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Why is perceptual organization a problem for the visual system? According to the Gestalt psychologists, how does the visual system go about solving this problem? (In your answer, make sure you talk about the Gestalt principles and figure-ground organization).
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Get Help Now!There are two questions to answer in this essay so make sure you answer both. Make sure to refer to the evidence from the book and the powerpoints. Your discussion posts in week five are relevant to this essay.
Organizing objects and scenes
Week 7 and Week 8
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Remember to read the assigned parts of the textbook too (Chapter 5)
introduction
Think about these questions:
What would it look like if the visual world had no organization at all?
Are we born with the ability to organize the world perceptually? Or are we born with no perceptually organized world and have to learn through experience?
What does a newborn baby see?
Is the organization of the visual world given in the retinal pattern?
Also, think about this: How would an engineer create a “seeing” machine e.g. a machine that can recognize what it is looking at? The machine would obviously have to be connected to some kind of device that could capture images (a camera), but think about it – the camera would only record the intensity of light at various pixels. What is needed is some way to put all of those pixels of light together to create a whole. This organization is not given in the retinal image (nor in the image in the camera example). Therefore, our brains must be involved in taking this raw data and organizing it so that it means something for us.
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Look at these bi-stable images carefully for a while. Each can be interpreted (organized) in two mutually exclusive ways: the black area as the object, or figure, and the white area as background, or ground. Or vice versa. You will learn about them this week. Now, what is happening here perceptually? What is happening here in the stimulus? Well, perceptually, you can see that you can alternate between the different interpretations of each stimulus. As for the stimulus, nothing changes.
So, what this shows us is the brain or mind’s tendency to organize things visually (and of course with all of the other senses); to try to make sense of what is in front of it given the inverse problem.
These last two slides show us that the brain has the tendency to organize. There seems to be some organizing principle at work. Look at the example on this slide. See how many interepretations of what it is you can come to. What interpretation does your brain prefer? (e.g. black as object, white as background , or vice versa).
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Introduction
William James called a newborn’s world “a blooming, buzzing confusion” suggesting that it lacks organization
What would it look like if perception had no organization at all?
Perhaps the best description is that it would be like watching a snowstorm of swirling, multicolored confetti resulting from the output of millions of unrelated retinal receptors
The problem of perceptual organization
The problem of grouping:
“I stand at the window and see a house, trees, sky.
Theoretically, I might say that there were 327 brightnesses
and nuances of color. Do I have “327”? No. I have sky,
house, and trees.” (Wertheimer, 1923)
Again, think about it: in the picture above, all that is there are different intensities of light (like different pixels). Why do we see those pixels organized as a house etc and not just lots of different colors? That is the crucial question.
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The problem of perceptual organization
The concept of perceptual organization originated with the Gestalt psychologists early in the 20th century.
It was one their central concepts in their attack on the atomic assumption of Structuralism
The Structuralists conceived of visual perception as a simple concatenation of sensory atoms, consisting of pointlike color sensations.
This view is local in the sense that each atom is defined by a particular retinal position and thought to be independent of other atoms
The Gestaltists, in contrast, believed that visual perception arose from global interactions within the nervous system and resulted from the overall structure of visual stimulation itself
Max Wertheimer first posed the problem: how are people able to perceive a coherent visual world that is organized into meaningful objects rather than the chaotic juxtaposition of different colors that stimulate the individual retinal receptors
Why does visual experience have the organization it does?
The naïve realist says, “Because it reflects the structure of the external world”
However, the difficulty with this answer is that the visual system does not have direct access to facts about the environment; it has access only to facts about the image projected onto the retina
That is, an organism can only know the world though sensory information
Remember the difference between the proximal stimulus and the distal stimulus- we only have direct access to the proximal stimulus
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The Gestaltists referred to the naïve realist’s approach as the experience error, because it arises from the false assumption that the structure of perceptual experience is somehow given in the array of light that falls on the retinal mosaic
This optic array contains an infinity of possible organizations only one of which the visual system usually achieves
Stop! And think about how the second bullet point above is true. Look around you. What do you actually see? But how else could your visual experience be organized? (and if you think this is a silly exercise, remember, there are people with all kinds of agnosias who are unable to organize their visual world so that is makes sense). The face that our brains come to similar organizations of the visual world is amazing and needs to be explained.
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The confusion that underlies the experience error is to suppose that the starting point for vision is the distal stimulus rather than the proximal stimulus
Taking the distal stimulus as the starting point for vision underestimates the difficulty of visual perception because it presupposes that information comes for free
The structure of the environment is more accurately regarded as the result of visual perception than its starting point
Perceptual grouping
Perceptual grouping: how the various elements in a complex display are perceived as “going together”
Think about this throughout the following slides (it’s difficult, but it’s a good meditation) – no perceptual objects are present on the retina; they exist only in our minds, and only as the result of many levels of processing and interpretation applied to the retinal image
And visual disorders bear the above out! People with visual agnosias have no retinal damage; their inability to perceptually organize a scene or an object comes from damage much higher up in the brain
But our minds have an urge to organize!
