Sensation & Perception. Chapter 6 Perception. Myers PSYCHOLOGY. Attention: Theoretical Issues. Perception Outline

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1 Myers PSYCHOLOGY C6:1 Sensation & Perception C6:2 Chapter 6 Perception Sensation - Process by which sensory receptors and nervous system receive and represent stimulus energy (+1) Perception - Process of organizing and interpreting sensory information to recognize meaningful objects and events - Subject to host of psychological influences (+2) Visual Information Processing C6:3 C6:4 Hastorf & Cantril (1954) Classic case study on role of values in perception. Selective perception of 1951 football game between Dartmouth and Princeton. Princeton won. A very rough game, many penalties. Princeton quarterback, All-American in last college game, left in 2 nd quarter with broken nose and mild concussion. In 3 rd quarter Dartmouth quarterback's leg broken. A week later, Hastorf and Cantril had Dartmouth and Princeton psychology students fill out questionnaire, and authors analyzed answers of those who had seen either the game or movie of game. Two other groups viewed film of game and tabulated number of infractions seen. Question: "Which team do you feel started the rough play?" Pr Da Both Neither/No Answer Dartmouth Students Princeton Students Question: "Do you believe game was clean and fairly played or unnecessarily rough and dirty?" C&F R&F R&D Don t Know Dartmouth Students Princeton Students When shown film, Princeton students "saw" Dartmouth team make over 2x as many infractions as were seen by Dartmouth students. Perception Outline Selective Attention Perceptual Illusions Perceptual Organization - Form Perception - Depth Perception - Motion Perception - Perceptual Constancy C6:5 Perceptual Interpretation - Sensory Deprivation and Restored Vision - Perceptual Adaptation - Perceptual Set - Perception and the Human Factor Is there Extrasensory Perception? - Claims of ESP - Premonitions or Pretensions? - Putting ESP to Experimental Test Attention: Theoretical Issues Attention: ability to perceive part of environment, and ignore rest Number of fundamental issues - Early vs. Late selection - Mechanisms (analogies) Attention as Filter Attentional Spotlight Attention as Limited Resource - Do unattended stimuli have an influence? C6:6 1

2 Attention: Findings Binocular Rivalry Ambiguous stimuli - Necker Cube, Old/Young Woman,... Consciously experience only one object at a time Attention a limited capacity system C6:7 Necker Cube X C6:8 Box on left can be seen in two ways - By one interpretation, X is at center of front wall, which faces down to left - By other interpretation, X is at center of back wall, and front wall faces up to right Old or Young Woman? C6:9 Auditory Attention Findings Cocktail Party Effect - Dichotic Listening or Shadowing task Hear two different messages in headphones, one to each ear (+1) - What known about message to ignored ear? Identify gender, loudness Not language, content But something particularly salient (e.g., your name) may be noticed C6:10 Shadowing Task C6:11 Selective Attention: Stroop C6:12 2

3 C6:13 Fascinating Finding Neisser basketball game film - Unaware of woman with umbrella crossing screen or even person in ape suit Change Blindness Change Blindness: 1 2 C6:14 People fail to notice pronounced changes in perceptual stimuli, even introduction of completely different person into conversation 3 Subliminal Perception C6:15 Can unattended stimuli affect us? Natural observations or myths - Eat Popcorn / Drink Coca-Cola Hoax Denied by owner, Factual errors 1/24th sec duration not subliminal Subliminal Experimental Studies Shadowing messages, heard tunes in other ear - Recognition at chance level - Implicit memory (familiarity) > chance Processing ambiguous stimuli - Homonyms: We stood by the bank. - Affected by context in unattended ear: river, money Salient stimuli - If someone at loud party says your name, then you attend... but how? Name must have registered at some, subliminal level. C6:16 Perception Outline Selective Attention Perceptual Illusions Perceptual Organization - Form Perception - Depth Perception - Motion Perception - Perceptual Constancy C6:17 Perceptual Interpretation - Sensory Deprivation and Restored Vision - Perceptual Adaptation - Perceptual Set - Perception and the Human Factor Is there Extrasensory Perception? - Claims of ESP - Premonitions or Pretensions? - Putting ESP to Experimental Test C6:18 Illusions Perceptual illusions - Many based on interplay between visual stimulation and contextual cues (e.g., about distance) - Can involve quite complex computations that we are unaware of - Vertical-Horizontal Illusion St. Louis landmark Vertical=Horizontal 3

