Sensation and Perception - UNI Flashcards
(239 cards)
1
Q
What is attention?
A
Attention is the ability to preferentially process some
parts of a stimulus at the expense of processing of
other parts of the stimulus.
2
Q
Example of attention
A
For example, if you focus your attention on my face,
you will preferentially process my face at the
expense of processing other objects in the scene.
Consequently, you will perceive my face more clearly
than other objects in the scene.
3
Q
4 reasons we need attention
A
- Your perceptual system has a limited capacity.
- You can’t process everything in the visual scene
simultaneously - For example, in front of me now there are lots of
people. I can’t look at everyone at the same time. To avoid being overwhelmed, I pay attention to only
one person at a time and ignore the rest. - Attention therefore helps us avoid becoming
overwhelmed.
4
Q
What is overt attention?
A
looking directly at an object
5
Q
What is covert attention?
A
looking at one object but
attending to another object
6
Q
How can you tell where someone is attending?
A
By tracking their eye movements (where they are looking)
7
Q
When a person looks at a object, they are said to______on it
A
fixate
8
Q
What are they eye movements between fixations known as & what is the speed of these movements?
A
Ballistic & very fast
9
Q
What is the term for when your eyes jump from one part to another of a visual scene (as opposed to smooth movements)
A
saccades
10
Q
What are the rests between saccade jumps known as?
A
Fixations
11
Q
What are fixations determined by?
A
Your goals and expectations
12
Q
What two processes direct our attention?
A
An initial involuntary process (mediated by attentional
capture)
A subsequent voluntary process (guided by your goals and
expectations)
13
Q
What happens in your brain when a scene is first presented?
A
your fixations are captured by salient parts of the scene (features of the scene)
14
Q
What is fixation on salient parts of a scene known as?
A
attentional capture
15
Q
Is attentional capture voluntary or involuntary?
A
Involuntary
16
Q
What happens after the first few fixations?
A
Your fixations can be directed according to your goals
17
Q
Is the directing of fixations voluntary or involuntary?
A
Voluntary
18
Q
Define salience
A
the quality of being noticeable
19
Q
What is attentional capture determined by?
A
the salience of the object
20
Q
What was Theeuwes 1992 study about?
red circle
A
The task was to report the
orientation of the line in the
square
The red circle was irrelevant.
However, because it was
salient, attention was initially
directed to it, and participants
often reported the orientation
of its line.
21
Q
What captures attention?
A
Contrast
22
Q
4 types of contrast
flicker
A
Regions of colour contrast or luminance contrast
Regions of size contrast
Regions orientation contrast
Regions of motion/flicker contrast
23
Q
What did Parkhurst et al. (1992) describe?
A
Visual maps vs Saliency maps
(visual = normal, saliency map = black and white, pixellated)
24
Q
What does salinecy determine?
A
What we attend to first
25
What did Yarbus (1967) describe?
| map
Scan paths. Pattern of eye movements that map an object
26
How do expectations determine fixations?
If an object is unexpected, you will fixate on it more often and focus on it more
27
Describe Vo & Henderson (2009)
Fixation Duration and Repeated
Fixations.
Semantically consistent vs semantically inconsistent object - put a saucepan on stove, then a printer (?), then saucepan floating above stove
28
Summarise what directs attention?
Initially, fixations are often involuntary
attentional capture
Then, the fixations are voluntary, goal directed and are
influenced by our expectations
29
What are the 3 main effects of attention?
Attention speeds responses
Attention can influence appearance
Attention can influence physiological responding
30
Posner (1978) - GET DETAIL AT LECTURE
In the Posner (1978) study, researchers investigated whether responses to stimuli would be faster if subjects knew the location of the stimulus. They used reaction time differences to stimuli at expected and unexpected positions to measure the efficiency of detection due to turning attention toward the expected location. The study aimed to determine if attentional shifts, rather than eye movements, influenced reaction times.
31
Describe Carrasco et al. (2004)
Attention Can Change the Apparent
Contrast of an Object:
Required to report
orientation of higher
contrast grating
When both gratings were of
equal contrast, typically
reported orientation of cued
grating...
...suggesting that cued
grating appeared to be
higher contrast
32
What did Carrasco show?
attention can
make objects appear to have a higher contrast
33
What have other studies shown about attention? (Anton-Erxleben et al., 2007; Fuller &
Carrasco, 2006; Turatto et al., 2007).
that attention can make
objects appear bigger, faster, and more richly
coloured
34
What do neurons in the brain respond more strongly to?
attended stimuli than to unattended
stimuli
35
Why is attention needed?
Your perceptual system has a limited capacity.
You can’t process everything in the visual scene
simultaneously.
To avoid being overwhelmed, you pay attention to
only part of the scene at a time and ignore the rest.
Attention therefore helps you avoid becoming
overwhelmed.
36
What directs your attention?
What you attend is usually determined by where you
fixate.
Initially, fixations are often involuntary and are
determined by the saliency of the scene (i.e.
attentional capture).
Then, the fixations are voluntary, goal directed, so
are influenced by your goals and expectations.
37
What are the effects of attention?
Attention speeds responses
Attention can influence appearance
Attention can influence physiological responding
38
What is the binding problem?
