perception-colour vision

Question 1

perception is what you see ,and what you see is an ______ of the nervous system

Answer 1

interpretation
-suggests our realities are different - same applies to pets animals as they have different interpreations

Question 2

learning objectives

Answer 2

-Visible light in the context of E-M spectrum
-A visual system with a single photoreceptor type and the principle of univariance
-Colour vision in a visual system with two or more photoreceptor types
-Cone excitation responses
-Trichromacy in human vision
-Colour matching and colour spaces
-Evidence for opponent colour processing
-Colour mixing by primary colours
-Metamers
-Colour spaces and charts

Question 3

where colour is important

Answer 3

-in wildlife, animals use colours to attract males or females
-also important for the predator, and the predators nervous system, e.g. camouflage may be well in one animals eyes but not be camouflage at all in predators eyes
-makeup , fashion
-colour is associated with emotion ,
-social factors-sports teams etc
-culture associate colours differently

Question 4

-what can colour influence
- our ability to see colour has ____ and _____ functions

Answer 4

our moods, emotions, sensory perception
-practical,adapative

Question 5

why is it important to see colours

Answer 5

-colour facilitates object detection by increasing figure/ground segmentation.
-aids in object detection by allowing objects to be distinguished on the basis of colour (e.g. ripe fruit)
(look at slides-flowers-shows you cant make out the petals or leaves when the photo is black and white)
e.g. - so is important if you want to find food-you need to distinguish between berries and leaves around us

Question 6

what is electromagnetic radiation

Answer 6

-form of energy
-surrounding us , the light is electromagnetic radiation
-any source that radiates (eg light coming from the screen and hitting the screens around us) is electromagnetic radiation
-light is reflected causing er
-we need light in order to scatter from surroundings from objects

Question 7

-electromagnetic spectrum
-how can electromagnetic radiation be characterised
-er is measure by

Answer 7

-The electromagnetic spectrum consists of many bands of electromagnetic radiation
-er we can characterise by based on frequency or wavelength (these two are inversely proportional to each other)
-metres or nanometres

Question 8

radio waves

Answer 8

eg- radio noise is sensitive to electromagnetic radiation in the radio part of the spectrum

Question 9

the visible light section of the ER
how many nm

Answer 9

-Visible light is the radiation our eyes and nervous system can detect , it makes up only small part of the electromagnetic spectrum.
our nervous system is sensitive to that tiny section
- Visible light is split into seven different colours that have different wavelength and frequencies

Question 10

visible light spectrum extends from wavelength of ____ to ____ nm

Answer 10

400nm (blue) to 700nm (red)

Question 11

receptors are _____ and _____

Answer 11

rods (night vision) cones (day vision) (3 classes of cones)

Question 12

newtons experiment of white light

Answer 12

-when a beam of white light is passed through a prism grating onto the screen a continuous spectrum is seen
-white light can be broken into components (all the colours)

Question 13

surface and er

Answer 13

-surfaces scatter light (they are not source of light like sun) but scatter
-every surface scatters a part of the electromagnetic radiation
-if a surface absorbs and attracts all electromagnetic radiation and doesn’t emit any of it it will look black
- white surface however it wont absorb any and reflect all aspects of the spectrum
- look at graph, blue pigment only scatters that part of spectrum, very short wavelength (only colour something blue doesn’t absorb is blue)

Question 14

scotopic and photopic spectral sensitivity curves
-what wavlength are we most sensitive to in day and night

Answer 14

-Photopic vision typically dominates under normal lighting conditions, for instance during daytime.
- humans sensitive to around 555nm so matches brightness of the sun
-scotopic vision used rods to see
for
-the moon we are sensitive to round about 507nm,
peak of scoptic (moon) is higher as the sun is brighter than moon

Question 15

what is a sensor
-talk of how opsins work

Answer 15

-a molecule which absorbs light, so when light hits that molecule it will change shape temporarily
-opsin molecules are sensors, in our retina as a part of our photopigment
-when light hits and opsin changes shape, it leads to a series of chemical reactions that end up with an impulse going to your brain/nervous system for you to interpret

Question 16

sensors are sensitive to ______ parts of electromagnetic radiation

Answer 16

particular
-so by tiny adjustments in opsin molecules you get t sensors sensitive to reds, greens, blues etc in all animals

