Introducing Perception

1. AP PsychologyPERCEPTIONChapter 5 (Bernstein), pages 152-190&DISORDERS OF PERCEPTIONChapter 19 (Bernstein), pages 776-780

2. Introducing Perception • PERCEPTION is the process through which we interpret sensations. • This involves using knowledge and understanding of the world so the perceptions become meaningful experiences. • Our brain takes sensations and creates a coherent, understandable world from them. • Can people perceive what cannot be sensed?

3. SO... • Can people perceive what cannot be sensed? • EXTRASENSORY PERCEPTION (ESP) the claim that some people have the ability to perceive stimuli from the past, the present, and the future through a mechanism beyond that of vision, hearing, touch, taste, and smell. • CLAIRVOYANCE perceiving signals from objects that cannot be seen or heard • TELEPATHY ability to read another person’s thoughts/communicating between individuals using extrasensory signals • PSYCHOKINESIS the use of mental processes to move or control objects • OUT OF BODY EXPERIENCE (OOB) floating outside one’s body and seeing yourself • PRECOGNITION (a.k.a. “Second Sight”)perception that involves the acquisition of future information that cannot be deduced from presently available and normally acquired sense-based information; knowledge of something in advance of its occurrence • “NO WAY NO HOW!!!”

4. or in more intellectual language... • The majority of the scientific community remains skeptical of ESP. • “There is no scientific justification for it.” • “No such thing.” • “It has not been empirically proven.” • says the National Research Council (NRC)which functions under the auspices of the National Academy of Sciences (NAS), the National Academy of Engineering (NAE), and the Institute of Medicine (IOM). • The NAS, NAE, IOM, and NRC are part of a private, nonprofit institution that provides science, technology and health policy advice under a congressional charter signed by President Abraham Lincoln that was originally granted to the NAS in 1863. Under this charter, the NRC was established in 1916, the NAE in 1964, and the IOM in 1970. The four organizations are collectively referred to as the National Academies. • So why do 50% of people believe they have it & why do so many of us believe in it? • Entertainment • Our “Willing Suspension of Disbelief” • Fascination with the Supernatural and Unexplainable

5. Introducing Perception • SO ONCE AGAIN... • PERCEPTION is the process through which we interpret sensations. • This involves using knowledge and understanding of the world so the perceptions become meaningful experiences. • Our brain takes sensations and creates a coherent, understandable world from them. • Without the sensation, there is no perception!

6. The Perception Paradox * A paradox is a statement or proposition that seems self-contradictory or absurd but in reality expresses a possible truth. • Perceptual processing often appear to be rapid and effortless. • perception is actually very complex. • Perceptual errors or perception failures provide clues to how perceptual systems work.

7. Three Approaches to Perception • COMPUTATIONAL APPROACH • This approach tries to determine the computations that a computer would have to perform to solve perceptual problems. • The goal is to explain how complex computations of the nervous system turn raw sensory stimulation in a representation of the world. • The computational approach focuses on the nervous system’s manipulation of incoming signals. • Theorists who follow this approach hope to eventually build computerized robots for uses such as bomb detection and product inspection.

8. Three Approaches to Perception • CONSTRUCTIVIST APPROACH • This earlier approach argues that perceptual systems “construct” or build a representation of reality from fragments of sensory information. • This representation is strongly influenced by three things: LEARNING, EXPECTATIONS, and INFERENCES FROM PAST EXPERIENCES. • The constructivist approach, then, is influenced largely by culture. • Example:A television program in the U. S. is understood by most people around the world to be either live or recorded entertainment that is broadcast from the source (studio camera, TV station, etc.) via “cable” to your television. How might someone from a culture that doesn’t know what a television is perceive a TV show? • Example: Seeing a person sitting behind a desk doesn’t mean only half a person is there. We “see” the person as a complete human being because experience tells us to expect people to remain intact even when parts of them are obstructed from view.

