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University of Guelph
PSYC 2410
Anneke Olthof

Cognitive Psychology: Chapter 3 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”  What we perceive is a lot more rich and powerful than what we actually know - 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: - Two different perceptions of depth are possible, given the line on the page - In the Face-Vase figure, two interpretations are possible, each based on different figure/ground organization - This again shows that perception goes “beyond the information given”  What you perceive depends on your interpretation, depending on what you think the “background” is - These example might suggest that perception proceeds in two stages 1) Where visual features are processed 2) 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 - 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 - 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  Your interpretation has to at least fit in to the input to some degree - 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 - In order to perceive this as 2 Vs, you have to place the 2 Vs together, which requires a lot more thinking, therefore we immediately perceive this as an X 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  Ex. 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 - For instance, this image is likely to be read as “THE CAT” and not “TAE CAT,” even though the letters “H” and “A” are identical here - Recognition might begin with the input pattern’s features – the small elements out of which more complicated patterns are composed - Note that here the features are not those of the raw input, but rather those that result from more organized perception form - All of these figures can be recognized as triangles, even though the essential features (3 lines, 3 angles) are present in only one - The features are inferred, however, in the visual system’s organized perception form - We’re good at tuning in to what the relevant features are in a stimulus - Advantages of feature-based system:  Features could serve as building blocks, allowing a single object-recognition system to deal with a variety of targets  Focusing on features might allow us to concentrate on what is common to otherwise variable objects -- Focusing on relevant features helps us hone in to what’s really in front of us and ignore all the irrelevant stimuli  Experimental tasks such as visual search suggest that features do have priority in perception  Other data suggest that the detection of features is a distinct step in object recognition: -- A disorder called integrative agnosia, caused by parietal cortex damage, involves a preserved ability to detect whether certain features are present in a display but a disrupted ability to judge how features are bound together in objects -- A similar dissociation has been produced using transcranial magnetic stimulation (TMS) Word Recognition - Some methodology for studying word recognition:  The tachistoscope is a device for presenting stimuli for precisely controlled amounts of time. Today, computers are used for this purpose.  Word stimuli may be followed by a mask – a stimulus designed to disrupt further sensory processing of the words – such as a random string of letters. - Visual words can be recognized with extremely brief presentations (e.g., 40 ms) under the right conditions:  Words that are more frequent in the language are better recognized -- People do better with familiar
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