UNIT IV Sensation & Perception

1. UNIT IV Sensation & Perception

2. Sensation • Sensation • a process by which our sensory receptors and nervous system receive and represent stimulus energy • Perception • a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

3. Sensation • Our sensory and perceptual processes work together to help us sort out complex processes • What’s going on here? • Title: “The Forest Has Eyes”

4. Sensation • Bottom-Up Processing • analysis that begins with the sense receptors and works up to the brain’s integration of sensory information • Top-Down Processing • information processing guided by higher-level mental processes • as when we construct perceptions drawing on our experience and expectations (stored knowledge that helps make sense of new sensory input)

5. Sensation- Basic Principles • Psychophysics • study of the relationship between physical characteristics of stimuli and our psychological experience of them • Light- brightness • Sound- volume • Pressure- weight • Taste- sweetness • Questions we ask: What stimuli can we detect? How sensitive are we to changing stimulation?

6. Sensation- Thresholds • Absolute Threshold • minimum stimulation needed to detect a particular stimulus 50% of the time • Difference Threshold • minimum difference between two stimuli required for detection 50% of the time • just noticeable difference (JND)

7. Sensation- Thresholds • Signal Detection Theory • predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise) • assumes that there is no single absolute threshold • detection depends partly on person’s • experience • expectations • motivation • level of fatigue • In what jobs might understanding this theory be important? Theorists ask: • Why do people respond differently to the same stimuli? • Why do the same people respond to the same stimuli differently in different circumstances? • Subliminal Stimulation – means “below threshold”

8. 100 Percentage of correct detections 75 50 Subliminal stimuli 25 0 Low Absolute threshold Medium Intensity of stimulus Sensation- Thresholds • Subliminal • When stimuli are below one’s absolute threshold for conscious awareness

9. Sensation- Thresholds • Weber’s Law- to perceive as different, two stimuli must differ by a constant minimum percentage • light intensity- 8% • weight- 2% • tone frequency- 0.3% • Sensory adaptation- diminished sensitivity as a consequence of constant stimulation

10. Vision • Transduction • conversion of one form of energy to another • in sensation, transforming of stimulus energies into neural impulses • Wavelength • the distance from the peak of one wave to the peak of the next – Figure 18.1 and 18.2

11. Vision • Hue • dimension of color determined by wavelength of light – Figure 18.2a • Intensity • amount of energy in a wave determined by amplitude – Figure 18.2b • brightness • loudness

12. The spectrum of electromagnetic energy

13. Great amplitude (bright colors, loud sounds) Short wavelength=high frequency (bluish colors, high-pitched sounds) Long wavelength=low frequency (reddish colors, low-pitched sounds) Small amplitude (dull colors, soft sounds) Vision- Physical Properties of Waves

14. Vision Figure 18.3 • Pupil- adjustable opening in the center of the eye • Iris-a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening • Lens- transparent structure behind pupil that changes shape to focus images on the retina

15. Vision

16. Figure 18.5

17. Vision • Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina – (p.172) • Retina- the light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information

18. Retina’s Reaction to Light- Receptors • Figure 18.4 • Rods • peripheral retina • detect black, white and gray • twilight or low light • Cones • near center of retina • fine detail and color vision • daylight or well-lit conditions

19. Retina’s Reaction to Light • Optic nerve- nerve that carries neural impulses from the eye to the brain • Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there • Fovea- central point in the retina, around which the eye’s cones cluster

21. Receptors in the Human Eye (Table 18.1) Cones Rods Number 6 million 120 million Location in retina Center Periphery Sensitivity in dim light Low High Color sensitive? Yes No Vision- Receptors

22. Visual Info Processing - Pathways from the Eyes to the Visual Cortex (Figure 18.6)

23. Cell’s responses Stimulus Visual Information Processing • Feature Detectors • nerve cells in the brain that respond to specific features • shape • angle • Movement How can these specialized detectors help us to survive?

24. Figure 18.8

25. How the Brain Perceives

26. Illusory Contours

27. Visual Information Processing • Parallel Processing • simultaneous processing of several aspects of a problem simultaneously – Figure 18.9 – Colour, Motion, Form, Depth. • Two-track mind – exemplified by “Blindsight” (p.177)

28. Look also at Figure 18.10

29. Visual Information Processing • Trichromatic (three color) Theory • Young and Helmholtz • three different retinal color receptors • red • green • Blue

30. Color-Deficient Vision • People who suffer red-green blindness have trouble perceiving the number within the design • Mono-, Di-, and Tri-CHROMATIC

31. The Dress & the Shoe

32. Visual Information Processing Opponent-Process Theory- opposing retinal processes enable color vision “ON” “OFF” redgreen greenred blueyellow yellowblue black white white black

33. Opponent Process- Afterimage Effect Figure 18.12

34. Visual Information Processing • Color Constancy (p.187) • Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object • Lightness Constancy • Perceiving an object as having a constant brightness, even while illumination varies. Relative luminance means brightness is determined relative to the surrounding objects. See Figures 19.6 and 19.7.

35. 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

36. The Intensity of Some Common Sounds

38. Audition- The Ear • Middle Ear • chamber between eardrum and cochlea containing three tiny bones (hammer, anvil, stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window • Inner Ear • innermost part of the ear, contining the cochlea, semicurcular canals, and vestibular sacs • Cochlea • coiled, bony, fluid-filled tube in the inner ear through which

39. Audition • Place Theory • the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated • Frequency Theory • the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

40. How We Locate Sounds

41. Audition • Conduction Hearing Loss • hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea • Nerve Hearing Loss • hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve

42. Amplitude required for perception relative to 20-29 year-old group 1 time 10 times 100 times 1000 times 32 64 128 256 512 1024 2048 4096 8192 16384 Frequency of tone in waves per second Low Pitch High Audition • Older people tend to hear low frequencies well but suffer hearing loss for high frequencies

43. Touch • Skin Sensations • pressure • only skin sensation with identifiable receptors • warmth • cold • pain

44. Pain • Gate-Control Theory • theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain • “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

45. Taste • Taste Sensations • sweet • sour • salty • bitter • Sensory Interaction • the principle that one sense may influence another • as when the smell of food influences its taste

46. Olfactory nerve Olfactory bulb Receptor cells in olfactory membrane Nasal passage Smell

47. Number of correct answers Women and young adults have best sense of smell 4 Women 3 Men 2 0 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 Age Group Age, Sex and Sense of Smell

48. Body Position and Movement • Kinesthesis • the system for sensing the position and movement of individual body parts • Vestibular Sense • the sense of body movement and position • including the sense of balance