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Sensation and Perception

Sensation and Perception. Chapter 3. Sensation vs. Perception. Sensation The experience of sensory stimulation Perception The process of creating meaningful patterns from raw sensory information. The Nature of Sensation. The Basic Process. Receptor cells

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Sensation and Perception

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  1. Sensation and Perception Chapter 3

  2. Sensation vs. Perception • Sensation • The experience of sensory stimulation • Perception • The process of creating meaningful patterns from raw sensory information

  3. The Nature of Sensation

  4. The Basic Process • Receptor cells • Specialized cells that respond to a particular type of energy • Doctrine of specific nerve energies • One-to-one relationship between stimulation of a specific nerve and the resulting sensory experience • For example, applying pressure with your finger to your eye results in a visual experience

  5. Sensory Thresholds • Absolute threshold • The minimum amount of energy that can be detected 50% of the time

  6. Absolute Thresholds • Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water • Smell: 1 drop of perfume diffused throughout a three-room apartment • Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch) • Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions • Vision: a candle flame seen from 50km (30 miles) on a clear, dark night

  7. Sensory Thresholds • Sensory adaptation • An adjustment of the senses to the level of stimulation they are receiving • Difference threshold • The smallest change in stimulation that can be detected 50% of the time • Also called the just noticeable difference

  8. Sensory Thresholds • Weber’s Law • States that the difference threshold is a constant proportion of the specific stimulus • Senses vary in their sensitivity to changes in stimulation

  9. Subliminal Perception • The notion that we may respond to stimuli that are below our level of awareness • Research shows that the effect only occurs in controlled laboratory studies • Research outside the laboratory shows no significant effect of subliminal information

  10. Extrasensory Perception • Refers to extraordinary perception such as • Clairvoyance – awareness of an unknown object or event • Telepathy – knowledge of someone else’s thoughts or feelings • Precognition – foreknowledge of future events • Research has been unable to conclusively demonstrate the existence of ESP

  11. Vision

  12. The Visual System • Cornea • Transparent protective coating over the front of the eye • Pupil • Small opening in the iris through which light enters the eye • Iris • Colored part of the eye

  13. The Visual System • Lens • Focuses light onto the retina • Retina • Lining of the eye containing receptor cells that are sensitive to light • Fovea • Center of the visual field

  14. Receptor Cells • Cells in the retina that are sensitive to light • Visual receptors are called rods and cones

  15. Rods About 120 million rods Respond to light and dark Very sensitive to light Provide our night vision Cones About 8 million cones Respond to color as well as light and dark Work best in bright light Found mainly in the fovea Receptor Cells

  16. Receptor Cells • Bipolar cells • Receive input from receptor cells • Ganglion cells • Receive input from bipolar cells • Blind spot • Area where axons of ganglion cells leave the eye

  17. Adaptation • Dark adaptation • Increased sensitivity of rods and cones in darkness • Light adaptation • Decreased sensitivity of rods and cones in bright light • Afterimage • Sense experience that occurs after a visual stimulus has been removed

  18. From Eye to Brain • Optic nerve • Made up of axons of ganglion cells • carries neural messages from each eye to brain • Optic chiasm • Point where part of each optic nerve crosses to the other side of the brain

  19. Color Vision • Properties of color • Hue – refers to colors such as red and green • Saturation – refers to the vividness of a hue • Brightness – the nearness of a color to white

  20. Theories of Color Vision • Additive color mixing • Mixing of lights of different hues • Lights, T.V., computer monitors (RGB) • Subtractive color mixing • Mixing pigments, e.g., paints

  21. Theories of Color Vision • Trichromatic theory • Three different types of cones • Red • Green • Blue-violet • Experience of color is the result of mixing of the signals from these receptors • Can account for some types of colorblindness

  22. Forms of Colorblindness • Approximately 10% of men and 1% of women have some form of colorblindness • Dichromats • People who are blind to either red-green or blue-yellow • Monochromats • People who see no color at all, only shades of light and dark

  23. Theories of Color Vision • Trichromatic theory cannot explain all aspects of color vision • People with normal vision cannot see “reddish-green” or “yellowish-blue” • Color afterimages

