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Chapter 3

Chapter 3 Summary PSYC 2650.docx

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University of Guelph
PSYC 2650
Roderick Barron

Chapter 3 pp. 75-88, 104-116 Chapter 3 Summary (pp.115-116) Visual perception is a highly active process in which the perceiver goes beyond the information given in organizing and interpreting the visual input. The process must specify a figure/ground organization for the input and how the figure is organized in depth. The interpretive process is guided by certain principles, including those catalogued by the Gestalt psychologists. Importantly, though, the interpretation seems to be guided simultaneously by the input’s features and its overall configuration. We easily recognize a wide range of objects in a wide range of circumstances. Our recognition is heavily influenced by context, which we can determine how or whether we recognize an object. To study these achievements, investigators have often focused on the recognition of printed language, using this case as a microcosm within which to study how object recognition in general might proceed. Many investigators have proposed that recognition begins with the identification of features in the (organized) input pattern. Crucial evidence for this claim comes from neuroscience studies showing that the detection of features is separate from the processes needed to assemble these features into more complex wholes. To study word recognition, investigators often use tachistoscopic presentations. In these studies, words that appear frequently in the language are easier to identify, and so are words that have been recently viewed – an effect known as repetition priming. The data also show a pattern known as the word-superiority effect; this refers to the fact that words are more readily perceived than isolated letters. In addition, well-formed nonwords are more readily perceived than letter strings that do not conform to the rules of normal spelling. Another reliable pattern is that recognition errors, when they occur, are quite systematic, with the input typically perceived as being more regular than it actually is. These finding together indicate that recognition is influenced by the regularities that exist in our environment (e.g., the regularities of spelling patterns). These results can be understood in terms of a network of detectors. Each detector collects input and fires when the input reaches a threshold level. A network of these detectors can accomplish a great deal; for example, it can interpret ambiguous inputs, recover from its own errors, and make inferences about barely viewed stimuli. The feature net seems to “know” the rules of spelling and “expects” the input to conform to these rules. However, this knowledge is distributed across the entire network and emerges only through the network’s parallel processing. This setup leads to enormous efficiency in our commerce with the world because it allows us to recognize patterns and objects with relatively little input and under highly diverse circumstances. But these gains come at the cost of occasional error. This trade-off may be necessary, though, if we are to cope with the informational complexity of our world. A feature net can be implemented in different ways – with or without inhibitory connections, for example. With some adjustments (e.g., the addition of geon detectors), the net can also recognize three-dimensional objects. However, some stimuli – for example, faces – probably are not recognized through a feature net but instead require a different sort of recognition system, one that is sensitive to relationships and configurations within the stimulus input. The feature net also needs to be supplemented to accommodate top-down influences on object recognition. These influences can be detected in the benefits of larger contexts in facilitating recognition and in forms of priming that are plainly concept-driven rather than data-driven. These other forms of priming demand an interactive model, which merges bottom-up and top-down processes. pp. 75-88 Form Perception  We receive information about the world through various sensory modalities: sound, smell, touch etc.  Vision is the dominant sense o If visual information conflicts with information received from other senses, we usually place our trust in vision o This is the basis for ventriloquism: we see the dummy’s mouth moving but hear the dummy’s master; we experience the illusion that the voice is coming from the puppet  Form perception: the process through which you manage to see the basic shape and size of an object  Object recognition: the process through which you identify what the object is Why is Object Recognition Crucial?  If we couldn’t recognize objects, we would not be able to use them or know what they are intended for  Object recognition is essential whenever you want to apply your knowledge to the world  Crucial for learning – without object recognition you wouldn’t be able to combine information bits collected on different occasions Beyond the Information Given  Early 20 century Gestalt psychologist noted that our perception of the visual world is organized in ways that the stimulus input is not o They argued that organization must be contributed by the perceiver  Jerome Bruner (1973) voiced similar clams and coined the phrase “beyond the information given” to describe some of the ways that our perception of a stimulus differs from (and goes beyond the stimulus itself  The Necker cube o Example of a reversible figure – people first perceive it one way, and then another o The middle cube can be perceived as if viewed from above (in which case is a transparent version of the cube on the left) or as if viewed from below (i.e. a transparent version of the cube on the right) o Both perceptions fit perfectly well with the information received by your eyes, and so the drawing itself is fully compatible with either of these perceptions o Individual perceptions change – to one person the cube on the left may be the opaque view of the middle cube, whereas other people might see the cube on the right  Ambiguous figures o The first figure could be perceived as a vase centered in the picture, or it can be perceived as two profiles facing each other  The drawing by itself is fully compatible with either of these perceptions, and so again the drawing is neutral with regard to perceptual organization  In particular, it’s neutral with regard to figure/ground organization: the determination of what is the figure (the depicted object, displayed against a background) and what is the ground The Gestalt Principles  If you stare at any of these pictures your perception changes, yet the geometrical arrangement stays the same o The change is therefore caused by you  Many figures are ambiguous and in need of interpretation o We don’t detect the ambiguity because the interpretation is done so quickly that we don’t notice it  Your perception is guided by principles of proximity and similarity o If, in the visual scene, you see elements that are close to each other, or elements that resemble each other, you assume these elements are part of the same object  These perceptual principles are quite straightforward, but they are essential if your perceptual apparatus is going to make sense of the often-ambiguous, often-incomplete information provided by your senses  Everyone’s perception is guided by the same principles, and that’s why you generally perceive the world the same way that other people do o We all tend to impose the same interpretation, because we’re all governed by the same rules Organization and “Features”  Perception proceeds in two broad steps: first, we collect information about the stimulus, then we interpret it o From “raw data” to “beyond the information given” o Determining what is figure and what is ground  However, interpretation of the input sometimes seems to happen before we start cataloguing the input’s basic features  With one organization, features may be absent; with another, they’re plainly present (see page 83 Figure 3.6)  Features are very much “in the eye of the beholder”  Figure 3.7 page 84 o You have no difficulty reading the word even though most features needed for recognition are absent o We “provide” the missing features through interpretation  Features must be in place before an interpretation is offered, because the features govern the interpretation; yet the features you find in an input depend on how the figure is interpreted o Therefore, it is the interpretation, not the features, that must be first  The brain’s functioning depends on parallel processing, with different brain areas all doing their work at the same time  Perception of features guided by configuration, analysis of configuration guided by features o Neither type of processing “goes first” o Both work together, with the result that the perception that is achieved makes sense at both large-scale and fine-grained levels Object Recognition  We’re able to identify objects we encounter – recognize a shape as a truck, a tree, or a video game character Recognition: Some Early Con
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