Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

perception > Brightness & colour > Flashcards

Brightness & colour Flashcards

1
Q

visible light

A

band of energy within the electromagnetic spectrum, can be described by:

  • its wavelength (difference in peaks of the electromagnetic waves)
  • its intensity/luminance (amount of photons)
  • wavelengths from 400-700nm
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

light

A

type of electromagnetic radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

increased luminance =

A

lots of photons and increased brightness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

3 ways light interacts with objects and surfaces in the environment

A
  1. absorption = as photons collide with particles of matter
  2. reflection = as light strikes opaque surfaces
  3. transmission = as light passes through transparent matter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

human eye

A
  • eyes use convex cornea and lens to project and acts to focus light and form image at the back of the eye (retina) where the sensation happens
  • photoreceptors, which are cells that convert light into neural signal, transduce light into an electrical potantial
  • then use other cells to process info to pass it onto the retinal ganglion cells
  • these signals then flow through a network of neurons to retinal ganglion cells and then out the back of the eye via the optic nerve
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

2 types of photoreceptors:

A
  1. Rods: located in peripheral retine
    - Sensitive to low light levels therefore capable of operating in low light levels (can detect single photon)
  2. cones: concentrated in centre of retina (fovea)
    - not sensitive to light therefore require higher light levels to respond
    - 3 difference photopigments, sensitive to short, medium, and long waveleghtns
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

photopigments

A

= part of receptor that responds to light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

in the visual pathways..

A

..Visual info is transmitted from the retinal to the brain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The main pathway for vision consists of

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what happens at the optic chiasm

A

they get info from 2 eyes being re organised so anything happening in the right visual field can be reflected to the left side of the brain + vice versa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

relationship between light intensity and perceived brightness

A

higher intensity tend to be perceived as brighter

- however not straightforward as brightness perception is influenced by both bottom-up and top-down processes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

why are some parts of a picture of a dog lighter

A

because more light/photons are being received

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what factors is our perception of brightness heavily influenced by:

A
  1. Bottom up factors:
    - light and dark adaptation
    - lateral inhibition
  2. top down factors
    - impact of shadows
    - likely direction of lighting source
  • These factoids help function in normal environments e.g. achieve brightness constancy but can result in illusions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

why is brightness constancy important

A

important otherwise it would be harder for us to see under different lighting conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

light/dark adaptations

A

when light levels are high lets adjust sensitivity levels of retina cells so it takes more light to get same response

  • the sensitivity of retina is constantly adjusted to compensate fro changes in mean luminance
  • sensitivity is reduced when the mean intensity of the image is high and increased when it is low
  • This process dictates that the retina encodes contrast (the ratio of an objects luminance relative to the mean or background luminance) plays a critical role in achieving brightness constancy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

negative afterimages

A

Adapting different parts of retinal to different amounts of light - bits that were back keep sensitivity high and whites turn down

17
Q

lateral inhibition

A

Bottom up process
- makes visual system sensitive to changes in luminance

  • early form of information processing in retina
  • retinal ganglion cells receive both excitatory (+ more likely to respond) and inhibitory (- less likely to respond) from neighbouring photoreceptors
  • arranged in a centre-surround configuration across the retinal image
18
Q

Brightness perception - top down influences

A

Shadows

  • visual system tries to maintain brightness constancy when the amount of light falling on a surface is affected by shadows
  • this can result in ‘errors’ in 2D images portraying 3D scenes
  • The checker-shadow illusion tricks brain as because B is in a shadow you would expect it to be brighter to have the same luminance
  • our visual systems try to account for how the 3D structure of objects will affect the amount of light falling on them
19
Q

Colour perception - why does the world appear devoid of colour under low-light conditions?

A

when light levels are low only rod photoreceptors are sensitive enough to operate

  • rods contain a single type of photopigment (rhodopsin)
  • light of different wavelengths and intensities can elicit identical responses
  • This makes it impossible to accurately signal different wavelengths therefore you cannot perceive colour
20
Q

cone photoreceptors contain one of 3 different photopigments.. name them

A
  1. s-cones: cones that are preferentially sensitive to short wavelengths (blue cones)
  2. M-cones: cones that are preferentially sensitive to middle wavelengths (green cones)
    L: cones that are preferentially sensitive to long wavelengths (red cones)
21
Q

trichromacy

A

the relative outputs of the three cone types allows unambiguous signalling of wavelength

22
Q

what are the 3 variations of trichromacy

A
  1. monochromacy = either 0 or 1 functioning cone type
  2. dichromacy = only 2 functioning cone types
    - Protanpia = missing L cones
    - Deuteranopia = missing M cones
    - Tritanopia = missing S cones
  3. anomalous trichromacy = defect in one of the cone types
    - protanomaly = L cone defect
    - Deuteranomaly = M cone defect
    - Tritanomaly = S cone defect
23
Q

Colour opponency

A
  • Retinal ganglion cells receive excitatory (+) and inhibitory (-) from different cone types
  • This results in distance red/green and blue/yellow pathways
24
Q

colour perception - negative afterimages

A

colour opponency can be demonstrated using negative afterimages

  • e.g. staring at a red object will result in a green afterimage
  • adaptation to red causes a reduction in the sensitivity of the long wavelength cones, creating an imbalance in the inputs to red/green opponent retinal ganglion cells that our brain perceived as a colour

The lilac chase

  • green blob is a negative afterimage
  • pink disappears because we are adapting and reduce sensitivity
25
Q

colour perception bottom up and top down influences

A

bottom up = colour opponent processing

top down = Our visual systems also try to achieve colour constancy by accounting for the intensity and composition of light hitting different surfaces

perception (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions