High level of vision

Question 1

What is the visual system?

Answer 1

Hierarchically structured
Large no. of feedback connections from higher areas down to lower areas in the hierarchy, as far as the LGN.

Question 1

What is the visual system?

Answer 1

Hierarchically structured
Large no. of feedback connections from higher areas down to lower areas in the hierarchy, as far as the LGN.

Question 2

How many cones does colour vision depend on?

Answer 2

3

Question 3

How is colour vision imaged?

Answer 3

through adaptive optical imaging
Deformable mirror = compensates for moment-by)moment motion in the mirror + stables the image @ fixed position

Question 4

Describe the 3 types of cones

Answer 4

The are sensitive to short, medium and long wavelengths of light
Called the S, L, M Cones

Question 5

How is colour information encoded?

Answer 5

1. The retina by midget cells (signaling red-teal
   differences)
2. Small bistratified ganglion cells (signaling lime-violet differences).

Question 6

What do selective ganglion cells do with visual information?

Answer 6

Two colour-selective cells types send diff. visual info to the brain in 2 parallel processing streams

Question 7

What are the genes responsible for colour vision?

Answer 7

Genes encoding L and M photosensitive pigments lie on X-chromosome
Trichromats = 1 copy of L photopigment gene + more copies of M photopigment gene after. First 2 genes = expressed.

Question 8

What happens in dichromacy colour vision?

Answer 8

M or L photopigment gene is missing+ retina contains only 2 types of cones bc line up wrong in cell division.

Dichromats = colours one dimension only

Question 9

What is anomalous trichromacy?

Answer 9

1 photopigment gene = hybrid, sections of M + L photopigment genes.

3 cones types but 2 very similar sensitivities.

the red-teal signal carried by midget cells = weaker (bc 2 types provide similar info) + colour perception of red-teal colour differences is presumably muted

Question 10

How does individual differences affect colour perception

Answer 10

small genetic differences = change function of cone types = huge impact on perception

Question 11

Is bottom-up signals from the retina the only thing needed for colour vision?

Answer 11

Also depends on higher level perceptual processes (e.g conception of the illumination + 3D interpretation of the scene)

Question 12

What is colour constancy?

Answer 12

How we perceive the colours of objects as stable despite changes in colour illumination + sometimes large changes in the spectrum of light the object reflects.

Question 13

What is the problem of maintaining colour constancy?

Answer 13

Light reflected from objects = object’s reflectance spectrum
(the proportion of light reflected at each wavelength) + the illumination spectrum.

Question 14

What is the spectrum of light?

Answer 14

Falls on the retina

A product of illumination spectrum + reflection spectrum

Question 15

bottom-up signals (spectrum of illuminants) affect maintaining colour constancy?

Answer 15

Signals sent by the 3 classes of cone when exposed to the light reflected from the object = different under the two different illuminants

Question 16

How does the visual system maintain colour constancy?

Answer 16

The visual system must discover the spectrum of the illuminant to discount it, so that perception can represent the object’s stable reflectance spectrum.

Question 17

How does the visual system find the colour of illumination?

Answer 17

Colour memory
grey world
brighter is white
highlights
3D structure of the scene and shadows

Question 18

Why is colour constancy sometimes wrong?

Answer 18

Objects appear to “change colour” = different illuminations.

Bc unusual illuminant spectrum/ reflectance spectrum or unusual
features of the image = the observer misinterprets the illuminant.

Question 19

Example of individual differences affecting perception of a dress

Answer 19

Research = low-level and high-level contributing factors:
individual differences in sensitivity to short wavelength light (reduces with age)
Differences in the interpretation of the scene.

Sensitivity to short wavelength light reduces w/ age as the
lens yellows = White/gold perceptions + increase with age

Question 20

What is lightness constancy?

Answer 20

Perception of the lightness of surfaces = the proportion of light they reflect, + not the intensity of the illumination.

Question 21

What is Wallach (1948) ratio law?

Answer 21

perception of lightness is determined by the ratio of
the luminance of a surface with its background.

They make perceptual matches when both patches make have the same luminance ratio w/ their surrounds.