The issue of how an object’s individual features are
combined (i.e. bound) to create a coherent percept
39
When does the binding problem become an issue?
When there are multiple objects for you to look at - how do you see them individually?
40
What is the Feature Integration Theory?
suggests that the
binding problem is solved by attending to only one
location at at time. Crucially, only features associated with that location
are processed, so only those features are bound
together.
This avoids binding features from different objects
41
What is a prediction of FIT?
is that if attention is inhibited,
features from different objects will be incorrectly bound together - known as illusory conjunctions
42
What did Treisman & Schmidt (1982) show?
| ICs happen
That illusory conjunctions do occur (associating wrong colour with wrong letter - for more info see slide 48-49)
43
What is Balint’s Syndrome?
RM (patient) had parietal lobe damage, developed BS.
When multiple objects are present, RM has difficulty
focusing attention on a single object.
When shown two letters, each with a different colour,
reported the wrong letter colour combinations on 23% of
the trials, even when allowed to view the letters for as
long as 10 seconds!
So, RM very prone to experiencing illusory conjunctions
because he could not focus attention on just a single
object.
44
Some forms of visual search require______to occur
binding, for example, binding is required if the target contains the
same features as the distractors.
45
define conjunction search
If the target differs from the distractors only by its particular
conjunction of features
46
What does Feature Integration Theory predict for conjunction searches?
in conjunction searches attention needs to
be applied to each object in turn (i.e. one at a time) to
determine whether or not the attended object is the target
47
Are conjunction searches fast or slow?
Slow
48
Can other types of visual searches be performed without solving the binding problem?
Yes
49
What is a feature search?
the target contains a feature that the distractors
do not contain
50
What does Feature Integration Theory predict for feature searches?
ecause binding does not need to occur,
attention does not need to be applied to each item in turn
51
Are feature searches fast or slow?
fast
52
Attention can also determine what we ______
remember
53
If you don’t attend to it, chances are you_____
remember it
won’t
54
What is change blindness?
The parts of a scene (like 2 spot the differences) that you don't pay attention to can change, and chances are you won't notice the change
55
Why doesn’t change blindness occur all the
time?
Because changes usually generate motion
transients that draw attention to the location change,
thereby making it easy to spot the change.
56
What is the difference between adding a blank screen between to spot the differences?
motion transients occurred for every part of the image -
not just the parts that changed.
This meant that motion transients did not guide attention
to the change.
57
Who demonstrated that change blindness can occur in the real world?
Simons and Levin (1998)
58
How many objects can you attend to at a time and still notice the change?
4
59
What is the binding problem?
The issue of how an object’s individual features are
combined (i.e. bound) to create a coherent percept is
known as the binding problem.
Different aspects of a stimulus are processed
independently, often in separate brain areas.
For example, motion is processed by the dorsal
stream and form is processed by the ventral stream
60
What is an illusory conjunction?
A prediction of FIT is that if attention is inhibited, features
from different objects will be incorrectly bound together.
61
Why Are Conjunction Searches Predicted To Be Slow?
FIT predicts that in conjunction searches attention needs to
be applied to each object in turn (i.e. one at a time) to
determine whether or not the attended object is the target
Thus, these searches are predicted to be very slow
62
What is the problem with perception?
It seems effortless, but requires a lot of work
63
Are computers better or worse than humans at percieving objects
Worse
64
What systems do computer object
recognition systems use?
artificial neural networks
65
What did Athalye et al. (2018) investigate?
hat sort of images
these object recognition systems would misclassify.
Based on what they discovered, they then designed
images that would fool these systems.
66
What did the computer system ensorFlow’s InceptionV3 classify a picture of a turtle as?
A rifle
67
What did Alcon, 2019 state?
Misclassifications commonly occur with natural images if they (computers) are presented at unexpected orientations
68
What are the 3 factors that make object perception so hard?
The stimulus on the retina is ambiguous
Objects can be hidden or blurred
Objects look different from different viewpoints
and in different poses
69
Describe how the stimulus on the retina can be ambiguous?
All these lines form the same retinal image.
Thus, this 1D retinal image is ambiguous
Similarly, 2D retinal images are also ambiguous
in that multiple stimuli can give rise to the same
2D retinal image
70
Describe how Objects Can Be
Partially Occluded or Blurred
In the above photo, can you see my glasses that are
partially occluded by the book?
Most likely a machine would have difficulty
recognising my glasses because they are partially
occluded.
71
Describe how objects look different in different poses and from different viewpoints
Machines find it hard to recognise objects when they appear in unexpected poses or are viewed
from unexpected angles
72
How do humans solve these problems and
successfully perceive objects and scenes?
Too complex for this lecture alone, but two competing schools of thought:
Structuralism
Gestaltism
73
Who was structuralism proposed by?
Edward Titchener,
based on his studies under Wilhelm Wundt
74
What does structuralism distinguish between?
sensations and
perceptions
75
What are structuralism sensations?
elementary processes occur in response
to stimulation
76
What are structuralism perceptions?
Concious awareness of objects and scenes
77
What does Structuralism claim?
That sensations combine to form
perceptions. In other words, according to Structuralism, conscious
awareness is the sum of these elementary
sensations, and contains nothing that was not already present in these elementary sensations
78
What do Gestaltists claim?
