PSYC 1113 Chapter 3


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PSYC 1113 Chapter 3

  1. 1. IntroChapter 3:Sensation andPerception
  2. 2. The Major Senses• There are 6 major senses.– vision– hearing– touch– taste– pain– smell• The list can be extended with balance, jointsenses, and others.• Vision has been studied most extensively.
  3. 3. Principles of Sensation• Transduction—physical energy to neural signal• Absolute threshold—smallest strength of a stimulusthat can be detected• Difference threshold—(just noticeable difference)smallest difference that can be detected• Weber’s law—for each sense the size of a justnoticeable difference is a constant proportion of thesize of the initial stimulus• Sensory adaptation—the decline in sensitivity toconstant stimulus
  4. 4. VisionPurpose of the Visual System–transform light energy into anelectrochemical neural response–represent characteristics of objectsin our environment such as size,color, shape, and location
  5. 5. Vision Key Terms• Cornea—clear membrane that covers thefront of the eye, helps gather and directincoming light• Pupil—the opening in the middle of the iristhat changes size to let in differentamounts of light• Iris—the colored part of the eye; themuscle that controls the size of the pupil
  6. 6. Vision Key Terms• Lens—a transparent structure behind thepupil; bends light as it enters the eye• Retina—a thin, light-sensitive membranelocated at the back of the eye that containssensory receptors for vision• Accommodation—the process by which thelens changes shape to focus incoming lightso that it falls on the retina
  7. 7. Light: The Visual Stimulus
  8. 8. Light: The Visual Stimulus• Light can be described as both a particleand a wave• The wavelength of a light is the distance ofone complete cycle of the wave• Visible light has wavelengths from ~400nmto 700nm• The wavelength of light is related to itsperceived color
  9. 9. Distribution of Rods and Cones• Cones—concentrated in centerof eye (fovea)–~6 million• Rods—concentrated in periphery–~120 million• Blind spot—region with no rodsor cones
  10. 10. Differences BetweenRods and Cones• Cones– allow us to see in bright light– allow us to see fine spatial detail– allow us to see different colors• Rods– allow us to see in dim light– can not see fine spatial detail– can not see different colors
  11. 11. Rod Vs Cone Visual Acuity• Cones—one cone often synapses ontoonly a single ganglion cell• Rods—the axons of many rods synapseonto one ganglion cell• This allows rods to be more sensitivein dim light, but it also reduces visualacuity
  12. 12. Processing Visual Information• Ganglion cells—neurons that connect to thebipolar cells; their axons form the optic nerve• Bipolar cells—neurons that connect rods andcones to the ganglion cells• Optic chiasm—point in the brain where theoptic nerves from each eye meet and partlycrossover to opposite sides of the brain
  13. 13. Color Vision• Our visual system interprets differencesin the wavelength of light as color• Rods are color blind, but the conesallow us to see different colors• This difference occurs because wehave only one type of rod but threetypes of cones
  14. 14. Properties of Color• Hue—property of wavelengths of lightknown as color; different wavelengthscorrespond to our subjective experience ofcolor (hue)• Saturation—property of color thatcorresponds to the purity of the light wave• Brightness—perceived intensity of a color,corresponds to amplitude of the light wave
  15. 15. Color Mixing• Two basic types of color mixing–subtractive color mixture• example: combining different colorpaints–additive color mixture• example: combining different colorlights
  16. 16. Additive Color Mixture• By combining lights ofdifferent wavelengthswe can create theperception of newcolors• Examples:– red + green = yellow– red + blue = purple– green + blue = cyan
  17. 17. Trichromatic Theory ofColor Vision• Researchers found that by mixing onlythree primary lights (usually red, green,and blue), they could create the perceptualexperience of all possible colors• This lead Young and Helmholtz to proposethat we have three different types ofphotoreceptors, each most sensitive to adifferent range of wavelengths
  18. 18. Trichromacy and TV• All color televisions are based on the fact thatnormal human color vision is trichromatic• Although we perceive the whole range of colorsfrom a TV screen, it only has three coloredphosphors (red, green, and blue)• By varying the relative intensity of the threephosphors, we can fool the visual system intothinking it is seeing many different colors
