1. Chapter 4: Sensation & Perception

2. Sensation and Perception:
The Distinction
Sensation: a process by which our sensory receptors and nervous system receive and represent stimulus energy
Perception: selection, organization, and interpretation of sensory input. Enables us to recognize meaningful things
Psychophysics = the study of how physical stimuli are translated into psychological experience
Ch.4- Sensation & Perception

3. Ch.4- Sensation & Perception
The Distinction between Sensation & Perception
Ch.4- Sensation & Perception

4. Sensation vs Perception
Ch.4- Sensation & Perception

5. Sensation: Principles
Psychophysics: study of the relationship between physical characteristics of stimuli & our psychological experience of them
Fechner: the concept of the threshold
Absolute threshold: detected 50% of the time
Just noticeable difference (JND): smallest difference between 2, detectable 50% of the time
Weber’s law: size of JND proportional to size of initial stimulus
Weber’s Fraction: Applies to different types of sensory input
Weight= 1/30 of an increase the JND becomes larger
Ex: 30 ounces JND=1/90 ounces JND=3
Ch.4- Sensation & Perception

6. The Absolute Threshold25 50 75
100
Low
Absolute
threshold
Medium
Intensity of stimulus
Percentage
of correct
detections
Subliminal
stimuli
When stimuli are detectable less than 50% of the time (below one’s absolute threshold) they are “subliminal”
Ch.4- Sensation & Perception

7. Psychophysics: Concepts and Issues
Signal-Detection Theory: Sensory processes + decision processes
Subliminal Perception: Existence vs. practical effects
Sensory Adaptation: Decline in sensitivity to prolonged stimulation
Ch.4- Sensation & Perception

8. Signal-detection theory
Ch.4- Sensation & Perception

9. Ch.4- Sensation & Perception
Basics of Color Vision
Wavelength determines color
Longer = red / shorter = violet
ROY G BIV
Amplitude determines brightness
Purity determines saturation
Additive Color Mixing: Light/White
Subtractive Color Mixing: Paint/Black
Ch.4- Sensation & Perception

10. Ch.4- Sensation & Perception
Wavelength
Ch.4- Sensation & Perception

11. Ch.4- Sensation & Perception
Amplitude
Ch.4- Sensation & Perception

12. Light, the Physical Stimulus for Vision
Ch.4- Sensation & Perception

13. Ch.4- Sensation & Perception
The color solid
Ch.4- Sensation & Perception

14. Additive vs. Subtractive Color Mixing
Ch.4- Sensation & Perception

15. The Eye: Converting Light into Neural Impulses
Eye Components:
Cornea: where light enters the eye
Lens: focuses the light rays on the retina
Accommodation=adjusting (Close=Round Far=Flatten)
Iris: colored ring of muscle, constricts or dilates via amount of light
Pupil: regulates amount of light
Process:
Cornea-Pupil-Iris-Fovea-Retina-Optic Nerve
Ch.4- Sensation & Perception

16. Ch.4- Sensation & Perception
The Human Eye
Ch.4- Sensation & Perception

17. The Retina: An Extension of the CNS
Retina: absorbs light, processes images to the brain
Optic disk: optic nerve connection/blind spot
Receptor cells: 20/1
Rods: black and white/low light vision
Cones: color and daylight vision
Adaptation: becoming more or less sensitive to light as needed
Dark Adaptation: eye becomes more sensitive to light, 30 min
Light Adaptation: eye becomes less sensitive to light
Information processing:
Receptive fields: the retinal area, when stimulated, affects the firing of that cell
Lateral antagonism: when neural activity in a cell opposes activity in surrounding cells
Ch.4- Sensation & Perception

18. Nearsightedness & Farsightedness
Ch.4- Sensation & Perception

19. Ch.4- Sensation & Perception
The Retina
Ch.4- Sensation & Perception

20. The Process of Dark Adaptation
Ch.4- Sensation & Perception

21. The Retina and the Brain: Visual Information Processing
Light  rods and cones  neural signals  bipolar cells  ganglion cells  optic nerve  optic chiasm  opposite half brain
Main pathway: lateral geniculate nucleus (thalamus)  primary visual cortex (occipital lobe)
Second pathway: superior colliculus  thalamus  primary visual cortex
Ch.4- Sensation & Perception

