Perception PDF

PERCEPTION PERCEPTION Process by which we recognize what is represented by the information provided by our sense organs. This process gives unity and coherence to this input.  GESTALT Organizing and patterning allows us to understand the whole, rather than discrete parts of the stimulus. Figure...

PERCEPTION PERCEPTION Process by which we recognize what is represented by the information provided by our sense organs. This process gives unity and coherence to this input.  GESTALT Organizing and patterning allows us to understand the whole, rather than discrete parts of the stimulus. Figure / ground – distinguish between the main focus of attention and the background or surroundings  Form Perception Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Time Savings Suggestion, © 2003 Roger Sheperd. 4 M.C.Escher 8 9 ILLUSION False or misleading impression produced by errors in the perceptual process or by actual physical distortions. Illusory Contours DELUSION False beliefs Often of persecution or grandeur May accompany psychotic disorders HALUCINATION False sensory experiences, such as seeing something in the absence of an external visual stimulus Hallucinogenic OPTICAL ILLUSIONS Seeing is believing, but seeing isn’t always believing correctly (Lilienfeld et al, 2010, p.7) SELECTIVE ATTENTION The process that controls our awareness of, and readiness to respond to, particular categories of stimuli or stimuli in a particular location FEATURE DETECTORS Nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement HABITUATION Decreasing responsiveness to repeated stimulation. Sensory adaptation Troxler’s Fading FORM PERCEPTION Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Proximity Continuity Closure Similarity Connectedness Grouping After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using grouping rules. 34 Similarity Unity Continuity Closure Proximity Grouping & Reality Although grouping principles usually help us construct reality, they may occasionally lead us astray. Magazine..© 1983 PCS Games Limited Partnership Both photos by Walter Wick. Reprinted from GAMES 40  Depth Perception Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even newborn animals show depth perception. Innervisions Visual Cliff 41 CONVERGANCE The result of vergence eye movements whereby the fixation point for each eye is identical – feedback from these movements provides information about the distance of objects from the viewer BINOCULAR DEPTH CUES  Retinal disparity: Images from the two eyes differ. Try looking at your two index fingers when pointing them towards each other half an inch apart and about 5 inches directly in front of your eyes. You will see a “finger sausage” Monocular Cues Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away. 45  46 Interposition: Objects that occlude (block) other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli. Monocular Cues Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance. from cartoonbank.com. All rights reserved. © The New Yorker Collection, 2002, Jack Ziegler 47 Monocular Cues Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower. adapted from stimuli that appered in Vecrera et al., 2002 Image courtesy of Shaun P. Vecera, Ph. D., 48 Monocular Cues Relative motion: Objects closer to a fixation point move faster and in opposing direction to those objects that are farther away from a fixation point, moving slower and in the same direction. 50 TEXTURE GRADIENT Nearby objects have a coarser and more distinct texture than distant ones AERIAL PERSPECTIVE Monocular Cues Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away. All rights reserved. S. Ramachandran. © 1988 by Scientific American, Inc. From “Perceiving Shape From Shading” by Vilayaur 54 PERCEPTUAL CONSTANCY Perceiving objects as unchanging, (having constant shape, size, brightness, colour), even as illumination and retinal images change COLOUR CONSTANCY Perceiving familiar objects as having consistent colour even when changing illumination filters the light reflected by the object Colour Constancy Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object. Color Constancy 57 Shape Constancy  Size-Distance Relationship Both girls in the room are of similar height. However, we perceive them to be of different heights as they stand in the two corners of the room. Both photos from S. Schwartzenberg/ The Exploratorium 59 Ames Room The Ames room is designed to demonstrate the size- distance illusion. 60 TRICHROMATIC THEORY The theory that colour perception results from mixing three distinct colour systems – red, green, and blue OPPONENT-PROCESS THEORY The theory that colour perception is based on three systems of colour receptors, each of which responds in an on-off fashion to opposite colour stimuli Blue – yellow Red – green Black - white  Perceptual Interpretation Immanuel Kant (1724-1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences. John Locke (1632-1704) argued that we learn to perceive the world through our experiences. How important is experience in shaping our perceptual interpretation? 63 INTERPRETATION - Perceptual adaption Perceptual set Frame of reference Bottom-up / top/down processing Perceptual Set A mental predisposition to perceive one thing and not another. What you see in the center picture is influenced by flanking pictures. From Shepard, 1990. 65 Perceptual Set Other examples of perceptual set. Frank Searle, photo Adams/ Corbis-Sygma Dick Ruhl (a) Loch ness monster or a tree trunk; (b) Flying saucers or clouds? 66 FRAME OF REFERENCE BOTTOM UP / TOP DOWN Bottom up – analysis of the perceived item begins with the sensory receptors and works up to the brain’s integration of sensory information Top down – information processing is guided by higher level mental processes, as when we construct perception drawing on our Perception Revisited Is perception innate or acquired? 69 SCIENCE AND ESP Perception without sensory input is called extrasensory perception (ESP). A large percentage of scientists do not believe in ESP.