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1 Psychology 40S Sensation and Perception C. McMurray Source: PSYCHOLOGY (9th Edition) David Myers Worth Publishers, 2010 Chapter 6

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2 Sensation & Perception How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organize, and interpret our sensations, the process is called perception.

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Sensation and Perception Sensation - the process by which we detect physical energy from the environment and encode it as neural signals. Perception the process of selecting, organizing and interpreting our sensations. Sensation and perception blend into one continuous process. 3

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Basic Steps of Sensation and Perception 4

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A Gestalt The German Gestalt psychologists of the nineteenth century believed that the whole is different from the sum of its parts. Because of the way these parts are arranged, we perceive much more. 1.You can make the tiny X in the center seem to be on either the front edge of the cube or the back (but not both at the same time). 2.You can make the cube seem to appear in front of the paper with red circles, or behind a paper with holes cut out of it. Can you see both 1 and 2? 5

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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.

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7 Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT

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8 Our sensory and perceptual processes work together to help us sort out complex images. Making Sense of Complexity The Forest Has Eyes, Bev Doolittle

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Sensation and Perception 9

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Top-Down Processing When we use Top-down processing, we perceive by filling in gaps in what we sense. For example, try to read the following sentence: I _ope you _av_ a ni_e we_ken_. 10

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Top Down Processing I _ope you _av_ a ni_e we_ken_. I hope you have a nice weekend. Top-Down processing occurs when you use your background knowledge to fill in gaps in what you perceive. 11

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12 Exploring the Senses What stimuli cross our threshold for conscious awareness?

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Threshold In order to establish laws about how people sense the external world, psychologists first try to determine how much of a stimulus is necessary for a person to sense it at all. How much energy is required. 13

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14 Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. It is the weakest amount of a stimulus required to produce a sensation. For example: I drink black coffee. How many grains of sugar are needed in my coffee before I taste the sweetness. The point where I think I taste it (50% of the time ) is my absolute threshold.

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Subliminal Threshold 15 Subliminal Threshold: When stimuli are below ones absolute threshold for conscious awareness. Kurt Scholz/ Superstock

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Rods and Cones The eye has receptor cells called rods and cones. Visual processing begins when light strikes these receptor cells. Cones produce colour sensations and fine details. Rods produce only black and white sensations and allow us to see in very dim light. You have 6.5 million cones in each eye and 100 million rods! 16

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Color Vision Trichromatic theory: Theory of colour vision based on three cone types: red, green and blue Opponent-process theory: Theory of colour vision based on three pairs of receptors (red/green, blue/yellow and black/white) According to the theory, when one colour of the pair is fatigued this will produce an afterimage of the opposite colour in that pair as the system recovers. Eg. If you stare at a red object for a period of time and look away, you will see a green afterimage.

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18 Opponent Colors Gaze at the middle of the flag for about 30 Seconds. When it disappears, stare at the dot and report whether or not you see Britain's flag.

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Stare at the blue dots while you count slowly to 30. 21

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23 Color Blindness Ishihara Test Color vision is dependent on the interaction of the three cones, one of which is particularly sensitive to red light, another to green light, and a third to blue light. When one or more of these cones in an individual's retina is absent or damaged, some kind of color vision impairment will result.

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Colour Depends on Context All 3 blue circles are the same colour of blue! 24

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25 Perceptual Organization How do we form meaningful perceptions from sensory information? We organize it. Gestalt psychologists showed that a figure formed a whole different than its surroundings.

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Perceptual Organization Gestalt: the experience that comes from organizing bits and pieces of information into meaningful wholes Seeing things as a whole 26

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Gestalt grouping principles such as closure and continuity are at work here. 28

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Illusions Illusions are incorrect perceptions. Illusions can be useful in teaching us about how our sensation and perceptual systems work. Illusions are created when perceptual cues are distorted so that our brains cannot correctly interpret space, size and depth cues. 30

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A Lake or a Baby? 31

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How many Faces? 32

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Young Lady or Old Lady? 34

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This logo for Pittsburgh Zoo is a nice illusion. As well as the tree, what animals can you see? 35

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Can you see the deliberate mistake? 37

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Adelson checkerboard visual demo Tile A and B are the same colour! Checkerboard explained Checkerboard explained in a video 38

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Rotating Mask Watch rotating mask Click on watch video on this site 39

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Dragon Illusion Watch the Dragon Illusion 40

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Head Trick Watch the Head Trick 41

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Miachael Bachs Website of Illusions: LOTS of Illusions to click on!! 42

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A Game of Ping Pong? Watch matrix Ping Pong 43 Watch fighting Gravity

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Leaning Tower of Pisa Illusion Which of the following two images of the tower of Pisa seems to be leaning more? The images are actually identical, but the tower on the right seems to lean more because the human visual system treats the two images as one scene. Our brains are conditioned to expect parallel towers to converge toward a common vanishing point, but because the tower on the right does not converge, our visual system interprets that it is leaning at a different angle. -------------------------------------------------------------------------------- 44

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Journal Entry Topic: Sensation and Perception Comment on something that you learned in this unit. Explain using specific terms that you learned in class. Elaborate and give details (and examples.) 45