Week 11 Flashcards
(63 cards)
1
Q
Why can you not have a reddish green?
A
Because red and green are opponent colours; mixing them creates yellow.
2
Q
What is the afterimage of a blue object?
A
It is a yellow afterimage, due to opponent processing.
3
Q
What determines the colour of reflected light?
A
Reflectance and illumination.
4
Q
How does the visual system achieve colour constancy?
A
Through habituation and discounting the illuminant.
5
Q
What are the three depth cue groups?
A
Oculomotor, monocular, and binocular cues.
6
Q
What are the oculomotor depth cues?
A
Binocular convergence and accommodation.
7
Q
What are the monocular depth cues?
A
Accommodation, pictorial cues, movement-based cues.
8
Q
List four pictorial depth cues.
A
Occlusion, relative height, texture gradient, shadows.
9
Q
What causes size constancy?
A
Size of retinal image and perceived distance to the object.
10
Q
What equation represents size constancy?
A
S = K × (R × D), where S is apparent size.
11
Q
What is the physical definition of sound?
A
Pressure changes in a medium like air or water.
12
Q
What is the perceptual definition of sound?
A
The experience or sensation we have when we hear.
13
Q
What does the ‘missing fundamental’ phenomenon show?
A
Humans perceive the fundamental frequency even if it’s absent.
14
Q
What is timbre?
A
The perceptual quality that differentiates sounds with the same pitch.
15
Q
What are the two attributes of pitch?
A
Tone height and chroma.
16
Q
What is auditory localisation based on?
A
Binaural and monaural cues.
17
Q
What causes the cone of confusion?
A
Points with same interaural differences that can’t be distinguished.
18
Q
How do humans determine sound elevation?
A
By frequency notches created by the pinna.
19
Q
What is the precedence effect?
A
Sounds heard within 5–20 ms are fused; no echo is perceived.
20
Q
What factors affect architectural acoustics?
A
Reverberation time, intimacy time, bass ratio, spaciousness factor.
21
Q
How do we perceive depth?
A
By using a number of different cues, which can be divided into three groups:
Oculomotor cues
- Cues based on our ability to sense the position and state of our eyes
Monocular cues
- Cues based on the visual information available within on eye
Binocular cues
- Cues that depend on visual information within both eyes
22
Q
What are the two main oculomotor cues?
A
- Binocular convergence
- Accommodation
23
Q
What are the three main monocular cues?
A
Accommodation
Pictorial cues
Movement-based cues
24
Q
What are the 7 main pictorial cues?
A
There are 7 main pictorial cues
Occlusion
Relative height
Familiar and relative size
Perspective convergence
Atmospheric perspective
Texture gradient
Shadows
25
Why do we have shadows?
Cue for relative depth
Cue for depth perception (humans assume light is coming from above)
26
What are the two main movement-based cues?
Motion parallax
Deletion and accretion
27
What are the cues that indicate relative depth?
Occlusion, Deletion & Accretion, Relative height, Atmospheric perspective
28
What are the cues that indicate absolute depth?
Size of retinal image, texture gradients, motion parallax, accommodation, convergence
29
What is Binocular disparity?
Because the left and right eyes are offset relative to each other, they see the world from slightly different viewpoints.
To be more precise, we need to consider the retinal images.
The lens of the eye creates an image of the outside world on the retina…
…but this image is flipped up/down and left/right.
Because the left and right eyes see slightly different versions of the scene…
…the left and right retinal images are different
When the person looks at Bill (i.e. fixates on Bill), the retinal images of Bill occur at the same point on the left and right retinas.
However, the retinal image of Mary occurs to the left of the retinal image of Bill in the left eye…
…but to the right of the retinal image of Bill in the right eye.
30
What is the correspondence problem?
If the object in the visual scene are made distinct from each other…
…by colour each one a different colour…
…the associations become unambiguous.
31
What is the relationship between depth & Size?
Depth and size are closely related.
How big an object appears can affect how far away it appears and…
…how far away an object appears can affect how big it appears…
…as demonstrated by the following picture.
32
How do we perceive size?
The perceived size of an object is determined by two factors
Its angular size
Its perceived depth
33
What is angular size?
Angular size is just the visual angle an object subtends.
The closer an object is to person, the larger its angular size
34
What is Size constancy?