9. Three Approaches to Perception • ECOLOGICAL APPROACH • This approach states most perceptional experience comes directly from the environment rather than from interpretations or expectations. • Stimuli directly give most of the information needed to make sense of the world. • Proponents of this approach believe the primary goal of perception is to support actions by “tuning in” to those stimuli in the environment that are most important for performing those actions. • Example:We use visual information from a person behind the desk, from the desk, and from other objects in the room to guide us as we walk to a chair and sit down. We don’t really think about drawing conclusions about whether the person behind the desk is whole or not.

10. PSYCHOPHYSICS • PSYCHOPHYSICSdescribes the relationship between the physical energy in the environment and the psychological experience of that energy. • ABSOLUTE THRESHOLD is the smallest amount of physical energy a sensory system can detect. • Subliminal Stimuli--too weak or brief to be perceived (Do subliminal messages influence us or lead to “mind control”?) • Supraliminal Stimuli--strong enough to be consistently perceived (these do have the power to persuade!) • Absolute Threshold is NOT an all-or-nothing phenomenon. It has actually been redefined as the minimum amount of energy that can be detected 50% of the time.

11. PSYCHOPHYSICS • PSYCHOPHYSICSdescribes the relationship between the physical energy in the environment and the psychological experience of that energy. • ABSOLUTE THRESHOLD is the smallest amount of physical energy a sensory system can detect. • Subliminal Stimuli--too weak or brief to be perceived (Do subliminal messages influence us or lead to “mind control”?) • Supraliminal Stimuli--strong enough to be consistently perceived (these do have the power to persuade!) • Absolute Threshold is NOT an all-or-nothing phenomenon. It has actually been redefined as the minimum amount of energy that can be detected 50% of the time.

12. PSYCHOPHYSICS • SIGNAL-DETECTION THEORY • Sensitivity a person’s ability to pick out a particular stimulus or signal • Sensitivity influenced by 3 factors arriving at the same time: • 1. intensity of signal • 2. capacity of sensory systems • 3. amount of background stimulation (noise) • (Internal noise is the spontaneous random firing of neurons and is always present and always changing; like snow on a TV set or radio static) • Response Criterion or Bias a person’s willingness to respond to a stimulus; affected by motivation, needs, and expectations • Signal-Detection Theory mathematical model of how a person’s sensitivity and response criterion combine to determine decisions about whether a near-threshold stimulus has occurred • Example:Researchers may manipulate response criterion by altering expectations. If a person is more expectant of a signal, his/her response criterion will lower--he/she will say a signal has occurred more readily.

13. PSYCHOPHYSICS • SIGNAL-DETECTION THEORY (page 2) • Each response to a series of signal variations is placed into one of four categories, and the resulting pattern of responses is analyzed. • When no signal is presented, but participant decides there was a signal anyway, the error is called a false alarm. • When a signal occurs but is not detected, the error is called a miss. • when a signal occurs and the participant detects it, the response is called a hit. • Not reporting a signal when none was given is called acorrect rejection. • Why is signal-detection theory important? • suggests that detecting signals does not depend on stimuli or sensitivity alone • personal context in which signals occur play a role • helps us figure out why people sometimes fail to detect important signals or report signals that aren’t there • helps us understand errors in real world situations like spotting tornadoes, inspecting luggage, or diagnosing medical conditions

14. PSYCHOPHYSICS • Weber’s Law • The smallest difference between stimuli that we can detect is called the DIFFERENCE THRESHOLD or the JUST-NOTICABLE DIFFERENCE (JND). • The weaker the stimuli, the easier it is to detect small differences between them. • Example:It’s easier to detect weight difference between two light envelopes than between similarly heavy boxes. • WEBER’S LAW states the smallest detectable difference in stimulus energy is a constant fraction of the intensity of the stimulus. • JND = KI (K is the constant fraction and I is the intensity) • There are separate Ks for different types of sensory input. The smaller the value of K, the more sensitive a sense is to a stimulus difference. • Weber’s constants vary among people, and, in general, we tend to become less sensitive to stimulus differences as we get older. • Weber’s law does not hold if stimuli are very intense or very weak; it does hold for simple and complex stimuli.

