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Psychology 101: Chapter 5

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Psychology 101: Chapter 5

  1. 1. Chapter 5 Sensation and Perception
  2. 2. What’s It For? Building the World of Experience <ul><li>Translating the Message </li></ul><ul><li>Identifying the Message Components </li></ul><ul><li>Producing a Stable Interpretation </li></ul>
  3. 4. Vision: Learning Goals <ul><li>Explain how light gets translated into the electrochemical language of the brain. </li></ul><ul><li>Discuss how the basic features of the visual message, such as color, are identified by the brain. </li></ul><ul><li>Explain how a stable interpretation of visual information is created and why the interpretation process sometimes produces visual illusions. </li></ul>
  4. 5. Translating the Message <ul><li>Visible light = One part of the spectrum of all electromagnetic energy </li></ul><ul><ul><li>Three main properties: </li></ul></ul><ul><ul><ul><li>Wavelength </li></ul></ul></ul><ul><ul><ul><li>Intensity </li></ul></ul></ul><ul><ul><ul><li>Purity </li></ul></ul></ul><ul><li>Enters the eye through the cornea, pupil, and lens </li></ul>
  5. 8. Transduction of Light <ul><li>Light strikes the retina, where light-sensitive cells react to light by creating neural impulses </li></ul><ul><ul><li>Rods: Sensitive to low light </li></ul></ul><ul><ul><li>Cones: Sensitive to fine detail, color </li></ul></ul><ul><ul><ul><li>Concentrated in the fovea </li></ul></ul></ul><ul><ul><li>Photopigments chemically react to light </li></ul></ul><ul><ul><ul><li>These break down in bright light, regenerate after time in low light, causing dark adaptation </li></ul></ul></ul>
  6. 9. Processing in the Retina <ul><li>Rod and cone cells pass information to bipolar cells, then to ganglion cells </li></ul><ul><li>Ganglion cells have receptive fields, meaning: </li></ul><ul><ul><li>Input received from a number of other cells </li></ul></ul><ul><ul><li>Responds only to a particular pattern </li></ul></ul><ul><li>Many have center-surround fields </li></ul><ul><ul><li>Respond to light in middle, not on periphery, of receptive field </li></ul></ul>
  7. 13. Identifying Message Components <ul><li>Neural messages travel to brain via optic nerve </li></ul><ul><ul><li>Splits at optic chiasm </li></ul></ul><ul><ul><li>Information from right visual field goes to left hemisphere; info from left visual field goes to right hemisphere </li></ul></ul><ul><li>Next stops: lateral geniculate nucleus and superior colliculus </li></ul>
  8. 15. Identifying Features: The Visual Cortex <ul><li>From lateral geniculate nucleus, messages relayed to parts of the occipital lobe that process vision (“visual cortex”) </li></ul><ul><li>Visual cortex picks out and identifies components called features </li></ul><ul><ul><li>Example: Bars of light at a particular angle; corners </li></ul></ul>
  9. 17. Higher Level Feature Detection <ul><li>Some feature detectors respond to more complex patterns, such as corners, moving bars, bars of certain length </li></ul><ul><li>Some respond to faces only </li></ul><ul><ul><li>In humans, certain forms of brain damage cause prosopagnosia (inability to recognize faces) </li></ul></ul><ul><li>Other parts of the brain specialized to handle other aspects of vision, such as motion </li></ul>
  10. 18. Color Vision: Trichromatic Theory <ul><li>Three types of cones in retina, each maximally sensitive to one range of wavelengths </li></ul><ul><ul><li>Wavelengths correspond to blue, green, and red </li></ul></ul><ul><li>Colors sensed by comparing amount of activation coming from each type </li></ul><ul><ul><li>Most colors are a mix (such as orange) </li></ul></ul><ul><li>Certain kinds of color blindness result from having wrong kind of photopigment in cones </li></ul>