Size constancy is the phenomenon where an object’s apparent size does not depend on is physical distance.
When an object is far away it appears to be the same size as when is it closer…
…even though its visual angle is much larger in the latter case.
To achieve size constancy an observer needs to consider both the size of the retinal image and the distance of the object.
35
How to achieve size constancy?
To achieve size constancy an observer needs to consider both the size of the retinal image and the distance to the object.
S = K x (R x D)
Where
S = apparent size of an object
K is a constant
R = size of the retinal image
D = perceived distance to the object
36
Why is size and apparent depth so closely linked?
If someone misestimates the distance of an object, they will probably misestimate the size of the object.
37
What causes size illusions?
Most size illusions are caused by causing people to mistake the distance to an object so that it appears larger or smaller than it really is.
If an object appears closer than it really is, it will appear smaller than it really is.
If an object appears further away than it really is, it will appear larger than it really is
38
What is the Holway and Boring (1941) study?
Holway and Boring (1941) investigated how observers accurately estimate the size of objects.
In particular, they investigated how depth cues influence size judgments.
- Observer sat at an intersection of two corridors and could view a test circle in one corridor and comparison circle in the other corridor.
- Their task was to adjust the size of the comparison circle to match the size of the test circle.
- The test circles were of different sizes but were presented at different distances so that their angular size was always the same.
39
What were the conditions of Holway and Boring (1941) study?
In condition 1, observers could determine the depth of the test patch using binocular disparity, motion parallax and shadows.
- condition allowed for binocular disparity, motion parallax and shadows
In condition 2, observers viewed the test circle with one eye to remove binocular disparity cues.
- condition allowed for motion parallax and shadows
In condition 3, observers viewed the test circle through a peephole to remove motion parallax cues.
- condition allowed for shadows
In condition 4, in addition to viewing the circle through a peephole, drapes were used to remove the shadows
- condition allowed for none of the size perception cues
40
What is the Physical aspects of sound?
The term “sound” is often used to refer to both the physical phenomenon (e.g. people talk about “sound waves”) and to the perceptual phenomenon.
So, you have to be very clear as to which definition you are using.
Physical definition: Sound is pressure changes in the air or other medium (e.g. sound waves in water).
Perceptual definition: Sound is the experience (i.e. sensation) we have when we hear.
41
What happens to sound as pressure changes?
The pressure waves (i.e. the sound waves) move though air at 340 m/s and water at 1,500 m/s.
However, only the pressure wave is moving.
Each air molecule is just moving back and forth to create regions of high and low pressure.
I can’t show you the movement of individual air molecules, but I can show you a longitudinal wave on a slinky spring!
42
What are pure tones?
A pure tone occurs when the change in air pressure occur in a pattern described by a mathematical function called a sine wave.
The higher the frequency the higher the pitch (for pure tones)
1 Hz (spelt Hertz) = 1 oscillation per second
Humans can hear tones ranging from about 20 Hz to about 20,000 Hz
43
What is Amplitude?
The greater the amplitude, the louder a sound seems.
Amplitude is measured in decibels (db)
dB = 20 x logarithm(p/po)
Where p is the pressure (i.e. amplitude) of the sound (measured in micropascals)
po is the reference pressure, usually set to 20 micropascals
44
What are the complex tones?
The 200 Hz tone is known as the fundamental frequency and is also known as the first harmonic.
400 Hz is the second harmonic
600 Hz is the third harmonic
800 Hz is the fourth harmonic
Because the first harmonic is 200 Hz, this means that the wave repeats every 5 ms.
45
How is loudness determined?
The greater the amplitude, the louder a sound seems.
However, the actual loudness of sound also depends on the frequency
Perceptually loudness is measured in phons
Phons are units of loudness for pure tones.
46
How is pitch determined?
For a pure tone, pitch is determined by the frequency.
For a complex tone, pitch is usually determined by the fundamental frequency.
Why do I say usually?
Because pitch is a psychological quantity, not a physical quantity, and depends on a number of factors.
You can say a tone has a frequency of 200 Hz
But you cannot say a tone has a pitch of 200 Hz
Instead, you typically describe pitch in terms of musical notes…
…saying things like “A”, “B” or “C”
Neighbouring letters of the same type (e.g. C1 and C2) on the keyboard are separated by an octave.