The Gestaltists claim that conscious awareness
is more than the sum of the elementary
sensations (in direct contradiction with structuralism)
In other words, conscious awareness can have a
characteristics not present in any of the
elementary sensations.
79
What 2 pieces of evidence are there for Gestaltists?
Apparent motion
Illusory contours
80
What does an observer see in apparent motion?
An observer sees two stationary
dots flashed in succession.
Although each of the dots is stationary, the observer
perceives motion.
In other words, the conscious awareness has a
character (i.e. motion) not present in the elementary
sensations (because they were both stationary).
The conscious percept of motion was constructed
and was not present in the elementary sensations.
The physical stimulus itself is not moving.
81
What are illusory contours?
where the
conscious awareness has a characteristic not
present in the elementary sensations.
Illusory contours are seen in
locations where there are no
physical contours.
The conscious awareness of the
illusory contour is constructed –
there is no physical contour at
these locations.
82
Which is an overall better theory (structuralism or gestaltism)?
Gestaltism (the rest of the lecture will focus on this)
83
According to Gestaltism, humans are able to
perceive objects and scenes because of____________
Perceptual
organisation.
In other words, humans are able to make sense of a
visual image because they can perceptually
organise it into the constituent objects
84
Perceptual organisation is achieved by the
processes of____________ and ______________
grouping, segregation
85
What is grouping?
the process by which parts of an image
are perceptually bound together to form a perceptual
whole (e.g. the perception of an object)
86
What is Segregation?
the process by which parts of a
scene are perceptually separated to form separate
wholes (e.g. the perception of separate objects)
87
Together, what do grouping and segregation allow?
a scene to
perceptually organised into its constituent objects
thereby allowing observers to make sense of the
scene.
88
Take-home message of grouping and segregation
To make sense of scenes, both grouping and
segregation are needed.
Otherwise, the scenes cannot be perceptually
organised into meaningful units.
89
What are the 5 Gestalt principles of grouping?
Good continuation
Prägnanz
Similarity
Proximity
Common fate
Two additional ones (added later)
Common region
Uniform connectedness
90
What is the principle of good continuation?
Aligned (or nearly aligned)
contours are grouped together to
form a single object (see contour slide 37, lecture 2)
91
What does Prägnanz mean?
“Good figure”.
“principle of good
figure” or “principle of simplicity”
Essentially, groupings occur to
make the resultant figure as
simple as possible.
In the figure to the right you see a
panda, not a collection of splotches (see WWF logo)
92
What is the phenomenon of similarity?
The more similar objects are, the
more likely they will be grouped
together.
In a), all the dots are the same
colour so it is unclear whether
things are organised vertically or
horizontally.
In b), colour similarity groups the
dots into columns.
93
What is the phenomenon of proximity?
The closer the dots are, the more
likely they are to be grouped
together.
94
What is the phenomenon of common fate?
Things that are moving in the same way are
grouped together
95
What is the phenomeonon of Common Region?
Elements that are within the same region of
space tend to group together (Palmer, 1992)
96
What is the phenomenon of uniform connectedness?
Connected regions with the same visual
characteristics (e.g. colour) tend to group
together (Palmer & Rock, 1994)
97
What is the take home message for grouping images to form perceptual wholes?
There are a number of principles that help people to
group together parts of an image to form perceptual
wholes.
98
What are the three main difficulties of object perception?
There are a number of difficulties, but the three
most important ones are
The stimulus on the retina is ambiguous
Objects can be hidden or blurred Objects look different from different viewpoints
and in different poses
99
Describe two bits of evidence for Gestaltism?
There are two main pieces of evidence that support the claim that conscious awareness can
be more than the sum of the elementary sensations
These two pieces of evidence are:
Apparent motion
Illusory contours
100
How does Gestaltism claim that perceptual organisation is
achieved?
Perceptual organisation is achieved by the
processes of grouping and segregation.
Grouping is the process by which parts of an image
are perceptually bound together to form a perceptual
whole (e.g. the perception of an object)
Segregation is the process by which parts of a
scene are perceptually separate to form separate
wholes (e.g. the perception of separate objects).
Together, grouping and segregation allow a scene to
perceptually organised into its constituent objects
thereby allowing observers to make sense of the
scene.
101
Name four of the Gestalt principles of grouping
Good continuation
Prägnaz
Similarity
Proximity
Common fate
Common region
Uniform connectedness
102
What is segregation?
Seperating objects from each other, and objects from the background. If you didn't do this, the whole image = one object, = very confusing
103
What is figure to ground segregation?
Objects = figures
Background = ground
If you can identify what the figure is, you can typically identify the objects
104
When are regions of an image more likely to be seen as figures?
If:
They are in front of the rest of the image
They are at the bottom of the image
They are convex
They are recognisable
105
What is the Rubin vase?
Ambiguous image - can be a vase or 2 faces.
If vase is brought in front of image = seen as figure
If faces are brought in front of image = seen as figure
This shows that depth ordering affects figure perception
106
Are lower or higher areas seen as figures?
Lower
107
Is there a left-right bias for figures?
No
108
What did Peterson and Salvagio (2008) show?
| convex figure stuff
That if you
see a single border, there is a slight tendency to
perceive the convex region as figure.