4 Size/Distance Illusion C6:19 Size & Ponzo Illusions C6:20 Small figure at front is same size as figure at back, as are two arrows. Front figures appear much smaller. If figures dragged from back to front, would appear to shrink. Ponzo Illusion C6:21 Muller-Lyer Illusion C6:22 AB BC Muller-Lyer Illusion C6:23 Inward pointing arrows appear on edges extending towards us Outward pointing arrows appear on edges receding away 2 lines, same image on retina; one (>-- <) appears further away than other (<- ->) must be longer. Seen as so! Perceptual Illusions C6:24 4

5 Ames Room: Size-Distance Relation C6:25 Perception Outline Selective Attention Perceptual Illusions Perceptual Organization - Form Perception - Depth Perception - Motion Perception - Perceptual Constancy C6:26 Perceptual Interpretation - Sensory Deprivation and Restored Vision - Perceptual Adaptation - Perceptual Set - Perception and the Human Factor Is there Extrasensory Perception? - Claims of ESP - Premonitions or Pretensions? - Putting ESP to Experimental Test Form Perception Gestalt - An organized whole - Tend to integrate pieces of information into meaningful wholes Figure-Ground - Perceive objects against background - Illustrated on next few slides C6:27 Form: Figure Ground Grouping of elements and other processes lead to classification of shapes as figures and ground - Figure: coherent, structured object - Ground: background, context for objects Gestalt principles applied to figure-ground problem C6:28 C6:29 Figure-Ground Gestalt principles Closure: prefer shape that is closed as figure Relative size: see smaller shape as figure against larger ground Surroundedness: Figure / Ground effects enhanced if ground shape surrounds figure Symmetry: symmetry enhances grouping and perception of figure Ambiguous Vase/Faces Figure and Ground - Organization of visual field into objects (Figures) that stand out from their surroundings (Ground) - In ambiguous Figure / Ground stimuli, ambiguous which part is figure and which ground C6:30 5

6 Figure/Ground: Ambiguous Images C6:31 C6:32 Gestalt Laws: principles that govern / describe how perceptual system groups together stimulus pieces in environment (see below and next few slides) - Proximity: group nearby figures together - Similarity: group figures that are similar - Continuity: perceive continuous patterns - Closure: fill in gaps - Connectedness: spots, lines and areas are seen as unit when connected Grouping C6:33 Gestalt principle: Proximity Proximity one of most important factors for perceptual organization Here elements grouped as columns, dots, and rows depending on spacing (proximity) C6:34 Gestalt principle: Similarity C6:35 Gestalt principle: Continuity C6:36 Things that look similar tend to be grouped together The dots image now appears to be rows What makes images similar is empirical issue - In circular image task is to identify odd quadrant of circle, easier for leftmost of two images: distinctiveness? Left we see straight line figure as two separate lines crossing at rather than other configurations, such as kissing beaks Right, proximity, similarity and continuity interact to yield same image structure 6

7 Gestalt Principles: Closure C6:37 C6:38 Parts of occluded objects are completed by visual system The Law of Common Fate Elements that move together seen as forming common object - Animals may blend into background (above), until they move. Suddenly visible. - As an example, next few slides and ovement/dots3.mov Common Fate Example - 1 C6:39 Depth Perception C6:43 Perception of Depth and Distance - Ability to see objects in three dimensions - Allows us to judge distance Motion and Depth: Kinetic Depth Two primary types of cues - Binocular and Monocular Cues - Development Depth Perception Binocular cues - Require use of two eyes - Retinal Disparity Images from the two eyes differ Closer object, larger the disparity (right) - Convergence Neuromuscular cue Two eyes move inward for near objects (+1) C6:44 Convergence The larger the angle represented by A and B in figure, nearer the object C6:45 7

