Chapter 4 Sensation & Perception

1. Chapter 4 Sensation & Perception psychophysics: the study of how physical stimuli are translated into psychological experience

2. Sensation • Sensation • the process by which our sensory receptors and nervous system receive/detect and represent stimulus energy • Perception • the 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 images

4. The Major Senses • There are 6 major senses • vision • hearing • touch • taste • pain • smell • The list can be extended with balance, joint senses and others • Vision has been studied most extensively

5. 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 • Ex. You expect the family reunion to be awful, and thus it is! • Subjective Contours: Top-down processing allows for detection of form without feature detectors

6. Importance of Sensation with Perception • Visual Agnosia: an inability to recognize objects • Prosopagnosia: complete sensation but incomplete perception. Ex. Seeing and recognizing a face based upon autonomic responses but being unable to determine who it is http://www.youtube.com/watch?v=vwCrxomPbtY&feature=related

7. 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

8. 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) Smaller (more difficult); more difficult to determine for pitch in sound than adjustment in light

9. Here we measure the smallest change in a face that can be discriminated. A morphing algorithm mixed two faces in variable proportions to create a series of synthetic faces that each differed by a tiny amount. By selecting from this series, a test face could be chosen so as to reach a just noticeable difference from a sample face. Face-discrimination thresholds were about 7% of the average difference between two faces,

10. Absolute vs. Difference ThresholdGo Formative Activity https://goformative.com/formatives/pFT6DFxARSEkyCdLo/view

11. 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

12. 100 Percentage of correct detections 75 50 Subliminal stimuli 25 0 Low Absolute threshold Medium Intensity of stimulus Sensation- Thresholds • Subliminal Stimuli • when stimuli are below one’s absolute threshold for conscious awareness • Thus, we process things outside of conscious awareness

13. Sensation- Thresholds • Weber’s Law • to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount) • light intensity- 8% • weight- 2% • tone frequency- 0.3%

14. Sensation- Thresholds • Sensory Adaptation • diminished sensitivity as a consequence of constant stimulation • dark adaptation: eyes become more sensitive to light in low illumination • light adaptation: eyes become less sensitive to light in high illumination • Selective Attention • focusing of conscious awareness on a particular stimulus • as in the cocktail party effect- not attending to all stimuli at once

15. Now you see it, now you don’t!

16. Perception Selective Attention

17. Change Blindnesshttp://www.youtube.com/watch?v=VkrrVozZR2c Changes made when the eyes are moving go unperceived by the brain, termed. In other words, we are BLIND to CHANGE

18. Vision • Sensory 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; this determines the hue (color)

19. Vision • Hue • dimension of color determined by wavelength of light • Intensity • amount of energy in a wave determined by amplitude; influences: • Brightness • Loudness • The brighter and louder: the greater the amplitude

20. The spectrum of electromagnetic energy Shortest waves TO Longest waves

21. 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

22. Color Vision • Age old question… • If a tree falls in the forest and no one hears it, does it make a sound? • We can ask the same question about color • If no one sees the tomato, is it red? • The answer is NO! Tomatoes are everything but red, because it rejects (reflects) the long wavelengths of red.

23. Vision • Pupil-adjustable opening in the center of the eye; allows light to reach the edge of the periphery • Iris- a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening & amount of light entering the eye • Lens-transparent structure behind pupil that changes shape to focus images on the retina

24. VisionKnow the pathway- CPLR

25. Vision • Accommodation-the process by which the eye’s lens changes shape to help focus near or far objects on the retina • 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

26. Vision • Acuity- the sharpness of vision • Nearsightedness-condition in which nearby objects are seen more clearly than distant objects because distant objects focus in front of retina • Farsightedness-condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

27. Vision • Farsighted Nearsighted Normal Vision Vision Vision

28. Retina’s Reaction to Light- Receptors • Rods • peripheral retina receptors • detect black, white and gray • for peripheral or twilight conditions; • super sensitive to light • Cones • receptors near center of retina • fine detail and color vision • for daylight or well-lit conditions

29. 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 -don’t usually detect these because the brain fills in the missing information • Fovea-central point in the retina, around which the eye’s cones cluster

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

32. Pathways from the Eyes to the Visual Cortex

33. Cell’s responses Stimulus Visual Information Processing • Feature Detectors • nerve cells in the brain that respond to specific features • shape • angle • Movement Figure 4.23- feature analysis

34. How the Brain Perceives

35. Illusory Contours

36. Visual Information Processing • Parallel Processing • simultaneous processing of several aspects of a problem simultaneously; better than computer which performs step-by-step processing • True for other senses as well: such as sound: pitch, loudness, melody, & meaning

38. Visual Information Processing • Trichromatic (three color) Theory • Young and Helmholtz • three different retinal color receptors • Red • Green • Blue • When stimulated in combination, can produce any color

39. Color-Deficient Vision • People who suffer red-green deficiency have trouble perceiving the number within the design • Red-green cone insensitivity is the most common type of color blindness

41. Color Blindness

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

43. Opponent-Process Theory: Afterimage Effect

44. Visual Information Processing • Color Constancy • Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object

45. MOVED BY BEAUTY: Beauty is less in the eye of the beholder than in the motor cortex of the brain, which is activated differently depending on whether you judge a painting lovely or ugly. Landscapes, portraits, and abstract art each excite distinct areas of the brain, but the motor cortex seems to be the seat of beauty perception. Vision

46. Hearing

47. 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 (ex. Soprano has short-high frequency soundwaves) or lowness (ex. Bass has long-low frequency soundwaves) depend on the wavelength • Also depends on frequency

48. The Intensity of Some Common Sounds

50. 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 sound waves trigger nerve impulses