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Chapter 3

Chapter 3

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Gabriela Ilie

Chapter 3 Perception: take sensory input and interpret Brain responsible for visual processing occupy half of total cortex Types of perception: visual, auditory, olfactory, haptic and gustatory Classic approach to perception Object to be perceived is a distal stimulus Reception of information and registration make up the proximal stimulus Retinal image: image at the back of the retina that is formed o 2D image, and size depends on distance from window and object o Left right and up down are reversed. Meaningful interpretation = percept (seeing and recognizing) Size constancy: size does not change even if the size in retinal image changes o Perception is something beyond retina images Pattern recognition: recognition of a particular object, even to belong to a certain class most percepts involve classification Ames room: trapezoid design, brain knows room as parallel Experience and expectation contribute to how we see our environment Bottom up Processes Data/stimulus driven Stimulus determines percept direction is stimulus to onput Building percepts from small units Template matching, feature analysis, prototype matching Perceiver starts with small bits of information that combine to form a percept. One direction: input to interpretation, system cannot go back, and incidents right now are unaffected by later processing. o Information about a stimulus, and relatively uninfluenced by expectations or previous learning. Posner/Raichele argue bottom up are automatic and reflexive even when person is passively regarding the information. Gestalt Perception involves segmentation or parsing of visual stimuli into objects and backgrounds focus on how we recognize objects as forms Form perception: segregation of whole display into objects and backgrounds Salvador Dali: Slave Market with Disappearing Bust of Voltaire Figure: definite shape, ground: shapeless, less formed, far in space Illusionary contours/subjective contours: Illusory outline created by visual cues that lead to erroneous form perception. o Perception is a construction process, and requires participation Perceive units as a whole, not by its parts Gestalt principles of perceptual organization o Proximity close things, nearness o Similarity similar objects group o Good continuation: form straight or curve lines o Closure: illusionary closures o Common fate: elements that move together will group together. Law of pragnanz: This law holds that objects in the environment are seen in a way that makes them appear as simple as possible. Minimal model theory: formalizing law of pragnanz Drawbacks: unsure how principles are translated into cognitive or physiological processes Law can be circular without further specification Template Matching Correspondence between external and stored patterns in memory (templates) o Pattern is identified and compared to templates to identify the best match Example: UPC bar codes for products Process of perception involves comparing incoming information that are stored o Further processing is needed to find the most appropriate fit o Many models exist in knowledge Problems o Need impossibly large number of templates o Does not explain how new objects are recognized, and how they are kept track and created o Does not explain how patterns that are similiar, even when patterns differ Surface variation of stimuli Unlikely used in every day perception o How does a perceiver know which orientation and template to use? o Possible if stimuli is relatively clean and known ahead of time to be relevant o Does not explain noisy patterns and objects, such as blurred, blocked, etc. Feature Analysis Analysis of a whole into parts o Objects = combination of features o Features are small templates that can be combined in many ways Recognize features to recognize the combination Break down an object into many components Lettvin: implant electrodes into frogs and found that certain stimuli can make them fire more frequently o Some cells responded to borders edge detectors o Bug detector respond to black dot in a field of vision Huble/Wiesel: visual cortex of cats and monkeys respond to particular orientation: vertical/horizontal Lettin and H/W research show that detectors look for certain features and retinal cortical cells have these in existence confirm feature analysis model applicable Eleanor Gibson tabulated features of Roman Alphabet (C and G similar, not F) Neisser: people use features to identify letters o Perform visual search task easier to find letters in a group that did not share features (Q/Z in round letters and straight letters non targets make search harder Similar findings in audition syllables which share articulatory features are more likely to be confused (da/ta confused more than da/sa) Articulatory features include: o Voicing (vibration of vocal chords) o Nasality (passing of air through nasal) o Duration (how long sounds are) o Place of articulation (where in mouth) Selfridge Pandemonium Model o Different levels of demons that function as feature detectors
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