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Perception and Pattern Recognition

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Decision Demon: Has the final say in recognizing the pattern. Pandemonium Model ... Can copy drawings ... from memory nor identify the drawing that he copied ... – PowerPoint PPT presentation

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Title: Perception and Pattern Recognition


1
Chapter 3
  • Perception and Pattern Recognition

2
Visual Perception
CHILVR Cornea, aqueus Humor, Iris, Lens,
Vitreous humor, Retina
3
Eye Anatomy
  • Iris
  • Cilliar Muscle
  • Aqueous Humor
  • Pupil
  • Lens
  • Cornea
  • Retina
  • Vitreous Humor
  • Fovea
  • Blind Spot
  • Optic Nerve
  • Rod
  • Cone
  • Ganglion Cell
  • Bipolar Cell
  • Horizontal Cell

4
The Fovea
  • Light from direct focus lands in the Fovea.
  • Contains almost all cones.
  • Acuity -- accurate, precise vision-- is best in
    the fovea.
  • Rods are abundant at the sides (periphery) of the
    fovea.

5
Sensation versus Perception
  • Sensation
  • The reception of energy from the environment, and
    its initial encoding into the nervous system.
  • Perception
  • The process of interpreting and understanding
    sensory information.

6
Sensation Perception
7
Gathering Visual Information
  • Saccades Rapid eye movements.
  • Last between 25 and 100 msec.
  • Fixations Pauses between saccades.
  • The eye takes in visual information during
    fixations.
  • 200msec

8
Gathering Visual Information
  • Change Blindness The failure to notice changes
    in visual stimuli (e.g. photographs) when those
    changes occur during a saccade.
  • Inattentional Blindness We sometimes fail to
    see an object we are looking at directly, even a
    highly visible one, because our attention is
    directed elsewhere.

9
Visual Sensory Memory
  • Also known as Iconic Memory.
  • Visual persistence The apparent persistence of a
    visual stimulus beyond its physical duration (To
    demonstrate Rapidly wobble a pencil between two
    fingers).

10
Sensory Memory
  • How do you study sensory memory?
  • Because it is so brief it is difficult to study
  • Sperling (1960) hypothesized that we have a
    visual memory
  • He couldnt prove it because it always faded
    before people could report it
  • What to do?

11
Sperlings Experiment (Overview)
  • Used a tachistoscope to rapidly present images to
    the eyes.
  • Subjects saw a 3 x 4 grid of letters, presented
    very briefly (50 ms).
  • Subjects were asked to recall all the letters
    (Whole Report)
  • Whole report performance was poor (about 37
    accuracy).

12
Whole Report

?

A N X B L F S M R P K V
(5-500ms)
(50ms)
13
Sperling (1960)
  • In the whole report condition, subjects had to
    recall all the letters they could
  • Performance was poor
  • 4.5/12 letters
  • 37 accuracy
  • The span of immediate memory
  • The number of individual items recalled after a
    short delay

14
Sperling (1960)
  • But is this correct?
  • All the letters might be available initially, but
    then fade before they can be reported
  • If this is correct then subjects should be
    accurate reporting on any one row (before too
    much fading takes place)

15
Sperlings Experiment
  • The partial report condition, in which only one
    of the rows was to be reported
  • A tone was used as a cue
  • A high pitch tone cued recall of the top row
  • A medium pitch tone cued recall of the middle row
  • A low pitched tone cued recall of the bottom row

16
Sperlings Experiment
  • Partial report accuracy was much better
  • 0 ms delay 76 accuracy
  • So memory for entire display is about 76
  • A lot more information is there, than can be
    reported
  • 250ms delay 36 accuracy
  • Like the whole report condition

17
Sperlings Experiment
18
Sperlings Experiment(Continued)
  • In the partial report condition, a tone was
    sounded right after the letter grid disappeared.
  • A high pitch tone cued recall of the top row a
    medium pitch tone cued recall of the middle row
    a low pitched tone cued recall of the bottom row.
  • Partial report accuracy was at 76.