Notes with the same letter sound similar.
They are said to have the same chroma.
As one moves from left to right on the piano keyboard, the tone height increases
47
What is Pitch?
Pitch is a psychology variable with two attributes
- Tone height
- Chroma
Chroma is cyclic in that neighbouring letters of the same type (e.g. C1 and C2) sound similar
Conversely, tone height increase from left to right on the piano keyboard in a continuous manner.
Thus, when talking about pitch you need to be clear whether you are talking about tone height or chroma
48
What is fundamental frequency?
Recall that complex tones can be decomposed into their constituent frequency components.
For many sounds they frequency components are multiples of a particular frequency.
This frequency is called the fundamental frequency.
For example, if a tone comprises four frequencies, 200 Hz, 400 Hz, 600 Hz and 800 Hz, the fundamental frequency is 200 Hz as all the frequencies are multiples of 200 Hz
Thus, the tone will repeat at 200 Hz.
49
What is Missing fundamental?
Consequently, humans will perceive the fundamental frequency to be present even when it is absent.
In other words, they will perceive the “missing fundamental”
The missing fundamental will determine the pitch of the complex tone (even though it is absent!)
This is why you can hear over the telephone the low pitch (i.e. tone height) of a male voice corresponding to a 100 Hz frequency even though telephones do not reproduce sounds below 300 Hz.
50
What is Timbre?
When two different instruments play the same note, they don’t sound the same
This is because, in addition to playing the fundamental frequency, each instrument plays many of the harmonics (i.e. multiples) of the fundamental frequency.
The amplitude of these harmonics will be different for different instruments…
…which makes the resultant waveform different…
…which is why different instruments sound different.
They are said to have different timbres.
51
What is Periodic vs Aperiodic?
Up to now we have been talking about musical sounds…
…all of which have been periodic.
This means that each wave form repeats at a regular interval
However, it is also possible to have waveforms that don’t repeat.
For example, a door slamming shut or a gunshot.
These sounds are aperiodic.
52
How does auditory localisation occur?
Auditory localisation is based on both binaural and monaural cues.
Binaural cues include:
- Interaural time difference
- Interaural level difference
53
How to determine interaural level difference
For high frequency sounds, there can be a large interaural level difference between the two ears due to the sound shadow caused by the head.
For low frequency sounds, the interaural level difference is much less
54
What is the monaural cue for elevation?
Sound coming from different elevations bounces off different parts of the pinna before entering the ear canal.
55
How is the monaural cue for elevation determined?
sound acquires characteristic frequency notches that depend on its elevation
These can be used to determine the elevation of the sound source
56
What is the precendence effect?
If you hear the same sound twice with a temporal separation of 5-20ms, you will not register the second sound.
You will not hear an echo.
This is why you typically hear only the direct sound.
However, if the temporal separation between the two sounds is more than about a 10th of a second, you will hear the two sounds as separate…
…so, you will hear an echo.
57
What are Architectural acoustics
Although you typically don’t hear the indirect sound, it will affect the perceived quality of the sound.
Consequently, the architectural acoustics of a concert hall affect the quality of the sound in the concert hall.
58
WHat are the four factors that determine the quality of the architectural acoustics?
There are four factors that determine the quality of the architectural acoustics
Reverberation time
Intimacy time
Bass ratio
Spaciousness factor
59
What is reverberation time?
This is the time it takes for sound to decreased by 60 dB.
For a concert hall it should be about 2 seconds.
For an opera hall, ideally it would be about 1.5 seconds to make the voices more distinguishable.
60
What is intimacy time?
This is the temporal difference between when the direct sound arrives, and the first indirect sound arrives.
Concert halls that are considered to have “good acoustics” typically have an intimacy time of about 20 ms.
61
What is the base ratio?
Measured for the indirect sound.
It is the ratio of low frequencies to middle frequencies for the indirect sound.
Ideally, you want a high base ratio.
62
What is the spaciousness factor?
The ratio of indirect sound to total sound.
The greater the proportion of indirect sound the greater the spaciousness factor.
Ideally you want a high spaciousness factor
63
What are the five cues that people tend to use to separate sound sources?
There are five cues that people tend to use:
Location
Onset Time
Timbre and Pitch
Auditory Continuity
Experience