The centre-surround structure of retinal ganglion cell receptive fields signals the difference between centre and surround, so low-level visual processing accounts for at least part of the influence of context on perception.

Question 22

What does Wallach (1948) ratio law and how does it affect light perception?

Answer 22

ratio law can partly = lightness constancy but higher-level factors
(like the perception of the scene geometry, shadows and illuminants = play a role).

Question 23

What does Gilchrist’s (2006) experiment show?

Answer 23

Importance of perception of the 3D geometry of the scene for the visual system’s perception of lightness.

Question 24

What were the results of Gilchrist (2006) and how does this effect light perception?

Answer 24

Observer’s interpretation of the 3D scene = huge impact on their
perception of the lightness of the flaps.

condition 1 = one eye 9 (no depth)
condition 2 = both eyes (depth perception)

Can’t be explained by low level mechanisms

Question 25

What is the Gelb effect, and how does this effect light perception?

Answer 25

Perceived lightness can flip from white to black once the true
the luminance of the illumination is known.

Question 26

What is perceived transparency, and how does this affect light perception?

Answer 26

Transparency through semi-opaque foreground media can also influence perception of the lightness of surfaces

Question 27

What is size constancy?

Answer 27

Objects don’t typically seem smaller = further away from observer bc the visual system maintains size constancy, perceptually scaling objects to their perceived distance = maintain a constant perceived size.

Question 28

When does size constancy fail?

Answer 28

Can fail = situation we are unfamiliar with + where
we can’t accurately judge depth.

Question 29

How is the corridor illusion an example of size constancy being wrongly applied?

Answer 29

two images of the same physical size appear to be different sizes bc the visual system perceptually scales up the size of the further object to compensate for its greater depth.

Question 30

What is Emmett’s law?

Answer 30

Perceived size is proportional to the product of retinal
image size and perceived distance.

Perceived size = k(retinal image size)(perceived distance)

Question 31

What is the Ame’s room and how does it show size constancy being wrongly applied?

Answer 31

If the visual system = is tricked into thinking an object is nearer/ further than it is (by providing cues to estimate depth = sizes
misperceived.

In same room, both people appear to be at the same distance, but actually, one = further away + casts a small retinal image.
Bc cues in the scene tell the visual system object is near = size isn’t scaled up perceptually (to compensate for distance) and it seems much smaller than it should be.

Question 32

What is an unconscious inference?

Answer 32

Helmholtz, 1867

visual perception = ‘unconscious judgements’. Rather than the retinal image, what we perceive is the result of what we infer to be the stimulus, via a collection of unconscious processes.

Question 33

What does the idea of ‘inference’ suggest?

Answer 33

To some extent we see what we expect to.

We use learnt info from experiences = reconstruct best guess of what external objects must have given to the retinal image

Question 34

What is an assumption of inference?

Answer 34

light comes from above = causes to infer which of these discs are bumps and which are indentations, and biases our perception of the stimulus.

Question 35

What is the uniformity illusion?

Answer 35

Caused by applying into peripheral vision (where vision has lower acuity) what we expect, based on info in the centre of the visual field.

Question 35

What is the uniformity illusion?

Answer 35

Caused by applying into peripheral vision (where vision has lower acuity) what we expect, based on the info in
the centre of the visual field.

Question 36

What is another of uniformity illusion?

Answer 36

Cohen et al. (2020) = participants fail to notice when the stimulus to their peripheral vision is rendered without colour.

Our perception = peripheral visual field is colourful + detailed may be largely constructed by the brain.

Question 37

What is the bayesian inference?

Answer 37

Idea of inference or “seeing the expected” can be brought into the mathematical framework of Bayes’ theorem.

The uncertainties associated with the ‘signal’ and our ‘prior expectation’ determine how strongly we will weight them in perception.

Bayes rule = p(object|image) = kp(image|object)p(object)

Question 38

How bottom-up and top-down signals work together for perception?

Answer 38

both ‘bottom-up’ signals from the sense organs

+

‘top down’ signals from the brain

= carry info abt expectation + context

Question 39

True or false

The retinal image is inherently ambiguous, but perception uses
contextual information to maintain constancy and reconstruct the
properties of objects independently from unstable viewing conditions

Answer 39

True