  11. 20. Color Vision: Opponent Processes <ul><li>Trichromatic theory can’t explain everything about color vision: </li></ul><ul><ul><li>Why does yellow seem like a primary color too? </li></ul></ul><ul><ul><li>Why do we see afterimages of complementary colors? </li></ul></ul><ul><li>Additional process: Receptors in visual system respond positively to one color and negatively to that complementary color </li></ul>
  12. 22. Producing Stable Interpretations <ul><li>Perception depends on context, expectations as well as sensory messages </li></ul><ul><ul><li>Bottom-up processing: Controlled by physical messages delivered to the senses </li></ul></ul><ul><ul><li>Top-down processing: Controlled by one’s beliefs, expectations about the world </li></ul></ul><ul><li>Also: Inborn tendencies to group visual information in certain ways </li></ul>
  13. 25. Laws of Visual Organization: Gestalt Principles <ul><li>Proximity: Elements that are close to each other seen as being part of the same object </li></ul><ul><li>Similarity: Items sharing physical properties are put into the same set </li></ul><ul><li>Closure: Figures with gaps or small missing parts of the border are seen as complete </li></ul><ul><li>Good continuation: Lines that are interrupted are seen as continuously flowing </li></ul><ul><li>Common fate: Things moving in the same direction are seen as a group </li></ul>
  14. 26. Object Recognition <ul><li>Recognition by components theory (Biederman): </li></ul><ul><ul><li>Objects broken down into simple geometrical forms (geons) before identifying whole object </li></ul></ul><ul><ul><li>Easy to identify incomplete or degraded objects this way </li></ul></ul><ul><li>Evidence: Fast, easy recognition of degraded objects as long as geons easily visible </li></ul>
  15. 27. Perceiving Depth: Depth Cues <ul><li>Monocular: Require input from only one eye </li></ul><ul><ul><li>Includes linear perspective, shading, relative size, overlap, and haze </li></ul></ul><ul><li>Binocular: Depend on both eyes </li></ul><ul><ul><li>Retinal disparity: Difference between location of images in each retina </li></ul></ul><ul><ul><li>Convergence: How far the eyes turn inward to focus on an object </li></ul></ul>
  16. 28. Motion Perception <ul><li>Note: Images always moving around on the retina, whether the objects are still or not! </li></ul><ul><li>Sometimes we perceive motion when there isn’t any </li></ul><ul><ul><li>Phi phenomenon </li></ul></ul><ul><li>A variety of cues contribute to movement perception, including changes in retinal images, relative positions of objects </li></ul>
  17. 29. Perceptual Constancies <ul><li>Sensory messages are unstable, always changing, yet we perceive a stable world </li></ul><ul><ul><li>Size constancy </li></ul></ul><ul><ul><li>Shape constancy </li></ul></ul><ul><li>How do we do it? </li></ul><ul><ul><li>Make assumptions that allow us to guess, for example, about relative distances of objects </li></ul></ul>
  18. 32. The Price of Constancy: Perceptual Illusions <ul><li>Inappropriate interpretations of physical reality </li></ul><ul><li>Example assumptions and related illusions: </li></ul><ul><ul><li>Rooms are rectangular -> Ames room illusion </li></ul></ul><ul><ul><li>Linear perspective cues -> Ponzo illusion </li></ul></ul><ul><ul><li>Converging lines are corners -> Müller-Lyer illusion </li></ul></ul>
  19. 34. The Moon Illusion <ul><li>Why does the moon look larger on the horizon than when it’s higher in the sky? This illusion is explained as it relates to size constancy, perception, and depth cues. </li></ul>
  20. 35. PLAY VIDEO The Moon Illusion
  21. 36. Cultural Influences on Illusions <ul><li>Navajos raised in traditional circular homes (hogans) less subject to Mülller-Lyer illusion </li></ul><ul><ul><li>Similar findings for traditional Zulu </li></ul></ul><ul><li>However: The illusion still persists to some degree </li></ul><ul><ul><li>Some inborn tendency toward these illusions, modified by experience </li></ul></ul>
