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Chapter 3

Chapter 3- Recognizing objects.docx

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Dwayne Pare

Chapter 3: Recognizing Objects Form Perception Vision is very important to us; it is the dominant sense taking up a better part of our brain. 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: perception of the world is organized in contribution with the perceiver; this is why the perceptual whole is often different than the sum of its parts Bruner: “beyond the information given” Eg. The Necker cube is an example of an irreversible figure  You go beyond the information in the drawing, and specify an arrangement BUT the drawing itself is neutral with regard to perceptual organization, or more specifically Figure/Ground Organization – determination of what is the figure and what is the ground  Other similar examples: vase/faces, Schroeder staircase The Gestalt Principles With reversible figures, the information that is actually reaching your eyes is constant, the change is caused by you. Eg. fruit basket; telling which fruits are which, perceiving the fruits as continuous, etc. Interpretation of stimulus is guided by principles that were catalogued by Gestalt psychologists: 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 using parallel processing; 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 We recognize objects even if it’s partially seen, and we take context into consideration.  Eg. reading THE CAT instead of TAE CHT Context comes from 2 influences:  Bottom-Up Influences – influences coming from the stimulus; “stimulus driven”  Top-Down Influences – influences coming from you allowing interpretation and applying your knowledge; “knowledge or expectation driven” Features Recognition might begin with the identification of Visual Features – the vertical lines, curves, diagonals, etc. – In the input pattern  Eg. horizontal line + vertical = right angle + 4 right angles = square Various studies 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 TMS and other studies show damage to parietal cortex can lead to Integrative Agnosia – 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 Word Recognition Factors Influencing Recognition Participants have been shown stimuli for brief durations by means of Tachistoscope – a device designed to produce stimuli, usually words for controlled amount of time. Each stimulus is followed by a post stimulus Mask – often a random jumble of letters – which serves to interrupt any continued processing. We can measure familiarity by counting how often that word appears in print and these counts are excellent predictors of tachistoscope recognition. Primes – first exposure of a word allowing recognition Repetition Priming – second exposure of the word, allowing better repetition The Word-Superiority Effect Word-Superiority Effect – words that are frequently viewed are easier to perceive and words themselves are easier to perceive as compared to isolated letters  “two-alternative, forced-choice” procedure; E or K in DARK?  Accuracy rates are higher in the word condition and recognizing words is easier than recognizing isolated letters Degrees of Well-Formedness Context is important  HYZE has an EE, but this does NOT show a word-superiority effect  Pronounceablility – words like FIKE that are not familiar but do produce a context effect and are easier to recognize  Probability of letter combinations; Englishness – degree to which the letter sequence in the string conforms to the usual spelling patterns in English o More Englishness = more recognition & context Making Errors Context promotes letter recognition but only if the context conforms with normal spelling Tendency to misread less common letter sequences as if they were more common patterns.  Eg. TPUM is read as TRUM or DRUM Feature Nets and Word Recognition The Design of a Feature Net Feature Nets – a network of detectors, organized in layers, with each subsequent layer concerned with more complex, larger-scale objects.  Flow of information is bottom- up (from lower levels towards the upper levels) Each detector in the network has a particular Activation Level; when the detector receives input its activation level increases up to a response threshold and then it fires.  Recency & Frequency & Strength = higher activation level  The activation will reach the detector’s Response Threshold – where the detector will fire – send its signal to the other detectors to which it is connected Frequent words  detectors needed for recognizing these words have been frequently used Repetition priming  presenting a word once will cause relevant detector to fire and once fired, activation levels will be temporarily lifted. A weak signal will be needed to make the detectors fire again and word will be more easily recognized the second time. The Feature Net and Well-Fo
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