SENSATION AND PERCEPTION CHAPTER 6 AP Psychology ~ Ms. Justice BIG IDEAS Seeing the World: Some Basic Principles Thresholds Vision Hearing Other Important Senses Perceptual Organization Perceptual Interpretation Is There Extrasensory Perception? 1: What are sensation and perception? What do we mean by bottom-up and top-down processing? 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. 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.” We process this way when we have no prior knowledge: we start at the bottom and work our way up. TOP-DOWN PROCESSING Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT We process this way when we have prior knowledge: we start at the top and have to work to process details. MAKING SENSE OF COMPLEXITY Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes,” Bev Doolittle 2: What are absolute and difference thresholds, and do stimuli below the absolute threshold have any influence? PSYCHOPHYSICS A study of the relationship between physical characteristics of stimuli and our psychological experience with them. Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet 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 SUBLIMINAL THRESHOLD Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. While much of our information processing occurs automatically (sensation), claims of subliminal persuasion have been discounted through research. WEBER’S LAW Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I. Stimulus Constant (k) Light 8% Weight 2% Tone 0.3% 3: What is the function of sensory adaptation? SENSORY ADAPTATION Sensory adaptation is the diminishing sensitivity to an unchanging stimulus. After constant exposure to a stimulus, our nerve cells fire less frequently. Put a band aid on your arm and after awhile you don’t sense it. Sensory adaptation offers the freedom to focus on informative changes in our environment: We perceive the world not exactly as it is, but as it is useful for us to perceive it. 4: What is the energy that we see as visible light? TRANSDUCTION Transduction is the transformation of stimulus energy (sights, sounds, smells) into neural impulses our brains can interpret. What we see as visible light is but a thin slice of the whole spectrum of electromagnetic radiation. Visible Spectrum PHYSICAL CHARACTERISTICS OF LIGHT Two physical characteristics of light help determine our sensory experience of them: 1. Wavelength (the distance from one wave peak to the next) determines hue or color 2. Intensity (the amount of energy in light waves) influences brightness WAVELENGTH (HUE/COLOR) Violet Indigo Blue Green Yellow Orange Red 700 nm 400 nm Short wavelengths Long wavelengths INTENSITY (BRIGHTNESS) Blue color with varying levels of intensity. As intensity increases or decreases, blue color looks more “washed out” or “darkened.” 5: How does the eye transform light energy into neural messages? THE EYE Label the diagram of the eye, providing a brief description of what each part of the eye does. (page 237) Label the cross section of the retina, explaining how light entering the eye is transformed into a neural message. (page 238) THE EYE TEST YOUR BLIND SPOT Use your textbook – PAGE 239. 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. PHOTORECEPTORS E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969 Table 6.1: page 239 6: How does the brain process visual information? VISUAL INFORMATION Ganglion axons forming the optic nerve run to the thalamus, where they synapse with neurons that run to the visual cortex. Any given retinal area relays its information to a corresponding location in the visual cortex, in the occipital lobe at the back of your brain. Figure 6.10, page 240 SHAPE DETECTION Ishai, Ungerleider, Martin and Haxby/ NIMH Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses. VISUAL INFORMATION PROCESSING Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form, movement, etc. FROM SENSATION TO RECOGNITION Figure 6.13 p. 243 7: What theories help us understand color vision? COLOR VISION Young-Helmholtz trichromatic theory: Thomas Young and Hermann von Helmholtz suggested that the eye must contain three receptors that are sensitive to red, blue and green colors in the 19th century. Years later, researchers confirmed this theory. The retina has three types of color receptors, each sensitive to one of three colors. When we stimulate combinations of these cones, we see other colors. For example, when both red-sensitive and green-sensitive cones are stimulated, we see yellow. COLOR BLINDNESS Genetic disorder in which people are blind to green or red colors. This supports the Trichromatic theory. Ishihara Test 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. 8: What are the characteristics of air pressure waves that we hear as sound? AUDITION Audition, or hearing, is highly adaptive. We hear a wide range of sounds, but we hear best those sounds with frequencies in a range corresponding to that of the human voice. We are also remarkably attuned to variations in sounds: For example, we easily detect differences among thousands of human voices. SOUND CHARACTERISTICS Sound waves are compressing and expanding air molecules. The wave’s frequency, or length, determine the pitch we experience. Long waves have a low frequency & pitch. Short waves have a high frequency & pitch. The wave’s intensity, or strength, determines the loudness we experience. 