However, if you see multiple convex regions,
each with the same colour, you are more likely
to perceive those regions as figure.
109
People also use _________ to segregate overlapping objects
past experience, also, once you have seen something based on past experience, you can't 'unsee' it
110
What is gist perception?
When scenes are flashed rapidly in front of an
observer, she may not be able to identify all the
objects in the scene.
Nevertheless, she get an overall impression of
what the scene is about.
For example, she might think that the image
shows “a crowded cafe”
That “overall impression” is what is known as the
“gist” of the scene.
111
What did Potter (1976) study and find?
| cafe
Gist perception, and gave participant a specific scene to look out for, and she saw 16 random ones for a very short time, then was asked if any fit the description of the specific scene. Results were near 100%
112
What did Fei-Fei investigate?
What the minimum scene
exposure time is needed to perceive a scene’s
gist.
Observers were presented with just a single
scene, followed by a mask
Observers were then asked to describe what
they had seen.
113
list four figural cues
They are in front of the rest of the image
They are at the bottom of the image
They are convex
They are recognisable.
114
What is the gist of the scene?
When scenes are flashed rapidly in front of an observer, she may not be able to identify all the
objects in the scene.
Nevertheless, she may get an overall impression
of what the scene is about.
For example, she might think that the image
shows “a crowded cafe”
That “overall impression” is what is known as the “gist” of the scene
115
How long do you need to get rudimentary gist?
27 ms
Couldn’t see much; it was mostly
dark w/ some square things, maybe
furniture. (Subject: AM)
40 ms
This looked like an indoor shot. Saw
what looked like a large framed
object (a painting?) on a white
background (i.e., the wall). (Subject:
RW)
116
What can motion perception do?
Help break camouflage
Help attract attention
Help segregate objects from the background.
Help us interpret events.
Help us determine the structure of objects
Help us determine what actions people are performing
117
Discuss Breaking Camouflage, Attracting Attention, Segregating Objects (motion)
A camouflaged animal can be virtually invisible –
until it moves.
When it moves, attention is attracted to it and its
camouflage is broken!
So, motion attracts attention...
...and help us segregate objects from the
background
118
Discuss Interpreting events (motion)
Motion can also allow us to interpret events
By seeing how objects interact, you can infer
causality relationships and even social relationships.
In the following video a large triangle gets into an
argument with a small triangle and a small circle.
The large triangle chases off the other two shapes
before destroying the house.
The entire story is conveyed using motion
information.
119
Discuss structure from motion
Motion can also allow us to infer structure
It can help us determine the shape of a moving
object
This is sometimes referred to as the “kinetic depth
effect”
In the following video the 3D shape of a number of
objects will be revealed by their motion.
Note that when these objects are stationary, their 3D
shape information is unclear.
Motion allows us to infer 3D shape.
120
Discuss interpreting actions
Motion can also allow us to interpret actions
While static poses are often ambiguous...
...when someone moves, their actions and intentions
are often made clear.
This phenomenon is typically demonstrated using
point-light walkers
121
What are Point Light Walkers?
Point-light walkers are created by placing lights on
a person’s joints and having them perform an
action (e.g. walking!)
They are videoed so that only the lights can be
seen.
Humans are so good at processing motion stimuli,
that they can guess what action the person was
performing.
122
What is akinetopsia?
Sometime due to either disease or trauma, a patient
will suffer damage to a part of the brain responsible
for motion perception.
Consequently, the person may no longer be able to
perceive motion.
123
Disucss patient L.M (akinetopsia)
Consequently, L.M. had difficulties
Pouring a cup of tea
Crossing the street
Following speech
Essentially, L.M. could see that things had moved
but couldn’t see them moving.
124
When Do We Perceive Motion?
Real motion (something actually moving)
Illusory motion (nothing actually moving)
Static image (e.g. rotating snakes illusion - Kitaoka &
Ashida, 2003)
Apparent motion
Motion aftereffects
Induced motion
Moving background (or a moving object) causes a
stationary object to appear to move
125
What is the rotating snake illusion?
Clearly, the percept of motion is caused by the
contrast between the colours – but it is unclear why
these contrast difference cause the percept of
motion
126
What is apparent motion?
Apparent motion occurs when a series of stationary
images are presented in succession to give the
impression of motion.
For example, if I alternate between the two slides
below, you wouldn’t see two separate dots.
Instead, you would see a single dot moving from left
to right.
127
Discuss apparent motion
Apparent motion works only if the dots are sufficiently close together
If they are too far apart and the alternation rate is too
fast, motion perception ceases to occur.
Instead, the percept will be of two separate flashing
dots
128
What is Korte's Third Law of Apparent Motion (1915)?
For apparent motion to occur, as separation
increases alternation rate needs to decrease
129
Is apparent motion sensitve to colour change?
No, however, colour can be used to disambiguate
ambiguous apparent motion
130
What is Motion Aftereffect?
Robert Adams (1834)
After staring at the waterfall
for several minutes, he then
shifted his gaze to the
rockface which appeared to
move upwards
131
What is Induced Motion?
A nearby object (usually a large one) either affects the
perceived motion of a second object (usually a small one) or causes a
second object to appear to move.
