Sensation and Perception

1. Chapter 6 Sensation and Perception PSYCHOLOGY David G. Myers C. Nathan DeWall Twelfth Edition

2. Chapter Overview • Basic Concepts of Sensation and Perception • Vision: Sensory and Perceptual Processing • The Nonvisual Senses

3. Basic Concepts of Sensation and Perception(part 1) • Under normal circumstances, sensation and perception are parts of one continuous process. • Sensation • The process by which our sensory receptors and nervous system receive and represent stimulus energies from the environment • Perception • The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

4. Basic Concepts of Sensation and Perception(part 2) • Bottom-up processing • Analysis that begins with the sensory 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

5. Basic Concepts of Sensation and Perception(part 3) • Our senses • Receive sensory stimulation, often using specialized receptor cells • Transform that stimulation into neural impulses • Deliver the neural information to our brain

6. Basic Concepts of Sensation and Perception(part 4) • Transduction • Conversion of one form of energy into another • In sensation, the transformation of stimulus energies, such as sights, sounds, and smells, into neural impulses the brain can interpret • Psychophysics studies the relationships between the physical energy we can detect and its effects on our psychological experiences.

7. Basic Concepts of Sensation and Perception(part 5) • Signal detection theory • Predicts how and when we will detect a faint stimulus amid background noise. • Individual absolute thresholds • Vary depending on the strength of the signal and on our experience, expectations, motivation, and alertness

8. How much of a stimulus does it take to have a sensation? (part 1) • Absolute threshold • Minimum stimulation needed to detect a particular stimulus 50% of the time • Can see a far-away light in the dark, feel the slightest touch • Subliminal • Input below the absolute threshold for conscious awareness • Priming • Activating, often unconsciously, associations in our mind, setting us up to perceive, remember, or respond to objects or events in certain ways

9. How much of a stimulus does it take to have a sensation? (part 2) • Difference threshold (just noticeable difference) • Minimum difference a person can detect between any two stimuli half the time; increases with stimulus size • Weber’s law • For an average person to perceive a difference, two stimuli must differ by a constant minimum percentage (not a constant amount); the exact proportion varies, depending on the stimulus.

10. Subliminal Persuasion • Subliminal stimuli: Stimuli that are too weak to detect 50 percent of the time. • Subliminal sensation: Sensation that is too fleeting to enable exploitation with subliminal messages. • Subliminal persuasion: May produce a fleeting, subtle, but not powerful, enduring effect on behavior (Greenwald, 1992). • Experiments discount attempts at subliminal advertising and self-improvement.

11. Basic Concepts of Sensation and Perception(part 5) • Sensory adaptation • Diminished sensitivity as a consequence of constant stimulation • Increases focus by reducing background chatter • Influences how the world is perceived in a personally useful way • Influences emotions

12. Emotion Adaptation • Gaze at the angry face on the left for 20 to 30 seconds, then look at the center face (looks scared, yes?). • Now gaze at the scared face on the right for 20 to 30 seconds, before returning to the center face (now looks angry, yes?). (From Butler et al., 2008.)

13. Perceptual Set • Perceptual set • A mental predisposition to perceive one thing and not another • What determines our perceptual set? • Schemas organize and interpret unfamiliar information through experience. • Preexisting schemas influence top-down processing of ambiguous sensation interpretation, including gender stereotypes.

14. Perceptual Set: Context Effects • Context effects A given stimulus may trigger different perceptions because of the immediate context. Culture and Context Effects What is above the woman’s head? In one study, nearly all the East Africans who were questioned said the woman was balancing a metal box or can on her head and that the family was sitting under a tree. What do you think Westerners said?

15. Perceptual Set: Motivation and Emotion • Motives give us energy as we work toward a goal. Like context, they can bias our interpretations of neutral stimuli. • Emotions can move our perceptions in one direction or another. Can you give examples of motives and emotions in action?

16. Terms to Learn (part 1) • Wavelength • Distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmissions. • Hue • Dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth. • Intensity • Amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave’s amplitude (height).

17. Terms to Learn (part 2) • Retina • The light-sensitive inner surface of the eye, which contains the receptor rods and cones plus layers of neurons that begin the processing of visual information • Accommodation • The process by which the eye’s lens changes shape to focus near or far objects on the retina

18. Sensory and Perceptual Processing in Vision • What is seen as light is only a thin slice of the broad spectrum of electromagnetic energy. • The portion visible to humans extends from the blue-violet to the red light wavelengths. • After entering the eye and being focused by the lens, light energy particles strike the eye’s inner surface, the retina. • The perceived hue in a light depends on its wavelength; its brightness depends on its intensity.

19. Light Energy: From the Environment Into the Brain • Waves vary in wavelength, the distance between successive peaks. • Frequency, the number of complete wavelengths that can pass a point in a given time, depends on the length of the wave. • Waves vary in amplitude, the height from peak to trough (top to bottom). Wave amplitude determines the brightness of colors (and the loudness of sounds).

20. Light Energy: From the Environment Into the Brain

21. Vision: The Eye

22. The Retina’s Reaction to Light

23. Rods and Cones • Cones and rods provide special sensitivities. • Cones are sensitive to detail and color. • Rods are sensitive to faint light.

