spatial vision and visual pathways

Question 1

what does wave height represent in visual stimuli?

Answer 1

brightness (amount of light reflected)

Question 2

what is spatial frequency?

Answer 2

number of oscillations per unit space

Question 3

what do high spatial frequencies represent?

Answer 3

fine details

Question 4

what do low spatial frequencies represent?

Answer 4

coarse shapes/ forms

Question 5

what type of photoreceptors support high spatial frequency vision?

Answer 5

cones

Question 6

what is phase in a grating?

Answer 6

position of the wave cycle

Question 7

how are images represented in vision?

Answer 7

as sums of sinusoidal components at different spatial frequencies

Question 8

how is acuity measured?

Answer 8

minimum resolvable cycle width in degrees of visual angle

Question 9

what is a useful real world reference for 1 degree?

Answer 9

fingernail at arms length

Question 9

what is visual acuity?

Answer 9

the finest spatial detail that can be resolved

Question 10

what is visual angle?

Answer 10

angle an object subtends at the eye

Question 11

what determines acuity limits?

Answer 11

cone spacing in the fovea

Question 11

what is the human resolution limit?

Answer 11

1 arc minute (1/60)

Question 12

why are two cones needed per cycle?

Answer 12

one for light bar, one for dark bar

Question 13

what happens if spatial frequency is too high?

Answer 13

bars blur together -> cannot be resolved

Question 14

what does 20/20 vision mean?

Answer 14

normal acuity (1 arc minute resolution)

Question 15

what does the snellen fraction represent?

Answer 15

numerator = your viewing distance
denominator = average person’s distance

Question 16

what is 20/10 vision?

Answer 16

better than average (see farther)

Question 17

what is 20/40 vision?

Answer 17

worse than average (must be closer)

Question 18

what is contrast sensitivity?

Answer 18

ability to detect differences in brightness

Question 19

what does low sensitivity mean?

Answer 19

more contrast is needed to detect a pattern

Question 20

what is the contrast sensitivity function (CSF)

Answer 20

relationship between sensitivity and spatial frequency

Question 21

at which spatial frequencies are humans most sensitive?

Answer 21

intermediate frequencies

Question 22

how does contrast sensitivity change with age?

Answer 22

develops over time and declines with age

Question 23

what is the optic chiasm?

Answer 23

point where visual fibres cross

Question 24

what is the lateral geniculate nucleus (LGN)

Answer 24

relay station between retina and cortex

Question 25

what are magnocellular (M) layers specialised for?

Answer 25

motion, large, fast objects

Question 25

what is monocular input?

Answer 25

input from one eye only

Question 26

what are parvocellular (P) layers specialised for?

Answer 26

detail, small, stationary objects

Question 27

what is bitemporal hemianopia?

Answer 27

loss of outer visual fields in both eyes (optic chiasm damage)

Question 28

what type of receptive fields do LGN neurons have?

Answer 28

centre-surround

Question 29

what happens if the optic nerve is damaged?

Answer 29

loss of vision in one eye

Question 30

what happens with optic tract or LGN damage?

Answer 30

loss of opposite visual field in both eyes

Question 31

how many layers does primary visual cortex (V1) have?

Answer 31

6 layers

Question 32

what is cortical magnification?

Answer 32

overrepresentation of the fovea in cortex

Question 33

what is a topographic map?

Answer 33

nearby points in space map to nearby neurons

Question 34

what are binocular neurons?

Answer 34

respond to input from both eyes

Question 35

what are ocular dominance columns?

Answer 35

columns responding preferentially to one eye

Question 36

what are orientation columns?

Answer 36

columns tuned to specific orientations

Question 37

what do V1 neurons respond to?

Answer 37

edges and bars (not spots)

Question 38

what are simple cells?

Answer 38

respond to bars in specific locations

Question 39

what are complex cells?

Answer 39

respond to bars anywhere in receptive field

Question 40

what is orientation tuning?

Answer 40

preference for specific angles

Question 41

what other features are neurons tuned to?

Answer 41

spatial frequency and motion detection

Question 42

what is visual adaptation?

Answer 42

reduced response after prolonged exposure

Question 43

what is the waterfall illusion?

Answer 43

motion aftereffect in opposite direction

Question 44

what is the tilt aftereffect?

Answer 44

perceived shift in orientation after adaptation

Question 45

why does adaptation occur?

Answer 45

neurons tuned to the stimulus become fatigued

Question 46

what is interocular transfer?

Answer 46

aftereffect transfer between eyes -> cortical processing

Question 47

what does no transfer suggest?

Answer 47

processing in retina or LGN (monocular)

Question 48

what is a visual channel?

Answer 48

group of neurons tuned to a specific spatial frequency

Question 49

what does a dip in sensitivity indicate?

Answer 49

presence of a specific channel

Question 50

how is perception constructed?

Answer 50

combination of multiple spatial frequency channels

Question 51

what happens in extrastriate cortex?

Answer 51

processing becomes more complex

Question 52

what does V4 respond to?

Answer 52

complex feature configurations

Question 53

what is the role of the inferotemporal cortex?

Answer 53

object and scene recognition

Question 54

how is the visual information processed overall?

Answer 54

simple feature -> edges -> patterns -> objects

Question 55

what builds final perception?

Answer 55

integration of activity across many specialised neurons