Ch06 Lecture Notes
- 1. 6: Perception CHAPTER PREVIEW Perception involves the selection, organization, and interpretation of sensory information. It quick- ly became one of psychology’s primary concerns as early researchers attempted to explain illu- sions. In organizing sensory data into whole perceptions, our first task is to discriminate figure from ground. We then organize the figure into meaningful form by following certain rules for grouping stimuli. We transform two-dimensional retinal images into three-dimensional perceptions by using binocular cues, such as retinal disparity, and monocular cues, such as the relative sizes of objects. Our brain computes motion as objects move across the retina. A quick succession of images can also create an illusion of movement. The perceptual constancies enable us to perceive objects as enduring in shape, size, and light- ness, regardless of viewing angle, distance, and illumination. The constancies explain several well- known illusions. Studies of sensory deprivation reveal that, for many species, infancy is a critical period during which experience must activate the brain’s innate visual mechanisms. For example, when cataracts are removed from adults who have been blind from birth, they can distinguish figure and ground and can perceive color, but they are unable to distinguish shapes and forms. At the same time, human vision is remarkably adaptable. Given glasses that turn the world upside down, people manage to adapt and move about with ease. Clear evidence that perception is influenced by our experience comes from the many demonstrations of perceptual set and context effects. Because perceptions vary, they may not be what the designer of a machine assumes. Human factors psychologists study how people perceive and use machines and how machines and physical environments can be better suited to that use. Although parapsychologists have tried to document ESP, most research psychologists remain skeptical, particularly because the results of experiments have not been reproducible. CHAPTER GUIDE ➤ Exercise: Fact or Falsehood? ➤ Videos: Moving Images: Experiencing Psychology Through Film, Program 10: Sensation Without Perception: Visual Prosopagnosia; Discovering Psychology, Updated Edition: Sensation and Perception; Sensation and Perception; Module 8 of Psychology: The Human Experience: Sensation and Perception 41
- 2. 42 Chapter 6 Perception Selective Attention ➤ Lecture: Inattentional Blindness; Change Blindness; Mindsight—A Sixth Sense ➤ Exercises: Field Dependence–Independence; Human Earphones ➤ Transparency: 80 Selective Attention ➤ Video: Video Clip 23 of Digital Media Archive: Psychology: Neisser’s Selective Attention Test 1. Describe the interplay between attention and perception. Selective attention means that at any moment, awareness focuses on only a limited aspect of all that we are capable of experiencing. For example, even if a stimulus figure can evoke more than one perception, we consciously experience only one at a time. The cocktail party effect provides another example of selective attention. The ability to attend to one voice among many enables us to converse coherently in the midst of auditory chaos. Selective attention also limits our percep- tion, as many stimuli will pass by unnoticed. This lack of awareness is evident in studies of inattentional blindness. Forms of this include change blindness, change deafness, and choice blindness. Perceptual Illusions ➤ Exercises: The Wundt-Jastrow Illusion; Perceptual Illusions and Principles; A Kinetic Depth Illusion; Musical Illusions and Paradoxes on CD ➤ Projects: Playing Cards and Illusions; Instant Object Recognition; Kinesthetic Capture ➤ PsychSim: Visual Illusions ➤ Film/Video: An Introduction to Visual Illusions; Segment 10 of the Scientific American Frontiers Series, 2nd ed.: Lights, Camera, Magic! ➤ Transparency: 81 Perceptual Illusions 2. Explain how illusions help us to understand some of the ways we organize stimuli into meaningful perceptions. Illusions mislead us by playing on the ways we typically organize and interpret our sensations, and thus understanding illusions provides valuable clues to the ordinary mechanisms of perception. For example, several well-known illusions are based in the perceived relationship between size and distance, which is generally valid. Others reflect group principles and assumptions made about the relationship between light and shadow. As visual illusions indicate, among our senses, vision is dominant. When there is a conflict between vision and other sensations, vision usually dominates, a phenomenon called visual capture. Hearing captures touch. Perceptual Organization ➤ Lectures: Object Recognition; Visual Agnosia; Autostereograms; Auditory Organization ➤ Exercises: Perceptual Organization; An Auditory Analogue of the Visual Reversible Figure; The Ganzfeld; Binocular Vision; Binocular Vision Versus Monocular Vision; Variation in the Size of the Retinal Image; Perceived Distance and Perceived Size; Brightness Contrast ➤ Project: Perceived Lunar Size ➤ Videos: Video Clips 4 and 5 of Digital Media Archive: Psychology: Depth Cues and Müller-Lyer Illusion ➤ Transparencies: 82 Reversible Figure and Ground; 83 Organizing Stimuli into Groups; 84 Monocular Cues; 85 The Interplay Between Perceived Size and Distance 3. Describe Gestalt psychology’s contribution to our understanding of perception. Gestalt psychologists described principles by which we organize our sensations into perceptions. They provided many compelling demonstrations of how, given a cluster of sensations, the human perceiver organizes them into a gestalt, a German word meaning a “form” or a “whole.” They fur- ther demonstrated that the whole may differ from the sum of its parts. Clearly, our brains do more than merely register information about the world. We are always filtering sensory information and inferring perceptions in ways that make sense to us.
