Sensation and perception

1. Sensation and perception

2. Sensory psychology • How we know about the world • General principles • Transduction • receptors • Adequate stimulus • Law of specific nerve energies • Battery experiment • Physical properties give rise to perceptual features • Color is NOT a property of light

3. Physical versus perceptual characteristics • Need to determine relationship between physical and perceptual characteristics • Vision – light travels in waves • Definition of wavelength

4. Wave characteristic of light Differences in wavelength are perceived as differences in color

5. Wave characteristic of light A and B have same wavelength B has higher amplitude Differences in amplitude are perceived as differences in brightness

6. Relationship between physical and perceptual characteristics of light

8. Visual transduction • Cornea • Light enters eye • Pupil • Contraction and dilation • Iris • Pigmented part • Lens • Focuses light on retina

9. Visual transduction • Optic disc • How to find your blind spot • Retina • Photoreceptors • Rods • Cones

10. Rods and cones

11. Visual transduction • Photochemicals in rods and cones respond to light • Fire action potential • Are carrots really good for your eyes?

12. Properties of rods and cones • Cones (about 7 million in each retina) • Respond best to bright light • Respond to color • Difficult to see color in dark • Rods (about 120 million in each retina) • Respond best to dim illumination • Do not respond to color

13. From retina to perception • Optic nerve • Occipital lobe • Feature detectors in the brain • Respond (fire action potential) only for very specific stimuli • Some will fire if see horizontal but not vertical line • Some will fire if see “L” but not for straight line

14. Perception of letter “t”

15. Summary of visual transduction • Adequate stimulus for vision is light • Enters the eye and is focused on retina • Retina has receptors (neurons) with photochemicals • Fire action potential when exposed to light • AP to occipital lobe via optic nerve

16. Color perception • Not in the stimulus • Species differences • No brain; no color • Different brain; different color • Question: What processes give PERCEPTION of color?

17. The spectrum of light • White light combination of all colors • ROYGBIV • Longest to shortest wavelenths • Red, orange, yellow, green, blue, indigo, violet • Infrared and ultraviolet

18. Theories of color vision • Do not know exactly how perceive color • Trichromatic theory (Young-Helmholtz) • Found three different kinds of cones • Each has different photochemical • 3 different photochemicals respond best to 3 primary colors (red, green blue) • Any color can be made from combination of primary colors

19. Trichromatic theory of color vision • Show a color (pink) • All three cones types respond (fire) • Cone type most responsive to red fires most • Cone types most responsive to green and blue fire less • INTERPRETATION of pattern is pink

20. Examples of color perception

21. Trichromatic theory and color blindness • How does color blindness result according to theory? • Selective color blindness • Problems for the trichromatic theory • After images

24. The opponent process theory • Photochemicals in cones arranged in opposed pairs • Red-Green • Blue-Yellow • Black – White • Colors oppose one another • When see red prevents from seeing green

25. The opponent process theory

26. Opponent process theory • Explanation for after images

27. Factors affecting color blindness • Gender • Race • Age

28. Hearing • General questions same as for vision (and all other senses) • What is adequate stimulus ? • How does adequate stimulus get transduced (cause action potential) • Physical properties map on to perceptual characteristics

29. Adequate stimulus • Changes in air pressure • Tuning fork example • Compression and expansion of air molecules

30. Physical properties of sound • Changes in air pressure can be fast or slow • Many or few cycles (compression-expansion) per second (Hertz –Hz) • Frequency • Air pressure changes can be high or low • Amplitude • Measured in decibels (after AGB)

31. Physical and perceptual properties of sound

32. Relationship between physical and perceptual features

33. Different pitches 10,000 (10 kHz) 2000 Hz 200 Hz 16,000 Hz

34. Species differences in perceiving frequencies

35. Changes in loudness Base sound 10 dB louder 20 dB louder 30 dB louder

36. How to buy stereo speakers

37. Decibel value of some sounds

38. Pinna

39. The outer ear Pinna • Pinna • External auditory canal

40. The middle ear Pinna • Tympanic membrane (ear drum) • Ossicles – hammer, anvil and stirrup

41. The inner ear Pinna • The cochlea- filled with fluid not air • Basilar membrane • Hair cells on the basilar membrane

42. Hair cells

43. Transduction in the auditory system • Changes in air pressure enter the external auditory canal • Vibrate the tympanic membrane • Vibrate the ossicles • Ossicles “bang” on the cochlea • Movement of fluid in cochlea • Bending of hair cells

44. The process of auditory transduction

45. Hearing without hair cells • Cochlear implants • Electrodes implanted in cochlear next to auditory nerve • Microphone (on belt) receives sound and transmits to electrodes • Electrodes directly stimulate the auditory nerve

46. Cochlear implants

47. Cochlear implants • What do they sound like? Normal Implant

48. Cochlear implants • Who should get them • Potential disadvantages • Controversy in deaf community

49. Factors that can affect hearing • Things that can’t control • Age • Gender • Things that can control • Noise • Duration and amplitude both important • Frequency • What frequencies important for speech • What frequencies noise damages • Environmental noise vs. loud music • “walkman” phenomenon

50. Damaged hair cells