15. PSYCHOPHYSICS • Weber’s Law (explained more simply) • In other words...a difference threshold or JND depends on the strength of the new stimulus in relation to the original stimulus! • Example: A person who weighs 200 pounds and a person who weighs 400 pounds both lose 20 pounds. the person who originally weighed 200 pounds will notice the loss more because the change in weight (intensity of the stimuli) is a larger % for that person than the % change in intensity of the heavier person. • GET IT? • Watch this video clip (starting at 2:42): http://www.youtube.com/watch?v=x6Ua5d3wlA0 • NOW DO YOU GET IT?

16. PSYCHOPHYSICS • Magnitude Estimation: How Intense is That? • Magnitude Estimation is how our perception of stimulus intensity is related to the actual strength of the stimulus. • The perception of magnitude is not absolute but relative. Our experience one one stimulus depends on its relationship to others. • Fechner’s Law says that constant increases in physical energy will produce smaller increases in perceived magnitude. • Example: It only takes a small increase in volume to make a soft sound seem twice as loud, but it will take an incredible increase in volume to make a rock band seem twice as loud. (This assumption applies to most but not all stimuli.) • Stevens’s Power Law for magnitude estimation works for a wider array of stimuli. It includes a factor that takes into account the differential sensitivity of various sensory systems. • Example: It takes larger and larger increases in light or sound to create the same amount of change in perceived magnitude, but it only takes only a small increase in intensity of an already painful electric shock before you perceive it as twice as strong.

17. ORGANIZING THE PERCEPTUAL WORLD • PERCEPTUAL ORGANIZATION the task performed by the perceptual system to determine what stimuli go together to form an object • Your perceptual system can organize unconnected elements into objects by creating imaginary connecting lines called subjective contours. • How we organize sensory stimuli into meaningful experiences is the interest of Gestalt psychologists. • Gestalt(German for “organization” or “whole figure”) is a field of psychology in which the whole is believed to be greater than the sum of its individual parts. • Gestalt psychology is based on the works of Max Wertheimer, Kurt Koffka, and Wolfgang Köhler, who said that human perception is based on the integration of individual elements into a whole. • Gestalt psychologists have identified certain “laws” or principles regarding perceptual organization.

18. ORGANIZING THE PERCEPTUAL WORLD • Figure-Ground Organization • When faced with a complex visual or auditory stimulus, the perceptual apparatus automatically picks out some objects or sounds to be figures (features to be emphasized), while others become the ground (less relevant background) • The figure has meaning, always stands in front of the rest, and always seems to include the contours or edges that separate it from the less relevant background. • Drawings that can be reversed between figure and ground (reversible figures) show that perception is not only an active process but also a categorical one. • Gestalt: Figure and Ground Video http://formulate.com.au/articles/padf-part4-figureground/

19. REVERSIBLE FIGURES

20. ORGANIZING THE PERCEPTUAL WORLD • Grouping • PROXIMITY the tendency to perceive objects that are close together as belonging together • SIMILARITY the tendency to group similar objects together to make one whole • CONTINUITY the tendency to see an object as continuing despite an obvious break • CLOSURE the tendency to fill int he missing spaces to complete the object and see it as a whole • COMMON FATE the tendency to see objects that move in the same direction as together _________________________________________ _________________________________________ _________________________________________ _________________________________________ _________________________________________

21. GESTALT...in Review • Gestalt Principles of Perception • Illusions in Advertising: Gestalt • More Illusions In Advertising

