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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
fovea/macula
the thing you're looking at is imaged here | many receptors, no blood vessels
25
ganglion cell activity
one ganglion cell receives input from many photoreceptors
26
retinal field =
where light falls on retina
27
receptor field for foveal vision
smaller rf. more densely packed greater acuity
28
fovea and cortical magnification and acuity
larger area of cortex for processing foveal vision (+ smaller rf) than for peripheral. explains why foveal vision has greater acuity/precision
29
2 characteristic of retinal ganglion cells
- small receptive fields | - centre sorround antagonism receptive fields
30
what happens when the retinal ganglion cell axons (bundle=optic nerve) leaves the eye
they terminate in LATERAL GENICULATE NUCLEUS (LGN) - > crossover at optic chiasm (partial decussation) - > LGN projects to V1 via OPTIC RADIATIONS
31
extrastriate cortical visual areas
30+ visual areas beyond V1 - each areas specialised for particular aspect of vision (v4=colour) - each is RETINOTOPIC (except MST)
32
ON centre
- tell us how bright an area is | - detect luminance increments
33
OFF centre
tell us how dark an area is | help us detect local luminance decrements
34
centre-sorround antagonism
ganglion cell receptive fields | excitation and inhibition
35
why have 2 sets of cells?
compliment each other | make sure dark spots are detected as easily as light ones
36
if there is light all over, or no light at all [on ganglion cell rf]
spontaneous activity only - no response
37
WHY centre sorrround antagonism?
tells us where CHANGES are in the image - exaggerates EDGES & sensitivity to CONTRAST between light and dark
38
describe the herman grid illusion (what you see)
illusory dark patches at the intersection, less noticeable close to the fovea
39
explain herman's grid illusion
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
sensitivity to contrasts. effect on cells
most visual cells increase activity in response to increases in contrast
41
LGN properties (5)
- 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
neurons in LGN
``` MAGNUCELLULAR = large RFs, process motion PARVOCELLULAR = small RFs, process colour ``` Koniocellular = betwee the M/P layers
43
role of optic radiations
carry neural signal from LGN to V1
44
properties of V1
- retinotopic - cortical magnification - channels selective to orientation/diff angles - selectivity for eye of origin / ocular dominance
45
filtering in vision
filter for many different properties
46
orientation tuning; selectivity
reduced activity as orientation departs from preferred cells
47
range of orientations to which the cell fires lots is a measure of
its bandwidth
48
V1 organisation
orientation columns & columns of ocular dominance vertical and horizontal
49
hypercolumn
= collection of orientation columns go round, 180 degress, back to original orientation
50
types of V1 cells
simple cells complex cells hypercomplex cells (end-stopped cells)
51
simples cells
respond to an orientated stimulus in a certain location within their RF - can be bar or edge detectors
52
complex cells
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
building of complex cells
connect several simple cells with same orientation preffered
54
hypercomplex cells / end-stopped cells
prefer stimuli with an END within their receptive field.
55
hypercomplex cell building
connect several complex cells to construct an end-stopped cell
56
how do we detect an illusory edge?
signalled by interconnected hypercomplex cells
57
low-pass filter
removes high frequency | reduces detail
58
high-pass filter
remove low frequency | more detail
59
size of stripes for what spatial frequency
fat stripes = low spatial frequency | thin stripes = high spatial frequency
60
range of visible spectrum
400-700 nm
61
how is spatial frequency measured
in cycles per degree of visual angle (the size of an object)
62
how does the lens adjust/accomodate
cilary bodies
63
optical power measure in...
diopters
64
retina is a layered network contain __ diff types of cell, whose nuclei are grouped in __ layers
5 types of cell | 3 layers
65
binocular neurons
receive signals from both eyes and compare the images from the left and right eyes
66
most common V1 cells
complex cells

Perception (7 decks)

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