Perception
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Perception

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Perception Perception Presentation Transcript

  • Chapter 5 Perception 5
  • Perception • Psychophysics • Organizing the Perceptual World • Recognizing the Perceptual World • Attention • Applications of Research on Perception • Linked Exercises 5
  • What Do You See? Look at this figure. Some people see – a tennis court – a window – a skylight Did you see these, or something else? Why do people see what they see? 5
  • Misperceiving Reality Which line is longer, AB or AC? They’re actually the same. What made AC look longer? From Perplexing Puzzles and Tantalizing Teasers (p. 75), by Martin Gardner, 1988, New York: Dover. Reprinted by permission of the author. 5
  • Three Approaches to Perception • Computational model – What steps would a computer take to solve perceptual problems? • Constructivist approach – We create representations from bits of information and our experiences. • Ecological approach – How does information help us adapt to and use the environment? Back to TOC 5
  • Psychophysics Focuses on • Relationship of physical energy in the environment and our psychological experiences of it 5
  • The Absolute Threshold The minimum amount of energy that can be detected 50% of the time Supraliminal stimulation – Energy we can detect Subliminal stimulation – Energy too weak to detect 5
  • Some Absolute Thresholds Jump to Thinking Critically 5
  • Signal Detection Theory Why Does the “Absolute” Threshold Vary? • Sensitivity: – Intensity of the signal – Capacity of sensory systems – Affected by noise level • • From background stimulation From random neural activity • Response criterion – Willingness to respond to a stimulus – Influenced by motivation and expectancies 5
  • Signal Detection • Hit: Responding to a real signal • False alarm: Responding when there is no signal • Miss: Not responding to a real signal • Correct rejection: Not responding when there is no signal Chart B shows a forecaster with a high response criterion Chart C shows a forecaster with a low response criterion 5 |
  • Judging Differences Between Stimuli • Difference Threshold (Just-Noticeable Difference) • Determined by: – Original stimulus level – Sense being stimulated 5 |
  • Weber’s Law • JND = KI Weber's Constant (K) for Different Stimuli – K = Weber’s constant for a particular sense – I = stimulus intensity 5 |
  • Magnitude Estimation • How is our perception of stimulus intensity related to actual stimulus strength? • Fechner’s law – Constant increases in stimulus strength result in diminishing perceptions of difference – Applies to most, but not all, stimuli • Stevens’s power law – Expanded on Fechner’s Law – Covers wider array of stimuli Back to TOC 5 |
  • Organizing the Perceptual World How do you make sense out of it all? 5 |
  • Basic Processes in Perceptual Organization • Figure-Ground Discrimination – Look at each reversible figure It’s hard to see both figures at once. You tend to see one as figure and lose the other as ground. But then you can reverse them. 5 |
  • Do you see the cube? Is it coming toward you from the screen, or behind the screen? 5 |
  • Basic Processes in Perceptual Organization • Gestalt principles of grouping – – – – – – – Proximity Similarity Continuity Closure Texture Simplicity Common fate 5 |
  • Basic Processes in Perceptual Organization • Palmer’s additional grouping principles – Common region – Connectedness – Synchrony 5 |
  • Why Do These Grouping Principles Guide Perceptual Organization? • Likelihood principle • Unlikely stimuli and misperceptions – These objects can exist as two-dimensional drawings. – Could they exist in threedimensional space? 5 |
  • Perception of Location and Distance • Localization of sounds • Visual cues often integrated with auditory cues – But there is a visual dominance 5 |
  • Stimulus Cues for Depth Perception • • • • • • • • Interposition Relative size Height in the visual field Gradient of texture Linear perspective Clarity Light and shadow Motion parallax 5 |
  • Cues Based on Properties of the Visual System • Ocular accommodation – Muscles change lens shape and bend light rays • Eye convergence – Eyes rotate inward as objects approach • Retinal disparity – Difference between images seen by each eye Jump to Retinal Disparity 5 |
  • Culture and Depth Cues • Which animal is closer to the hunter? • People from cultures that provide lots of experience with pictured depth cues choose the antelope. • Those from cultures less familiar with such cues may pick the elephant, which is closer to him on the page. Jump to Linkages 5 |
  • Perception of Motion • Optical flow cues – – – Motion Parallax Looming Role of the senses of equilibrium and touch • Sometimes lead us to perceive motion when there is none Looming 5 |
  • Perception of Motion • Researchers wonder: – How do we know whether the flow of images across retina is due to the movement of objects or to our own movements? – How do we compensate for the time-lag in the perception of movement? 5 |
  • Perception of Motion (cont’d) • Stroboscopic illusion – Based on principles of likelihood and simplicity 5 |
