Textbook Notes (363,507)
Canada (158,391)
Psychology (9,573)
PSYB57H3 (369)
Dwayne Pare (122)
Chapter 3


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University of Toronto Scarborough
Dwayne Pare

Chapter 3: Recognizing Objects Form Perception  Vision is a dominant sense; reflected in how much brain area is devoted to vision compared to how much is devoted to any other senses  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?  Object recognition is essential whenever you want to apply your knowledge to the world and is crucial for learning  Object recognition is crucial for learning  Without recognition, there will be no way for you to combine info bits collected on different occasions 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  E.g., Necker cube is an example of an irreversible figure o Can be perceived as if viewed from above or viewed from below  Fine/ground organization = determination of what is the figure (the depicted object, displayed, against a background) and what is the ground (Figure 3.2A) 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 (See Figure 3.4) o Assumed that contours are smooth, not jagged, and you avoid interpretations that involve coincidences (See Figure 3.5)  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  Gestalt Principles of Organization (Figure 3.4): o Similarity: we tend to group these dots into columns rather than rows, grouping dots of similar colour o Proximity: we tend to perceiving groups, linking dots that are close together o Good Continuation: we tend to see a continuous green bar rather than two similar rectangles o Closure: we tend to perceive an intact triangle, reflecting our bias toward perceiving closed figures rather than incomplete ones o Simplicity: we tend to interpret a form in the simplest way possible; we would see the form on the left as two intersecting rectangles (as shown on the right) rather than as a single 12-sided irregular polygon Organization and “Features”  Interpretation of input happens before we start cataloguing the input’s basic features, not after o E.g., figure 3.6, the shapes have no meaning but after a moment, most people discover the word hidden in the figure; people find a way to recognize the figure so that the familiar letters come into view  With one organization, the features are absent; with another they’re plainly present o 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 → Bottom-up influences o Stimulus driven o Effects governed by the stimulus input itself and that shape the processing of that input  Other influences come from you → Top-down influences o Knowledge driven/ expectation driven o Factors arising from your knowledge and expectations, and shaping your processing of the stimulus input Features  Recognition might begin with the identification of visual features in the input pattern (lines, curves, etc.)  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 o E.g., finding a vertical segment in a field of horizontals (Figure 3.9)  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 (50x in every million printed words) or infrequent (1-5x per million words of print) and they viewed the words for 35ms followed by a mask o They recognized twice as many of the frequent words (See Figure 3.10)  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→ this is a case of repetition priming  For words that were high in frequency, 68% of unprimed words were recognized, compared to 84% of the primed words  For words low in frequency, 37% of the unprimed words were recognized, compared to 73% of the primed 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 → Word-superiority effect  Usually demonstrated with a “two-alternative, forced-choice” procedure o Accuracy rates are higher in the word condition o Recognizing words is easier than recognizing isolated letters o 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 (like FIKE or LAFE) o If string is not easily pronounceable (e.g., HZYE), 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 (like FIKE or LAFE) 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 o So we have an easier time recognizing sequences that use common letter combinations  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 o "TPUM" is likely to be misread as "TRUM" or even "DRUM"  Misspelled words, partial words, or nonwords are read in a way that brings them into line with normal spelling. o 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 → how energized the detector is o When the detector receives input its activation level increases up to a response threshold and then it fires → sends its signal to other detectors to which it is connected 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
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