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PSYG1002 - Cognitive > Perception - Brightness and Colour > Flashcards

Perception - Brightness and Colour Flashcards

1
Q

What is light?

A

Stimulus for vision

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2
Q

What is visible light?

A

Band of energy within electromagnetic spectrum (wavelengths from 400-700nm)

Consisting of small packets of energy called photons

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3
Q

What is absorption?

A

As photons collide with particles of matter

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4
Q

What is reflection?

A

As light strikes opaque surfaces

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5
Q

Do bright or dark objects reflect more light?

A

Bright

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6
Q

What is transmission?

A

As light passes through transparent matter

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7
Q

How many chambers does a human eyes have?

A

Single-chambered eye

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8
Q

What does the human eye enable?

A

Directional sensitivity (represent spatial structure rather than sum total of light)

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9
Q

What do photoreceptors do?

A

See light and process it

Transduce light into electrical potential

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10
Q

How do signals move through the eye?

A

Flow through network of neurons to retinal ganglion cells then out back of eye via optic nerve

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11
Q

What are the types of photoreceptor in the retina?

A

Rods

Cones

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12
Q

Where rods primarily located?

A

Peripheral retina

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13
Q

What is the function of rods?

A

Capable of operating in low light levels (can detect single photon)

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14
Q

Where are cones primarily located?

A

Concentrated in centre of retina (fovea)

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15
Q

What is the function of cones?

A

Require higher light levels (daylight) to respond

2 different photopigments sensitive to different wavelengths of light

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16
Q

What is the visual pathway?

A

Retina -> optic nerve -> optic chiasm -> LGN -> primary visual cortex (V1)

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17
Q

What is intensity/luminance related to?

A

Brightness

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18
Q

What is luminance?

A

Numbers of photons per unit space

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19
Q

When are there more photons is it generally darker or brighter?

A

Brighter

20
Q

How does bottom up processing affect brightness perception?

A

Retina doesn’t simply record light intensities

Responses are shaped by processes occurring within the retina

21
Q

What are the examples of bottom-up processing for brightness perception?

A

Light/dark adaption

Lateral inhibition

22
Q

What is light/dark adaption?

A

Luminance of retinal image depends on amount of light falling onto object and relative reflectance of surface

Sensitivity low when mean intensity high and sensitivity high when mean intensity low

23
Q

What is brightness constancy?

A

Not having perception massively change when brightness changes

24
Q

In light/dark adaption, what does the retina encode?

A

Contrast (ratio of object’s luminance relative to the mean or background luminance)

Plays critical role in achieving brightness constancy

25
Q

What illusions can light/dark adaption produce?

A

Negative afterimages

26
Q

What is lateral inhibition?

A

Early form of information processing in retina

Retinal ganglion cells receive both inhibitory (-) and excitatory (+) input from neighbouring photoreceptors arranged in central configuration across retinal image

Makes visual system sensitive to changes in luminance

Can have dramatic effects on perceived brightness

27
Q

Why is it important that the visual system is sensitive to changes in luminance?

A

Detecting edges and borders of objects

28
Q

What illusion can have lateral inhibition produce?

A

Herman grid illusion

29
Q

What are the top-down influences on brightness perception?

A

Brain uses knowledge about how light interacts with 3D objects in the world when determining brightness

Tries to maintain brightness constancy when amount of light falling on surface is affected in shadows (can result in errors in 2D images portraying 3D scenes)

30
Q

What does wavelength affect the perception of?

A

Colour

31
Q

In low light conditions, what is colour perception like?

A

Often world devoid of colour

32
Q

Why is the world often devoid of colour in low light conditions?

A

Only rod photoreceptors sensitive to operate and they only contain single type of photopigment (rhodopsin)

Lights of different wavelengths can elicit identical responses so it’s difficult to accurately signal different wavelengths

33
Q

What is trichromacy?

A

When all the cone photoreceptors function correctly

Relative outputs of 3 cone types allows unambiguous signalling of wavelengths

34
Q

What are the three cone photoreceptors?

A

S-cones

M-cones

L-cones

35
Q

What are S-cones sensitive to?

A

Short wavelengths

Blue

36
Q

What are M-cones sensitive to?

A

Medium wavelengths

Green

37
Q

What are L-cones sensitive to?

A

Long wavelengths

Red

38
Q

What are variations from trichromacy?

A

Colour blindness

Monochromacy

Dichromacy

Anomalous trichromacy

39
Q

What is monochromacy?

A

Most severe

0 or 1 functioning cone type

Complete colour blindness

Extremely rare (~1 in 100,000)

40
Q

What is dichromacy?

A

2 functioning cone types

Protanopia = missing L-cones (1% males, 0.02% females)

Deuteranopia = missing M-cones (1% males, 0.01% females)

Tritanopia = missing S-cones (0.002% males, 0.001% females)

41
Q

What is anomalous trichromacy?

A

Defect in 1 of cone types

More common form

Commonly assessed using Ishihara Colour Test

Protanomaly = L-cone defect (1.3% males, 0.02% females)

Deuteranomaly = M-cone defect (5% males, 0.35% females)

Tritanomaly = S-cone defect (0.01% males, 0.01% females

42
Q

Is opponency a top-down or bottom-up process of colour perception?

A

Bottom-up

43
Q

What is opponency?

A

Retinal ganglion cells received excitatory (+) and inhibitory (-) input from different cone types

Distinct Red/Green and Blue-Yellow pathways

44
Q

What illusions can opponency cause in colour perception?

A

Negative afterimages

Staring at red object will result in green afterimage - adaption to red causes reduction in sensitivity to long wavelength cones, creating imbalance in inputs to red/green opponent retinal ganglion cells

45
Q

What are the top-down influences to colour perception?

A

Colour constancy by accounting for intensity and composition of light hitting surfaces

Gives rise to illusions where some wavelength of light perceived as different colours

46
Q

What is colour constancy?

A

Tendency for perceived colour of objects to remain the same even if lighting changes

PSYG1002 - Cognitive (7 decks)

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