  • Size Constancy • Changes in size of a retinal image interpreted as changes in distance, not changes in actual size • The size illusions below show how perceptions can fail. Ponzo Illusion The Muller-Lyer Illusion 5 |
  • Shape Constancy • The perceived shape of an object remains the same, even when seen at different angles • Watch a revolving door. – You perceive the doors as retaining their shape, even though they seem to change shape when they rotate. 5 |
  • Using Shape Constancy • Shape constancy breaks down at extreme angles. • Traffic engineers take this into account when designing road markings • At left, the arrow seems to be the same height as the lettering • Actually, it is greatly elongated, as shown at right Back to TOC 5 |
  • Recognizing the Perceptual World How will you know it when you see it? 5 |
  • Perceptual Processing • Bottom-up processing – Basic feature analysis • Top-down processing – Schemas & perceptual sets – Impact of context – Impact of motivation • What do you see? • How about now? 5 |
  • Video: A Top-Down Processing Failure 5 |
  • Pareidolia • Perception of an image in an ambiguous stimulus • Driven by top-down processing • Look at this photograph • Some people see a demonic face in the smoke – Requires specific knowledge – Involves certain expectations 5 |
  • Feature Analysis • Feature detectors analyze the stimuli at the left into the corners and angles shown in the center of this figure. • Bottom-up processing recombines these features to aid in pattern recognition, as shown on the right. 5 |
  • Network Processing • Parallel distributed processing (PDP) models • Shown by – Object superiority effect – Word superiority effect 5 |
  • Object Superiority Effect Patterns are more likely to be detected in three-dimensional objects, rather than random patterns of lines 5 |
  • Word Superiority Effect • Word superiority effect: – • Words are easier to detect than nonwords in strings of random letters. Word recognition – – Parallel processing activates possible interpretations of letters Strongest links determine the word perceived Back to TOC 5 |
  • Attention Can you run out of attention? 5 |
  • Attention • We use attention to: – Direct sensory and perceptual systems – Select specific information for further processing – Allocate mental energy for that processing – Regulate the flow of resources needed to perform a task or coordinate several tasks at once 5 |
  • Characteristics of Attention • Improves mental processing • Takes effort • Is limited Jump to Focus on Research Methods 5 |
  • Directing Attention • Overt orienting: – Looking directly at someone when talking to them • Covert orienting: – Listening to a conversation going on behind you while seeming to listen to your friends at dinner 5 |
  • Directing Attention • Voluntary (goal-directed) attention control – Top-down processing • Involuntary attention control – Bottom-up processing 5 |
  • Change Blindness • Look carefully at this photograph. • Now look carefully at this photograph. • Were they the same? • Did you notice the clump of trees behind and the left of the statue? 5 |
  • Video: Inattentional Blindness 5 |
  • Divided Attention: Multitasking • Attention is a limited resource • May cause inattentional blindness • Danger of driving while texting or on the phone • Easier if one task is automatic • Easier if tasks use different resources – Listening to music and walking 5 |
  • The Stroop Task Name the color of the INK in which each word is printed as rapidly as you can. This is hard because your brain automatically processes the meaning of each word, which then competes for attention with the response you are supposed to give. To do well, you must focus on the ink color and not allow your attention to be divided between color and meaning. 5 |
  • Attention and Automatic Processing • Parallel-processing describes ability to search for targets rapidly and automatically • Efforts to ignore certain stimuli may create negative priming – You might miss something if you ignore the wrong things Back to TOC 5 |
  • Applications of Research on Perception • Aviation psychology • Human-computer interaction • Traffic safety 5 |
  • Aviation Psychology and Perception • Pilot training programs emphasize the dangers of visual illusions and the importance of relying on flight instruments during landings • Instrument displays that present a realistic 3-D image of the flight environment • Warning signals that catch the pilot’s attention • Noise-canceling microphones • Visual message displays • Language to aid top-down processing with contextual cues 5 |
  • Perception and Human-Computer Interaction • Buttons on screen that look like real buttons • Interposition to make screens look as if they’re on top of each other • Blinking of the cursor to attract attention • Use of easy-to-identify icons 5 |
  • Perception and Traffic Safety • Better designed controls and instruments • Night vision displays • Special pavement marking techniques • Drawing attention to distracted driving – Cell phones and texting Back to TOC 5 |
  • End of the Perception Unit 5 |
  • Retinal Disparity • Close one eye and look at the image below. • Now change and look through your other eye. • Switching back and forth between your eyes makes the object seem to move. Jump to Cues 5 |
  • Height in the Visual Field Jump to Stimulus Cues 5 |