Moving background (or a moving object) causes a
stationary object to appear to move or changes the
apparent motion of a moving object
132
Describe four functions of motion perception
Help break camouflage
Help attract attention
Help segregate objects from the background.
Help us interpret events.
Help us determine the structure of objects
Help us determine what actions people are performing
133
Describe what life might be like without motion perception?
For example, at the beach, you may have seen a
ship on the horizon.
It may be so far away that it appears not to be
moving.
But when you glance up a few minutes later, you are
surprised to see that it has moved.
This is how L.M. experienced everyday life – she
constantly discovered that things had moved but
could not perceive them to be moving.
134
Describe 6 examples of perceiving motion
Real motion (something actually moving)
Illusory motion (nothing actually moving)
Static image (e.g. rotating snakes illusion - Kitaoka &
Ashida, 2003)
Apparent motion
Motion aftereffects
Induced motion
Moving background (or a moving object) causes a
stationary object to appear to move
135
What is motion induced blindness?
Although motion can make things more visible (e.g.
breaking camouflage), it can also cause things to
disappear, as in motion induced blindness (Bonneh,
Cooperman & Sagi, 2001)
Another motion-related phenomenon we don’t have
a good explanation for...
136
What is Motion Induced Change Blindness?
Motion can also make it harder to notice changes
When the dots (in e.g.) are stationary, it is very easy to notice them changing colour.
When they move, it is much more difficult to notice
that they change colour.
137
How does Motion Induced Change Blindness work?
Normally colour changes attract attention because of
the transient signals associated with the change (i.e.
the “flicker”)
However, when things are moving, there are
transient signals associated with all objects – not just
the ones that are changing
Thus, attention is no longer drawn preferentially to
the changing objects, so the changes are not
noticed.
138
How are Motion Illusions helpful?
can inform us of the processes
underlying motion perception.
For example, the Footsteps Illusion shows us that
contrast affects motion perception.
As the yellow and blue rectangles traverse the
striped background, they appear to speed up and
slow down asynchronously.
Contrast is key in this experiment! (see slide 64 for more detail)
139
Detail Footsteps Illusion and how it works
As the rectangles traverse the striped background
the contrast at the lead edges vary.
When the contrast is high, they appear to move
faster.
When the contrast is low, they appears to move
slower.
When the contrast the leading edge of the yellow
rectangle is high the contrast at the leading edge of
the blue rectangle is low (and vice versa)
Consequently, the yellow and blue rectangles
appear to speed up and slow down asynchronously.
140
What does the Footsteps Illusion tell us?
that contrast
affects motion perception.
Higher contrast objects appear to move faster and
lower contrast objects appear to move more
slowly
This could explain why people often
underestimate the speed of cars moving through
fog... ...a phenomenon that sometimes causes
accidents
141
What is the Apeture Problem?
If you can’t see the ends of a line, the movement of a
line is ambiguous.
Consequently, the motion of the line viewed through
an aperture is ambiguous and is “captured” by the
movement of the terminators (the points where the
line joins the aperture)
When the terminators move horizontally, the line
appears to move horizontally.
When the terminators move vertically, the line
appears to move vertically.
When we can see that actual ends of the line, we
can see its actual motion
142
What is the Barber Pole Illusion?
Same principles as Apeture Problem
In this illusion, lines curve around a cylinder creating
virtual terminators that move vertically.
Thus, the lines themselves appear to move vertically
143
Describe in words the motion induced blindness demo
of Bonneh et al. (2001)
| yellow triangle
3 yellow dots, one flashing green dot. Yellow dots rotate and focus on green dot = yellow dots disappear
144
Describe in words the motion induced change
blindness demo of Suchow & Alvarez (2011)
Change blindness = not occur in everyday life bc there is normally a motion transit, so we notice the change bc of the movement.
In this example, lots of dots moving in a circle and changing colour. Motion transit everywhere, means attention not on changing colour, so become blind to it.
145
Name two motion illusions
Apeture problem
Footsteps illusion
146
What is the function of colour perception?
It has been suggested that colour vision evolved
primarily to help humans search for things.
For example, foraging for berries
Colour perception can also make judgments (trying to figure out if fruit is ripe)
Also used to tell of animal is dangerous (poisonous animals often brightly coloured)
Also to attract mates (colour = health)
147
Describe the physics of colour
Visible light is electromagnetic radiation with
wavelengths varying from about 400 nm to about
700 nm
White light is a mixture of all these wavelengths
148
Describe colour of opaque objects
An opaque object is an object that light cannot pass
through. It is not at all transparent.
The colour of an opaque object is determined by the
light that it reflects
If an opaque object absorbs blue light but reflects
red light, it looks red.
If an opaque object reflects all light, it will appear
white.
149
Describe colour of transparent objects
The colour of a transparent object is determined by
the colour it transmits.
If an object absorbs blue but transmits red, then it
will appear red.
150
How does mixing paint effect colour transmission?
Blue paint absorbs red light but reflects blue and
green light.
Yellow paint absorbs blue light but reflects red and
green light.
Mixing blue and yellow paint results in a mixture that
absorbs both red and blue light but reflects green
light – so looks green
151
What wavelength of light does blue have?
Short (S)
152
What wavelength of light does green have?
Medium (M)
153
What wavelength of light does red have?
Large (L)
154
What happens when you mix yellow light with blue light?