24. Vision: Visual Information Processing • How does the brain turn light stimuli into useful information about the world? • Collection and analysis of sensory information • Linkage of the optic nerve with neurons in the thalamus Pathway from the eyes to the visual cortex The ganglion axons forming the optic nerve run to the thalamus, where they synapse with neurons that run to the visual cortex.

25. Information Processing in the Eye and Brain(part 1) • Color processing occurs in two stages. • The retina’s red, green, and blue cones respond in varying degrees to different color stimuli, as suggested by the Young-Helmholtz trichromatic theory. • Cones’ responses are then processed by opponent-process cells, as Hering’s theory proposed.

26. Feature Detection • Feature detection • Nerve cells in the brain respond to specific features of the stimulus, such as its shape, angle, or movement.

27. Information Processing in the Eye and Brain(part 2) • Hubel and Wiesel • The brain’s computing system deconstructs and then reassembles visual images. • Specialized occipital lobe neuron cells receive information from ganglion cells and pass it to supercell clusters.

28. Parallel Processing Studies of patients with brain damage suggest that the brain delegates the work of processing motion, form, depth, and color to different areas. After taking a scene apart, the brain integrates these subdimensions into the perceived image.

29. Visual Information Processing Simplified

30. Perceptual Organization: Gestalt Principles • Gestalt psychologists propose principles used to organize sensations into perception. • Form perception • Depth perception • Perceptual constancy

31. Vision: Visual Organization • How do we organize and interpret shapes and colors to create meaningful perceptions? • People tend to organize pieces of information into an organized whole, called a gestalt. Necker cube

32. Gestalt Principles: Form Perception • How do we know where one object begins and another ends? • Figure-ground • Organization of the visual field into objects that stand out from their surroundings • Grouping • Perceptual tendency to organize stimuli into meaningful groups

33. Grouping: Seeing Gestalts/Wholes • Human minds use these grouping strategies to see patterns and objects.

34. Gestalt Principles: Depth Perception • Depth perception • The ability to see objects in three dimensions, although the images that strike the retina are two-dimensional • Allows us to judge distance • Is present, at least in part, at birth in humans and other animals

35. The Visual Cliff • Test of early 3-D perception • Most infants refuse to crawl across the visual cliff • Crawling, no matter when it begins, seems to increase an infant's fear of heights

36. Seeing Depth: Binocular Cues • Binocular cues • Two eyes improve perception of depth • Retinal disparity • Binocular cue for perceiving depth • The brain calculates distance by comparing images from the two eyes • Used by 3-D filmmakers

37. Seeing Depth: Monocular Cues • Monocular cue • A depth cue, such as interposition or linear perspective, available to either eye alone • Light and shadow • Relative motion • Relative size • Linear perspective • Interposition • Relative height

38. Motion Perception • Humans are imperfect at motion perception. • When large and small objects move at the same speed, the large objects appear to move more slowly. • Phi phenomenon • An illusion of movement created when two or more adjacent lights blink on and off in quick succession

39. Perceptual Constancy • Objects are perceived as unchanging—having consistent color, brightness, shape, and size—even as illumination and retinal images change.

40. Color Constancy • Perceiving familiar objects as having a consistent color, even if changing illumination alters the wavelengths reflected by the object

41. Relative Luminance

42. Shape and Size Constancy • Size constancy • Perception of objects as having constant size even when our distance from them varies • Perception of the form of familiar objects as constant even when the retina receives changing images

43. Experience and Visual Perception: Perceptual Interpretation • Restored vision and sensory restriction • Effects of sensory restriction on infant cats, monkeys, and humans suggest there is a critical period for normal sensory and perceptual development. • Without stimulation, normal connections do not develop. • Perceptual adaptation • Ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field

44. The Nonvisual Senses: Hearing • Sound waves: From the environment into the brain • Sound waves compress and expand air molecules. • The ears detect these brief pressure changes. The Sounds of MusicA violin's short, fast waves create a high pitch. The longer, slower waves of a cello or bass create a lower pitch. Differences in the waves’ height (amplitude) also create differing degrees of loudness.

45. Hearing: Sound Characteristics (part 1) • Amplitude (height) determines the intensity (loudness) of sound waves. • Length (frequency) determines the pitch. • Sound is measured in decibels (dB).

46. Hearing: Sound Characteristics (part 2) • Sound waves are bands of compressed and expanded air. • Human ears detect these changes in air pressure and transform them into neural impulses, which the brain decodes as sound. • Sound waves vary in amplitude, which is perceived as differing loudness, and in frequency, which is experienced as differing pitch.

47. Hearing: Decoding Sound Waves • Sound waves strike the eardrum, causing it to vibrate. • Tiny bones in the middle ear transmit the vibrations to the cochlea, a coiled, fluid-filled tube in the inner ear. • Ripples in the fluid of the cochlea bend the hair cells lining the surface, which trigger impulses in nerve cells. • Axons from these nerve cells transmit a signal to the auditory cortex.

48. Decoding: Transforming Sound Energy Into Neural Messages

49. Hearing Loss • Sensorineural hearing loss (nerve deafness) • Damage to cell receptors or associated nerves • Conduction hearing loss • Damage to the mechanical system that conducts sound waves to the cochlea • Cochlear implant: A device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea

50. Intensity of Some Common Sounds