- 3. Chapter 6 Perception 43 4. Explain the figure-ground relationship, and identify principles of perceptual grouping in form perception. Our first task in perception is to perceive any object, called the figure, as distinct from its surroundings, called the ground. We must also organize the figure into a meaningful form. Gestalt principles for grouping that describe this process include proximity (we group nearby figures together), similarity (we group similar figures together), continuity (we perceive smooth, continu- ous patterns rather than discontinuous ones), connectedness (we perceive spots, lines, or areas as a single unit when uniform and linked), and closure (we fill in gaps to create a whole object). 5. Explain the importance of depth perception, and discuss the contribution of visual cliff research to our understanding of this ability. Depth perception is the ability to see objects in three dimensions although the images that strike the eye are two dimensional. It enables us to judge distance. Research on the visual cliff (a minia- ture cliff with a drop-off covered by sturdy glass) reveals that that depth perception is in part innate. Many species perceive the world in three dimensions at, or very soon after, birth. 6. Describe two binocular cues for perceiving depth, and explain how they help the brain to compute distance. Binocular cues require information from both eyes. In the retinal disparity cue, the brain com- putes the relative distance of an object by comparing the slightly different images an object casts on our two retinas. The greater the difference, the greater the distance. In the convergence cue, the brain calculates the degree of neuromuscular strain when our two eyes turn inward to look at a nearby object. The greater the strain, the closer the object. 7. Explain how monocular cues differ from binocular cues, and describe several monocular cues for perceiving depth. Monocular cues enable us to judge depth using information from only one eye. The monocular cues include relative size (the smaller image of two objects of the same size appears more distant), interposition (nearby objects partially obstruct our view of more distant objects), relative clarity (hazier objects appear more distant), texture gradient (a gradual change to a less distinct texture suggests increasing distance), relative height (higher objects are farther away), relative motion or motion parallax (as we move, objects at different distances change their relative positions in our visual image, with those closest moving most), linear perspective (the converging of parallel lines indicates greater distance), and light and shadow (dimmer objects seem more distant). Artists use monocular cues to portray depth on a flat canvas. 8. State the basic assumptions we make in our perception of motion, and explain how these perceptions can be deceiving. Our basic assumption is that shrinking objects are retreating and enlarging objects are approach- ing. The brain will also interpret a rapid series of slightly varying images as continuous move- ment, a phenomenon called stroboscopic movement. By flashing 24 still pictures a second, a motion picture creates perceived movement. The phi phenomenon, another illusion of movement, is created when two or more adjacent lights blink on and off in succession. Lighted signs exploit the effect with a succession of lights that create the impression of, say, a moving arrow. 9. Explain the importance of perceptual constancy. Perceptual constancy is necessary to recognize an object. It enables us to see an object as unchanging (having consistent lightness, color, shape, and size) even as illumination and retinal images change.
