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3. PSY270 Perception.docx

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Kristie Dukewich

PSY270 Ch.3 Perception 10/25/2012 10:09:00 PM Overview: Humans better at perceiving objects than computers due to our perceptual intelligence, knowledge gained by experience in perceiving. - Process of perception = incoming stimulus + existing knowledge - Perceiving objects = objects analyzed into features, organization of stimuli - Perceptual intelligence = Used to perceive objects 1. Bottom-up and top-down processing in perception 2. Recognizing letters and objects 3. Perceptual organization: putting together an organized world 4. Why computers have trouble perceiving objects 5. How experience and knowledge create “perceptual intelligence” 6. Perception depends on attention: change detection 1. Bottom-up and top-down processing in perception  Bottom-up processing = Incoming data/stimuli o Seeing a moth: o Light reflected from moth  image in her eye  image triggers the process of transduction.  Transduction (physiology), the transportation of stimuli to the nervous system. o Transduction  electrical signals from eye to brain o Sequence of events starting with stimulation of the receptors by a stimuli = Bottom up processing o Bottom-up processing = incoming data from the environment to form a perception.  Information enters the eyes in one direction (input), and is then turned into an image by the brain that can be interpreted and recognized as a perception (output). o Perception begins with bottom-up processing, but top-down processing becomes involved when the perceptual process is influenced by a person’s knowledge.  Top-down processing = Knowledge & Expectations o Processing that involves a persons knowledge. o Can collaborate with bottom-down to solve perceptual problems.  Ex. Rat-man demonstration = Recently acquired knowledge can influence perception. Expectancy.  Seeing a man’s face if shown many faces previously.  Seeing a rat if shown many animals beforehand.  Ex. Palmer’s kitchen scene = how context can influence perception. 2. Recognizing letters and objects  The old template-matching model cannot explain letter recognition.  The Interactive Activation Model o Feature detectors + oriented lines o Specific neuron response + specific line orientations  Inspired by Hubert & Wiesel (feature detectors – we respond to features that make up objects – lines, edges, shape, angle, movement)  The McClelland & Rumelhart word recognition model   First well known neural network model of reading = McClelland & Rumelhart’s interactive activation model o Solved the problems associated with template matching o Used the interactive activation model: 3 steps o (features + stages + top-down processing)  Illustrates a model in which processing begins with features and occurs in stages, and which also takes into account how top-down processing can influence our ability to recognize letters.  Models based on features can explain a number of things about letter recognition, including the word-superiority effect. o Easier to recognize letters when they appear in a real word, rather than in a non-word. o Processing of a letter is affected by each letter in its surroundings.  Feedback activation = FORK, K4  Top-down processing = expectations of letters around each other in a real word Feature integration theory (FIT; Treisman 1986)  o  Describes rapid processes that occur at the beginning of object perception o posits that different kinds of attention are responsible for binding different features into consciously experienced wholes. o Describes perception of 2-D objects o BUT doesn’t explain 3-D objects o 2 Stages of FIT perception:  1. Preattentive stage = detect features  Fast, automatic, unconscious processing  Several primary visual features are processed and represented with separate "feature maps" that are later integrated into "saliency (important/prominent/salient) maps" that can be accessed in order to direct attention to the most conspicuous areas.  During this stage, the object is analyzed with details such as shape, color, orientation and movement in mind.  Each of these aspects is processed in different areas of the brain.  Harder to find object when it has more shared features with distractors around it = need for focused attention  2. Focused attention stage = Combine features  This stage involves integrating individual features in order to perceive the whole object.  If the object is familiar, associations are made between the object and prior knowledge in order to aid in recognition (top-down processing)  Bálint's syndrome sufferers, who as a consequence of parietal lobe damage seem incapable of properly focusing attention, lend credence to this two-staged model of attention. Interactions between perceiving + action = what/where pathways  Milner & Goodale “Two Stream Hypothesis” = brains 2 distinct visual systems  What/Where = Different LOBES + PATHWAY o WHAT = Temporal, Ventral  object identification, recognition  Damage = Optic agnosia (like ignorance, not knowing), deficiency in ability to recognize visual objects.  Prosopagnosia (inability to recognize faces!) o WHERE = Parietal, Dorsal (WHERE is the door-sal)  object locating, HOW, motor movement  Damage = Optic ataxia, Balint Syndrome, Hemineglect  Optic Ataxia – Damage to the WHERE, Parietal, Dorsal pathways = inability to move the hand to a specific object by using vision. Impaired visual control of the direction of arm-reaching to a visual target, accompanied by defective hand orientation and grip formation o cortex is essentially divided into two functional streams:  an occipital-parietal-frontal pathway that processes "where" information  Sensing the location of where the object is  and an occipital-temporal-frontal pathway that provides "what" information to the individual  Naming what the object is  FIT & Illusionary conjunctions o Here participants accidentally combine features of two objects into one object, due to a lack of attention  Exp. Treisman & Schmidt required participants to see a visual presentation of black numbers and shapes in different colors.  Some shapes were larger than others but all shapes and numbers were evenly spaced and shown for 200 ms.  Due to the fact that the shapes and numbers were shown for such a short amount of time, when the participants were asked to recall them they reported answers such as a small green triangle instead of a small green circle.  If the space is smaller between objects illusory conjunctions happen more often. o Example of an Illusory Conjunction between two different shapes of different colors forming an entirely new object Recognition-by-components (RBC) theory - Biederman  Describes how a feature analysis approach can be applied to the perception of 3-D objects.  Object recognition  Irving Biederman  Bottom-up process (incoming data/stimulus  perception) o 1. Recognizing objects by separating them into geons  (the object’s main component parts)  Geons are based on basic 3-dimensional shapes  (cylinders, cones, etc.) o 2. Geon’s can be assembled in various arrangements to form a virtually unlimited amount of objects.  There are 36 different geons which are combined to create the objects we see in day to day life  Perceived geons are then compared with objects in our stored memory to identify what it is we are looking at.  The theory proposes that when we view objects we look for 2 important components: o Edges – This enables us to maintain the same perception of the object regardless of viewing orientation. o Concavities – The area where two edges meet. These enable us to observe the separation between two or more geons. o o o o o o  RBC Theory & viewpoint invariance o RBC Theory enables us to recognize objects regardless of viewing angle o Due to the invariant edge properties of geons:  Curvature (various points of a curve)  Parallel lines (two or more points which follow the same direction)  Co-termination (the point at which two points meet and therefore cease to continue – corners)  Symmetry and asymmetry  Co-linearity (points branching from a common line)  Advantages of RBC Theory o 1. Due to object properties & viewpoint invariance & geons discriminate from each other = a single geon description is sufficient to describe an object from all possible viewpoints o = Discriminability properties of geons o 2. A relatively small set of geons for
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