1. Perception

2. What you want to remember
Perception is more than photons and pressure.
Perception is divided from cognition/emotion but they are often intertwined.
Perception follows laws and heuristics. 2

3. Sensation - the registration of physical stimuli
Hearing - anatomy and function of the ear
Vision - anatomy and function of the eye 3

4. What is the purpose of sensory processing?
Sensation
What is the purpose of sensory processing?
To transform physical stimuli in the environment into neural signals in the brain
Example (Hearing): Sound waves are transformed into vibrations in the ear, and the strength of those vibrations are coded by sensory neurons 4

5. Some Questions of Interest
How can we perceive an object like a chair as having a stable form, given that the image of the chair on our retina changes as we look at it from different directions? 5

6. Some Questions of Interest
What are two fundamental approaches to explaining perception?
What happens when people with normal visual sensations cannot perceive visual stimuli? 6

7. Perception Is…
The process of recognizing, organizing, and interpreting information
How do you recognize these items? 7

8. Basic Concepts (Gibson)
Distal object
Grandma’s face
Informational medium
Reflected light from Grandma’s face
Proximal stimulation
Photon absorption in the rod and cone cells of the retina
Perceptual object 8

9. Perceptual Basics Sensory adaptation Our senses respond to change
Occurs when sensory receptors change their sensitivity to the stimulus
Constant stimulation leads to lower sensitivity
Our senses respond to change
Perceptual training 9

10. Perceptual Illusions Sometimes we cannot perceive what does exist
Sometimes we perceive things that do not exist 10

11. Perceptual Illusions
Sometimes we perceive what cannot be there 11

12. 12

13. Figure 7.4
Figure 7.4 The basilar membrane of the human cochlea. High-frequency sounds produce their maximum displacement near the base. Low-frequency sounds produce their maximum displacement near the apex. 13

14. Auditory Cortex Tonotopic organization in superior temporal lobe
Corresponds to apex of cochlea
Corresponds to base of cochlea
Primary auditory cortex
Secondary auditory cortex
Tonotopic organization in superior temporal lobe 14

15. Typical human range about 20 - 20 kHz
Audiograms for various species 15

16. Our Visual System
Light travels through the eye and focuses on the retina
Electromagnetic light energy is converted into neural electrochemical impulses 16

17. Our Visual System Three main layers of neural tissue in retina
Ganglion cells
Amacrine cells, horizontal cells, bipolar cells
Photoreceptors
Rods and cones 17

18. Visual Pathways in the Brain
What/where hypothesis
One path for identifying
Temporal lobe lesions in monkeys
Can indicate where but not what
Another for spatially locating
Parietal lobe lesions in monkeys
Can indicate what but not where 18

19. Theories of Perception
Bottom-up theories
Parts are identified, put together, and then recognition occurs
Top-down theories
People actively construct perceptions using information based on expectations 19

20. Bottom-Up Processing Theories
Bottom-Up Processing Theories
Direct perception
Template theories
Feature-matching theories
Recognition-by-components theory 20

21. Template Theories Basics of template theories
Template Theories
Basics of template theories
Multiple templates are held in memory
To recognize the incoming stimuli, you compare to templates in memory until a match is found
Search memory for a match
See stimuli 21

22. Template Theories Weakness of theory Problem of imperfect matches
Template Theories
Weakness of theory
Problem of imperfect matches
Cannot account for the flexibility of pattern recognition system
Search for match in memory
See stimuli
No perfect match in memory 22

23. Feature-Matching Theories
Feature-Matching Theories
Recognize objects on the basis of a small number of characteristics (features)
Detect specific elements and assemble them into more complex forms
Brain cells that respond to specific features such as lines and angles are referred to as “feature detectors” 23

24. Pandemonium Model Four kinds of demons Image demons Feature demons
Cognitive demons
Decision demons 24

25. Physiological Evidence for Features
Physiological Evidence for Features
Hubel & Wiesel (1979)
Simple cells detect bars or edges of particular orientation in particular location
Complex cells detect bars or edges of particular orientation, exact location abstracted
Hypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular direction 25

26. Recognition-by-Components (RBC) Theory
Recognition-by-Components (RBC) Theory
Biederman (1987)
Describes how 3D images are identified
Breaks objects down into geons
Objects are identified by geons, relationship between them 26

27. Gibson’s Theory of Direct Perception (Ecological psych)
The information in our sensory receptors is all we need to perceive anything
Do not need the aid of complex thought processes to explain perception 27

28. Gibson’s Theory of Direct Perception (Ecological psych)
Use texture gradients as cues for depth and distance
Allows us to perceive directly the relative proximity or distance of objects 28

29. Top-Down Processing (Constructive Approach)
Top-Down Processing (Constructive Approach)
Perception is not automatic from raw stimuli
Processing is needed to build perception
Top-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another 29

30. Evidence for Top-Down Processing
Evidence for Top-Down Processing
Context effects 30

31. Configural-Superiority Effect
Objects presented in context are easier to recognize than objects presented alone
Task: Spot the different stimuli, press button 31

32. Configural-Superiority Effect
Target
Composite
Measure reaction time
Target alone = 1884 Composite = 749
Target spotted faster in a context! 32

33. Which Approach Is Right?
Top-down or bottom-up
Perhaps a bit of both 33

34. Beginning of Gestalt psychology
1910 – Max Wertheimer on vacation noticed that distal objects seemed to move with the train; nearby objects went past. Why?
Study of apparent motion – why stationary objects appear to move 34