  19. 19. Opponent Process Theoryof Color Vision• Some aspects of our colorperception are difficult to explainby the trichromatic theory alone• Example: afterimages– if we view colored stimuli for an extendedperiod, we will see an afterimage in acomplementary color
  20. 20. ComplementaryAfterimages
  21. 21. Opponent-Process Theory• To account for phenomena likecomplementary afterimages, Herringproposed that we have two types ofcolor opponent cells– red-green opponent cells– blue-yellow opponent cells• Our current view of color vision is thatit is based on both the trichromatic andopponent-process theory
  22. 22. Overview of Visual System• The eye is like a camera, but instead of usingfilm to catch the light we have rods and cones• Cones allow us to see fine spatial detail andcolor, but cannot function well in dim light• Rods enable us to see in dim light, but at theloss of color and fine spatial detail• Our color vision is based on the presence of3 types of cones, each maximally sensitiveto a different range of wavelengths
  23. 23. Hearing: Sound Waves• Auditory perception occurs when soundwaves interact with the structures of the ear• Sound wave—changes over time in thepressure of an elastic medium (for example,air or water)• Without air (or another elastic medium) therecan be no sound waves, and thus no sound
  24. 24. • Frequency of a sound wave is related the pitch of a sound• Amplitude of a sound wave is related to loudness of a sound
  25. 25. Frequency of Sound Waves• The frequency of a sound wave ismeasured as the number of cyclesper second (Hertz)– 20,000 Hz Highest frequency we can hear– 4,186 Hz Highest note on a piano– 1,000 Hz Highest pitch of human voice– 100 Hz Lowest pitch of human voice– 27 Hz Lowest note on a piano
  26. 26. Intensity of Various SoundsExampleP (in sound-pressure units) Log P DecibelsSoftest detectable soundSoft whisperQuiet neighborhoodAverage conversationLoud music from a radioHeavy automobile trafficVery loud thunderJet airplane taking offLoudest rock band on recordSpacecraft launch from 150 ft.110100100010,000100,0001,000,00010,000,000100,000,0001,000,000,0000123456789020406080100120140160180
  27. 27. Anatomy of EarPurpose of the structures in the ear:–Measure the frequency (pitch) ofsound waves–Measure the amplitude (loudness)of sound waves
  28. 28. Major Structures of the Ear• Outer ear—acts as a funnel to directsound waves toward inner structures• Middle ear—consists of three smallbones (or ossicles) that amplify thesound• Inner ear—contains the structures thatactually transduce sound into neuralresponse
  29. 29. Transduction of Sounds• The structures of the ear transformchanges in air pressure (sound waves)into vibrations of the basilar membrane• As the basilar membrane vibrates itcauses the hairs in the hair cells to bend• The bending of the hairs leads to achange in the electrical potential within thecell
  30. 30. Distinguishing Pitch• Frequency theory—basilar membranevibrates at the same frequency as thesound wave• Place theory—different frequenciescause larger vibrations at differentlocations along the basilar membrane
  31. 31. Coding and Auditory Masking• The way in which waves traveldown the basilar membranecauses some sounds to interferewith (or mask) our ability to hearother sounds• Low-frequency sounds providebetter masking than high-frequency sounds
  32. 32. Auditory Masking• Low-frequencysounds effectivelymask high-frequency sounds.• High-frequencysounds cannoteffectively mask low-frequency sounds.Piccolo, softBassoon, loudPiccolo, loudBassoon, softDistance along basilar membraneDistance along basilar membraneEffect of bassoon on basilar membraneVibrationamplitudeof basilarmembraneVibrationamplitudeof basilarmembraneEffect of piccolo on basilar membranePiccolo, softBassoon, loudPiccolo, loudBassoon, softPiccolo, loudBassoon, softDistance along basilar membraneDistance along basilar membraneEffect of bassoon on basilar membraneVibrationamplitudeof basilarmembraneVibrationamplitudeof basilarmembraneEffect of piccolo on basilar membrane
  33. 33. Chemical and Body Senses• Olfaction (smell)• Gustation (taste)• Touch and temperature• Pain• Kinesthetic (location of body)• Vestibular (balance)
  34. 34. Olfactory System• Olfactory nerves are connected to the olfactorybulb in the brain• Olfactory bulb—enlarged ending of the olfactorycortex at the front of the brain where thesensation of smell is registered• Olfactory function declines with age• Pheromones—chemical signals released by ananimal that communicate information and affectthe behavior of other animals of the samespecies
  35. 35. Taste• Sweet• Sour• Salty• Bitter• Umami
