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Chapter 4 Sensation and Reality

Chapter 4 Sensation and Reality. Psychophysics. Study of relationship between physical stimuli and sensations they evoke in a human observer Absolute threshold: Minimum amount of physical energy necessary to produce a sensation

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Chapter 4 Sensation and Reality

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  1. Chapter 4Sensation and Reality

  2. Psychophysics • Study of relationship between physical stimuli and sensations they evoke in a human observer • Absolute threshold: Minimum amount of physical energy necessary to produce a sensation • Subliminal perception: Perception of a stimulus below the threshold for conscious recognition • Difference threshold: A change in stimulus intensity that is detectable to an observer

  3. Just Noticeable Difference (JND) • Any noticeable difference in a stimulus

  4. Weber’s Law • The amount of change needed to produce a constant JND is a constant proportion of the original stimulus intensity

  5. General Properties of Sensory Systems • Perceptual features: Basic stimulus patterns • Sensory coding: Converting important features of the world into messages understood by the brain

  6. Sensation and Perception • Sensation: Information arriving from sense organs (eye, ear, etc.) • Perception: Mental process of organizing sensations into meaningful patterns

  7. p. 120

  8. Vision: The Key Sense • Visible spectrum: Narrow spread of the electromagnetic spectrum to which the eyes respond

  9. Parts of the Eye • Lens: Structure in the eye that focuses light rays • Photoreceptors: Light-sensitive cells in the eye

  10. More Parts of the Eye • Retina: Light-sensitive layer of cells in the back of the eye • Easily damaged from excessive exposure to light (staring at an eclipse) • Cornea: Transparent membrane covering the front of the eye; bends light rays inward

  11. Accommodation • Changes in the shape of the lens of the eye

  12. Fig. 4-3, p. 123

  13. Fig. 4-1, p. 122

  14. Fig. 4-4, p. 124

  15. Video: Anatomy of the Eye: Virtual Reality After clicking ‘Play Video’ use your mouse to manipulate this active figure.

  16. Vision Problems • Hyperopia: Difficulty focusing nearby objects (farsightedness) • Myopia: Difficulty focusing distant objects (nearsightedness) • Astigmatism: Corneal, or lens defect that causes some areas of vision to be out of focus; relatively common • Presbyopia: Farsightedness caused by aging

  17. Fig. 4-5, p. 124

  18. Light Control • Iris: Colored circular muscle that controls amount of light entering the eye • Pupil: Opening at the front of the eye through which light passes

  19. Light Vision • Cones: Visual receptors for colors and bright light (daylight); 5 million in each eye • Rods: Visual receptors for dim light; only produce black and white; about 120 million total • Blind spot: Area of the retina lacking visual receptors

  20. Fig. 4-6, p. 125

  21. Fig. 4-7, p. 125

  22. Fig. 4-8, p. 126

  23. More on Light Control • Visual acuity: Sharpness of visual perception • Fovea: Area at the center of the retina containing only cones (50,000) • Peripheral vision: Vision at edges of visual field; side vision • Many superstar athletes have excellent peripheral vision • Tunnel vision: Loss of peripheral vision

  24. Fig. 4-9, p. 126

  25. Fig. 4-11, p. 127

  26. Video: Transmission of Light through the Eye

  27. Color Vision

  28. Trichromatic Theory • Color vision theory that states we have three cone types: red, green, blue • Other colors produced by a combination of these

  29. Opponent Process Theory • Color vision theory based on three “systems”: red or green, blue or yellow, black or white • Exciting one color in a pair (red) blocks the excitation in the other member of the pair (green) • Afterimage: Visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken)

  30. Fig. 4-12, p. 128

  31. Fig. 4-13, p. 128

  32. Simultaneous Color Contrast • Changes in perceived hue that occur when a colored stimulus is displayed on backgrounds of various colors

  33. Color Blindness • Color blindness: Inability to perceive colors; lacks cones or has malfunctioning cones • Total color blindness is rare • Color weakness: Inability to distinguish some colors • Red-green is most common; much more common among men than women • Recessive, sex-linked trait on X chromosome

  34. Ishihara Test • Test for color blindness and color weakness

  35. Fig. 4-16a, p. 129

  36. Fig. 4-16b, p. 129

  37. Fig. 4-16c, p. 129

  38. Fig. 4-17, p. 130

  39. Dark Adaptation • Increased retinal sensitivity to light after entering the dark; similar to going from daylight into a dark movie theater • Rhodopsin: Light-sensitive pigment in the rods; involved with night vision • Night blindness: Blindness under low-light conditions; hazardous for driving at night

  40. Fig. 4-18, p. 131

  41. Hearing • Sound waves: Rhythmic movement of air molecules • Pitch: Higher or lower tone of a sound • Loudness: Sound intensity

  42. Fig. 4-19, p. 132

  43. Hearing: Parts of the Ear • Pinna: Visible, external part of the ear • Tympanic membrane: Eardrum • Auditory ossicles: Three small bones that vibrate; link eardrum with the cochlea • Malleus (hammer) • Incus (anvil) • Stapes (stirrup)

  44. Fig. 4-20, p. 133

  45. Hearing: Parts of the Ear (cont) • Cochlea: Snail-shaped organ that makes up inner ear • Hair cells: Receptor cells within cochlea that transduce vibrations into nerve impulses

  46. Fig. 4-21, p. 134

  47. Fig. 4-22, p. 134

  48. How Do We Detect Higher and Lower Sounds? • Frequency theory: As pitch rises, nerve impulses of a corresponding frequency are fed into the auditory nerve • Place theory: Higher and lower tones excite specific areas of the cochlea

  49. Conduction Hearing Loss • Poor transfer of sounds from tympanic membrane to inner ear • Compensate with amplifier (hearing aid)

  50. Sensorineural Hearing Loss • Caused by damage to hair cells or auditory nerve • Hearing aids little or no help in these cases • Cochlear implant: Electronic device that stimulates auditory nerves directly

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