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Chapter 3

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Dwayne Pare

PSYB57 – Chapter 3: Recognizing Objects Form Perception  Form perception = process through which you manage to see the basic shape and size of an object  Object recognition = process through which you identify what the object is Why is Object Recognition Crucial?  Object recognition is essential whenever you want to apply your knowledge to the world and is crucial for learning Beyond the Information Given  Gestalt psychologists argued that organization must be contributed by the perceiver; this is why the perceptual whole is often different than the sum of its parts  Ex. The Necker cube is an example of an irreversible figure  Fine/ground organization = determination of what is the figure and what is the ground The Gestalt Principles  With reversible figures, the info that is actually reaching your eyes is constant, the change is caused by you  Interpretation of stimulus is guided by principles that were catalogued by Gestalt psychologists  Perception is guided by proximity and similarity o Elements that resemble each other are assumed to be parts of the same object o Assumed that contours are smooth interpretations that involve coincidences are avoided  Everyone’s perceptions are guided by the same principles; each of us imposes our own interpretations on the perceptual input but we all tend to impose the same interpretation Organization and “Features”  Interpretation of input happens before we start cataloguing the input’s basic features  With one organization, the features are absent; with another they’re plainly present. The features themselves depend on how the form is organized by the viewer, and so the features are as much “ in the eye of the beholder”  Features must be in place before an interpretation is offered because the features govern the interpretation. But the features you find in an input depend on how the figure is interpreted  It is the interpretations, NOT the features, that must be first  Brain areas that analyze a pattern’s basic features do their work at the same time as the brain areas analyzing the pattern’s large-scale configuration and these brain areas interact; the perception of the features is guided by configuration and analysis of the configuration is guided by the features Object Recognition Recognition: Some Early Considerations  Some influences come directly from the stimulus itself o Stimulus driven o Bottom-up influences  Other influences come from you o Knowledge driven/ expectation driven o Top-down influences Features  Recognition might begin with the identification of visual features in the input pattern  Various studied make it clear that people are fast and efficient when searching for a target defined by a simple feature and are much slower in searching for a target defined as a combination of features  Damage to parietal cortex can lead to integrative agnosia o People with this disorder appear normal in tasks requiring them to simply detect features in a display but are impaired in tasks that require them to judge how the features are bound together to form complex objects  Disruption of the parietal lobe had no impact on performance when participants were searching a display for targets defined by a single feature. But TMS slowed performance when participants were searching for a target defined by a conjunction of features Word Recognition  Object recognition does begin with the detection of simple features then separate mechanisms are needed to put the features together into a complete object Factors Influencing Recognition  In many studies, participants have been shown stimuli for brief durations by means of tachistoscope o A device designed to produce stimuli for controlled amount of time o This job is now done by computers but still are called “tachistoscope presentations”  Each stimulus is followed by a post stimulus mask (often a random jumble of letters) which serves to interrupt any continued processing that participants might try to do for the stimulus just presented  If the stimulus is a word, we can measure familiarity by counting how often that word appears in print and these counts are excellent predictors of tachistoscope recognition  An experiment showed participants words that were either very frequent or infrequent and they viewed the words for 35ms followed by a mask o They recognized twice as many of the frequent words  If participants view a word and then view it again a little later, they will recognize the word much more readily the second time around o First exposure primes the participant for the second exposure o Repetition priming  For words that were high and low in frequency, primed words were recognized more compared to the unprimed words The Word-Superiority Effect  Words that are frequently viewed are easier to perceive and words themselves are easier to perceive as compared to isolated letters o Word-superiority effect  Usually demonstrated with a “two-alternative, forced-choice” procedure  Accuracy rates are higher in the word condition and 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 appearing all by themselves Degrees of Well-Formedness  Easily pronounceable strings provide a context benefit o If string is not easily pronounceable, there is little or no context benefit  Pronounceable strings are generally easier to recognize after a brief exposure compared to unpronounceable strings  Englishness = degree to which the letter sequence in the string conforms to the usual spelling patterns in English o Englishness is a good predictor of word recognition o The more English-like the string the easier it will be to recognize that string and the greater the context benefit the string will produce Making Errors  Our perception of words is somehow influenced by spelling patterns  Context promotes letter recognition but only if the context conforms with normal spelling o Contexts that don’t follow normal spelling don’t promote letter recognition  With brief exposure word recognition is good but not perfect and the errors that occur are systematic  There is a strong tendency to misread less common letter sequences as if they were more common patterns  Irregular patterns are misread as if they were regular patterns  Misspelled words, partial words, or nonwords are read in a way that brings them into line with normal spelling. People perceive the input as being more regular than it actually is  Our recognition seems to be guided by some knowledge of spelling patterns Feature Nets and Word Recognition The Design of a Feature Net  There is a network of detectors, organized in layers, with each subsequent layer concerned with more complex, larger-scale objects  Networks of this sort are often called feature nets o Flow of info would be bottom-up (from lower levels towards the upper levels)  Each detector in the network has a particular activation level which reflects the status of the detector at just that moment. When the detector receives input its activation level increases up to a response threshold and then it fires o Detectors involve complex assemblies of neural tissue  Within the net, some detectors require a strong input to make them fire and some only need a weak input, depending on the level they start at o If already at a moderate activation level, then a weak input is enough to fire  Detectors that have fired recently will have a higher activation level  Detectors that have fired frequently in the past will also have a higher activation level  Activation level is dependent on FREQUENCY and RECENCY  Frequent words appear often
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