22. ORGANIZING THE PERCEPTUAL WORLD • PERCEPTION OF LOCATION AND DISTANCE • Two-Dimensional Location & the Computational Approach • Knowing an object’s two-dimensional position (left and right, up and down) helps you locate it. • Your brain estimates an object’s true location relative to your body. • VISION: You brain uses an equation (whatever! This is not math class...) that takes information about where an image strikes the retina and adjusts it based on information about movement of your eyes and head. • SOUND: The brain uses the slight differences in the timing and intensity of a sound (between the two ears) as cues to locate its source. • Visual dominanceis the bias toward using visual information when it conflicts with the information from the other senses. (ex. While watching television, you perceive the sound of someone speaking to be coming from the screen rather than from its actual source...the speaker.)

23. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION • Depth perception is the ability to perceive distance which allows people to experience the world in three-dimensions, even though the visual information received is projected onto two-dimensional retinas. • Depth perception is dependent on the following: Cues Based on the Physiology of the Eye • Cues Characteristic of Visual Stimuli

24. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • INTERPOSITION (OCCLUSION) closer objects block the view of things farther away. • RELATIVE SIZE If two objects are assumed to be the same size, the object producing a larger image on the retina is perceived as closer. • HEIGHT IN THE VISUAL FIELD More distant objects are usually higher in the visual field than those nearby. • LINEAR PERSPECTIVE The closer together two converging lines, greater distance is perceived. • TEXTURE GRADIENT Texture or grain appears as less detailed as distance increases. • MOTION PARALLAX This is the apparent movement of objects. Objects closest to you appear to move rapidly across the visual field, while those distant may appear motionless. Faster relative movement across the visual field indicates less distance. • CLARITY, COLOR, SHADOW Distant objects often appear hazier and tend to take on a bluish tone. Objects are seen as three-dimensional because of shadows.

25. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Interposition (Occlusion)

26. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Relative Size

27. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Height in the Visual Field

28. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Linear Perspective

29. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Texture Gradient

30. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Motion Parallax

31. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Characteristic of Visual Stimuli • Clarity, Color, and Shadow

32. ORGANIZING THE PERCEPTUAL WORLD • Identify the cues to depth used in this painting.

33. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • ACCOMMODATION The muscles surround the lens either tighten or (to make the lens more curved for focusing on close objects) or relax (to flatten the lens for focusing on more distant objects. Information from the muscles is relayed to the brain and helps create distance perception. • CONVERGENCE Involves each eye rotating inward to project the image of an object on each retina. Information about the rotation goes to the brain and the greater the rotation, the closer the object is perceived to be. • BINOCULAR DISPARITY The difference between the two retinal images of an object (one from each eye) provides distance cues. This difference decreases with increasing distances. Depth can be created by showing each eye a separate photograph of a scene, each taken from a slightly different angle.

34. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • Accommodation

35. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • Accommodation

36. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • Convergence

37. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • Binocular Disparity

38. ORGANIZING THE PERCEPTUAL WORLD • DEPTH PERCEPTION: Cues Based on the Physiology of the Eye • Binocular Disparity

39. ORGANIZING THE PERCEPTUAL WORLD • PERCEPTION OF MOTION • Perception of motion use cues that make use of optical flow, or the changes in retinal images across the entire visual field. • LOOMING, a rapid expansion in the size of an image so that it fills the retina, is automatically perceived as an approaching stimulus and not an expanding object. • If the brain determines that movement of the eyes and head account for all of the movement of images on the retina, then the outside world is perceived as stable, not moving. • There is about 1/20 of a second between the moment when an image is registered on the retina and the moment when the messages about that image reach the brain. The brain corrects for the image “delay” by predicting where the stimulus should be 1/20 of a second in the future. • The vestibular and tactile senses are employed in movement perception. Motion sickness may occur when vision supplies movement information but the other senses do not, or when other sensations provide movement information but there an inadequate view of the movement. • One illusion of motion,STROBOSCOPICMOTION, occurs because of our tendency to interpret as continuous motion a series of still images flashed in rapid succession. This accounts for our ability to see movement on films, videos, DVDs, and “chasing” holiday or theater lights. (one more)