8 Depth Perception Monocular Cues - Relative size: Smaller image more distant (+1) - Interposition: Closer object blocks distant object (+2) - Relative clarity: Hazy object seen as more distant (+3 +4) - Texture: Coarse close, Fine distant (+5) C6:46 Depth Perception: Relative Size C6:47 C6:48 Depth Perception: Clarity C6:49 Depth Perception: Interposition Clarity and Perceived Distance C6:50 Depth Perception: Texture Texture gradient - Stimuli that are nearer have coarser texture. C6:51 8

9 Depth Perception C6:52 Parallax C6:53 More Monocular Cues - Relative height: Higher objects seen as more distant - Relative motion (motion parallax): Closer objects seem to move faster (+1) - Linear perspective: Parallel lines converge with distance (+2) - Light and Shadow: Closer objects appear brighter (+3) Near objects move faster than distant objects Demonstration: MotionParallax Depth Perception: Perspective C6:54 Monocular Cues: Shading Major light sources tend to come from above, so shading is another source of depth information. Objects shaded lighter on top seen as sticking out towards us. Here, crater (top) becomes mound (bottom) when picture turned upside down. C6:55 Development of Depth Perception Visual Cliff: Used by Gibson & Walk to study depth perception in infants and animals C6:56 Infant on Visual Cliff C6:57 Research on infants and animals indicates that certain cues for depth/distance are innate and do not depend on experience, whereas other cues are learned and do not operate without experience 9

10 Culture and Depth Perception C6:58 Motion Perception Size of objects - Looming objects moving towards us - Critical for various activities: driving, flying plane, catching ball,... Phi phenomenon - Apparent motion - Similar to common fate example, but faster timing (+1) Motion illusions (above) - Focus on dot, move head forward and backward - Motion After-Effect C6:59 C6:60 C6:61 Perceptual Constancy Perceptual Constancy - Perceive objects as unchanged despite changes in retinal image Shape (above) Size Color (right) Brightness (+1) Brightness (Lightness) Constancy C6:62 Relative Nature of Brightness C6:63 White paper looks white whether in sunlight or shadow Brightness viewed not in absolute terms, but relative to brightness of context. When cloud passes over, everything gets less bright and, as a result, nothing really seems to change. - See next few slides 10

11 Brightness Constancy C6:64 Perception Outline Selective Attention Perceptual Illusions Perceptual Organization - Form Perception - Depth Perception - Motion Perception - Perceptual Constancy C6:65 Perceptual Interpretation - Sensory Deprivation and Restored Vision - Perceptual Adaptation - Perceptual Set - Perception and the Human Factor Is there Extrasensory Perception? - Claims of ESP - Premonitions or Pretensions? - Putting ESP to Experimental Test Sensory Deprivation and Restored C6:66 Vision Restored vision - Figure-Ground, sensed colours, not object identification Rearing animals with deprived visual input - Color, Brightness, but not Form - Held & Hein: vertical stripes (+1) Critical period for sensory development - Rationale for corrective surgery for cataracts early (few months) - Similar effect of cochlear implants Sensory Restriction C6:67 Blakemore & Cooper, 1970 Kittens raised without exposure to horizontal lines later had difficulty perceiving horizontal bars. Learning can also be studied by Perceptual observing how people or animals adapt to modified Adaptation perceptual experience - e.g., surgery, distorting prisms Displacing goggles contain prisms - Humans adapt quickly given visual-motor experience with feedback - Upside-down prism: Stratton (1896) - Adaptation varies across species Some species unable to adapt: chicks In some species (owls), depends on early infant experience C6:68 Perceptual Set C6:69 Predisposition to see one thing and not another (+1) - Expectations developed on basis of context Visual - Loch Ness monster or log, space ships or clouds, ambiguous figure Auditory - Cheer Up Satanic messages in backward tapes - -eel is on the wagon -eel is on the orange 11

