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Perception > vision > Flashcards

vision Flashcards

0
Q

visible spectrum

A

the small portion of the electromagnetic spectrum we can see

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1
Q

aspects of LIGHT

4

A

electromagnetic radiation
rays
particle (quanta)
wave

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2
Q

what is a wave measure in

A

nanometres

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3
Q

luminance scale

A

not all wavelengths are visible, this scale takes visibility into acount

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4
Q

high contrast

A

high difference between light and dark

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5
Q

cornea

A

transparent ‘window’ through which light enters eye

[curved and acts as lens]

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6
Q

pupil

A

dark circle opening where light enters

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7
Q

lens

A

adjustable
focus light on retina (ciliary muscles)

they have at least 1 curved surface
light travels slower thorugh lens [compared to air]

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8
Q

retina

A

back of eye contains the photoreceptors, sends the image to the optic nerve

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9
Q

iris

A

coloured part

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10
Q

aqueous/vitreous humor

A

squishy bits behind the corner

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11
Q

where does focussing occur?

A

recombining rays from various directions to form a single point on the imaging surface

3/4 of eyes focussing power comes from cornea
1/4 lens

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12
Q

emmetropia

A

normal refractive condition; appropriate focus

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13
Q

myopia

A

short-sightedness (good short vision)

  • focal length is too short
  • light is focused in front of retina
  • need concave corrective lenses; diverging lens [reduces power]
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14
Q

hyperopia/hypermetropia

A

long sightedness

  • focal length it too long, lens too weak
  • light focused behind retina
  • need convex corrective lens; converging lens
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15
Q

presbyopia

A

old age

lens looses its natural elasticity, inability to change accomodation

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16
Q

astigmatism

A

different focal lengths for different orientations

e.g., ok for vertical lines but myopic for horizontal lines

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17
Q

rods

A

more rods then cones

high sensitivity, NIGHT VISION

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18
Q

cones

A

lower sensitivity, DAYTIME

comes in 3 sorts; red, green, blue. refer to WAVELENGTH

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19
Q

scoptic

A

only rods are active

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20
Q

photopic

A

cones active

rods momentarily blinded

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21
Q

mesopic

A

in between, both rods and cones

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22
Q

blind spot/optic disk

A

where optic nerve leaves the eye

no photoreceptors

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23
Q

visual transduction

A

rods/cones pass electrical impulses to ganglion cells (via bipolar/amacrine/horizontal cells)

  • Ganglion cells have long axons that exit the eyeball via a bundle called the optic nerve
  • optic nerve carry info from eye to visual cortex
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24
Q

fovea/macula

A

the thing you’re looking at is imaged here

many receptors, no blood vessels

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25
Q

ganglion cell activity

A

one ganglion cell receives input from many photoreceptors

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26
Q

retinal field =

A

where light falls on retina

27
Q

receptor field for foveal vision

A

smaller rf.
more densely packed
greater acuity

28
Q

fovea and cortical magnification and acuity

A

larger area of cortex for processing foveal vision (+ smaller rf) than for peripheral.
explains why foveal vision has greater acuity/precision

29
Q

2 characteristic of retinal ganglion cells

A
  • small receptive fields

- centre sorround antagonism receptive fields

30
Q

what happens when the retinal ganglion cell axons (bundle=optic nerve) leaves the eye

A

they terminate in LATERAL GENICULATE NUCLEUS (LGN)

  • > crossover at optic chiasm (partial decussation)
  • > LGN projects to V1 via OPTIC RADIATIONS
31
Q

extrastriate cortical visual areas

A

30+ visual areas beyond V1

  • each areas specialised for particular aspect of vision (v4=colour)
  • each is RETINOTOPIC (except MST)
32
Q

ON centre

A
  • tell us how bright an area is

- detect luminance increments

33
Q

OFF centre

A

tell us how dark an area is

help us detect local luminance decrements

34
Q

centre-sorround antagonism

A

ganglion cell receptive fields

excitation and inhibition

35
Q

why have 2 sets of cells?

A

compliment each other

make sure dark spots are detected as easily as light ones

36
Q

if there is light all over, or no light at all [on ganglion cell rf]

A

spontaneous activity only - no response

37
Q

WHY centre sorrround antagonism?

A

tells us where CHANGES are in the image - exaggerates EDGES

& sensitivity to CONTRAST between light and dark

38
Q

describe the herman grid illusion (what you see)

A

illusory dark patches at the intersection, less noticeable close to the fovea

39
Q

explain herman’s grid illusion

A

RFs of periphery are large and less dense creating the illusory dark patches. move our eyes to get better acuity of object in foveal vision where RFs are small & densley packed.

centre sorround antagonism; intersection, more bright sorrounds so middle apears darker
dark sorround will make an area appear lighter

40
Q

sensitivity to contrasts. effect on cells

A

most visual cells increase activity in response to increases in contrast

41
Q

LGN properties (5)

A
  • 6 layers
    each is retinotopically organised
    all cells are monocular
    both eyes have inputs to LGN, but each eye goes to diff layerLGN receives input from diff sides
42
Q

neurons in LGN

A 
MAGNUCELLULAR = large RFs, process motion
PARVOCELLULAR = small RFs, process colour

Koniocellular = betwee the M/P layers

43
Q

role of optic radiations

A

carry neural signal from LGN to V1

44
Q

properties of V1

A
  • retinotopic
  • cortical magnification
  • channels selective to orientation/diff angles
  • selectivity for eye of origin / ocular dominance
45
Q

filtering in vision

A

filter for many different properties

46
Q

orientation tuning; selectivity

A

reduced activity as orientation departs from preferred cells

47
Q

range of orientations to which the cell fires lots is a measure of

A

its bandwidth

48
Q

V1 organisation

A

orientation columns
& columns of ocular dominance

vertical and horizontal

49
Q

hypercolumn

A

= collection of orientation columns go round, 180 degress, back to original orientation

50
Q

types of V1 cells

A

simple cells
complex cells
hypercomplex cells (end-stopped cells)

51
Q

simples cells

A

respond to an orientated stimulus in a certain location within their RF
- can be bar or edge detectors

52
Q

complex cells

A

respond to an orientated edge ANYWHERE within the receptive field
- do not have ON and OFF areas

  • phase insensitive; similar response across their RF (unlike simple cells)
53
Q

building of complex cells

A

connect several simple cells with same orientation preffered

54
Q

hypercomplex cells / end-stopped cells

A

prefer stimuli with an END within their receptive field.

55
Q

hypercomplex cell building

A

connect several complex cells to construct an end-stopped cell

56
Q

how do we detect an illusory edge?

A

signalled by interconnected hypercomplex cells

57
Q

low-pass filter

A

removes high frequency

reduces detail

58
Q

high-pass filter

A

remove low frequency

more detail

59
Q

size of stripes for what spatial frequency

A

fat stripes = low spatial frequency

thin stripes = high spatial frequency

60
Q

range of visible spectrum

A

400-700 nm

61
Q

how is spatial frequency measured

A

in cycles per degree of visual angle (the size of an object)

62
Q

how does the lens adjust/accomodate

A

cilary bodies

63
Q

optical power measure in…

A

diopters

64
Q

retina is a layered network contain __ diff types of cell, whose nuclei are grouped in __ layers

A

5 types of cell

3 layers

65
Q

binocular neurons

A

receive signals from both eyes and compare the images from the left and right eyes

66
Q

most common V1 cells

A

complex cells

Perception (7 decks)

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