9: How does the ear transform sound energy into neural messages? THE EAR Sound waves are converted into neural activity: Outer Ear: Collects and sends sounds to the eardrum. Middle Ear: Chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window. Inner Ear: Innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs. COCHLEA Cochlea: Coiled, bony, fluid-filled tube in the inner ear that transforms sound vibrations to auditory signals. INTENSITY (LOUDNESS) Intensity (Loudness): Amount of energy in a wave, determined by the amplitude, relates to the perceived loudness. LOUDNESS OF SOUND Richard Kaylin/ Stone/ Getty Images 120dB 70dB 120dB Page 248 10: What theories help us understand pitch perception? FREQUENCY (PITCH) Pitch: The dimension of frequency determined by the wavelength of sound. Frequency theory: The rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone; enabling us to sense its pitch. Best explains how we sense low pitches. Place theory: links the pitch we hear with the place where the cochlea's membrane is stimulated. Best explains how we sense high pitches. A combination of the two theories handle the pitches in the intermediate range. 11: How do we locate sounds? LOCALIZATION OF SOUNDS Because we have two ears, sounds that reach one ear faster than the other ear causes us to localize the sound. Your right ear would receive a more intense sound from this bell ringing, and it would receive the sound slightly sooner than your left ear. However, the intensity difference and time lag are extremely small. 12: What are the common causes of hearing loss, and why does controversy surround cochlear implants? HEARING LOSS & DEAF CULTURE Conduction hearing loss: problems with the mechanical system that conducts sound waves to the cochlea Sensorineural hearing loss: damage to the cochlea’s hair cell receptors or their associated nerves (more common) Cochlear implants: electronic devices that translate sounds into electric signals that convey some information about sound to the brain. 13: How do we sense touch and our body’s position and movement? How do we experience pain? TOUCH Bruce Ayers/ Stone/ Getty Images The sense of touch is a mix of four distinct skin senses—pressure, warmth, cold, and pain. BODY POSITION &MOVEMENT The sense of our body parts’ position and movement is called kinesthesis. The vestibular sense monitors the head (and body’s) position (including balance). Bob Daemmrich/ The Image Works http://www.heyokamagazine.com PAIN Pain tells the body that something has gone wrong. Usually pain results from damage to the skin and other tissues. A rare disease exists in which the afflicted person feels no pain: Ashlyn Blocker GATE-CONTROL THEORY Melzack and Wall (1965, 1983) proposed that our spinal cord contains neurological “gates” that either block pain or allow it to be sensed. Gary Comer/ PhototakeUSA.com The “gate” is opened by the activity of pain signals traveling up small nerve fibers, and is closed by activity in large nerve fibers or by information coming from the brain. BIOPSYCHOSOCIAL INFLUENCES Figure 6.22: p. 257 PAIN CONTROL Pain can be controlled by a number of therapies including, drugs, surgery, acupuncture, exercise, hypnosis, and even thought distraction. Todd Richards and Aric Vills, U.W. ©Hunter Hoffman, www.vrpain.com 14: How do we experience taste? TASTE Traditionally, taste sensations consisted of sweet, salty, sour, and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”. Sweet Sour Salty Bitter Umami (Savory meat taste: MSG) SENSORY INTERACTION When one sense affects another sense, sensory interaction takes place. So, the taste of strawberry interacts with its smell and its texture on the tongue to produce flavor. 15: How do we experience smell? SMELL • Like taste, smell is a chemical sense. • Odorants enter the nasal cavity to stimulate 5 million receptors to sense smell. • We can detect 10,000 odors! Figure 6.25 Page 261 SMELL AND MEMORIES The brain region for smell (in red) is closely connected with the brain regions involved with memory (limbic system). That is why strong memories are made through the sense of smell. 16: How did the Gestalt psychologists understand perceptual organization? PERCEPTUAL ORGANIZATION How do we form meaningful perceptions from sensory information? A group of German psychologists noticed that when given a cluster of sensations people tend to organize them into a gestalt, or an organized, meaningful whole. WHAT DO YOU SEE? Necker Cube p. 264 17: How do figure-ground and grouping principles contribute to our perceptions? FORM PERCEPTION Our brain must recognize objects as distinct from their backgrounds: The objects are figures. Their surroundings are the grounds. The same stimulus can trigger more than one perception, and allow the figure-ground relationship to reverse. Time Savings Suggestion, © 2003 Roger Sheperd. GROUPING After distinguishing the figure from the ground, our perception needs to organize the figure into a meaningful form using grouping rules. GROUPING & REALITY Although grouping principles usually help us construct reality, they may occasionally lead us astray. Both photos by Walter Wick. Reprinted from GAMES Magazine. .© 1983 PCS Games Limited Partnership p. 265 & 269 M.C. ESCHER 18: How do we see the world in three dimensions? DEPTH PERCEPTION Depth perception –the ability to see objects in three dimensions although the images that strike the retina are two dimensional- it enables us to judge distances. Cat with no depth perception: VISUAL CLIFF Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception using the visual cliff demonstration: BINOCULAR CUES Binocular cues are depth cues that depend on two eyes. Retinal disparity, which is the distance between the images received from the two retinas, is a binocular cue that allows us to perceive depth. The greater the disparity between the two images, the closer the object. MONOCULAR CUES Monocular cues are depth cues that are available to either eye alone. Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away. 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. MONOCULAR CUES Relative Height: We perceive objects that are higher in our field of vision to be farther away than those that are lower. 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. 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. 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. 19: How do we perceive motion? PERCEIVING MOTION Our brain computes motion based partly on its assumption that shrinking objects are retreating and enlarging objects are approaching. Large objects are also perceived to be moving more slowly that smaller objects. The brain will also perceive continuous movement in a series of slightly varying images. The illusion of movement is also created using the phi phenomenon – when two adjacent stationary lights blink on and off in quick succession 20: How do perceptual constancies help us organize our sensations into meaningful perceptions? PERCEPTUAL CONSTANCY Regardless of our viewing angle, distance, and illumination, the top-down processing ability called perceptual constancy allows us to identify people and objects in less time than it takes to draw a breath. Sometimes an object whose actual shape cannot change seems to change shape with the angle of our view. p. 269 COLOR CONSTANCY Perceiving familiar objects as having consistent color even when changing illumination filters the light reflected by the object. Color Constancy SIZE-DISTANCE RELATIONSHIP Experience tells us that a more distant object can create the same size image as a nearer one only if it is actually larger. As a result, we perceive the more distant monster and red bar as larger. Alan Choisnet/ The Image Bank From Shepard, 1990 p. 270 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 p. 271 AMES ROOM p. 271 The Ames room is designed to demonstrate the sizedistance illusion. LIGHTNESS CONSTANCY The color and brightness of square A and B are the same. p. 271 21: What does research on sensory restriction and restored vision reveal about the effects of experience? 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. not this guy SENSORY DEPRIVATION & RESTORED VISION How important is experience in shaping our perceptual interpretation? After cataract surgery, blind adults were able to regain sight. These individuals could differentiate figure and ground relationships, yet they had difficulty distinguishing a circle and a triangle (Von Senden, 1932). FACIAL RECOGNITION Courtesy of Richard LeGrand We perceive and recognize individual faces as a whole. The same top half of a face paired with two different bottom halves causes us to see the identical top halves as different. After blind adults regained sight, they were able to recognize distinct features, but were unable to recognize faces. 22: How adaptable is our ability to perceive? PERCEPTUAL ADAPTATION Courtesy of Hubert Dolezal Perceptual adaptation - the visual ability to adjust to an artificially displaced or inverted visual field Experiments involving inversion glasses reveal that after about a week people can adapt to the change, and even ride a motorcycle, ski, and fly an airplane 23: How do our expectations, contexts, and emotions influence our perceptions? PERCEPTUAL SET A perceptual set is a mental predisposition to perceive one thing and not another (top-down processing). Through experience we form concepts, or schemas, that organize and interpret unfamiliar information. The human brain is a hypersensitive face detector – we see faces in random configurations such as cloud formations, rocks, the moon’s landscape, and food. PERCEPTUAL SET What you see in the center picture is influenced by flanking pictures. PERCEPTUAL SET Other examples of perceptual set: Dick Ruhl Frank Searle, photo Adams/ Corbis-Sygma (a) Loch ness monster or a tree trunk? (b) Flying saucers or clouds? CONTEXT EFFECTS Context can radically alter perception. How tall is the basketball player in yellow? He is actually 6’9” But when compared to 7’9” Sun Ming Ming, he seems short! 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. PERCEPTION REVISITED Perception is a biopsychosocial phenomenon Figure 6-50 p. 279 24: How do human factors psychologists work to create userfriendly machines and work settings? HUMAN FACTORS PSYCHOLOGISTS These psychologists work with engineers to design appliances, machines, and work settings that fit our natural perceptions and inclinations. 25: What are the claims of ESP, and what have most research psychologists concluded after putting these claims to the test? IS THERE EXTRASENSORY PERCEPTION? Perception without sensory input is called extrasensory perception (ESP). A large percentage of scientists do not believe in ESP. CLAIMS OF ESP 1. 2. 3. Telepathy: Mind-to-mind communication. One person sending thoughts and the other receiving them. Clairvoyance: Perception of remote events, such as sensing a friend’s house on fire. Precognition: Perceiving future events, such as a political leader’s death. CLAIMS OF ESP Most research psychologists are skeptical about claims of ESP for two main reasons: 1. To believe in ESP you must believe that the brain is capable of perceiving without sensory input. 2. Psychologists and parapsychologists have been unable to replicate ESP phenomena under controlled conditions No psychic has been able to predict the outcome of a lottery jackpot or to make millions on the stock market. No psychic was able to predict 9/11, or to collect the $50 million reward for locating Osama bin Laden.