40. ORGANIZING THE PERCEPTUAL WORLD • PERCEPTUAL CONSTANCY • Perceptual constancyis the perception of objects as constant in size, shape, color, or other properties despite changes in their retinal image. • SIZE CONSTANCY • SHAPE CONSTANCY • COLOR CONSTANCY • BRIGHTNESS CONSTANCY

41. ORGANIZING THE PERCEPTUAL WORLD • SIZE CONSTANCY

42. ORGANIZING THE PERCEPTUAL WORLD • SHAPE CONSTANCY

43. ORGANIZING THE PERCEPTUAL WORLD • COLOR CONSTANCY

44. ORGANIZING THE PERCEPTUAL WORLD • BRIGHTNESS CONSTANCY

45. ORGANIZING THE PERCEPTUAL WORLD • PERCEPTUAL CONSTANCY • Perceptual constancyis the perception of objects as constant in size, shape, color, or other properties despite changes in their retinal image. • SIZE CONSTANCYperception that the size of an object remains the same despite the fact that size changes based on distance • SHAPE CONSTANCYperception that the size of an object remains the same despite a change in the angle from which it is viewed • COLOR CONSTANCYperception that the color of an object stays the same despite a change in the lighting • BRIGHTNESS CONSTANCYperception that the brightness of an object stays the same despite a change in the brightness of the background

46. RECOGNIZING THE PERCEPTUAL WORLD • RECOGNITION & PERCEPTUAL CATEGORIES • The brain analyzes the incoming pattern of stimulus and compares that pattern to information stored in memory. • If there is a match, recognition occurs, and the stimulus is classified into a perceptual category. • Two types of processing are involved in recognition: • TOP-DOWN PROCESSING guided by knowledge, expectations, and other psychological factors • BOTTOM-UP PROCESSING relies on specific, detailed information elements from the sensory receptors that are integrated and assembled into a whole

47. RECOGNIZING THE PERCEPTUAL WORLD

48. RECOGNIZING THE PERCEPTUAL WORLD

49. RECOGNIZING THE PERCEPTUAL WORLD • NETWORK PROCESSING the extensive and relatively automatic interaction of various neural feature analyzers • This explains object superiority effectand work superiority effect when the ability to detect an object or target letter is better if it is embedded in a pattern or word, rather than random lines and letters. • O.S.E. refers to the phenomenon that people will recognize a fully composed object faster than its individual parts • W.S.E. refers to the phenomenon that people are more accurate in recognizing a letter in the context of a word than they are when a letter is presented in isolation, or when a letter is presented within a nonword (e.g. "WXRG") • Parallel Distributed Processing Models (PDP), also called connectionistmodels, represent the computational approach to perception. These models explain that the units in a network operate in parallel--simultaneously. • In such neural network models, each element is connected to all other elements. Connections either excite or inhibit other units of the network. Using a connection may strengthen it. • Recognition occurs as a result of the simultaneous operation of connected units. As stimuli occur together, connections between units activated become stronger and detection of any of them will be made more likely by the presence of all the others.

50. RECOGNIZING THE PERCEPTUAL WORLD • ATTENTION the process of directing and focusing psychological resources on a task or object while ignoring other tasks or objects with the purpose of enhancing perception, performance, and mental experience • DIRECTS our sensory and perceptual systems toward certain stimuli • SELECTS specific information for further processing • IGNORES or screens out unwanted stimuli • ALLOCATES (or assigns) the mental energy to do the processing • REGULATES the flow of resources necessary for performing a task or coordinating several tasks at once • Attention has three characteristics: • improves mental processing • requires effort; prolonged attention can leave you feeling mentally “drained” • attentional resources are limited; we are often forced to select which things receive our attention