22. Visual Pathways Through the Brain
Ch.4- Sensation & Perception

23. The what and where pathways from the primary visual cortex
Ch.4- Sensation & Perception

24. Hubel and Wiesel: Feature Detectors and the Nobel Prize
Early 1960’s: Hubel and Wiesel
Microelectrode recording of axons in primary visual cortex of animals
Discovered feature detectors: neurons that respond selectively to lines, edges, etc.
Groundbreaking research: Nobel Prize in 1981
Later research: cells specific to faces in the temporal lobes of monkeys and humans
Ch.4- Sensation & Perception

25. Visual Information Processing
Abstraction:
Brain’s higher-level cells respond to
combined information from feature-
detector cells
Feature detection:
Brain’s detector cells respond to
elementary features-bars, edges, or
gradients of light
Retinal processing:
Receptor rods and cones
bipolar cells ganglion cells
Recognition:
Brain matches the constructed image
with stored images
Scene
Ch.4- Sensation & Perception

26. Theories of Color Vision
Trichromatic theory - Young and Helmholtz
Receptors for red, green, blue – color mixing (TV)
Opponent Process theory – Hering
3 pairs of antagonistic colors
red/green, blue/yellow, black/white
After Image Effect: image persist after a stimulus is removed
Current perspective: both theories necessary
Ch.4- Sensation & Perception

27. Ch.4- Sensation & Perception
Afterimage Effect
Ch.4- Sensation & Perception

28. Ch.4- Sensation & Perception

29. Hearing: The Auditory System
Stimulus = sound waves (vibrations of molecules traveling in air)
Amplitude (loudness)
Wavelength (pitch)
Purity (timbre) tone’s highness or lowness
Wavelength described in terms of frequency: measured in cycles per second (Hz)
Frequency increase = pitch increase
Ch.4- Sensation & Perception

30. Sound, the physical stimulus for hearing
Ch.4- Sensation & Perception

31. The Ear: Three Divisions
External ear (pinna): collects sound -> Tympanic Membrane (ear drum)
Middle ear: the ossicles (hammer, anvil, stirrup)
Inner ear: the cochlea
a fluid-filled, coiled tunnel
contains the hair cells, the auditory receptors
lined up on the basilar membrane
Ch.4- Sensation & Perception

32. Ch.4- Sensation & Perception
The Human Ear
Ch.4- Sensation & Perception

33. Ch.4- Sensation & Perception
The Basilar Membrane
Ch.4- Sensation & Perception

34. Ch.4- Sensation & Perception
The Auditory Pathway
Sound waves vibrate bones of the middle ear
Stirrup hits against the oval window of cochlea
Sets the fluid inside in motion
Hair cells are stimulated with the movement of the basilar membrane
Physical stimulation converted into neural impulses
Sent through the thalamus to the auditory cortex (temporal lobes)
Ch.4- Sensation & Perception

35. Theories of Hearing: Place or Frequency?
Hermann von Helmholtz (1863)
Place theory: Pitch corresponds to vibrations of different places along the basilar membrane
Other researchers (Rutherford, 1886)
Frequency theory: Pitch corresponds to the frequency of the entire basilar membrane vibrates
Georg von Bekesy (1947)
Traveling wave theory: Pitch corresponds in a wave (incorporates place & frequency theories)
Ch.4- Sensation & Perception

36. Auditory Localization: Where Did that Sound Come From?
Two cues critical:
Intensity (loudness)
Timing of sounds arriving at each ear
Head as “shadow” or partial sound barrier
Timing differences as small as 1/100,000 of a second
Ch.4- Sensation & Perception

37. Cues in Auditory Localization
Ch.4- Sensation & Perception

38. The Chemical Senses: Taste
Taste (gustation)
Physical stimulus: soluble chemical substances
Receptor cells found in taste buds
Pathway:
taste buds -> neural impulse -> thalamus -> cortex
Four primary tastes:
Sweet
Sour
Bitter
Salty
Taste: learned and social processes
Ch.4- Sensation & Perception

39. Ch.4- Sensation & Perception
The Tongue & Taste
Ch.4- Sensation & Perception

40. The Chemical Senses: Smell
Smell (Olfaction)
Physical stimuli: Chemicals carried in the air
dissolved in fluid, the mucus in the nose
Olfactory receptors = olfactory cilia
Pathway: Information is gathered from chemicals in the air. Inhaled molecules excite receptors in the olfactory epithelium. The olfactory bulb gathers messages from the olfactory receptor cells and sends them to the brain
Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (brain)
-Does not go through thalamus
Ch.4- Sensation & Perception

