Chapter 3: Perception

1. Chapter 3: Perception

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

3. Perceptual Illusions • http://www.michaelbach.de/ot/#history • Examine some of the illusions on this page • Some illusions cause you to perceive what is not there • Others lead you to perceive what cannot be

5. Perceptual Basics • Sensory Adaptation • Occurs when sensory receptors change their sensitivity to the stimulus • Constant stimulation leads to lower sensitivity • Our senses respond to change

6. Perceptual Basics • Perceptual Constancy • Object remains the same even though our sensation of the object changes • Example: • Shape constancy

7. Depth Perception • The ability to see the world in 3 dimensions and detect distance • Vision only has a 2-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

8. Monocular Depth Cues • Texture Gradients • Grain of item • Relative Size • Bigger is closer • Interposition • Closer are in front of other objects

9. Monocular Depth Cues • Linear Perspective • Parallel lines converge in distance • Aerial Perspective • Images seem blurry, the farther away • Motion Parallax • Objects get smaller at decreasing speed in distance

10. Binocular Depth Cues • Binocular Convergence • Eyes turn inward as object moves towards 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 3-d image

11. 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

12. 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

13. 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?

14. 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

15. 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 llll l l l l llll l l l l llll l l l l zzzTTTTTTTTTTzzzTTTTTTTTTTzzzTTTTTTTTTzzzTTTTTTTTTTzzzzTTTTT

16. Gestalt’s Principles of Visual Perception • 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 B A D C

17. Pattern Recognition Systems • One system • Recognize parts • Assemble into wholes • Second system • See wholes • Then analyze parts

18. Evidence for Two Pattern Recognition Systems • Farah’s Research • Face recognition and Object recognition use different systems • Functional independence

19. Functional Independence Evidence • Prosopagnosia • Inability to recognize faces after brain damage • Ability to recognize objects is intact • Associative Agnosia • Difficulty with recognizing objects • Can recognize faces • Demonstrates two different systems

20. “Special” nature of Facial Recognition • Tanaka & Farah (1993) • Participants studied • Faces and names • Pictures of homes and home owner’s names • At test, given only a piece of face (eg. Nose), whole face, whole home or a piece of the home (e.g., window) • Asked to recall names

21. Farah & Tanaka (1993) Results • What pattern would you expect if processing of homes (object) and faces were the same? • Which condition do you think had the highest memory for the names?

22. 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

23. Theories of Perception • Direct Perception theories • Perception comes from the stimuli in the environment • Bottom-up processing • Parts are identified, put together, and then recognition occurs • Constructive Perception theories • People actively construct perceptions using information based on expectations • Top-down processing

24. Gibson’s Direct Perception (Ecological model) All the information needed to form a perception is available in the environment Perception is immediate and spontaneous No top-down processing is necessary Perception and action cannot be separated Perception guides action and action generates more new perceptual information

25. 0 Bottom-Up Processing Theories • Template theories • Prototype theories • Feature theories • Structural description theories

26. 0 Template Theory • Basics of template theory • 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

27. 0 Template Theory • 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

28. 0 Prototype Theories • Modification of template matching (flexible templates) • Takes various instances of an object and abstracts out the common characteristics • No match is perfect; a criterion for matching is needed

29. 0 Prototype Evidence • Franks & Bransford (1971) • Presented objects based on prototypes • Prototype not shown • Yet participants are confident they had seen prototype • Suggests existence of prototypes

30. 0 Prototype Evidence • Solso & McCarthy (1981) • Participants were shown a series of faces • Later, a recognition test was given with some old faces, a prototype face, and some new faces that differed in degree from prototype

31. 0 Solso & McCarthy (1981) Results • Participants were more confident they had seen the prototype than actual items they had seen.

32. 0 Research on Prototypes • Researchers have found that prototypical faces are found to be more attractive to participants • Halberstadt & Rhodes (2000) • Examined the impact of prototypes of dogs, wristwatches, and birds on attractiveness of the stimuli • Results indicate a strong relationship between averageness and attractiveness of the dogs, birds, and wristwatches

33. 0 Feature 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”

34. 0 Feature Evidence • Hubel & Wiesel (1979) using single cell technique • 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

35. Navon (1977) Participants asked what they saw on the Global level Local Level Results depended on whether letters are more widely spaced. Local –precedence effect stimuli depicted here. Participants were faster at identifying local features of the letters.

36. 0 Structural-Description Theories • Biederman (1987) • Describes how 3D images are identified • Breaks objects down into geons • Objects are identified by geons and relationship between them

37. 0 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

38. 0 Top-down Processing (Constructive Perspective) • 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

39. 0 Top-down Processing Evidence • Context effects

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

41. Configural Superiority Effect Measure Reaction time Target alone = 1884 Composite = 749 Target spotted faster in a context! Target Composite

42. Which approach is right? • Top-down or Bottom-up • Perhaps a bit of both

43. 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

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

45. Deficits in Perception • Agnosia • Inability to recognize and identify objects or persons despite having knowledge of the characteristics of the objects or persons • Shows the specialization of our perceptual systems

46. 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

47. More Agnosias • Simultagnosic • Normal visual fields, yet act blind • Perceives only one stimulus at a time—single word or object • Spatial Agnosia • Cannot navigate in even familiar enviroment • Gets lost

48. More Agnosias • Auditory Agnosia • Cannot recognize certain sounds • Can not tell if two melodies are the same or different • Color Agnosia • Can see two colors are different, but cannot name the colors

49. Ataxia • Disruption of the “how” pathway • Optic ataxia • Cannot use vision to guide movement • Unable to reach for items

50. 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