Get light with blue, green, red & looks white, bc white light mix of all colours
155
What are the 3 ways the Munsell colour system categorises colour?
Value (lightness)
Hue (colour)
Chroma (saturation)
156
Describe the Trichromatic Theory of Vision
In the retina, there are photoreceptors known as
rods and cones.
Rods cannot distinguish between colours and are
active only at low light levels.
In normal light conditions, they are not active.
In normal light conditions, only cones are active
157
Describe the 3 types of cones in the Trichromatic Theory of Vision
S cones – 419 nm (blue mostly)
M cones – 531 nm (green + some red)
L cones – 558 nm (red + some green)
158
Describe the effect of the Trichromatic Theory of Vision
By comparing the relative activities of these three
types of cones, humans are able to distinguish
between colours.
For instance, if the L cones are most active, the light
is primarily red
Alternatively, if the S cones are the most active, the
light is primarily blue.
159
According to Trichromatic Theory of Vision, what will a green light with a wavelength of 500nm activate?
It will strongly activate the M
cones and the L cones but
only weakly activate the S
cones
It follows that if a patch of
light were to activate the S,
M and L cones to the exact
same extent it would look
identical to the test field
160
What does the Trichromatic Theory of Vision therefore state?
By adjusting the amount of blue, green and red light we
can exactly match the cone activations caused by 500
nm test field...
...even though the light patches themselves will be
physically different (i.e. one is pure 500 nm light while
the other is a combination of red, green and blue light).
Physically different stimuli that appear the same are
called metamers.
161
What are metamers?
Physically different stimuli that appear the same
162
What are the 2 main types of colour deficiency?
Monochromatism
Dichromatism
163
Describe Monochromatism
Monochromatism affects about 1 in 100,000 people
Monochromats usually have no functioning cones
Only have functioning rods
Thus, they are truly colour blind and see the world
only in shades of gray
Very sensitive to light – need to wear dark glasses
during the day.
164
Describe Dichromatism and the three types of cones they lack
Dichromats are lacking one of the three types of
cones
Three types of dichromats
Protanopes (no L cones) most common (can't see red and green)
Deuteranopes (no M cones) next rarest (can't see red and green)
Tritanopes (no S cones) - rarest (can't see blue and green)
165
What wavelengths of light are required for each type of dichromat to colour match?
Protanopia = 420 nm, 560 nm
Deuteranopia = 420 nm, 640 nm
Tritanopia = 560 nm, 640 nm
166
How do we know what dichromats see?
Luckily there are some unilateral dichromats
These people have normal trichromatic vision in one
eye but dichromatic vision in the other eye
Consequently, they can give use insight into what
dichromats actually experience.
Protanopes and deuteranopes (who cannot
distinguish between red and green) see the world in
shades of blue and a yellowish-green.
Tritanopes (who cannot distinguish between green
and blue) see the world in shades of blue and red.
167
What colours do you get if you mix red and green light?
Yellow light
168
What is the Process Theory of Colour Vision
What colour we perceived is determined not only by
the cones in our retina
The signals from these cones are processed by the
cortex where they are combined into three colour
opponent channels
Red-green (how red or green)
Blue-yellow (how blue or yellow)
White-black (how black or white)
169
What is Opponent-Process Theory and what are the two pieces of psychophysical evidence?
Afterimages
Impossible colours
170
Describe afterimages
Staring at something (usually a colour) and then when look at something without that colour, colour seems to be there.
e.g.
When viewing a red
stimulus, the L cones are
more stimulated than the
M cones.
Consequently, the “Red”
percept is more activated
than the “Green” percept,
which is subsequently
suppressed.
People, therefore see
red.
Over time, the L cones
habituate and become
less sensitive to the
stimulus.
When a white stimulus
is then shown, the
green cones respond
more strongly than the
red cones
Consequently, the
“Green” percept is
more strongly activated
than the “Red” percept.
171
Describe another example of afterimages
When viewing a yellow
stimulus, the L and M
cones are more
stimulated than the S
cones.
Consequently, the
“Yellow” percept is more
activated than the “Blue”
percept, which is
subsequently
suppressed
Over time, the L and M
cones habituate and
become less sensitive
to the stimulus
When a white stimulus is
then shown, the blue
cones respond more
strongly than the red and
the green cones
Consequently, the “Blue”
percept is more strongly
activated than the
“Yellow” percept.
Therefore, a blue
afterimage is seen.
172
Describe impossible colours
The second behavioural evidence for the opponent-
process theory of colour vision comes from the fact
that some colour combinations are impossible.
It is possible to have a bluish red (i.e. purple), a
yellowish red (i.e. orange), a yellowish green and a
bluish green.
However, we can’t perceive a bluish yellow or a
reddish green
(blue light + yellow light = white light, not blueish yellow. In this way, reddish green also impossible, because red + green = yellow)
173
What is colour constancy?
| jumper
The colour of light an object reflects is determined by
not only by its reflectance but also by the colour of
light shining on it.
If white light is shone onto a green
sweater, the green sweater will
predominantly reflect green light.
However, if the light shone on the sweater is
predominantly red, the sweater will reflect
predominantly red light.
Even though green objects absorb
red light, if you shine enough red light
on them, they will reflect some red.
