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Chapter 3 Part 1.docx

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Wilfrid Laurier University
Carolyn Ensley

Class 2, Lecture 3, Chapter 3: Recognizing Objects Form Perception  How do we perceive and recognize objects?  Form perception is the process through which the basic shape and size of an object are seen.  Object recognition is the process through which the object is identified.  Object recognition begins with the detection of simple visual features.  However, our perception of the visual world goes “beyond the information given” (Bruner, 1973). o All the demonstrations of optical illusions go to how that cognition interacts with perception, our assumptions and expectations and life experiences influence what we see  An early twentieth-century movement known as Gestalt psychology captured this idea as “the whole is different from the sum of its parts.”  The Necker Cube is an example of perception going “beyond the information given.” o Two different perceptions of depth are possible, given the lines on the page.  In the Face-Vase figure, two interpretations are possible, each based on a different figure/ground organization. o This again shows that perception goes “beyond the information given.”  These examples might suggest that perception proceeds in two stages: o One where visual features are processed o And a later stage in which perception goes “beyond the information given.”  However, this view presumes serial processing, not the parallel processing that characterizes the visual system.  Our interpretation of the visual input influences how basic visual features are processed.  In this image, it is only when the white parts of the figure are treated as figure, and not ground, that the features of letters are analyzed. o  o In this image, the word “perception” is recognized even though most of the features of the component letters are absent from the stimulus.  These examples illustrate that the brain areas that analyze basic visual features and the brain areas that analyze large scale form are interactive, each sending information to the other  This again is an example of parallel processing o What this means is that what we see is not just determined by the stimuli in front of our eyes, but also the brain’s interpretation of that stimulus. o The perceptual system operates as if it were generating hypotheses about what objects are being perceived, given the available data.  The visual system prefers the simplest explanation possible, avoiding interpretations that involve coincidences.  This figure is interpreted as two crossed lines, and not two V shapes precisely aligned. Object Recognition  Now let’s turn from form perception, the process through which the basic shape and size of an object are seen,  And discuss object recognition, the process through which the object is identified.  A first consideration about object recognition is that we can recognize objects when information is incomplete.  E.g., a cat behind a tree is recognized even if only the head and one paw can be seen.  The context in which objects are viewed also can have a large effect. o It is hard to see the item that is out of context in a scene.  Recognition might begin with the input pattern’s features – the small elements out of which more complicated patterns are composed  Not that here the features are not those of the raw input, but rather those that result from more organized perception of form  The feature of the triangles that are missing ALL of the characteristics are inferred, however, in the visual system’s organized perception of form.  Advantages of a feature-based system: o Features could serve as building blocks, allowing a single object-recognition system to deal with a variety of targets.  There can be variations in the physical characteristics as long as the frame for the object is there. Example: Varying looks of chairs yet we still know that they are chairs even if we have never seen them before.  Consistent on how we recognize novel examples from categories we have never seen before. o Focusing on features might allow us to concentrate on
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