  22. 37. Hearing: Learning Goals <ul><li>Explain how sound, the physical message, is translated into the electrochemical language of the brain. </li></ul><ul><li>Discuss how pitch information is pulled out of the auditory message. </li></ul><ul><li>Explain how the auditory message is interpreted and how sound is localized. </li></ul>
  23. 38. Translating the Message <ul><li>Sound is mechanical energy requiring a medium such as air or water to move </li></ul><ul><ul><li>Caused by vibrating stimulus </li></ul></ul><ul><ul><li>How fast stimulus vibrates -> Frequency </li></ul></ul><ul><ul><ul><li>What we hear as pitch (high or low) </li></ul></ul></ul><ul><ul><li>Intensity of the vibration -> Amplitude </li></ul></ul><ul><ul><ul><li>What we experience as loudness </li></ul></ul></ul><ul><ul><ul><li>Measured in decibels (dB) </li></ul></ul></ul>
  24. 39. Entering the Ear <ul><li>Outer ear: </li></ul><ul><ul><li>Sound funnels from pinna toward eardrum </li></ul></ul><ul><li>Middle ear: </li></ul><ul><ul><li>Malleus, incus, and stapes bones vibrate </li></ul></ul><ul><li>Inner ear: </li></ul><ul><ul><li>Vibrations sent to cochlea </li></ul></ul><ul><ul><li>Hair cells on basilar membrane send signals to brain </li></ul></ul>
  25. 41. Identifying Message Components <ul><li>Auditory nerve transmits messages from the hair cells to the auditory cortex </li></ul><ul><li>Place theory: Pitch determined by where hair cells on the basilar membrane are responding to sound </li></ul><ul><li>Frequency theory: Pitch determined partly by frequency of impulses coming from hair cells </li></ul><ul><ul><li>High-frequency sounds coded with volleys of firing </li></ul></ul>
  26. 42. Interpreting Sound <ul><li>Cells in auditory cortex respond to particular combinations of sounds </li></ul><ul><li>Sounds grouped, organized by pitch </li></ul><ul><ul><li>Prior knowledge (top-down processing) plays a role as well </li></ul></ul><ul><li>To localize sounds, we compare messages between two ears </li></ul><ul><ul><li>Time of arrival </li></ul></ul><ul><ul><li>Intensity </li></ul></ul>
  27. 43. The Skin and Body Senses: Learning Goals <ul><li>Explain how sensory messages delivered to the skin (touch and temperature) are translated and interpreted by the brain. </li></ul><ul><li>Describe how we perceive and interpret pain. </li></ul><ul><li>Discuss the operation and function of the body senses: movement and balance. </li></ul>
  28. 44. Skin Senses <ul><li>Touch </li></ul><ul><ul><li>When stimulated by pressure, receptor cells in skin send messages to somatosensory cortex (parietal lobe) </li></ul></ul><ul><li>Temperature </li></ul><ul><ul><li>Limited knowledge of how it is perceived </li></ul></ul><ul><ul><li>Cold fibers </li></ul></ul><ul><ul><li>Warm fibers </li></ul></ul>
  29. 45. The Sense of Pain <ul><li>Adaptive reaction by the body to stimuli intense enough to cause tissue damage </li></ul><ul><li>Gate-control theory </li></ul><ul><ul><li>Impulses from pain receptors can be blocked (“gated”) by the spinal cord </li></ul></ul><ul><ul><ul><li>Large fibers: Close the gate </li></ul></ul></ul><ul><ul><ul><li>Small fibers: Open the gate </li></ul></ul></ul><ul><ul><li>Also: Endorphins </li></ul></ul>
  30. 46. The Body Senses <ul><li>Kinesthesia: The ability to sense the position and movement of one’s body parts </li></ul><ul><ul><li>Many systems involved: receptors in muscles, joints, and skin; visual feedback </li></ul></ul><ul><li>Vestibular sense: The ability to sense changes in acceleration, posture </li></ul><ul><ul><li>Inner ear organs that contribute: Semicircular canals, vestibular sacs </li></ul></ul>
