Colour Perception and Spatial Vision

Question 1

consequence of overexposed images

Answer 1

measured colours being different from the real image

Question 2

how can viewing conditions cause variations in perceived colour?

Answer 2

change in image size and viewing angle

Question 3

what did livingston and hubel (1988) observe about colour processing?

Answer 3

V1, V2, and V3 are involved in colour processing

Question 4

how many cones are involved in daylight vision?

Answer 4

three types of cone receptors, which respond to a wide range of colours but respond maximally to their own

Question 5

how many rods are involved in night vision?

Answer 5

only one rod photoreceptor, explaining why we are colourblind at night

Question 6

what type of vision is more sensitive to light?

Answer 6

peripheral vision

Question 7

one cone type (monochromat)

Answer 7

can see a range of colours but not discriminate between them

Question 8

two cone types (dichromats)

Answer 8

can discriminate these colours but no others

Question 9

three cone types (trichromats)

Answer 9

can discriminate all possible colours in the visible spectrum

Question 10

what is the visible spectrum?

Answer 10

the part of the colour spectrum that human eyes are sensitive to

Question 11

what can colour blindness be caused by?

Answer 11

mistuned cone types
cerebral achromatopsia

Question 12

what is the result of mistuned cone types?

Answer 12

inability to discriminate between colours, most likely mistuned green cones

Question 13

what are rod monochromats?

Answer 13

have no cones at all, meaning they cannot see at all in daylight/truly colourblind

Question 14

how can cerebral achromatopsia result in colour cortical blindness?

Answer 14

damage to V8, leads to inability to differentiate colours

Question 15

what is colour-opponent processing?

Answer 15

the visual system processes complementary colours in pairs

1. the luminance + BY system
2. recent adaptation of a newer RG system

Question 16

what do the centre-surround properties of RGC provide?

Answer 16

the mechanism for colour constancy, by calculating the ratio of colours to provide edge detection

individual variations in colour-opponency systems explain differences in colour perception

Question 17

what does inhibition over space and time suggest for colour perceptions?

Answer 17

spatial context and lighting can affect colour perceptions, due to lateral inhibition compressing information about colour

simultaneous contrast illusions
colour after-effects

Question 18

what do colour centre-surround cells in the retina transmit?

Answer 18

only the colour edges, which allows the cortex to reconstruct the colour body of objects

• means surrounding colours might facilitate “filling-in” due to excitation in the cortex

Question 19

what is colour constancy?

Answer 19

using a white-balance correction to discount the light source colour which may influence perceived colour of an object

occurring in V8 (subsection of area V4)

Question 20

how are V1, V2, V4, and V8 involved in colour?

Answer 20

colour-sensitive cells in V1 and V2 pass signals onto V4 and V8 (responsible for conscious perception of colour, and colour constancy)

Question 21

classical view of lines (hubel and weisel, 1950s)

Answer 21

spatial relationships between parts of objects are processed through their oriented edges and bars

• simple cells
• complex cells
• hypercomplex cells

Question 22

properties of simple cells

Answer 22

• receptive fields
• well-defined on/off regions

Question 23

well-defined on/off regions

Answer 23

presenting a stimulus in the on-region excites the cell to generate an AP, but the reverse happens with light in the off-region

Question 24

selectivity within simple cells

Answer 24

• orientation selectivity
• position sensitivity
• sensitivity to size

Question 25

how does orientation selectivity occur in simple cells?

Answer 25

due to their oblong-shaped receptive fields, which allow increased AP when light aligns with the on-region

Question 26

how does position selectivity occur in simple cells?

Answer 26

they generate a higher AP when the object moves onto part of the receptive field

Question 27

how does size selectivity occur in simple cells?

Answer 27

able to respond to the width of stimuli, e.g., thinner light maximally excites the on-region to produce more APs

Question 28

how can V1 receptive fields be assembled?

Answer 28

can be assembled from the output of receptive fields at the LGN, as off-parts construct their respective parts in simple cells to allow for contrast

Question 29

properties of complex cells

Answer 29

• high resting output
• unstructured, with no defined on-off receptive field
• respond to orientation and size selectivity, but more for complex lines

Question 30

why do complex cells have no defined on-off receptive field?

Answer 30

they are constructed from the output of simple cells, resulting in an overlapping on-off receptive field for complex cells

Question 31

properties of hypercomplex cells

Answer 31

• similar to complex cells, but have a peak sensitivity for line length and orientation

Question 32

how are hypercomplex cells constructed?

Answer 32

by complex cells with two inhibitory receptive fields at either end

Question 33

what does the construction of hypercomplex cells allow them to do?

Answer 33

turn off when the stimulus gets greater than their peak sensitivity size

Question 34

what do inhibitory regions of hypercomplex cells provide?

Answer 34

an end-stop signal to cells upon excitation from the ends of the stimulus, enabling the visual system to work out the length of stimuli

Question 35

what does texture segmentation believe texture is?

Answer 35

spatial detail at a scale which is finer than the object scale

defines texture by statistical properties to work out boundaries, borders, and locations

Question 36

texton theory (julesz, 1984)

Answer 36

textures will segment if they differ in the density of their textons (simplest defining properties of textures, based on V1 properties

Question 37

orientation contrast model (nothdurft, 1990)

Answer 37

believes the brain can differentiate texture due to sensitivity to changes in local contrast and local orientation, rather than using statistical textons

Question 38

when does segmentation by orientation develop?

Answer 38

around 3m of age

Question 39

what does segmentation orientation contrast involve?

Answer 39

segmenting on the basis of local differences

it is also possible to segment objects based on local size differences

Question 40

types of centre-surround cells with receptive fields specialised for orientation

Answer 40

1. single opponent cells
2. double opponent cells

Question 41

single opponent cells (orientation sensitive)

Answer 41

sensitive to one orientation and local contrast, specifically for one orientation

Question 42

double opponent cells (orientation insensitive)

Answer 42

cells with sensitivity for both orientations – vertical and horizontal – and also local changes in vertical and horizontal stimuli

Question 43

what does the simultaneous tilt illusion show?

Answer 43

how orientation can be misinterpreted due to the inhibitory influence of surrounding orientations, as a result of data compression on centre-surround cells

Question 44

evidence of simultaneous contrast for size

Answer 44

ebbinghaus illusion presents inhibiton over space

Question 45

for spatial vision, what can inhibition over time result in?

Answer 45

colour and tilt after-effects, as long-time exposure inhibits orientation-sensitive cells

this increases the resting level of the opposite direction and results in a greater output, tricking us into misperceiving colour and orientation by changing the neural code