If you only shine red light on them,
the only colour they can reflect is red.
Key point is Reflectance x Illumination = Reflected light
174
Why do we continue to see the green
sweater as green even when it predominantly reflects
red light?
Part of the solution is that we habituate to the colour.
Habituation = becoming less sensitive to that colour
If the entire scene is under red light, we habituate to
red, so everything appears greener than it otherwise
would.
However, it turns out that habituation is not large
enough to explain colour constancy.
175
Describe Discounting the Illuminant
The scene on the left is bathed in predominantly
yellow light while the one on the right is bathed
predominantly in blue light.
Habituation cannot occur because, in total, there is
the same amount of yellow and blue.
The blue tile on the left reflects the same colour light
as the yellow tile on the right, yet the tile on the left
looks blue and the one on the right looks yellow.
It seems that humans are able to discount the blue
and yellow illuminations
176
What are the 2 ways visual system
achieves colour constancy?
Habituation
Discounting the illuminant
177
How do we percieve depth? (3 main ways)
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
178
What are the 2 main oculomotor cues?
Binocular convergence (how two sets of vision from eyes become one image, bring object closer to face, eyes converge, further away, eyes diverge)
Accommodation (changing shape of lens for viewing thigs close = thicker or far away = thinner)
179
What are the 3 main monocular cues?
Accommodation (as seen in other question)
Pictorial cues (7 of them)
Movement-based cues
180
What are the 7 main pictorial cutes?
Occlusion (gives relative depth/depth ordering)
Relative height (shorter = further away)
Familiar and relative size (know how big a thing should be, & how big it appears, you can estimate depth)
Perspective convergence (gives persepctive for how far away something is - lines on road are parallel, yet appear to converge when they get far away)
Atmospheric perspective (things far away obscured by atmosphere i.e. mist or cloud)
Texture gradient (how rough or smooth = how far away)
Shadows
181
What do shadows cue for?
Relative depth and depth perception (assume light coming from above bc where sun is)
182
What are the 2 types of movement based cues?
| train
Motion parallax, a monocular cue (e.g. in a train looking out window - closer things appear to move by faster than further away things bc has further to travel across retinal image)
Deletion and accretion (close-by objects sometimes occlude far away objects, so far away objects appear to be deleted and accreted)
183
What is binocular disparity?
Because the left and right eyes are
offset relative to each other, they see
the world from slightly different
viewpoints.
E.G.
When you close your left eye, your
near finger will appear to the left of
your far finger.
Conversely, when you close your right
eye, your near finger will appear to the
right of your far finger.
Note: whatever you fixate on will be on the centre of your retina
184
Does the point of fixation alter relative disparity?
No
185
What is the horopter?
a plane
containing all points that will fall on corresponding
parts of the two retinas
186
Does the point of fixation affect absolute disparity?
Yes
Whichever object is fixated on has zero absolute
disparity, bc image focussed on falls on centre of left and right retinas, so no difference between right eye and left eye.
That means the left and right images of this object
fall onto corresponding parts of the retina.
Indeed, all objects that lie on the horopter fall on
corresponding parts of the retinas
187
What is the correspondence problem?
| eyes are ambiguous
Retinal images can be ambiguous
If there are multiple identical objects in the scene it
can be hard to figure out which images in the left
retinal image should be associated with which
images in the right retinal image.
E.g. have 4 balls in a line, or 4 balls randomly arranged, and will still create same 4 points on the eye
Figuring out these associations is known as 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 and correspondence problem is solved
188
What is the relationship between depth and 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...
189
What 2 factors determine percieving size?
Its angular size (how large its retinal image is)
Its perceived depth (how far away it appears to be)
190
What is angular size?
The visual angle an
object subtends.
The closer an object is to person, the larger its angular size.
191
What is size constancy?
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.
192
How do observers achieve size constancy?
| formula
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
193
What are 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.
194
What did Holway and Boring investigate?
Holway and Boring (1941) investigated
how observers accurately estimate the
size of objects.
In particular, they investigated how depth
cues influence size judgments.
195
Describe Holway and Boring's 1914 experiment
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.
196
What were the 4 conditions of Holway and Boring's experiment?
In condition 1, observers could determine
the depth of the test patch using binocular
disparity, motion parallax and shadows.
In condition 2, observers viewed the test
circle with one eye to remove binocular
disparity cues.
In condition 3, observers viewed the test
circle through a peephole to remove
motion parallax cues.
In condition 4, in addition to viewing the
circle through a peephole, drapes were
used to remove the shadows
197
Summarise Holway and Boring's experiment
When there are sufficient depth cues, the
size of the test patch can be accurately
estimated.
When there are not sufficient depth cues,
the apparent size of the test patch is
biased towards the visual angle...
...further away test patches are perceived
as smaller than they really are.
Basically, accurate size estimates can occur only
when distance to the object can be
estimated accurately
198
What are the physical and perceptual definitions of sound?
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.
199
How many m/s does sound move through air and water?
air = 340
water = 1500
However, only the pressure wave is moving.
Each air molecule is just moving back and
forth to create regions of high and low
pressure
200
What is a pure tone?
A pure tone occurs when the change in air
pressure occur in a pattern described by a
mathematical function called a sine wave.