- 4. 44 Chapter 6 Perception 10. Describe the shape and size constancies, and explain how our expectations about perceived size and distance contribute to some visual illusions. Shape constancy is our ability to perceive familiar objects (for example, an opening door) as unchanging in shape, and size constancy is perceiving objects as unchanging in size, despite the changing images they cast on our retinas. Given the perceived distance of an object, we instantly and unconsciously infer the object’s size. The perceived relationship between distance and size is generally valid but under special circum- stances can lead us astray. For example, one reason for the Moon illusion is that cues to objects’ distances at the horizon make the Moon behind them seem farther away. Thus, the Moon on the horizon seems larger. Similarly, the lines in the Müller-Lyer illusion may be interpreted as varying in distance from us and thus are perceived to be of different lengths. Finally, in the distorted room illusion, we perceive both corners as being the same distance away. Thus anything in the near cor- ner appears disproportionately large compared to anything in the far corner. 11. Discuss lightness constancy and its similarity to color constancy. Lightness constancy enables us to perceive an object as having a constant lightness even when the light that falls on it changes. Perceived lightness depends on relative luminance. Color constancy is our ability to perceive the color of an object as unchanging even when its illumination changes. For both constancies, the brain perceives the quality of lightness or color relative to surrounding objects. Perceptual Interpretation ➤ Lectures: Functional Blindness; Cases of Restored Vision; “Thin-Slicing”; Context and Perception; Bad Human Designs; Banner Blindness and Web Design ➤ Exercises: Displacement Glasses; Discovering Personal Bias; Perceptual Set; Perceptual Set and Gender Stereotypes; Social Transmission of a Narrative ➤ Videos: Segment 11 of the Scientific American Frontiers Series, 2nd ed.: Cockpit Confusion; Module 10 of The Brain Series, 2nd ed.: Perception: Inverted Vision ➤ Feature Film: At First Sight ➤ Transparencies: 86 Perceptual Set; 87 Perception Is a Biopsychosocial Phenomenon 12. Describe the contribution of restored-vision and sensory deprivation research in our understand- ing of the nature-nurture interplay in our perceptions. In the classic version of the nature-nurture debate, the German philosopher Immanuel Kant main- tained that knowledge comes from our innate ways of organizing sensory experiences. On the other side, the British philosopher John Locke argued that we learn to perceive the world through our experiences of it. It’s now clear that different aspects of perception depend more or less on nature’s endowments and on the experiences that influence what we make of our sensations. For many species, infancy is a critical period during which experience must activate the brain’s innate visual mechanisms. When cataracts are removed from adults who have been blind from birth, these people remain unable to perceive the world normally. Generally, they can distinguish figure from ground and perceive colors, but they are unable to recognize shapes, forms, and com- plete faces. In controlled experiments, infant kittens and monkeys have been reared with severely restricted visual input. When their visual exposure is returned to normal, they, too, suffer enduring visual handicaps. 13. Explain how the research on distorting goggles increases our understanding of the adaptability of perception. Human perception is remarkably adaptable. Given glasses that shift the world slightly to the left or right, or even turn it upside down, people manage to adapt their movements and, with practice, to move about with ease. Although kittens and monkeys also can adapt, chicks cannot.
- 5. Chapter 6 Perception 45 14. Define perceptual set, and explain how it influences what we do and do not perceive. Clear evidence that perception is influenced by our experiences—our learned assumptions and beliefs—as well as by sensory input comes from the many demonstrations of perceptual set, a mental predisposition to perceive one thing and not another. Through experience, we also form concepts, or schemas, which organize and interpret unfamiliar information, a fact that helps explain why some of us “see” monsters, faces, and UFOs that others do not. 15. Explain why the same stimulus can evoke different perceptions in different contexts. A given stimulus may trigger radically different perceptions, partly because of our different schemas, but also because of the immediate context. For example, we discern whether a speaker said “morning” or “mourning” or “dye” or “die” from the surrounding words. 16. Describe the role human factors psychologists play in creating user-friendly machines and work settings. Human factors psychologists explore how people and machines interact and how physical envi- ronments can be adapted to human behaviors. They help to design appliances, machines, and work settings that fit our natural perceptions. Sometimes, they use “natural mapping” to make simple design changes that reduce our frustration in using common appliances. They are mindful of the “curse of knowledge,” whereby technology developers assume that others share their expertise. As psychologists, their most powerful tool is research. By testing users’ responses to several alterna- tives, they seek to increase both human safety and productivity. Is There Extrasensory Perception? ➤ Lecture: Belief in ESP ➤ Exercises: Belief in ESP Scale; ESP Tricks ➤ Projects: Testing for ESP; The Psychic Challenge ➤ Video: Segment 2 of the Scientific American Frontiers Series, 2nd ed.: Water, Water Everywhere 17. Identify the three most testable forms of ESP, and explain why most research psychologists remain skeptical of ESP claims. Claims are made by parapsychologists for three varieties of extrasensory perception (ESP): telepathy (mind-to-mind communication), clairvoyance (perceiving remote events), and precognition (perceiving future events). Closely linked with these are claims of psychokinesis, or “mind over matter.” Research psychologists remain skeptical because the acts of so-called psychics have typically turned out to be nothing more than the illusions of stage magicians, because checks of psychic visions have been no more accurate than guesses made by others, and because sheer chance guar- antees that some stunning coincidences are sure to occur. An important reason for their skepticism, however, is the absence of a reproducible ESP result. In addition, to believe in ESP, one must believe that the brain is capable of perceiving without sensory input.