Sensation & Perception Chapter 5

1. Sensation & PerceptionChapter 5

2. Sensing & Perceiving Information • Sensation: Receiving • Perception: Organizing & Interpreting

3. Vision – The Eye • Light enters eye through the cornea • Passes through the pupil and lens • Focused into an image on the retina • Retina • Light sensitive inner surface of the eye • Contains Rods & Cones • Receptor cells convert light to neural impulses and send to brain • Brain reassembles impulses into an image

4. Vision – The Eye

5. Vision – Retina Receptors • Rods • detect black, white, and gray • necessary for peripheral and twilight vision • Cones • concentrated near the center of retina • function in daylight or well-lit conditions • detect fine detail • color vision

6. Receptors in the Human Eye Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitive? Yes No Vision--Receptors

7. The Eye • Optic Nerve: nerve that carries neural impulses from the eye to the brain • Blind Spot: point at which the optic nerve leaves the eye • No receptor cells • creates a “blind spot”

9. Vision – Feature Detection • Feature Detectors • nerve cells that respond to specific features of a stimulus • shape, angle, or movement • fMRI can be used to determine what object a person is looking at

10. Visual Information Processing • Parallel Processing • processing many parts of a problem all at once • the brain’s natural mode of information processing for many functions (including vision)

11. Abstraction: Brain’s higher-level cells respond to combined information from feature-detector cells Feature detection: Brain’s detector cells respond to elementary features-bars, edges, or gradients of light Retinal processing: Receptor rods and conesbipolar cells  ganglion cells Recognition: Brain matches the constructed image with stored images Scene Visual Information Processing

12. Color-Deficient Vision • People who suffer red-green blindness have trouble perceiving the number within the design

13. Color Vision • Young-Helmholtz trichromatic (three-color) theory • retina has 3 different color receptors (red, green, blue) • different combinations allow for the perception of any color • Opponent-process theory • opposing processes of retina enable color vision • e.g., some neurons are turned on by red and off by green

14. Audition • Audition- the sense of hearing • Frequency- the number of complete wavelengths that pass a point in a given time • Pitch- a tone’s highness or lowness • depends on frequency • long sound waves = low frequency & low pitch • short sound waves = high frequency & high pitch

15. Audition--The Ear • Sound waves • auditory canal eardrum (vibrates with the waves) middle ear cochlea (in inner ear)  triggers neural impulses (auditory nerve)  thalamus  auditory cortex (temporal lobe) • Middle Ear • chamber between the eardrum and cochlea • contains 3 tiny bones (hammer, anvil, stirrup) that transmit vibrations to the cochlea

16. Audition--The Ear • Inner Ear • innermost part of ear • Contains the Cochlea • a fluid-filled tube through which sound waves trigger nerve impulses

18. Decibel Levels - Common Sounds

19. Locating Sounds • sound reaches one ear more intensely and more quickly • auditory system is able to detect tiny differences • hearing loss in one ear = difficulty locating sounds

20. Touch • Skin Sensations • pressure • only skin sensation with identifiable receptors • warmth • cold • pain • Rubber hand illusion • http://www.youtube.com/watch?v=TCQbygjG0RU

21. Pain • No theory explains all available findings • Gate-Control Theory (1960s) • provides a useful model for understanding pain • the spinal cord contains small fibers (conduct pain signals) and large fibers (conduct other sensory signals) • “gate” opened by the activity of pain signals traveling up small nerve fibers • “gate” closed by activity in larger fibers or by information coming from the brain

22. Pain Control • Massaging area next to pain • Distraction • Diverting the brain’s attention may bring relief • Pleasant imagery • Count backward • Virtual reality

23. Taste • Taste Sensations • sweet • sour • salty • bitter • savory (umami)

24. Taste • Taste receptors • reproduce themselves every 2 weeks • taste sensitivity and # of taste buds decrease as we age • Sensory Interaction • one sense may influence another sense • the smell of food influences its taste • smell + texture = flavor • rubber hand illusion (vision & touch interact)

