Overview of colour vision Flashcards

1
Q

Describe light as electromagnetic radiation

A
  • Light as a wave and equation:
    wavelength = speed of light / frequenc
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2
Q

What are photons

A

Radiation is emitted from a source in small packets of energy = photons

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3
Q

what speed do photons travel at?

A

speed of light

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4
Q

how do photons vibrate?

A

Photons vibrate at a frequency that increases with their energy

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5
Q

what is frequency?

A

the number of cycles per second pass a given point

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6
Q

describe the electromagnetic spectrum

A

as you go right wavelength increase and as you go left frequency increases

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7
Q

high energy photons vibrate…

A

at high frequency; shorter wavelength

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8
Q

what is visible light on the EM spectrum

A

narrow band

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9
Q

how does light quality vary?

A

-along 2 dimensions
-intensity and wavelength or chromaticity

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10
Q

what is intensity?

A

-can be measured as energy (watts/unit area)
-relates to brightness in visible spectrum

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11
Q

what is wavelength/chromaticity?

A

relates to colour

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12
Q

how to measure light as radiant energy?

A

can be measured in watts/m^2

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13
Q

how to measure light as luminance?

A

candela/m^2
-scaled by interaction conventions according to spectral sensitivity of human eye

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14
Q

how to measure light as photon flux (quantal flux)?

A
  • photons per unit area per unit time
  • on the longer wavelength end
  • stimulus intensity
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15
Q

Brightness is the same as luminance. TRUE OR FALSE

A

FALSE

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16
Q

what is hue?

A

Hue = colour appearance, which changes from blue to green to yellow to red as wavelength increases

17
Q

what are spectral colours?

A

Spectral colours are those that can be elicited by single wavelength

18
Q

what are non-spectral colours?

A

Many colours cannot be equated with specific wavelengths: purple, pink, brown… black, white (non-spectral)

19
Q

what does colour depend on?

A

Colour depends on wavelength but cannot simply be equated with wavelength

20
Q

what does colour vision entail?

A

Colour vision entails the ability to see colours and discriminate objects on the basis of colour

21
Q

describe colour as surface spectral reflectance

A

-Objects appear coloured due to the wavelength composition of the light reflected from the surface
- The SSR is a fixed physical/chemical property of a surface
- SSR describes the proportion of light reflected at each wavelength of the visible spectrum

22
Q

Is SSR the physical property that corresponds to colour?

A

Coloured objects do not reflect a single wavelength corresponding to a spectral colour

23
Q

colour appearance depends…?

A

Colour appearance depends on the relative amount of different wavelength

24
Q

Quality of the visible spectrum depends on …?

A
  • an organisms spectral sensitivity
  • e.g. humans have rather low sensitivity to wavelengths <400 nm
  • Wavelength. Chromaticity or perceived hue, changes with wavelength
  • signalled by comparison of cone signals
25
what does human colour vision depend on?
3 spectral classes of cone
26
what are the 3 spectral classes of cone
Blue, green and red; more correctly termed SW, MW and LW cones
27
Explain photoreceptor spectral sensitivity
- Summed photoreceptor signals determine luminous* sensitivity over visible spectrum - * determined by sums of photoreceptor signals across classes - Brightness increases when total signal summed from photoreceptor increases
28
Vertebrates have a duplex retina. What are rods and cones for?
- rods for scotopic vision - cones for photopic vision
29
The quality of light varies along two dimensions. State them.
- Intensity - other things being equal, luminance and perceived brightness increase with intensity - Wavelength - chromaticity or perceived hue, changes with wavelength
30
Wavelength discrimination is a prerequisite for colour vision. Explain.
- The ability to discriminate changes in wavelength independently from changes in intensity - need to show discrimination based purely on wavelength differences - control for achromatic differences in intensity
31
Is wavelength discrimination possible with a single spectrally-tuned photoreceptor?
- No, e.g. a low intensity at 560 could produce the same response as a higher intensity 450 - In theory, any two stimuli in the spectral range could be adjusted in relative intensity to produce the same response - cannot disentangle wavelength and intensity - a single photoreceptor is colour blind
32
Principle of univariance: a single cone is colour blind
- Phototransduction signal depends on rate of photon absorption (quantal catch) - Probability of absorption depends on wavelength
33
Wavelength discrimination requires comparison of photoreceptor responses
- Two spectral classes: - LW peak 560 nm - SW peak 440 nm - A decrease in intensity at 550 would decrease activity in both photoreceptors - but a decrease in wavelength from 550 would decrease response of LW but increase response of SW responses
34
Photoreceptors spectral classes
mono-, di-, tri-, tetra-chromats
35
MONOCHROMATS:
animals with only a single spectral class of photoreceptors
36
DICHROMATS:
two spectral classes: SW plus MW or LW, most mammals; some humans with colour deficiency
37
TRICHROMATS:
three spectral classes: SW, MW, LW, old world primates (humans); some invertebrates - bees
38
TETRACHROMATS
4 spectral classes, most vertebrates (birds, reptiles, fish); some invertebrates - butterflies