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Psych 1XX3 Form Perception I Lecture Notes.pdf

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Joe Kim

Psychology 1XX3 Notes – Form Perception I – Mar 12, 2010 Gestalt Principles:  In the 1920s and 1930s, a group of psychologists in Germany began to study how people perceive the world around them.  These psychologists were called Gestalt psychologists, and with respect to perception, they firmly believed that "the whole is different than the sum of its parts."  They believed that people tended to perceive the whole stimulus rather than just putting together a collection of the stimulus' discrete parts. The Gestalt movement was in part a reaction to the structuralist approach in vogue at the time, which suggested that everything could be reduced to basic elements.  The Gestalt psychologists proposed laws  These laws of organization are called the Gestalt principles, and it's thought that they are innate, or that we acquire them rapidly. Six Gestalt Principles: Figure-Ground:  One of the most fundamental Gestalt principles for form perception is figure- ground, or the ability to determine what aspect of a visual scene is part of the object itself and what is part of the background.  In the simplest scenario, you would have a small, enclosed region that is completely surrounded by a larger region, which would be the background. The figure would tend to have distinct borders or edges that give it a perceptible form.  This seemingly simple process can be more difficult if the cues that are used to make these figure-ground decisions aren't clean as is the case with reversible figures. (I.E. the wine glass/two faces kissing image) Proximity:  One Gestalt principle that helps with grouping is proximity, which says that elements that are close together in space tend to belong together. For example,  Field of daisies: The daisies aren't all uniformly spaced apart but tend to have regions where they're clustered close together in some areas and fewer in numbers in other areas. You will naturally see the regions of high daisy density as one group of daisies because of their proximity to each other, rather than grouping together some daisies from one cluster with some from another cluster. Closure:  Closure is the Gestalt principle that refers to the fact that if there are gaps in the contours of a shape, we tend to fill in those gaps and perceive a whole object.  I.E. a telephone pole is in front of a truck, however, we fill in the mixing part of the truck instead of thinking the truck is two parts. Similarity:  Another Gestalt principle is similarity or the tendency for us to group together elements that are physically similar.  Suppose you were driving by a farmer’s field that had alternating rows of sunflowers and corn. Even though the distance between rows might be the same as, or even less than, the distance between plants within a row you will tend to group together the vegetation of the same type. Continuity:  Continuity is the Gestalt principle that lets us perceive a simple, continuous form rather than a combination of awkward forms.  For instance, the letter "X" tends to be perceived as two continuous lines, "/" and "\", that cross in the middle, rather than seeing a combination of two “V”s joined in the middle.  The same idea applies to seeing a vase or flowers. We’re likely to perceive each stem as a continuous line, even though they’re likely to be criss-crossed with other stems. Common Fate:  Another Gestalt principle that helps us group elements together is common fate - the idea that things that change in the same way should be grouped together  For example, we tend to group elements together if they are moving together in the same direction at the same time.  If we look at a school of fish and see them moving together in the same direction, we will tend to group them together. This tendency is strong enough to lead us to a perception of the group of elements as a kind of object on its own.  Common fate can also explain why we can suddenly see a camouflaged animal once lt moves, like a moth against the bark of a tree.  When the moth is still, it’s almost impossible to see where the wings of the moth end and the bark begins. But as soon as the moth moves, there are elements within the moth’s pattern that are moving together in the same direction and at the same time.  These moving elements with a common fate allow the contour of the moth's shape to be perceived, and suddenly the moth seems to pop out against the tree. Pattern/Object Recognition:  What a person expects to see can influence what they do see. Processes of Object Recognition:  The preliminary steps in object recognition involve identifying what aspect of the scene is the figure and what is the background.  Once that is established, the parts of the figure are identified and grouped together into a single object.  Once you have this single object against a background, how do you go about recognizing what that object is? Recognizing an object is really a combination of two processes:  The first of these is bottom-up processing, where the features that are present in the stimulus itself guides object recognition.  For example, you recognize a cow as being a cow because it has four legs, goes "moo", has an udder, a big nose, two long ears on the side of its head, and two big eyes.  So bottom-up processing says you recognize what you see by analyzing the individual features and comparing those features to things with similar features that you have in memory.  The other process is top-down processing, where your own beliefs or expectations are the primary influence for determining what you're seeing.  We already saw evidence for this type of processing with the ambiguous stimuli, but here are some other examples.  In this example, the second letters in both words are physically identical. Yet, you still read it as "THE CAT" because you are influenced by the context. Priming Experiments:  Another example is with an effect called priming. In a priming experiment, the experimenter measures how fast a participant can read a word that is flashed on a screen. If you tell the participant that the next word is an animal, you'll find a priming effect because words like dog or duck will be recognized a lot faster here than words like log or puck.  This shows that processing of a word is more efficient if the participant is primed to expect a word from a certain category.  Top-down processing cannot work alone because you need some input from the stimulus itself before your expectations about that stimulus can influence your recognition of it.  Bottom-up processing cannot explain everything alone either because, as we just saw, expectations certainly do influence our perceptions.  So it seems most reasonable to think that both of these processes must be involved and that we’re dealing with bi-directional activation, where processing occurs in both directions at once. In this way, the features of the object in combination with our expectations guides object recognition. Theories of Object Recognition: Biederman’s Geon Theory:  Suggests that we have 36 different geons, or simple geometrical forms. stored in memory.  These would be forms like a cone, a sphere, and a cylinder. According to this theory, using just these 36 geons, its possible to recognize over 150 million different objects.  So, for example. an ice cream cone is just a cone and a sphere. A garbage can or a glass are just cylinders.  Problems with the idea that we store 36 geons to recognize everything. There are certain stimuli, like faces or crumpled pieces of paper, for which it is difficult to determine what geons would be used, yet we have no difficulty recognising these stimuli.  Also, there is evidence that some forms of brain damage lead to very specific deficits. For example, people suffering from these brain injuries may not be able to recognize different types of fruit, but they can name different types of tools.  If geons were involved in object recognition, you might expect deficits in recognizing all types of objects based on their shapes and not a specific category of objects.  Keep in mind, however, that it is also possible that geons could be processed at a different level of processing separate from the area of brain damage. Template Theory:  Another theory of how we recognize objects is that we store many different templates in memory, and when we come across an object, we compare that object to all the templates in memory.  If a match is found, then it's a familiar object and the person could name it by activating connections to other language areas in the brain.  If no match is found, then it's an unfamiliar object and a new template is stored in memory.  Most psychologists don't find the idea of templates very compelling because we would have to store an incredible number of different templates to recognize all of the different objects that we encounter: Just think of all the different templates you'd need to recognize familiar faces that can appear to us in many different configurations.  For example, my mother's face has many different facial expressions, hairstyles, lighting conditions, and points of view. I would need countless mother templates, and that's just to recognize one person! Prototype Theory:  A theory that overcomes the storage problems of the template theory is the prototype theory, which says that we store the most typical or ideal example of an object.  This system is much more flexible because you don't need an exact match between the observed object and what is stored in memory. This is how we can easily recognize common objects that we've never seen before, like a new dog or coffee mug.  However, we also recognize specific individual objects, like our favourite coffee mug or our own dog.  So it's likely that we have more than one type of representation for each object, like an ideal prototypical dog and also all the dogs that we are personally familiar with. The Importance of Parallel Processing:  Much of the neural processing of ob
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