior colliculus, lateral geniculate nucleus, V1 (region around the calcarine sulcus)

Question 16

what can V2 cells adjacent to V1 do

Answer 16

respond to illusory boundaries and complex relations among the parts of their receptive fields

Question 17

what do V4 adjacten to V2 cells do

Answer 17

strong response to orientation, frequency, and color, response to intermediate complexity and geometric shapes

Question 18

what do V5 cells do

Answer 18

respond to moving visual stimuli, specialized for motion and direction

Question 19

what do V6 cells do

Answer 19

respond to self-motion, behaviors like reaching

Question 20

what is the ventral stream

Answer 20

V1 -> V2 -> V4 -> inferior temporal cortex

useful for object identification and recognition

Question 21

what is the dorsal stream

Answer 21

V1 -> V2 -> V5 -> V6 -> posterior parietal cortex

associated with motion and control of limbs

Question 22

what is akinestopsia

Answer 22

cannot perceive continuous motion, appears as still images; damage to V5

Question 23

what is blindsight

Answer 23

inability to consciously perceive visual cues, but can discriminate based on them; damage in V1

Question 24

what is scotoma

Answer 24

blind spots caused by damage; can be temporary or permanent; damage in

Question 25

what is amblyopia

Answer 25

misalignment of the eyes, causing one to become functionally blind

Question 26

how is color perceived

Answer 26

photos travel in wavelengths of light that have different properties; these difference create perception of color

Question 27

what are the three levels of color processing

Answer 27

level of the photoreceptor level of the LGN level of the cortex

Question 28

what is the trichromatic theory

Answer 28

all colors are a result of activation across three type of cones: short blue cones, medium green cones, and long red cones; brain compares activation and extracts color information

Question 29

what is color-blindness

Answer 29

cannot distinguish between certain hues; most common is in M cones (green).

Question 30

what is the opponent processing theory

Answer 30

ganglion cells and LGN cells- a cell can activate red/green or blue/yellow, so when one color is activated, the other color is inhibited

Question 31

what does the cortex do in lvl 3 color perception

Answer 31

V1 - basic processing of color, opponent cells and double opponent cells V4 - primary color center, processes brightness, texture motion, depth, helps to differentiate

Question 32

what is cerebral achromatopsia

Answer 32

lack of the perception of color, caused by damage in the cortex color processing stuff

Question 33

how do afterimages work

Answer 33

you stare at something green -> green part of ganglion and LGN cells are activated and the red is inhibited -> initial activation of green -> over time signal is weaker -> white background causes other color cells to activate in addition to green, i.e. red -> strong signal of red overpowers green

Question 34

whole vision pathway

Answer 34

photon -> cornea -> pupil -> lens -> retina -> photoreceptors -> bipolar cells -> ganglion cells -> optic nerve -> optic chiasm -> optic tract -> pretectum, hypothalamus, superior colliculus, LGN -> V1

Question 35

What does the pupil do?

Answer 35

lets light in

Question 36

What does the cornea do?

Answer 36

protects eyes from UVs and refracts light

Question 37

What do the iris and ciliary muscles do?

Answer 37

iris controls size of pupil and ciliary muscles control shape of the lens

Question 38

What does the lens do?

Answer 38

focus light on the retina

Question 39

What does the retina do?

Answer 39

Receives light and acts as the center of transduction.

Question 40

What does the optic disc do?

Answer 40

It is where blood vessels and ganglion axons leave the eye.

Question 41

What causes the blindspot?

Answer 41

the lack of photoreceptors in that area of the retina