Sensation and Perception - UNI Flashcards
(113 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?
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
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?
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
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?
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?
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?
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