41. Ch.4- Sensation & Perception
The Olfactory System
Ch.4- Sensation & Perception

42. Ch.4- Sensation & Perception
Skin Senses: Touch
Physical stimuli = mechanical, thermal, and chemical energy impinging on the skin.
Pathway:
Sensory receptors -> the spinal column -> brainstem -> cross to opposite side of brain -> thalamus -> somatosensory (parietal lobe)
Temperature: free nerve endings in the skin
Pain receptors: also free nerve endings
Two pain pathways: fast vs. slow
Ch.4- Sensation & Perception

43. Pathways for Pain Signals
Ch.4- Sensation & Perception

44. Ch.4- Sensation & Perception
Pain
Gate Control Theory
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
Ch.4- Sensation & Perception

45. Other Senses: Kinesthetic & Vestibular
Kinesthesis - knowing the position of the various parts of the body
Receptors in joints/muscles
Vestibular - equilibrium/balance
Semicircular canals
Ch.4- Sensation & Perception

46. Ch.4- Sensation & Perception
Reversible figures: drawing with 2 interpretations that can shift back & forth *Perception of the World is Highly Subjective*
Perceptual sets: (Expectations)
Inattentional blindness/Selective Attention: Expectations lead you to focus on a particular thing
Feature detection theory - bottom-up processing
Form perception - top-down processing
Subjective contours: perception of contours where none exist
Gestalt psychologists: the whole is greater than the sum of its parts
Ch.4- Sensation & Perception

47. A Famous Reversible Figure
Ch.4- Sensation & Perception

48. Ch.4- Sensation & Perception
The Necker cube
Ch.4- Sensation & Perception

49. Feature Analysis in Form Perception
Ch.4- Sensation & Perception

50. Ch.4- Sensation & Perception
Subjective Contours
Ch.4- Sensation & Perception

51. Principles of Perception
Gestalt principles of form perception:
Figure-ground
Proximity
Similarity
Continuity
Closure
Simplicity
Common fate: objects moving in the same direction belong together
Recent research:
Distal (stimuli outside the body)
Proximal (stimulus energies impinging on sensory receptors)
Perceptual hypotheses
Context. Which distal stimulus is responsible for proximal stimulus sensed
Ch.4- Sensation & Perception

52. Perceptual Organization
Figure and Ground organization of the visual field into objects (figures) that stand out from their surroundings (ground)
Ch.4- Sensation & Perception

53. Gestalt Principles of Perceptual Organization
Ch.4- Sensation & Perception

54. Distal & Proximal Stimuli
Ch.4- Sensation & Perception

55. Ch.4- Sensation & Perception
Context Effects
Ch.4- Sensation & Perception

56. Depth & Distance Perception
Binocular cues – clues from both eyes together
Retinal disparity: Difference between vision in both eyes
Convergence: Focus on object close eye turn inward
Monocular cues – clues from a single eye
Motion parallax: Images at different distances moving at different rates
Pictorial depth cues
Linear Perspective
Texture Gradient
Interposition
Relative Size
Height in Plane
Light/Shadow
Ch.4- Sensation & Perception

57. Ch.4- Sensation & Perception
Depth Cues
Ch.4- Sensation & Perception

58. Ch.4- Sensation & Perception
Relative Size
Ch.4- Sensation & Perception

59. Ch.4- Sensation & Perception
Interposition
Ch.4- Sensation & Perception

60. Stability in the Perceptual World: Perceptual Constancies
Perceptual constancies – stable perceptions amid changing stimuli
Size
Shape
Brightness
Hue
Location in space
Ch.4- Sensation & Perception

61. Optical Illusions: The Power of Misleading Cues
Optical Illusions - discrepancy between visual appearance and physical reality
Famous optical illusions:
Muller-Lyer Illusion
Ponzo Illusion
Poggendorf Illusion
Upside-Down T Illusion
Zollner Illusion
The Ames Room
Impossible Figures
Ch.4- Sensation & Perception

62. The Muller-Lyer illusion
Ch.4- Sensation & Perception

63. Explaining the Muller-Lyer Illusion
Ch.4- Sensation & Perception

64. Ch.4- Sensation & Perception
The Ames Room
Ch.4- Sensation & Perception

65. Four Geometric Illusions
Ch.4- Sensation & Perception

66. Three Classic Impossible Figures
Ch.4- Sensation & Perception