12 Expectations and Set C6:70 Set (and Illusion) C6:71 Does front monster appear frightened and back one ferocious? Actually, exactly the same expression (also same size). More examples of set Interpretation of neutral facial expression - Prior Image Interpretation dead woman soup playing child sad thoughtful happy C6:72 C6:73 - Mental representation of concepts based on past experience important for effect of set - Myer s discussion of schemas Organized, mental representation of objects in external world (e.g., face) Children s schemas quite primitive, basic Play sad or happy music - People asked to interpret homophones mourning/morning, die/dye, pain/pane C6:74 Representation of Concepts Person without mental concept of Dalmatian or Cow is unlikely to perceive these images as objects Concept Representation Parts of occluded objects completed by visual system. Requires representations (+1) C6:75 12

13 C6:76 Schemas for Faces Face schemas exert influence on perception - C6:78 Perception and Human Factors C6:80 C6:77 Below, exaggerated version of Michael J. Fox recognized better than actual image Inverted faces present perceptual difficulties (+1) Culture and Context Effects Airplane Accidents C6:79 C6:81 Many applied implications - Medical Procedures Critical periods and corrective surgery - Human Factors Research Design of instruments, appliances, etc.: Right stove below allows more natural interpretation of controls Airplane accidents (+1) 13

14 Perception Outline Selective Attention Perceptual Illusions Perceptual Organization - Form Perception - Depth Perception - Motion Perception - Perceptual Constancy C6:82 Perceptual Interpretation - Sensory Deprivation and Restored Vision - Perceptual Adaptation - Perceptual Set - Perception and the Human Factor Is there Extrasensory Perception? - Claims of ESP - Premonitions or Pretensions? - Putting ESP to Experimental Test Is there Extrasensory Perception? C6:83 Extrasensory Perception - Claim that perception can occur without normal sensory input Telepathy: mind-to-mind communication Clairvoyance: perceive distant objects/events Precognition: perceive event in future Parapsychology - The study of paranormal phenomena ESP Psychokinesis: mental bending/moving of objects C6:84 Natural Observations of ESP Apparent success Vague predictions: Nostradamus Chance - Two students in different classes taught by same instructor are partners - but, 40 x 60 = 2400 pairs of students, and many possible relationships Fraud, post-diction Little success for psychic predictions Newspaper psychics Police departments Spontaneous visions/dreams - Lindbergh baby: only 4/1300 dreams involved body in trees C6:85 Experimental Studies of ESP Myers quote - A reproducible ESP phenomenon has never been discovered, nor has anyone produced any individual who can convincingly demonstrate psychic ability. USA military: $20,000,000 on psychic spies - Nothing to show Predicting coin toss - 28,000 people predicted 110,972 tosses, 49.8% right Ganzfeld Procedure (+1) Ganzfeld Experiments Use sensory deprivation to minimize distractions Bem and Honorton (1994) review: 32% vs. 25% - Concerns about some procedures (Susan Blakemore) Milton & Wiseman (1999) - 30 follow-up studies - No statistically significant effect C6:86 C6:87 Critical Scientific Attitude Many such claims - e.g., therapeutic touch: energy fields that practitioners believe are sensed and affected by energy fields of another person Can be VERY difficult to dissuade people - Frustrating for scientist, which can lead to dismissive tone - MANY efforts to demonstrate ESP have failed, yet still many believers Scientific attitude - Extremely critical, skeptical - Important to consider and weigh ALL of evidence - Not out of negativity, but ONLY way to determine whether ideas are valid or not is to subject them to most difficult tests possible - Does not mean close-mindedness OR perpetual openmindedness 14