  24. Theories of Color Vision • Opponent-process theory • Three pairs of color receptors • Yellow-blue • Red-green • Black-white • Members of each pair work in opposition • Can explain color afterimages • Both theories of color vision are valid

  25. Color Vision in Other Species • Other species see colors differently than humans • Most other mammals are dichromats • Rodents tend to be monochromats, as are owls who have only rods • Bees can see ultraviolet light

  26. Sound • Sound waves • Changes in pressure caused by molecules of air moving • Frequency • Number of cycles per second in a wave, measured in Hertz (Hz) • Frequency determines pitch

  27. Sound • Amplitude • Magnitude (height) of sound wave • Determines loudness, measured in decibels (dB) • Overtones • Multiples of the basic tone • Timbre • Quality of texture of sound

  28. The Ear • Eardrum • Middle ear • Contains three small bones; the hammer, anvil, and stirrup • These bones relay and amplify the incoming sound waves

  29. The Ear • Oval window • Membrane between middle ear and inner ear • Cochlea • Part of inner ear containing fluid that vibrates • This causes the basilar membrane to vibrate

  30. The Ear • Basilar membrane • Membrane in the cochlea which contains receptor cells, called hair cells • Auditory nerve • Connection from ear to brain • Provides information to both sides of brain

  31. Theories of Hearing • Place theory • Pitch is determined by location of vibration along the basilar membrane • Frequency theory • Pitch is determined by frequency hair cells produce action potentials • Volley Principle • Pattern of sequential firing determines pitch

  32. Hearing Disorders • About 28 million people have some form of hearing damage in the U.S. • Can be caused by • Injury • Infections • Explosions • Long-term exposure to loud noises

  33. The Other Senses

  34. Smell • Detecting common odors • Odorant binding protein is released and attached to incoming molecules • These molecules then activate receptors in the olfactory epithelium • Axons from those receptors project directly to the olfactory bulb

  35. Smell • Women have a better sense of smell than men • Anosmia • Complete loss of the ability to smell

  36. Smell • Pheromones • Used by animals as a form of communication • Provides information about identity • Also provides information about sexual receptivity • Pheromones stimulate the vomeronasal organ (VNO) • Information from the VNO is sent to a special part of the olfactory bulb used for pheromonal communication

  37. Taste • Four basic tastes • Sweet • Salty • Sour • Bitter • Recent discovery of fifth taste • Umami

  38. Taste • Receptor cells are located in taste buds • Taste buds are located in papillae on the tongue • Chemicals dissolve in saliva and activate receptors

  39. The Other Senses

  40. Kinesthetic Senses • Kinesthetic senses provide information about speed and direction of movement • Stretch receptors sense muscle stretch and contraction • Golgi tendon organs sense movement of tendons

  41. Vestibular Senses • Vestibular senses provide information about equilibrium and body position • Fluid moves in two vestibular sacs • Vestibular organs are also responsible for motion sickness • Motion sickness may be caused by discrepancies between visual information and vestibular sensation

  42. The Skin Senses • Skin is the largest sense organ • There are receptors for pressure, temperature, and pain • Touch appears to be important not just as a source of information, but as a way to bond with others

  43. Pain • Serves as a warning about injury or other problem • Large individual differences in pain perception • Gate control theory • Neurological “gate” in spinal cord which controls transmission of pain to brain

  44. Pain • Biopsychosocial theory • Holds that pain involves not just physical stimulus, but psychological and social factors as well • Placebo effect • Shows that when a person believes a medication reduces pain, their pain is often reduced even though no medication was given • Pain relief is likely the result of endorphin release

  45. Pain • Alternative approaches • Hypnosis • Self-hypnosis • Accupuncture

  46. Perception

  47. Perceptual Organization • Figure-ground • We perceive a foreground object (figure) against a background (ground) • Animals may look like the background they inhabit as a way of destroying figure-ground distinction

  48. Perceptual Organization • Other principles of organization • Proximity • Similarity • Closure • Continuity

  49. Perceptual Organization • Perceptual Constancy • Our tendency to perceive objects as stable and unchanging despite changing sensory information • Size constancy • Shape constancy • Brightness constancy • Color constancy

  50. Perception of Distance and Depth • Monocular cues – those that require only one eye • Aerial perspective • Texture gradient • Linear perspective • Motion parallax • Superposition

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