M2 Lecture 10: Feb 14

Question 1

what is Opponent color theory

Answer 1

The theory that perception of color depends on the output of three mechanisms, each of them based on an opponency between two colors: red–green, blue–yellow, and black–white

Question 2

Ewald Hering (1834–1918) noticed that some color combinations are “legal” while others are “illegal.”
 explain

Answer 2

We can have bluish green (cyan), reddish yellow (orange), or bluish red (purple).
We cannot have reddish green or bluish yellow

Question 3

explain Hue cancellation experiments

Answer 3

Start with a color, such as bluish green.
The goal is to end up with pure blue.
Shine some red light to cancel out the green light.

Adjust the intensity of the red light until there is no sign of either green or red in the blue patch

Question 4

If you do hue cancellation across the entire spectrum, there are certain colors that …

Answer 4

can’t be “cancelled” by adding red/green or yellow/blue

Question 5

what is Unique hue:

Answer 5

Any of four colors that can be described with only a single color term: red, yellow, green, blue.
For instance, unique blue is a blue that has no red or green tint.
Note: “unique red” has a longer spectral locus

Question 6

Cones in general are very sensitive to the intensity of the light, for a wide range of wavelengths.

-> The absolute level of activity of a particular cone type is therefore relatively what

Answer 6

uninformative (i.e. “there is a lot of light”).

Question 7

The difference of activity between types of cones is what

Answer 7

much more informative

Question 8

what are the equations to determine what wavelength you are actually seeing

Answer 8

[L – M] or [M – L] compute red vs. green.

- [L + M] – S or S – [L + M] compute blue vs. yellow.
- [L – S] or [S – L] and [M – S] or [S – M] are not that 	informative because L and M are so similar and are not 	used 
- [L + M + S] encodes general brightness

Question 9

what are Afterimages

Answer 9

A visual image seen after a stimulus has been removed.

Question 10

afterimages are caused by what

Answer 10

habituation (chromatic adaptation) of activated cones

Question 11

what is Negative afterimage

Answer 11

An afterimage whose polarity is the opposite of the original stimulus.
Light stimuli produce dark negative afterimages.
Colors are complementary. Red produces green afterimages and blue produces yellow afterimages (and vice versa).
This is a way to see opponent colors in action

Question 12

what is Color constancy

Answer 12

The tendency of a surface to appear the same color under a fairly wide range of illuminants.

Question 13

To achieve color constancy, we must what

Answer 13

discount the illuminant and determine what the true color of a surface is regardless of how it appears.

Question 14

what is Illuminant

Answer 14

The light that illuminates a surface.

Question 15

For the same surface, the pattern of activation of S, M and L cones can vary greatly depending on the what.

Answer 15

illuminant

Question 16

How is constancy achieved?

Answer 16

1. Discounting the illuminant

2. Deduction

Question 17

what is Discounting the illuminant

Answer 17

• Calculating the mean spectrum across the visual field and subtracting it from the pattern of cone activity.
  
  • Habituation (chromatic adapation): the cones activated by the illuminant spectrum get “tired”

Question 18

what is Deduction

Answer 18

• Intelligent guesses about the illuminant
• Assumptions about light sources
• Assumptions about surfaces

Question 19

what is Euclidian geometry

Answer 19

Parallel lines remain parallel as they are extended in space.
Objects maintain the same size and shape as they move around in space.
Internal angles of a triangle always add up to 180 degrees, etc.

Question 20

are the images projected onto the retina are Euclidean!

Answer 20

no

Therefore, our brains work with non-Euclidean geometry all the time, even though we are not aware of it.

Question 21

(Euclidean ) line that are parrallel in the external world, converge towards the ____ in our retinal image of the world.

Answer 21

horizon

Question 22

(Euclidean ) Objects that are the same size in the external world,_____ with distance in our retinal image of the world.

Answer 22

shrink

Question 23

How do we perceive space?

Answer 23

Monocular cues

Binocular Vision and Stereopsis

Question 24

what are the types of monocular cues

Answer 24

Optic flow
Metrical depth cue
Nonmetrical depth cue: 
Relative size
Familiar size
Relative height
texture gradient
Relative metrical depth cue: 
linear perspective
Vanishing point
motion parlax

Question 25

what is Occlusion:

Answer 25

A cue to relative depth order in which, for example, one object partially obstructs the view of another object.

Question 26

most reliable of all of the depth cues (only other possibility is what

Answer 26

accidental viewpoint

Question 27

what are the types of Occlusion

Answer 27

Metrical depth cue

Nonmetrical depth cue

Question 28

what is Metrical depth cue

Answer 28

A depth cue that provides quantitative information about distance in the third dimension.

Question 29

what is Nonmetrical depth cue:

Answer 29

A depth cue that provides information about the depth order (relative depth) but not depth magnitude.

Question 30

what is Relative size

Answer 30

A comparison of size between items without knowing the absolute size of either one.
All things being equal, we assume that smaller objects are farther away from us than larger objects.

Question 31

what is Familiar size

Answer 31

A comparison of size between items when knowing the absolute size one of the items.
In this case, we can infer the absolute distance because we know the exact size of one of the objects.

Question 32

what is Relative height:

Answer 32

For objects touching the ground, those higher in the visual field appear to be farther away. In the sky above the horizon, objects lower in the visual field appear to be farther away.

Question 33

what is Texture gradient:

Answer 33

A depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get.
Texture gradients result from a combination of the cues of relative size and relative height.

Question 34

The metrical cues of relative size and height can give the visual system more or less information than a nonmetrical cue like occlusion can.

Answer 34

more

Question 35

what is Relative metrical depth cue:

Answer 35

A depth cue that could specify, for example, that object A is twice as far away as object B without providing information about the absolute distance to either A or B.

Question 36

what is Linear perspective

Answer 36

Lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image as they extend into the distance

Question 37

what is Vanishing point:

Answer 37

The apparent point at which parallel lines receding in depth converge.

Question 38

Linear perspective also result from what

Answer 38

a combination of the cues of relative size and relative height.

Question 39

what is Aerial perspective:

Answer 39

A depth cue based on the implicit understanding that light is scattered by the atmosphere.

More light is scattered when we look through more atmosphere.
Thus, more distant objects appear fainter, bluer, and less distinct.

Question 40

what is Motion parallax

Answer 40

Images closer to the observer move faster across the visual field than images farther away.
The brain uses this information to calculate the distances of objects in the environment.
Head movements and any other relative movements between observers and objects reveal motion parallax cues.

Question 41

what is Optic flow

Answer 41

the apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene.

• Objects that are closer to the observer will move more rapidly.
• Objects in the focus of expansion won’t move