1. Chapter 3: Visual Perception

2. 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?

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

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

5. Basic Concepts Distal object Informational medium Proximal stimulation
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

6. 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
Ganzfeld effect

7. Perceptual Illusions Sometimes we cannot perceive what does exist
Sometimes we perceive things that do not exist
INSERT FIG 3.3 & FIG 3.4

8. Perceptual Illusions Sometimes we perceive what cannot be there
INSERT FIG 3.5

9. Perceptual Illusions Some other illusions to explore:

10. Our Visual System
Light travels through the eye and focuses on the retina
Electromagnetic light energy is converted into neural electrochemical impulses
INSERT FIG 3.7

11. Our Visual System Three main layers of neural tissue in retina
Ganglion cells
Amacrine cells, horizontal cells, bipolar cells
Photoreceptors
Rods and cones
INSERT FIG 3.8

12. 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

13. Visual Pathways: Alternative
What/how hypothesis
Where something is located in space
How do we reach for it?

14. 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

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

16. Gibson’s Theory of Direct Perception
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

17. Gibson’s Theory of Direct Perception
Use texture gradients as cues for depth and distance
Allows us to perceive directly the relative proximity or distance of objects
INSERT FIG 3.10

18. Gibson’s Theory of Direct Perception
Mirror neurons start firing ms after a visual stimulus
INSERT VIDEO #18, Mirror Neurons

19. 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
One click to view the words “See Stimuli” and then the demonstration will illustrate the template theory. All images obtained from Microsoft clips.
Search memory for a match
See stimuli

20. 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
One click to view the words “See Stimuli”, then the demonstration of the weakness of the theory will occur. All images taken from Microsoft clips.
If these clips are being removed, then you can INSERT FIG 3.11 instead
Search for match in memory
See stimuli
No perfect match in memory

21. 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”

22. Pandemonium Model Four kinds of demons Image demons Feature demons
Cognitive demons
Decision demons
INSERT FIG 3.12

23. Navon (1977) Participants asked what they saw on the
Global level
Local level
Global precedence effect found when letters were closer together.
INSERT FIG 3.13 & FIG 3.14
Results depended on whether letters are more widely spaced
Participants were faster at identifying local features of the letters

24. 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
INSERT FIG 3.15

25. 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
INSERT FIG 3.16

26. Evidence for Geons Biederman & Cooper (1991)
Evidence for Geons
Biederman & Cooper (1991)
Used visual priming to demonstrate the existence of geons in a picture naming task
Subjects were shown a series of fragmented pictures and were asked to identify the objects
BUT there are neurons sensitive to viewpoint-invariant properties
Biederman, I., & Cooper, E. E.  (1991).   Priming contour-deleted images:  Evidence for intermediate representations in visual object recognition.  Cognitive Psychology, 23,   

27. 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

28. Evidence for Top-Down Processing
Evidence for Top-Down Processing
Context effects
INSERT FIG 3.9

29. Configural-Superiority Effect
Objects presented in context are easier to recognize than objects presented alone
Task: Spot the different stimuli, press button
INSERT FIG 3.17

30. Configural-Superiority Effect
Target
Composite
Pomerantz (1981)
Measure reaction time Target alone = 1884 Composite = 749 Target spotted faster in a context!

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

32. Object Perception Viewer-centered representation
Object is stored in the perspective seen
Store multiple views of object as seen under various conditions
Viewpoint dependent process
Object-centered representation
Object is stored in a way that best represents the object
Viewpoint invariant process
Realism Link: Why is this important?
Understanding how information is coded in our minds helps us to better understand how to create computers that can also perceive objects or to enhance our own recognition abilities.

33. Object Perception Evidence supports both How to reconcile?
Maybe both contribute to object recognition
Two ends of a continuum that contribute to object recognition
Burgund & Tarr researched this issue

34. Landmark-Centered Orientation
Information is coded by its relation to a well-known or prominent item
Consider your college campus
What is a prominent item you use to orient yourself on campus?

35. 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

36. Gestalt’s Principles of Visual Perception
INSERT FIG 3.18

37. 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
INSERT FIG 3.19

38. 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
Check out Kanizsa’s figure at It appears as if a white square were in front of four black circles, representing both closure and symmetry.

39. Pattern Recognition Systems
Feature analysis system
Recognize parts of objects
Assemble parts into wholes
Configurational system
Recognize larger configurations

40. Evidence for Separate Systems
Tanaka & Farah (1993)
Participants studied
Faces and names
Pictures of homes and home owner’s names
At test, given only a piece of face (e.g., nose), whole face, whole home, or a piece of the home (e.g., window)
Asked to recall names

41. Tanaka & Farah (1993) Results
People have more difficulty recognizing parts of faces than parts of houses
INSERT FIG 3.21

42. 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

43. 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

44. Perceptual Constancy
Object remains the same even though our sensation of the object changes
Size constancy vs. shape constancy
INSERT FIG 3.23 & FIG 3.24

45. 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

46. Monocular Depth Cues Texture gradients Relative size Interposition
Grain of item
Relative size
Bigger is closer
Interposition
Closer are in front of other objects
Teaching Tip: Use a photograph to illustrate cues these cues. Microsoft clips is a good starting point.

47. 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
Teaching Tip: Use a photograph to illustrate cues these cues. Microsoft clips is a good starting point.

48. 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

49. 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

50. Deficits in Perception
Disruption of the “what” pathway
Agnosia
Inability to recognize and identify objects or people, despite having knowledge of the characteristics of the objects or people
Shows the specialization of our perceptual systems

51. Deficits in Perception
Disruption of the “what” pathway
Simultagnosic
Normal visual fields, yet act blind
Perceives only one stimulus at a time—single word or object

52. Deficits in Perception
Disruption of the “what” pathway
Prosopagnosia
Inability to recognize faces, including one's own
Cannot recognize person from face
Knows a face is a face  
Can recognize individuals from voice
Can recognize objects
Can discriminate whether two faces are same or different

53. Deficits in Perception
Disruption of the “how” pathway
Optic ataxia
Cannot use vision to guide movement
Unable to reach for items