19
Sperlings Experiment(Conclusion)
  • Why did Sperling argue that decay rather than
    interference is the loss mechanism in iconic
    memory?
  • How long does information remain in iconic
    memory?

20
Lab Journal - Overview
  • Only write up experiments on syllabus
  • Single Page per Expt
  • Number Pages -- everyones page 23 should have
    the same one.
  • Use graphs when possible (picture 1000 words)
  • Turn in at Midterm (for review) and then at Final
    Exam for scoring

21
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22
One subjects results on the number of letters
available for report
23
Erasure and Masking Averbach and Coriell (1961)
  • Presented two rows of eight letters each.
  • Used a visual cue, above or below the
    to-be-recalled letter.
  • The circle-maker cue masked perception of the
    letter.
  • Backward Masking When a later visual stimulus
    affects perception of an earlier one.

24


X R F T L W Z P C A K N D E W J
50 ms
25


X R F T L W Z P C A K N D E W J
50 ms
26
Averbach Coriell (1961)
  • With the bar cue accuracy was similar to
    Sperlings original findings
  • High performance with short delays
  • Lower performance with longer delays
  • Effective duration of about 250 ms

27
Averbach Coriell (1961)
  • With the circle cue performance decreased
    dramatically
  • Accuracy was at chance
  • Participants did not even see a letter in that
    location, they only saw the circle
  • The circle erased or masked the memory for that
    letter

28
Averbach Coriell (1961)
  • Backward Masking When a later visual stimulus
    affects perception of an earlier one
  • Incoming information (circle) masked information
    that was already in iconic memory (letter)
  • Implicit priming Information is still being
    processed, even though it has not been
    transferred into awareness

29
Ecological Validity and the Icon
  • Haber (1983)
  • The iconic memory is irrelevant to real-world
    perception.
  • Data are useful only if reading in a lightning
    storm
  • Criticisms of Haber?
  • 1. Text reading task shows that perception
    actually is like reading in a lightning storm
    -- we only fixate for 50msec
  • 2. Reductionism

30
Pattern Recognition
  • How do we assemble visual input into meaningful
    shapes?
  • Recognition of Letters
  • Pandemonium
  • Recognition of Objects
  • Recognition by Components
  • Context and Connectionism
  • Visual Agnosia

31
Models of Pattern Recognition
  • The Template approach
  • Feature analysis / Feature detection
  • Connectionism
  • Recognition by components (object recognition)

32
Template Matching
  • Categorize based on a Template (stored
    representation of all patterns)
  • To perceive meaning, simply match the sensory
    input with a stored patten. When a match is
    found, you are done.

33
Template Matching
  • Aa
  • Aa
  • Aa

34
Template Matching Problems
  • Only possible in very limited domains (such as
    reading numbers 012345679)
  • How would training work?
  • Evidence clearly shows you can recognize (pattern
    match) objects youve never seen before.
  • Conclusion -- probably not how the brain works,
    and probably not a great way to program a
    computer either.

35
Feature Analysis ? Letters
  • Categorization by features
  • A simple fragment or component that can appear in
    combination with other features
  • Recognize letters by breaking them apart into
    features
  • H A T L F

36
Feature Analysis ? Letters
  • We recognize the features of letters (lines,
    curves) not the letters themselves
  • Pandemonium Model (Selfridge, 1959)
  • Decision Demons
  • Cognitive Demons
  • Computational Demons
  • Data Demons

37
Pandemonium
38
Pandemonium Model(Selfridge, 1959)
  • Demons Mental mechanisms that process visual
    stimuli ? Shout as they identify patterns
  • Data Demons Encode a pattern
  • Computational (Feature) Demons Feature
    analyzers each has a single feature it tries to
    match
  • Cognitive Demons Each represents a letter of
    the alphabet wait for the right combination of
    features
  • Decision Demon Has the final say in recognizing
    the pattern

39
Pandemonium Model
  • Each node has only one simple job to do
  • Includes parallel-processing
  • Neurologically valid

40
Context Effects
  • Data Driven (bottom-up)
  • Processing is driven by the stimulus.
  • Conceptually Driven (top-down)
  • Processing is driven by higher level knowledge.