  36. 36. Skin and Body Senses• Pressure—Pacinian corpuscles• Itch—response to histamine• Temperature—receptors reactive tocold or warm, simultaneousstimulation produces sensation of hot• Pain—free nerve endings arereceptors
  37. 37. Elements of Pain• Gate-control theory of pain—pain is aproduct of both physiological andpsychological factors that cause spinalgates to open and relay patterns of intensestimulation to the brain; the brainperceives them as pain• Phantom limb pain—when a personcontinues to experience intense painfulsensations in a limb that has beenamputated
  38. 38. Movement, Position, and Balance• Kinesthetic—sense of location ofbody parts in relation to one another• Vestibular—sense of balance,receptors located in the inner ear• Proprioceptors—receptors in musclesand joints that provide informationabout body position and movement
  39. 39. PerceptionThe process of integrating,organizing, and interpretingsensory information
  40. 40. Perceptual Processing• Bottom-up processing—emphasizes theimportance of sensory receptors indetecting the basic features of a stimulus;moves from part to whole; also called data-driven processing• Top-down processing—emphasizesimportance of observer’s cognitiveprocesses in arriving at meaningfulperceptions; moves from whole to part;also called conceptually driven processing
  41. 41. Perceptual Organization• Some of the best examples ofperceptual organization were providedby the Gestalt psychologists• Gestalt psychologists hypothesized that“the whole is greater than the sum ofthe parts”• They were interested in showing theglobal nature of our perceptions
  42. 42. Gestalt Grouping PrinciplesGestalt theorists argued that our perceptualsystems automatically organized sensoryinput based on certain rules• Proximity• Similarity• Closure• Good continuation• Common movement• Good form
  43. 43. Figure and GroundGestalt psychologistsalso thought animportant part of ourperception was theorganization of a sceneinto its figure (theobject of interest) andits ground (thebackground)
  44. 44. Depth Perception• One of our more important perceptualabilities involves seeing in threedimensions• Depth perception is difficult because weonly have access to two-dimensionalimages• How do we see a 3-D world using onlythe 2-D retinal images?
  45. 45. Depth Perception Cues• Cue—stimulus characteristicsthat influence our perceptions• We are able to see in 3-Dbecause the visual system canuse depth cues that appear inthe retinal images
  46. 46. Types of Depth CuesDepth cues are usually divided intocategories; we will consider two typesof depth cues•Monocular—depth cues that appear inthe image in either the left or right eye•Binocular—depth cues that involvecomparing the left and right eye images
  47. 47. Monocular Depth Cues• Relative image size• Overlap• Aerial perspective• Texture gradient• Linear perspective• Motion parallax
  48. 48. Binocular Depth Cues• Monocular depth cues allow us to see in3-D with the view of only one eye, but ourbest depth perception occurs if we lookthrough both eyes• This is because our right and left eyes seea slightly different view of the world• The difference between the image in thetwo eyes is know as binocular disparity
  49. 49. Stereogram• Another way to create the illusion ofdepth through binocular stereopsisis with an stereogram• An stereogram is formed byrepeating columns of patterns
  50. 50. Stereogram
  51. 51. Perceptual Constancy• When viewing conditions change, theretinal image changes even if the objectsbeing viewed remain constantExample: As a person walks away from youtheir retinal image decreases in size• Important function of the perceptualsystem is to represent constancy in ourenvironment even when the retinal imagevaries
  52. 52. Size Constancy• The cylinders atpositions A and B arethe same size eventhough their imagesizes differ• The depth cues suchas linear perspectiveand texture help thevisual system judge thesize accurately Point APoint BPoint APoint B
  53. 53. Shape Constancy• It is hard to tell if thefigure on the upperright is a trapezoid ora square slantedbackward.• If we add texture, thetexture gradient helpsus see that it isactually a square
  54. 54. Perceptual SetThe influence of prior assumptions andexpectations on perceptual interpretations
  55. 55. Müller-Lyer Illusion• Perceptual psychologistshave hypothesized thatthe left horizontal linelooks longer because italso looks farther away.• Specifically, the inwardpointing arrows signifythat the horizontal line isclosest to you, and theoutward pointing arrowssignify the opposite case.
  56. 56. Moon Illusion