  31. 47. The Chemical Senses: Learning Goal <ul><li>Describe how chemical stimuli lead to neural activities that are interpreted as different odors and tastes. </li></ul>
  32. 48. The Chemical Senses <ul><li>Include smell (olfaction) and taste (gustation) </li></ul><ul><ul><li>Both involve chemoreceptors </li></ul></ul><ul><li>Smell: Receptor cells in upper part of nasal cavity send messages to olfactory bulb </li></ul><ul><li>Taste: Receptor cells on tongue (taste buds) respond to sweet, bitter, salty, sour tastes </li></ul><ul><ul><li>Distinct from experience of flavor </li></ul></ul><ul><ul><li>Relayed to thalamus, somatosensory cortex </li></ul></ul>
  33. 49. Pheromones <ul><li>Chemicals that cause highly specific reactions when detected by other members of the species </li></ul><ul><ul><li>Examples: sexual behavior, aggression </li></ul></ul><ul><li>Do humans react to pheromones, e.g., in perfume? </li></ul><ul><ul><li>None so far produce reliable reactions </li></ul></ul>
  34. 50. From the Physical to the Psychological: Learning Goals <ul><li>Explain stimulus detection, including techniques designed to measure it. </li></ul><ul><li>Define difference thresholds, and explain Weber’s Law. </li></ul><ul><li>Discuss stimulus adaptation and its adaptive value. </li></ul>
  35. 51. Stimulus Detection <ul><li>Absolute threshold: Intensity level at which people detect the stimulus 50% of the time </li></ul><ul><ul><li>May vary from trial to trial </li></ul></ul><ul><li>Signal detection technique: Used to determine detection ability; also may vary from trial to trial </li></ul><ul><ul><li>Compare hits to false alarms, correct rejections to misses </li></ul></ul>
  36. 54. Difference Thresholds and Weber’s Law <ul><li>Smallest detectable difference in magnitude </li></ul><ul><ul><li>Just noticeable difference (JND) depends on how intense the stimuli are overall </li></ul></ul><ul><li>Weber’s law: Ability to notice a difference in two stimuli is a constant proportion of the size of the standard stimulus </li></ul><ul><li>Sensory adaptation: Tendency of sensory systems to reduce sensitivity to a stimulus source that remains constant </li></ul>

Notes de l'éditeur

  • The Chapter 5 slides are relevant to APA Outcome 1.2a(3). Specific slides are additionally relevant to other outcomes as noted on the notes page associated with the relevant slide.
  • Figure 5.2. To build an internal representation of the outside world, the brain solves three fundamental adaptive problems for each of its sensory systems. (a) It translates messages from the environment into the language of the nervous system; (b) it identifies the elementary components of the messages, such as colors, sounds, simple forms, and patterns of light and dark; and (c) it builds a stable interpretation of those components once they’ve been extracted.
  • Figure 5.3. Visible light is actually only a small part of the electromagnetic spectrum, which includes such other energy forms as X rays and radio and TV waves. Changes in the wavelength of light from about 400 nanometers to 700 nanometers are experienced as changes in color; short wavelengths are seen as violets and blues; medium wavelengths as yellows and greens; and long wavelengths as reds.
  • Figure 5.4. Light enters the eye through the cornea, pupil, and lens. As the lens changes shape in relation to the distance of the object, the reflected light is focused at the back of the eye where, in the retina, the visual message is translated.
  • Figure 5.5. Rods and cones send signals to other cells in the retina. Ganglion cells in the fovea, which receive input from cones, tend to have smaller receptive fields than cells located in the sides of the retina, which receive input from rods. This helps to explain why we see fine detail better in the fovea and why we see better out of the sides of our eyes when light levels are low.