25. Smell • humans can detect 10,000 odors • olfactory receptor cells • respond to aromas • messages sent through receptor axons to the olfactory bulb in the brain • messages then travel from olfactory bulb to temporal lobe & limbic system • odors can evoke memories

26. Smell

27. Body Position and Movement • Sixth sense • Kinesthesis • the system for sensing the position and movement of individual body parts • interacts with vision • Vestibular sense • monitors head and body position to maintain balance • fluid in the inner ear moves when head moves • messages are sent to the cerebellum

28. Perceptual Organization- organizing & interpreting info from senses • Gestalt • an organized whole • tendency to integrate pieces of information into meaningful wholes • Necker cube

29. Perceptual Organization • First: Need to discriminate objects from backgrounds • Figure and Groundperceiving an object (figure) as distinct from its surroundings (ground) • In a busy restaurant: • voice you attend to = figure • all other voices = ground

30. Perceptual Organization- Gestalt • Next step: Need to organize the figure into a meaningful form • Grouping • the tendency to organize stimuli into meaningful groups • grouping rules identified by Gestalt psychologists • the “whole” that we perceive differs from the sum of its parts

31. Perceptual Organization- Gestalt • Grouping Rules • proximity - we group nearby figures together • similarity - we group similar figures together • continuity – we perceive continuous patterns • closure – we fill in gaps to create complete objects • connectedness - spots, lines, and areas are seen as a unit when connected

32. Proximity Similarity Continuity Closure Connectedness Perceptual Organization- Gestalt

33. Perceptual Organization-Depth Perception Visual Cliff

34. Perceptual Organization • Depth Perception • seeing objects in three dimensions • allows us to estimate distance • Visual Cliff • laboratory technique used to test depth perception • http://www.youtube.com/watch?v=eyxMq11xWzM

35. Perceptual OrganizationDepth Perception • Binocular cues – • depth cues • depend on use of two eyes • retinal disparity • images from the two eyes differ • brain compares the images to compute distance • the larger the difference, the closer the object

36. Perceptual OrganizationDepth Perception • Monocular Cues • depth cues needed for objects at further distances • available to each eye separately • relative height • higher objects seen as more distant • relative size • smaller image is more distant

37. Depth Perception • Monocular Cues (continued) • interposition • if one object blocks our view of another, we perceive that object to be closer

38. Depth Perception • Monocular Cues (continued) • relative clarity • hazy object seen as more distant • relative motion • as we move, stable objects appear to also move • fix gaze on object: those beyond appear to move with you; those in front appear to move backward • relative brightness • dimmer objects seem farther away

39. Depth Perception • Monocular Cues (continued) • linear perspective • parallel lines appear to converge with distance

40. Perceptual Constancy • perceiving objects as unchanging despite changes in illumination and retinal image • able to recognize objects despite changes in color, shape, & size

41. Shape Constancy Shape constancy – as a door opens the shape projected on retina looks more like a trapezoid…but we still perceive it as rectangular.

42. Perceptual Constancy • Color depends on context • Color Constancy • we perceive familiar objects as having consistent color • even if illumination changes and alters the wavelengths reflected by the object

43. Perceptual OrganizationSize-Distance Relationship

44. Perceptual Organization- Size-Distance Relationship

45. Depth Perception

46. Perceptual OrganizationMüller-Lyer Illusion

47. Perceptual OrganizationBrightness Contrast

48. Perceptual Interpretation • Perceptual Adaptation • (vision) ability to adjust to an artificially displaced visual field • glasses that invert view of the world (looks upside down) • humans can adapt relatively quickly and learn to coordinate movements accurately

49. Perceptual Interpretation • Perceptual Set • a mental predisposition to perceive one thing and not another • our experiences and expectations influence what we perceive

50. Perceptual Set – context effect