Chapter 3: Perception - PowerPoint PPT Presentation

Loading...

PPT – Chapter 3: Perception PowerPoint presentation | free to download - id: 3ff60e-ZTcxZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Chapter 3: Perception

Description:

Visual Pathways in the Brain Visual Pathways : Alternative Deficits in Perception Prosopagnosia More Agnosias More Agnosias Ataxia Agnosias, Ataxias ... – PowerPoint PPT presentation

Number of Views:59
Avg rating:3.0/5.0
Slides: 51
Provided by: Donn138
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: 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

4
(No Transcript)
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
Gestalts 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
Gestalts 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
zzzTTTTTTTTTTzzzTTTTTTTTTTzzzTTTTTTTTTzzzTTTTTTTTT
TzzzzTTTTT
16
Gestalts 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
  • Farahs 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 owners 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
Gibsons 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
Bottom-Up Processing Theories
0
  • Template theories
  • Prototype theories
  • Feature theories
  • Structural description theories

26
Template Theory
0
  • 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
Template Theory
0
  • 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
Prototype Theories
0
  • 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
Prototype Evidence
0
  • Franks Bransford (1971)
  • Presented objects based on prototypes
  • Prototype not shown
  • Yet participants are confident they had seen
    prototype
  • Suggests existence of prototypes

30
Prototype Evidence
0
  • 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
Solso McCarthy (1981) Results
0
  • Participants were more confident they had seen
    the prototype than actual items they had seen.

32
Research on Prototypes
0
  • 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
Feature Theories
0
  • 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
Feature Evidence
0
  • 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
Structural-Description Theories
0
  • Biederman (1987)
  • Describes how 3D images are identified
  • Breaks objects down into geons
  • Objects are identified by geons and relationship
    between them

37
Evidence for Geons
0
  • 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
Top-down Processing (Constructive Perspective)
0
  • 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
Top-down Processing Evidence
0
  • 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








Target
Composite
  • Measure Reaction time
  • Target alone 1884 Composite 749
  • Target spotted faster in a context!

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 timesingle 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
About PowerShow.com