  • Figure 5.6. Receptive fields in the retina often have a center-surround arrangement. Light falling in the center of the field has an opposite effect from light falling in the surround. (a) Light in the center of the field produces an excitatory response (green). (b) Light falling in the surround produces an inhibitory response (purple). (c) When light falls equally in both regions, there is no net increase in the cell’s activity compared to its no-light baseline activity level. This kind of receptive field helps the brain detect edges.
  • Figure 5.8. Your eyes gradually adjust to the dark and become more sensitive; that is, you can detect light at increasingly low levels of intensity. The rods and cones adapt at different rates and reach different final levels of sensitivity. The dark adaptation curve represents the combined adaptation of the two receptor types. At about the 8-minute mark there is a point of discontinuity; this is where further increases in sensitivity are due to the functioning of the rods.
  • Figure 5.9. Input from the left visual field falls on the inside half of the left eye and the outside half of the right eye and projects to the right hemisphere of the brain; input from the right visual field projects to the left hemisphere. Visual processing occurs at several places along the pathway, ending in the visual cortex, where highly specialized processing takes place.
  • Figure 5.10. Hubel and Wiesel discovered feature detectors in the brains of cats and monkeys. Feature detectors increase their firing rates to specific bars of light presented at particular orientation.
  • Figure 5.11. Blue-sensitive cones are most likely to respond to short wavelengths of light; green-sensitive cones respond best to medium wavelengths; red-sensitive cones respond best to long wavelengths. Notice that rods are not sensitive to long wavelengths of light. (Based on Jones &amp; Childers, 1993.)
  • Figure 5.12. Stare closely at the middle of this face for about a minute. Then focus on the black dot on the right. What do you see now? The demo works better in a brightly lit environment.
  • Figure 5.13. Whether you detect meaningful images in (a) and (b) depends on how much prior knowledge you bring to perceptual interpretation. (From Coren, Ward, &amp; Enns, 1994.)
  • Figure 5.15. We have a natural tendency to divide any visual scene into a discernible “figure” and “background.” This task can be difficult, as with the “hidden faces” painting (a); or it can be easy but ambiguous (b): Which do you see - a vase or a pair of profiles?
  • This slide relates to 1.2b, as the Gestalt school is a historical perspective in psychology.
  • Figure 5.17. Notice all the changes in the image of a door as it moves from closed to open. Yet we perceive it as a constant rectangular shape.
  • Figure 5.18. We see these three planters as matching in size and shape partly because of depth cues in the environment: Each covers three tiles in length and three in width.
  • Figure 5.19. The girl on the right appears to be much larger than the girl on the left. But this is an illusion, induced by the belief that the room is rectangular. In fact, the sloping ceiling and floors provide misleading depth cues. To the viewer looking through the peephole the room appears perfectly normal. This famous illusion was designed by Adelbert Ames.
  • This slide is relevant to Outcomes 1.2c and 1.2d(1): the influence of experience and culture on psychological processes.
  • Figure 5.23. Sound enters the auditory canal and causes the tympanic membrane to vibrate in a pattern that is then transmitted through three small bones in the middle ear to the oval window. The oval window vibrates, causing fluid inside the cochlea to be displaced, which moves the basilar membrane. The semicircular canals contribute to our sense of balance.
  • Outcome 3.1 (using critical thinking effectively) may be seen as relevant to this slide as it evaluates popular claims students may have heard regarding pheromones.
  • Psychophysics, described on this slide and the next four, concerns the relationship between the objective world of reality and the subjective one of appearance, a persisting issue in psychology. Objective 1.2d(4) is relevant.
  • Figure 5.25. The more intense the stimulus, the greater the likelihood that it will be detected. The absolute threshold is the intensity level at which we can detect the presence of the stimulus 50% of the time.
  • Figure 5.26. There are four possible outcomes in a signal detection experiment: (a) If the stimulus is present and correctly detected, it’s called a hit . (b) If the stimulus is absent but the observer claims it’s present, it’s a false alarm . (c) A miss is when the stimulus is present but not detected; and (d) A correct rejection is when the observer correctly recognizes that the stimulus was not presented.