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Chapter 3

Cognitive Psychology - In and Out of the Laboratory: Chapter 3

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Western University
Psychology 2135A/B
Robert Brown

Chapter 3 - Object Perception and Pattern Recognition - perception: interpretation of sensory information to yield a meaningful description - areas of brain responsible for visual processing occupy up to half of total cortex space - perception divided into visual, auditory, gustatory, olfactory, haptic - "classic" approach to defining perception: - distal stimulus: stimulus that exists in the world - proximal stimulus: reception of information and its registration by a sense organ - percept: outcome of a perceptual process; meaningful interpretation of incoming information - retina: back of eye - retinal image: two-dimensional image; closer to object, larger the image; upside down and reversed with respect to left and right; formed on retina - size constancy: phenomenon that one's perception of an object remains constant even as the retinal image of the object changes size - pattern recognition: classification of a stimulus into a category - most, if not all, instances of perception involve pattern recognition Gestalt - we interpret stimulus arrays as consisting of objects and backgrounds - form perception: process by which brain differentiates objects from their backgrounds - objects are figures and the background is ground - figure is seen as having a definite shape, better remembered - ground is seen as more shapeless, less formed, and farther away in space - subjective (illusory) contours: illusory outline created by certain visual cues that lead to erroneous form perception - subjective contours come to be through a simplifying interpretation the perceiver makes; perception not completely determined by the stimulus display - Gestalt psychologists assert whole is not the same as the sum of its parts; we recognize objects as a whole instead of individual features - Gestalt principles of perceptual organization: laws that explain regularities in the way people come to the perceptual interpretations of stimuli - principle of proximity (nearness): group together things that are nearer to each other - principle of similarity: grouping elements that are similar - principle of good continuation: group together objects whose contours form a continuous straight or curved line - principle of closure: mentally filling in gaps; creates subjective contours - principle of common fate: group elements that move together (includes luminance change even if stimuli differ in brightness) - law of Pragnanz: most Gestalt principles subsumed here; of all the possible ways of interpreting a display, we tend to select organization that yields the simplest and most stable shape or form - simple and symmetry forms are seen more easily - infants as young as three demonstrate use of some Gestalt principles - formalization of Gestalt law of Pragnanz creates minimal model theory - Gestalt approach does not answer how these principles are translated into cognitive or physiological processes - law of Pragnanz can be circular (why do we see two triangles? interpretation makes for a simple, stable figure. How do we know this figure is simple and stable? Because we so readily see it) Bottom-up Processes - bottom-up (data-driven) process: perceiver starts with small bits of information from environment and combines them in various ways to form a percept - system has no way of going back to an earlier point to make adjustments - lower level of processing is taking information about a stimulus - higher level process includes expectations or previous learning - bottom-up processes are relatively uninfluenced by expectations or previous learning - bottom-up processes involve automatic, reflexive processing that occurs even when perceiver is passively regarding information - two biggest problems are context effects and expectation effects - context effects: effect on a cognitive process due to information surrounding target object or event; sometimes called expectation effect since context is thought to set up certain expectations - three examples of bottom-up models: template matching, featural analysis, prototype matching Template Matching - templates: previously stored patterns - every stimulus is compared to some previously stored pattern, or template - if a number of templates match, further processing needed to sort out which template is most appropriate - model implies we have stored millions of different templates - model cannot provide complete explanation - first, for complete explanation, need to have stored impossibly large amount of templates - second, does not explain how and when templates are created and how we keep track of an ever-growing number of templates - third, people recognize many patterns as more or less the same thing, even when stimulus patterns differ greatly i.e. handwriting - must of stimulus information we perceive is far from regular i.e. alteration, degradation, unfamiliar orientation (upside-down); is separate template needed for each variation; how do we know how an object should be before matching to a template - cannot know before whether an input pattern should be adjusted before matching to templates - good for relatively clean stimuli, but does not explain how we perceive effectively among all the "noise" in everyday life Featural Analysis - features: parts searched for and recognized - recognition of a whole object depends on recognition of its features - certain detectors in senses appear to scan input patterns, looking for a particular feature i.e. horizontal line - visual search task: task where subjects asked to detect presence of particular target against an array of similar stimuli - harder to find target among similar stimuli - Pandemonium: model of letter perception based on a bottom-up hierarchy of feature detectors - first, detectors respond more strongly or weakly depending on clarity and quality of input; allows for real-life stimuli often degraded or incomplete, yet can still be recognized - second, feature detectors can be linked to cognitive detectors in a way that more important features ca
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