35. Apparent motion
Phi phenomenon – flashing a vertical light that is followed msec later by a horizontal light produces the appearance of movement. The light appears to move from vertical to horizontal
Movement only perceived if delay was 50 – 60 msec
The perceptual experience had properties the individual components did not
1st Gestalt paper presented in 1912 35

36. Basic premise of Gestalt psychology
Humans are not passive receivers of sensory information. Our perceptions are active, lively, and organized
We actively organize perceptions into coherent wholes – today the process is referred to as top-down or conceptually driven processing 36

37. Scientific Method They emphasized the physical environment.
Gestalt perspectives on scientific method reflect their acceptance of field physics as a model for psychology.
They emphasized the physical environment.
They used experience to guide analysis in psychology.
They started research with phenomenological investigation.
They accepted a broad range of methods in psychology. 37

38. Mind and Brain
Gestalt perspectives on mind and brain reject reductionistic and linear models of mind.
Köhler argued for models of mind based in natural systems.
He used models of mind based in the brain.
He described models in terms of free dynamics.
Köhler advocated isomorphism (ex. psychophysical isomorphism).
There is a structural correspondence between experience and underlying brain processes. 38

39. Geographical environment – the physical world
Key terms in gestalt psychology: Geographical versus behavioral environment
Geographical environment – the physical world
Behavioral environment – our interpretation of the physical world
Our interpretation or organization can produce a behavioral world that is very different from the physical world
Illusions, dreaming, fantasies 39

40. Gestalt’s View of Perception
Basic tenet
“The whole is more than a sum of its parts”
Law of Prägnanz
Individuals organize their experience in as simple, concise, symmetrical, and complete manner as possible 40

41. 41

42. 42

43. Perception is not just detection
Perception is not just about detecting color or shape.
Perception is about organizing visual information.
How do we organize visual information? 43

44. Müller-Lyer-illusion Ponzo illusion44

45. Or when do we fail to organize visual information?45

46. Gestalt’s Principles of Visual Perception46

47. Closure 47

48. Gestalt’s Principles of Visual Perception
Figure-ground
Organize perceptions by distinguishing between a figure and a background
Proximity
Elements tend to be grouped together according to their nearness
Similarity
Items similar in some respect tend to be grouped together 48

49. The figure represents “some thing.”
The contours belong to the figure rather than to the ground. 49

50. Which one if the figure and which is the ground?
This is easy.
The figure tends to have solid and continuous surface. 50

51. Gestalt’s Principles of Visual PerceptionB
Continuity
Based on smooth continuity, which is preferred to abrupt changes of direction
Closure
Items are grouped together if they tend to complete a figure
Symmetry
Prefer to perceive objects as mirror images A D C

53. Rules for Linking Contours
Good continuation: group elements to form smoothly continuing lines 53

54. The Relatability Principle54

55. Non-accidental features provide clues to object structure
Meaning in the Edges
Non-accidental features provide clues to object structure 55

56. Is the Whole Seen Before the Parts?
Global superiority effect (Navon, 1977) 56

57. Complex listening: several concurrent sound sources
Auditory scene analysis
“cocktail-party effect”

58. Stream segregation

59. Continuity

60. Grouping by similarity

61. Tactile illusions 61

62. Depth Perception
The ability to see the world in three dimensions and detect distance
Vision only has a two-dimensional view
We must interpret the information given to perceive depth
We take flat images and create a three- dimensional view
Optical illusions demonstrate that this interpretation does not always have to be correct 62

63. Monocular Depth Cues Texture gradients Relative size Interposition
Grain of item
Relative size
Bigger is closer
Interposition
Closer are in front of other objects 63

64. Monocular Depth Cues Linear perspective Aerial perspective
Parallel lines converge in distance
Aerial perspective
Images seem blurry farther away
Motion parallax
Objects get smaller at decreasing speed in distance 64

65. Binocular Depth Cues Binocular convergence Binocular disparity
Eyes turn inward as object moves toward you; brain uses this information to judge distance
Binocular disparity
Each eye views a slightly different angle of an object; brain uses this to create a 3D image 65

66. Agnosias, Ataxias, & Cognition
Demonstrate the modularity of cognition
Help us to understand what brain locations are associated with different types of higher-level processing
Provide us with a model of how normal processing must work 66

67. Deficits in Perception
Disruption of the “what” pathway
Inability to recognize and identify objects or people, despite having knowledge of the characteristics of the objects or people
Disruption of the “how” pathway
Cannot use vision to guide movement
Unable to reach for items

68. Fusiform Gyrus in Temporal Lobe
Implicated in pattern recognition
Studies illustrate it is active in facial recognition
However, also active if high expertise in any item (birds, cars) recognition
Expert individuation hypothesis 68

69. Evidence for Separate Systems
Prosopagnosia
Inability to recognize faces after brain damage
Ability to recognize objects is intact
Associative agnosia
Difficulty with recognizing objects
Can recognize faces 69

70. Psychophysics the measurement of sensory experiences Webers Law
Δφ = cφ φ = Stimuli
Fechners Law
Ψ = log φ Ψ = Sensation magnitude 70

71. Perception or Attention
Movement patterns / reflexes
What cannot be unseen / heard
Pop-out effect
Change blindness 71

72. What you want to remember
Perception is more than photons and pressure.
Perception is divided from cognition/emotion but they are often intertwined.
Perception follows laws and heuristics. 72