Sensation and Perception Chapter 6 Sensation The Eye 3 Photoreceptors E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969 4 Perception Test your Blind Spot Use your textbook. Close your left eye, and fixate your right eye on the black dot. Move the page towards your eye and away from your eye. At some point the car on the right will disappear due to a blind spot. 6 Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.” 7 Feature Detection Ross Kinnaird/ Allsport/ Getty Images Nerve cells in the visual cortex respond to specific features, such as edges, angles, and movement. 8 Visual Information Processing parallel processing The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc. 9 Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT 10 Thresholds Proportion of “Yes” Responses 1.00 0.50 0.00 Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. 0 5 10 15 20 Stimulus Intensity (lumens) 25 11 Subconscious Sense and Perception Subliminal Threshold: Priming Length of effects 12 Adaptation/Habituation • Stare at the image, don’t move your eyes around Perceptual Organization 15 Flipped image Figure/Ground Time Savings Suggestion, © 2003 Roger Sheperd. 17 Grouping 18 Innervisions Depth Perception Visual Cliff 19 Binocular 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” as shown in the inset. 20 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. 21 Monocular Cues 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. 22 Monocular Cues Relative motion: 23 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. © The New Yorker Collection, 2002, Jack Ziegler from cartoonbank.com. All rights reserved. 24 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. From “Perceiving Shape From Shading” by Vilayaur S. Ramachandran. © 1988 by Scientific American, Inc. All rights reserved. 25 Perceptual Constancy Perceiving objects as unchanging even as illumination and retinal images change. 26 Color Constancy Color Constancy 27 Lightness Constancy The color and brightness of square A and B are the same. 28 Size-Distance Relationship Alan Choisnet/ The Image Bank From Shepard, 1990 29 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 30 Ames Room The Ames room is designed to demonstrate the sizedistance illusion. 31 Perceptual Interpretation How important is experience in shaping our perceptual interpretation? 32 Facial Recognition Courtesy of Richard LeGrand After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. Normal observers also show difficulty in facial recognition when the lower half of the pictures are changed. 33 Sensory Deprivation Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars. Blakemore & Cooper (1970) 34 Top down emotional effects • • • • Music Fatigue Carrying heavy versus light objects Previous performance Cultural Context Context instilled by culture also alters perception. To an East African, the woman sitting is balancing a metal box on her head, while the family is sitting under a tree. 36 Taste Sweet Sour Salty Bitter Umami (Fresh Chicken) 37 Gustation/Tast e – a close-up view of the tongue Why does some food taste “hot”? • Hot chili peppers are sensed by pain fibers in the tongue, which are activated by capsaicin • Was evolved in the peppers to prevent them from being eaten Smell 40 What is your favorite scent? Smell and Memories 42