  • Linked Exercises • Focus on Research Methods: An Experiment in“Mind-Reading” • Linkages: Perception and Human Development • Thinking Critically: Can Subliminal Stimuli Influence Your Behavior? 5 |
  • Thinking Critically: Can Subliminal Stimuli Influence Your Behavior? • What am I being asked to believe or accept? – Subliminal stimuli can influence behavior Vote for Douglas A. Bernstein!! 5 |
  • Thinking Critically: Can Subliminal Stimuli Influence Your Behavior? • What evidence is available to support the assertion? – Research on priming shows at least a temporary impact on judgment and emotion – Impacts on physiological arousal – Testimonials from satisfied customers 5 |
  • Thinking Critically: Subliminal Stimuli Influence (cont’d) • Are there alternative ways of interpreting the evidence? – Many claims were publicity stunts – Some results may be due to placebo effect – Testimonials may be biased • What additional evidence would help evaluate the alternatives? – Experiments that carefully control for expectations 5 |
  • Thinking Critically: Subliminal Stimuli Influence (cont’d) • What conclusions are most reasonable? – – – – Subliminal perception does occur No potential for “mind control” Subliminal effects are usually small and short-lived Mainly affect simple judgments and general arousal Back to Absolute Thresholds Back to Linked Exercises 5 |
  • Linkages: Perception and Human Development • Habituation and dishabituation used to study how infants perceive the world. • Newborns can perceive differences among different black-and-white contrasts. – By three months can discriminate among blue, green, yellow, and red. • Newborns can perceive differences in the angles of lines. Jump to Culture and Depth Cues 5 |
  • Linkages: Perception and Human Development (cont’d) • At one month of age, infants concentrate their gaze on one part of an object. • By two months, infants systematically scan the perimeter of an object. Back to Linked Exercises 5 |
  • Infants Seem Innately Tuned to Perceive the Human Face Show more interest in face-like patterns (such as at left) 5 |
  • The Visual Cliff Depth perception appears shortly after birth, but fear and avoidance of dangerous depth do not develop until an infant is old enough to crawl into trouble. • Infants too young to crawl perceive the depth but are not frightened by it. • A 10-month-old will hesitate and cry rather than crawl over the “cliff”. Jump to Culture and Depth Cues Back to TOC 5 |
  • Focus on Research Methods: An Experiment in “Mind-Reading” • What was the researchers’ question? – What changes in perceptual processing occur when people covertly shift their attention to a specific location in space? • How did the researchers answer the question? – Participants to indicate when they detected square on computer screen out of corner of eye – Participants given correct, incorrect, or neutral cues. – Researchers measured speed of target detection 5 |
  • Focus on Research: An Experiment in Mind Reading • What did the researchers find? – Faster detection with accurate cues – Slower detection with inaccurate cues 5 |
  • Focus on Research Methods: “Mind-Reading” Experiment (cont’d) • What do the results mean? – Attention can enhance information processing one location. – It does so at the expense of processing information elsewhere • What do we still need to know? – How quickly can attention be shifted? – How quickly can attention shift between sensory modalities? Jump to Characteristics of Attention Back to Linked Exercises 5 |
  • In Class Writing Exercises The following slides may be used as advance organizers for the topics in this unit. • Place one at the start of your presentation. • Have your students write for a minute or two about the quote on the slide. • This will help them center themselves on the topic to be covered in class. • You may wish to use their responses to generate class discussion. 5 |
  • In Class Writing Exercise: What you see is what you get. And what you don’t is better yet! —Flip Wilson 5 |
  • In Class Writing Exercise: Love is an ideal thing, marriage a real thing: a confusion of the real with the ideal never goes unpunished. Goethe 5 |
  • In Class Writing Exercise: You see things; and you say, “Why?” But I dream things that never were; and I say, “Why not?” George Bernard Shaw 5 |
  • In Class Writing Exercise: We are all in the gutter, but some of us are looking at the stars. Oscar Wilde 5 |
  • In Class Writing Exercise: Change your thoughts and you change your world. Norman Vincent Peale 5 |
  • In Class Writing Exercise: The real voyage of discovery consists not in seeking new lands, but in seeing with new eyes. Marcel Proust 5 |
  • In Class Writing Exercise: Never argue with a fool. Someone watching may not be able to tell the difference. Anonymous 5 |
  • In Class Writing Exercise: When I hear somebody sigh, “Life is hard,” I am always tempted to ask, “Compared to what?” Sydney J. Harris 5 |
  • In Class Writing Exercise: The softer you sing, the louder you’re heard. Donovan 5 |
  • In Class Writing Exercise: Artists can color the sky red because they know it’s blue. Those of us who aren’t artists must color things the way they really are or people might think we’re stupid. Jules Feiffer 5 |