Sensation and Perception

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