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Chapter 3

PS260 Chapter 3 - Recognizing Objects.docx

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Wilfrid Laurier University
Anneke Olthof

Chapter 3: Recognizing Objects Visual Perception For humans, the vision is the dominant sense. We usually place our trust in vision known as ventriloquism.  first, form perception: the process through which you manage to see what the basic shape and size of an object are.  next, the problem of object recognition: the process through which you identify what the object is. Why is Object Recognition Crucial? Without recognition, you cannot bring your knowledge to bear on the world. Object recognition is also crucial, one must combine new info with info learned previously, and for this to happen, one must categorize things properly.  without proper categorization, there is no way to combine and integrate info  the process of object recognition begins with the detection of simple visual features.  Gestalt psychologists argued that the organization must be contributed by the perceiver; this is why the perceptual whole is often different from the sum of its parts.  when looking at a figure or drawing, it is neutral with regard to figure/ground organization: the determination of what is the figure and what is the ground.  e.g. the ambiguous vase/profile figure  the Necker Cube  our perceptions contain info about how the form is arranged in depth, or about which part of the form is figure and which is ground Organizations and "Features"  we don't just pick up the information in the stimulus  as demonstrated lateral inhibition (the visual system manages to emphasize some aspects of the input and de-emphasize others from the very beginning. )  our interpretation, our organization of the input, happens BEFORE we start cataloguing the input's basic features  the cataloguing of the input's features depend on a prior step in which the form is organized by the viewer  the features are as much "in the eye of the beholder" as they are in the figure itself  e.g. the Hidden figure (pg 64)  with one organization, the key features are absent; with another; they're plainly present  the brain areas analyzing a pattern's basic features do their work at the same time as the brain areas analyzing the pattern's large-scale configuration.  the two brain areas constantly interact to make sense of both levels. The Logic of Perception  The organization is "in the eye of the beholder" and not in the stimulus itself.  These organizing steps proceed in parallel with - and so can influence and be influenced by - the very earliest "pick-up" of information from the stimulus.  organization determines our most immediate impressions of the stimulus 1. the interpretation achieved by the perceptual system must fit with all the incoming stimulus info 2. the perceptual system seems to prefer the simplest explanation for of the stimulus 3. the perceptual system seems to avoid interpretations that involve coincidences  the perceptual system does work as if it were generating hypotheses and the like Object Recognition Your recognition of various objects is influenced by the context in which the objects are encountered. Features Recognition might begin with the identification of features in the input pattern.  with features appropriately catalogued, you can start assembling the larger units.  we recognize objects by detecting the presence of the relevant features.  focusing on features might allow us to concentrate on what is common to the various tasks, and so might allow us to recognize despite their apparent diversity.  visual search task: study where participants have to indicate whether a certain target is or isn't present in a display.  the detection of features is a separate step in object recognition, followed by steps in which the features are assembled into more complex wholes  integrative agnosia: damage to the parietal cortex - people with this disorder are impaired in tasks that require them to judge how the features are bound together to form complex objects.  Ashbridge, Walsh, and Cowey  disruption of the parietal lobe had no impact on performance Word Recognition Once object recognition is detected of simple features, separate brain mechanisms are needed to put features together and assemble them into complete objects. Factors Influencing Recognition  tachistoscope: a device designed to present stimuli for precisely controlled amounts of time.  factors such as:  familiarity of the stimulus o can be measured by counting how often that stimulus appears o frequency of the stimulus  recency of view o the first exposure primes the participant for the second exposure (repetition priming) The Word-Superiority Effect word-superiority effect: Words are easier to perceive than individual letters.  accuracy rates are higher in the word condition, and so, recognizing words is easier than recognizing isolated letters.  participants are more accurate in identifying letters if those letters appear within a word as opposed to appear all by themselves. Degree of Well-Formedness Having a context is helpful even if the context is neither familiar nor meaningful. Not all contexts provide an advantage.  if a string is well formed according to the rules of the language, it will be easier to recognize and will produce a word-superiority effect.  pronounceable strings are also easier to
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