Question 17

problem- an animal has only one type of photorecptor kind which is highly sensitive to one part and less to the other, and the photoreceptor tells you whether there is or isnt light (nothing about colour)

Answer 17

univariance principle

Question 18

explain the univariance principle

Answer 18

-a photoreceptors response is summarised by one variable that specifies the amount of light absorbed
-each photopigment responds to a preferred wavelength but the neural response of the photoreceptor does not specify the wavelength (it just tells you there is light or there’s not )

Question 19

given the proper intensity , all wavlengths can affect…

Answer 19

a single pigment receptor in the same way

Question 20

what happens if you only have one type of photo pigment

Answer 20

an eye with only one type of photo pigment cannot see colours
-many human diseases can lead to this

Question 21

examples of photos and how people with one photopigment would see them

Answer 21

if there sensitive to red , then red will be bright and everything will be dark
watch video

Question 22

how do rods work

Answer 22

highly sensitive and only work in the dark conditions at night
-eg when your room is dark your rods are activated (they saturate quickly)
-however rods dont have high resolution so if you saw the world with only rods it would be blurry

Question 23

density of rods and cones

Answer 23

-look at graph
-where you look is 0, the surroundings are around
-so your cones drop significantly in your peripheral vision-we aren’t great at detecting colour if we aren’t directly looking at it
- rods are high in peripheral vision(eg dim stars sometimes cant see them directly but can see them if you look at an angle)

Question 24

explain the graph, which shows what it looks like when someone has two photoreceptor kinds

Answer 24

-in the graph, one p kind peaks at blue and one around yellow
-the moment the nervous system has more sensors it starts processing, meaning you have a measure of colour
-if you shine a laser beak and it shines about 600, you know its slightly reddish, (reference the graph )
-

Question 25

a two photopigment system (possessed by some mammals) enables the eye to.....

Answer 25

extract some wavelength information (has mor understanding of the colours around them)

Question 26

why does a two pigment system sometimes confuse colours ?

Answer 26

-because any one wavelength can be matched by a pair of wavelengths -look at slides (shining light at around 420, and 620 would have the same effect as shining it at 460 (where the two overlap) -still better than having a single one

Question 27

what is trichromatic system -why does this system confuse colours less

Answer 27

-the human eye has 3 cone photoreceptors under photopic conditions so it is trichromatic (three coloured ), sensitive to blue,greens and reds (reference graph) -any wavelength will produce three responses , a trio that is les likely to be confused with any other single wavelength

Question 28

what are the 3 cone types

Answer 28

-the 3 cone pigment types named for their wavelength sensitivity - L,M,S -L cones are long wavelength sensitive (reds orange, yellows) -M cones are medium wavelength sensitive (yellows-greens) -S cones are short wavelengths sensitive (blues)

Question 29

pattern of cones in retina -approximatley twice as many __ as ___ -many fewer __ than __ and __ cones -central parts of the retina have no __ cones -central parts of the retina have an additional overlying ____ _____ called the ____ ____ -hence colour vision _____ in different parts of the _____

Answer 29

-twice as man L than M -many fewer S than M and L -central part has no S cones -additional overlying yellow pigment called macular pigment -hence colour vision varies in different parts of the retina

Question 30

explain the nervous system interpreting colours according to the graphs

Answer 30

-when your nervous system has 3 inputs (reds, greens, blues) it starts to do many more calculations from it -look at graph, if you shine light on the visual system and it has a response of say (short blue signal going to brain, longer red signal and really long green signal-(cone excitation) -if you look at some white patch that is the response, however when you look at something slightly more blue the blue signal (cone excitation) goes higher as the brain interprets the blue as more saturated same with green and red etc

Question 31

psychophysical evidence for trichromacy -colour opponency

Answer 31

-if you stare at a green image for a minute and then look at a white or grey patch , a red aftereffect of the image is seen for a few moments -similar with yellow and blue -this demonstrates colour opponency

Question 32

trivarient processing

Answer 32

trivariant means 3 different calculations -subsequent processing os trivariant i.e two oponent colour channels and one brightness channel -oponent colour channels are red/green and yellow/blue -the opponent brightness channel is light /dark

Question 33

n