Organizing objects and scenes
Week 7 and Week 8
1
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.
3
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).
5
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.
7
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
10
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.
11
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.
14
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.
15
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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