So, the Gestalt psychologists argued that the brain contains “principles” or “rules” that are built in that enable us to organize the world.
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The urge to organize!
I hope on this slide you see the patterns that your brain is imposing on the stimulus. I see circles within circles. Squares. Many different patterns. Your brain going from one interpretation to another.
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The Gestalt school of psychology were interested in processes that cause certain elements in the retinal image to seem to be part of the same group
Their basic observation was that elements within a pattern do not seem to operate independently
There seem to be attractive “forces” among the elements that cause them to form a meaningful figure, much as gravity organizes the planets, sun, and moons of our solar system
The whole is more than the sum of its parts
Gestalt grouping principles
So, the Gestalt psychologists are looking at the various rules that the visual system seems to use in organizing the pattern of light impinged upon the retina.
What are these rules or principles?
See the textbook (Chapter 5) for some more examples of the following grouping principles.
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Grouping principles
Proximity
Similarity
Common fate
Symmetry
Parallelism
Good continuation
Closure
Proximity
So, think about what the Gestalt psychologists were saying about the above stimulus. We all see it as 3 columns of 5 objects. The question they were asking is, Why do we see it as 3 columns? Why not see it as 5 rows? (and think of the other ways that you could organize it e.g. 9 squares upper left forming one group and the others forming the other). Each is a valid interpretation. The Gestalt psychologists argued that we have these innate principles guiding our organization. Here, in the above, the principle is, things that are close together will group together.
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Proximity
Similarity
Similarity
Why do you see a cross here? Because you are grouping the elements according to similarity. Let’s say for some reason the part of your brain that groups “breaks down” due to brain damage. Would you see a cross? No. Because you wouldn’t be able to group according to similarity. What would you see then?
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Common fate
Common fate means “common movement”. Elements that move together are seen as belonging to the same group.
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Symmetry
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Symmetry
Parallelism
Grouping by parallelism. Why do we see the three parallel lines as going together? Because we group them according to this principle.
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Good continuation
Closure
New principles of grouping
Recently 3 new grouping factors
Synchrony – all else being equal, visual events that occur at the same time will tend to be perceived together
See image Palmer, p260
Element connectedness: Palmer and Rock argue that what goes together in the strongest physical sense are those pieces of matter that are actually connected, not those that are merely close together. It makes sense for the visual system to be especially sensitive to connectedness as an indication of how to predict what will happen in the world. Element connectedness usually results in the perception of a single object consisting of different parts, whereas proximity results in the perception of a looser aggregation of several separate but related objects
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Common region – all else being equal, elements that are located within the same closed region of space will be grouped together
Element connectedness – all else being equal, elements that are connected by other elements tend to be grouped together
Another grouping factor: Meaningfulness
Things are more likely to be grouped together if the groups appear meaningful
What do you see here? Just rocks and trees and men on horses? Look more closely.
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Meaningful On Mars
Pareidolia (payr.eye.DOH.lee.uh) n. The erroneous or fanciful perception of a
pattern or meaning in something that is actually ambiguous or random
Because our minds have this tendency to organize, we see things that arent really there.
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Meaning On Google Earth
Meaning in smoke, fire, snow
October 16, 2007: Is this Pope John Paul II waving from beyond the grave? Vatican TV director says yes
This fiery figure is being hailed as Pope John Paul II making an appearance beyond the grave.
The image, said by believers to show the Holy Father with his right hand raised in blessing, was spotted during a ceremony in Poland
In rocks
Meaning in trees
Meaning on food
Figure-ground organization
Figure/ground organization
Region segmentation will partition an image into two uniform connected regions, one white and the other black
But when you look at it you will see a white object on a black background or a black object on a white background
This is called figure/ground organization (Rubin, 1921)
The figure appears closer and has the shape given by the contour. In contrast, the ground appears father away and extends behind the contour
See the textbook for more information. Given the retinal stimulation (the proximal stimulus) the visual system has to work out what is the object (the figure) and what is the background (the ground). Again, think about how difficult it would be to create a “seeing” machine that could work out given the pattern of light what is the object and what is the background given that all that is present is a sea of light intensities.
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Interesting…
IMPORTANT TO REALIZE THAT THE BORDER BETWEEN THE FIGURE AND GROUND IS COMPLETELY AMBIGUOUS UNTIL IT IS ASSIGNED TO BE EITHER GROUND OR FIGURE, AND WHEN IT IS IT TAKES ON A FORM.
This is an example of an ambiguous figure. The pinkish area can become figure (a vase) and then the black becomes background. Or the black area can become figure (two faces) and the pinkish area becomes the background. It is important to remember that our visual system is constantly having to work out what is figure what is background in the retinal stimulation.
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The figure acquires meaning (it is an object in the world) and a shape.