41
Examples of Top-Down Processing
42
Connectionism
  • Input Units
  • Hidden Units
  • Output Units
  • Back Propagation
  • Delta Rule
  • Distributed Representation
  • Local Minima
  • Massively Parallel Processing

43
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44
Feature Analysis ? Objects
  • Recognition by Components (RBC)
    (Biederman, 1987, 1990)
  • All objects are a combination of geons ? Look up
    the combination to see which object matches
  • Geons
  • Feature detectors identify the geons based on

45
Geons The Objects They Make
46
Evidence for RBC
  • Data on Non-Recoverable Drawings
  • Impaired recognition if not able to identify the
    geons
  • Degraded so no intersections
  • Performance at chance
  • When the same percentage of information was
    deleted but NOT at intersections (recoverable
    drawings) performance was at 75 accuracy

47
RBC
  • Limitations of the model
  • Only allows for data-driven processes (parsing
    and assembling)
  • Whole vs. part perception
  • Suggests that the whole is perceived by
    identifying the parts first ? but people perceive
    the overall shape as quickly and accurately as
    they perceive the components
  • Neuropsychological evidence
  • Object recognition is a joint effort between two
    mental processes ? one for features, one for
    global shape

48
Recognition by ComponentsBiederman (1987)
  • Geons building blocks of visual objects.
  • Data on Non-recoverable Drawings.
  • Limitations of the model
  • Over-reliance on data-driven processes?
  • Whole versus part perception?
  • Neuropsychological evidence?

49
Agnosia
  • Failure or deficit in recognizing objects. Not
    blindness or poor vision.
  • Apperceptive Agnosia (patterns)
  • Associative Agnosia (meanings)
  • Prosopagnosia Associative agnosia for faces

50
Example of Copying by a Patient with Apperceptive
Agnosia
51
Neuropsychology of Object Recognition
  • Associative Agnosia
  • Can copy drawings
  • Can combine the features into a whole pattern,
    but cannot associate the pattern with meaning
  • Can copy a drawing of an anchor and give an
    accurate definition of an anchor
  • Cannot draw the anchor from memory nor identify
    the drawing that he copied
  • Damage to both hemispheres (temporal lobe)

52
Example of Copying by a Patient with Associative
Agnosia
53
Neuropsychology of Object Recognition
  • Prosopagnosia
  • The Man Who Mistook His Wife for a Hat Ch1
  • Associative agnosia that is specific for faces
  • May not recognize self, or familiar friends and
    family
  • Dissociation between face recognition and object
    recognition
  • Are faces special?

54
Material not covered in class
55
Auditory Perception
56
Ear Anatomy
  • Outer Ear
  • Inner Ear
  • Middle Ear
  • Eardrum
  • Ossicles
  • Semicircular Canals
  • Cochlea
  • Oval Window
  • Basilar Membrane
  • Hair Cells
  • Organ of Corti
  • Round Window
  • Auditory Nerve

57
Auditory Sensory Memory
  • Also known as Echoic memory.
  • Studying ASM
  • Three-eared man technique
  • Modality Effect
  • Suffix Effect

58
Auditory Pattern Recognition
  • Templates
  • --the problem of invariance?
  • Feature Detection
  • Conceptually Driven Processing
  • --Warren and Warrens (1990) study

59
Summary of Major Topics Covered in Chapter 3
  • Visual Perception
  • Pattern Recognition
  • Object Recognition
  • Agnosia
  • Auditory Perception
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