201
Describe frequency
| the_____ the frequency the _______ the pitch
The higher the frequency the higher the
pitch (for pure tones)
1 Hz (spelt Hertz) = 1 oscillation per
second
202
What is the range of tones humans can hear?
Humans can hear tones ranging from
about 20 Hz to about 20,000 Hz
203
The ________ the amplitude, the _______ a sound seems
greater, louder
204
What is amplitude measured in?
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
205
What is the fundamental frequency and the first harmonic?
200Hz
All tones that we make are multiples of this tone, can make tones by adding these multiples (known as harmonics) together to make complex tones
206
What are the 2nd, 3rd and 4th harmonics?
400Hz
600Hz
800Hz
the wave repeats every 5ms (for first harmonic)
207
What is loudness dependent on and what is it measured in (for pure tones)?
frequency, phons
208
For a pure tone, pitch is determined by the _________
frequency
209
For a complex tone, pitch is ususally determined by the ____________ ________
| ff
fundamental frequency.
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”
210
On a piano, all notes corresponding to the same letter are multiples of the same ____________, yet the _______ increases
frequency, pitch
211
Notes with the same letter sound similar and are said to have the same ____, and moving left to right, the _______ _______ increases
chroma, tone height
212
What are two variables of pitch
Tone height and chroma
213
What is chroma?
| octaves
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
214
Complex tones can be __________ into their ______________ ____________ ________________
decomposed , constituent frequenct components
215
What is an example of the missing fundamental?
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.
However, the complex tone will continue to
repeat at the fundamental frequency, even
when the fundamental frequency is absent because all the other components of the
tone are multiples of the fundamental
frequency.
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!)
216
Example of the missing fundamental (no.2)
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
217
What is timbre?
| pitch and tone
when the pitch did not change but
the tone still sounded different.
218
Why, when 2 instruments play the same note, do they not 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.
219
What are waveforms that don't repeat, and 2 examples of them
Aperiodic, gunshot or door slamming
220
What is an example of auditory localisation?
Imagine that you are walking along the street
when you suddenly hear a large crash.
You instinctively turn to see what is going on.
How did you know whether to turn to your left
or to your right?
221
What is auditory localisation based on?
binaural and monaural cues
222
What do binaural cues include?
Interaural time difference
Interaural level difference
223
Describe Interaural time difference
Sound closer to each ear will be heard by that ear first
The left ear will
hear sound A before
the right ear.
The right ear will
hear sound B before
the left ear
224
What is 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
225
Describe the 'cone of confusion'
Any two points connected by a circumference line on the surface of this
cone have the same difference in distance to the two ears.
Thus, they will have the same interaural time difference and interaural
level difference.
So binaural cues cannot be used to distinguish between the two points
226
Describe monaural cues for elevation
Sound coming
from different
elevations
bounces off
different parts of
the pinna before
entering the ear
canal.
Consequently, sound
acquires characteristic
frequency notches that
depend on its
elevation
These can be used to
determine the
elevation of the sound
source
227
Why do we not hear echos all the time?
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
228
What are 4 factors that determine the quality of architechtural acoustics
Reverberation time
Intimacy time
Bass ratio
Spaciousness factor
229
Describe 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
230
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.
231
What is 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
232
What is 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
233
What is a final factor to consider when designing a concert hall?
The final factor to consider when designing a
concert hall is the pillows on the seats!
When the concert hall is full, the people in the
audience will absorb a lot of sound.
Thus, if the concert hall is fine-tuned to produce
good quality sound when the audience is full....
...it may sound very bad when the it is empty.
Solution: Have pillows where each pillow absorbs
the same amount of sound as the average person!
Thus, the acoustics of the hall will be the same
whether it is full or empty
234
What are 5 cues people use to seperate sound sources?
Location
Onset Time
Timbre and Pitch
Auditory Continuity
Experience
235
Describe location as a method for seperating sound sources?
Because the three musicians will not be
playing exactly the same notes at exactly
the same time, you will be able to hear that
they occupy separate locations using the
mechanisms that we discussed earlier.
In particular, you will make use of interaural
time differences and interaural level
differences.
Location is a very strong cue for segregation.
However, it is not necessary.
Even if all the sound were to come from just
one location (e.g. a single speaker), you would
still be able to segregate the three musicians.
236
What is onset time as a method for seperating source sounds?
If two sounds start at different times,
chances are they originate from different
sources.
Conversely, if two sounds start at the same
time, chances are they come from the
same source.
237
How are timbre and pitch used as methods for seperating sound sources?
It is easy to segregate musical
instruments that have different timbres.
Even instruments with the same timbre
can be separated on the basis of pitch.
238
How is auditory continuity used for seperating sound sources?
Tones interrupted by silence are heard as
distinct
Tones interrupted by noise (or another
stimulus) are heard as continuous
(Deutsch, 1999)
Humans assume tones continue through
the noise
Tones separated by
silent gaps are
heard as distinct
Tones separated by
noise are perceived
as...
...continuing
through the noise
239
How is experience used to seperate sound sources?
If two melodies are played
simultaneously, you are more likely to be
able to segregate them if you know the
two melodies separately.
Similarly, if you know what a particular
person or a particular animal sounds
like, you are more likely to be able to
detect the presence of that sound in
background noise.
