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Queen's University
PSYC 371
Sidney Eve Matrix

Chapter 7: Perception Primary function of senses is to guide behaviour perception a rapid, automatic, unconscious process by which we recognize what is represented by information provided by our sense organs if we see something ambigious and must figure out what it is, it is problem solving, not perception Brain Mechanisms of Visual Perception perception takes place in brain optic nerve sends signals to thalamus, which relays information to primary visual cortex (located in occipital lobe), neurons in primary visual cortex send visual information to two successive levels of visual association cortex first level located in occipital lobe, surrounds primary visual cortex second level divided into 2 parts, one is middle of parietal lobe and one in lower part of temporal lobe often described as hierarchy of information processing circuits of neurons analyze particular aspects of visual information and send results of analysis to another circuit, which performs further analysis at each step successively more complex features are analyzed and higher levels interact with memories Primary Visual Cortex knowledge of early stages of visual analysis comes from investigations of activity of individual neurons in thalamus and primary visual cortex David Hubel and Torsten Wiesel inserted microelectrodes into regions of visual system in anasthetized cats and monkeys (unconsious but visual system still active) to detect Aps produced by individual neurons found place in visual field with most response and objects with most response found that surface of retina is mapped on surface of primary visual cortex centre of visual field is largest area 2,500 blocks of tissue .5x.7 mm in size containing 15,000 neurons each, receiving information from same small region of retina, and thus small region of visual field (amount seen through soda straw) neural circuits within module analyzes various characteristics of their own particular field (receptive field) detected presence of lines and signalled orientation of lines, thickness of lines, movement and its direction receptive field that portion of visual field in which presentation of visual stimuli will produce an alteration in firing rate of particular neuron particular neuron responds to particular orientation (50 degrees, etc) Visual Association Cortex first level of visual association cortex contains several subdividions, each of which contain map of visual scene each subdivision receives information from different types of neural circuits within modules of primary visual cortex orientation and widths of lines and edges involved in perception o movement keeps track of relative movement of objects colour 2 regions of association cortex put together information ghathered and processed by subdivisions of first level shape, movement and colour combined in visual association cortex in lower part of temporal lobe (3-d form perception) form perception information from motor system and body senses about movement of eyes, head, and body combined in parietal lobe (location of object), part of system for object-directed behaviour space perception Effects of Brain Damage on Visual Perception primary visual cortex damage blind in portion of field visual association cortex damage difficulty in perceiving shapes and objects or particular visual characteristics achromatopsia inability to discriminate among different hues damage produces achromatopsia in contralateral field (total achromatopsia results from bilateral damage) difficulty to perceive movement and keep track of moving objacts (first level damage) Balint's syndrome difficulty in perceiving location of objects and reaching for them under visual guidance, difficulty keeping track of them in visual scene, can see object when looking directly at it but cannot see where located (bilateral parietoccipital region); deficit in spatial perception visual agnosia diffuclty recognizing objects (damage to visual association cortex in temporal lobe) prosopagnosia form of visual agnosia where there is difficulty recognizing faces and some other complex stimuli, can recognize categories but not individual differences Perception of Form Figure and Ground objects or background objects have particular shape and particular locations in space and backgrounds are formless and serve mostly to help us judge location of objetcs we see in front of them figure visual stimuli perceived as self-contained object ground visual stimuli perceived as formless background on which objects are seen Organization of Elements: Gestalt Laws of Grouping gestalt psychology branch of psychology that asserts that perception of object is produced by particular configurations of elements of stimuli based on tendency to organize elements and empty space into cohesive forms task of perception was to recognize objects in environment according to organization of their elements - whole is more than sum of its parts; emhasize relationship of elements to one another, not just elements several principles of grouping can predict combination of these elements laws of organization: law of proximity elements closest to each other are perceived as belonging to same figure law of similarity similar elements are perceived as belonging to same figure good continuation given two or more interpretations of elements that form outline of figure, simplest interpretation is preferred law of closure elements missing from outline of figure are filled in by visual system law of common fate elements that move together give rise to perception of particular figure Alais, Blake, and Lee found that law of common fate applies to changes other than movement visual objects stand out in background to extent that they exhibit contrasts in brightness and colour common tempo Models of Pattern Perception cognitive psychologists study perception Templates and Prototypes templates hypothetical pattern that resides in nervous system and is used to perceive objects or shapes by process of comparison; too simplistic prototype hypothetical idealized pattern that resides in nervous system and is used to perceive objects or shapes by process of compariosn, recognition can occur even when exact match is not found non-human studies suggest that familiarity with cate
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