Notice the background is perceived as being shapeless and extending behind the object
Notice that the brain in this example is unsure about the interpretation (it’s a vase!) and can flip to another interpretation (it’s two faces)
When it flips, it does so as a whole. Now other shapes are seen (e.g. the two faces) and the interpretation changes
Remember, the contour between the areas in this image is ambiguous until it is assigned to one or the other interpretation
What do these show us?
Among other things they
show the constructive nature
of the brain.
The brain assigns the
contour (which remember
could belong to the figure of – in
this case – the person OR the
columns). When it does assign it to one, the other is not perceived.
These examples are interesting
also because they show us how when there is ambiguity, the
brain flips from one interpretation
to another)
Why is the square in the white background “stable” i.e. the figure ground relationship is not ambiguous?
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The meaning we assign the image depends on what our brains construct as figure and what they construct as ground
Escher’s Evolution – figure ground
Escher – figure ground
Is there memory for figure-ground?
Rock (1983) (see Palmer)– using a recognition memory paradigm showed subjects a series of ambiguous figure/ground stimuli.
Subjects remembered the figural test shapes quite well but remembered the ground test shapes no better than chance. Suggests that they had never perceived the grounds as having shapes in the first place
See also the following article:
Rubin, N. (2001).Figure and ground in the brain. Nature Neuroscience
Such results show that the visual system has a strong preference to ascribe the contour to just one of its bordering regions and to perceive the other side as part of a surface extending behind it
Intimately related to depth perception – the figure is always seen as lying in front of the ground region
Figure/ground principles
How does the brain decide which is figure and which is ground?
Remember again, that this information (i.e. this is the figure and this is the ground) is NOT given in the retinal image (an example of the Gestalt psychologists’ experience error)
The brain has to decide
The following are cues the brain uses (like depth cues) to decide
They are probabilistic i.e. usually right, but not always
Principles of figure/ground organization
The visual system has distinct preferences for perceiving certain kinds of regions as figure
Surroundedness – if one region is completely surrounded by another, the surrounded region is perceived as figure and the surrounding region as ground
But remember only probabilistic! Why in this example?
See images Palmer, p282
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Size – the smaller region is perceived as the figure
Orientation – the set that is horizontal or vertical tends to be perceived as figure than does the oblique set
Contrast – the regions with greater contrast to the surrounding area tend to be taken as figure
Symmetry – symmetrical regions tend to be seen as figure
Convexity – convex regions tend to be perceived as figure and concave ones as ground (and can override symmetry)
Parallelism – figure has parallel contours
More ambiguity…
All of these pieces of art are great examples of showing
how perception is an active process, and that we cannot think
of perception as a camera. Your brain is actively constructing
what you see. There are rules it follows (the figure-ground
Principles), but these are probabilistic.
Development of perceptual organization
So who is right –
the nativist or the empiricist?
There is a third alternative to these two, which is that organizational processes are not present at birth but develop in a predetermined way as the infant matures
Are these organizational rules present at birth (as the nativist would argue), or do we have to learn them (the empiricist)?
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The habituation paradigm
How do we answer these question when newborn babies cannot describe their visual experience?
The habituation paradigm – babies shown a novel stimulus and allowed to look at it as much as they want; after some time, the look at it less as the novelty wears off – they habituate. Then they are shown another display. It could be the same or it could be different. Even young infants will spend more time looking at the novel display than the old one, known as dishabituation
The habituation paradigm
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Kellman and Spelke (1983) tested them with two disoccluded displays – one showing a single connected object and the other 2 disconnected objects
This technique was applied to the problem of grouping in infants (see image) – in this example, do the infants perceive the two ends of the display as being connected behind the occluder into a single object?
Do babies see the black line in ‘A’ as continuing behind the grey rectangle (as we do)? Or do they see two black lines abutting a rectangle?
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If the infants had perceived the center-occluded display as covering a single object, they should spend more time looking at the fragmented display and vice versa
If 4-month-old infants are shown the static display, they don’t look much anyway and show no preference for looking at the fragmented rod when they are tested after habituation
However, if 4-month-old infants are shown a moving display in which the two ends of the rod oscillate back and forth in common motion, after they have habituated, they show a preference for the fragmented test display
See link to Perceptual Development – Occluded object perception in infancy
We can conclude that infants perceived the occluded habituation display as a single, connected object in the moving condition but not in the static condition
Thus, what Wertheimer (1923/1950) called “common fate” seems to be a principle of perceptual organization for 4-month-olds
Does not prove that grouping by common fate is innate; it could have been learned during the previous four months
Other grouping factors do not produces this pattern of results – if the habituation display contains two stationary parts that are similar in size, color, orientation, and texture and have good continuation of edges across the occluded contour, infants show no measurable preference for the separated over the connected display
So, what does this tell us about infants’ grouping abilities? Are they perceptually organizing their visual world? Or not?
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This indicates that 4-month-olds do not use these static grouping factors to complete the two visible ends in the display
Contrary to the beliefs of the Gestaltists, it appears that static similarity grouping is not an innate ability, but one that is learned through experience and develops as the infant develops
